Gas cut risk quantitative evaluation method based on controllable overflow early warning value

Abstract

The invention discloses a gas cut strength grading method based on a controllable overflow early warning value criterion. According to the method, the gas cut rate is inversed based on adjacent well data of a target well, a gas cut shaft gas-liquid two-phase flow model is constructed to calculate the pressure, the gas cut gas position and the overflow quantity after gas cut, a time-bottom hole pressure plate, a time-overflow quantity plate and a well depth-gas position plate after gas cut are drawn, the maximum allowable well shut-in casing pressure is determined, and the maximum allowable well shut-in casing pressure is calculated. And establishing a gas cut overflow risk grade judgment chart integrating time, well depth, overflow quantity and well shut-in casing pressure by combining bottom hole pressure and formation pressure, fully considering emergency time of well site workers and a gas shallowest leakage position, determining the maximum limit early warning overflow quantity, and judging the gas cut overflow risk grade of the gas cut overflow risk grade after the maximum limit early warning overflow quantity is determined. The gas cut risk grade of the target layer is evaluated by utilizing the controllable gas cut overflow early warning value grading criterion, and well control measures are taken, so that timely early warning of the gas cut risk is realized, safe production of a well site is guaranteed, and the gas cut risk prevention and control capability of oil field enterprises is improved.

Description

Technical Field

[0001] The invention relates to the technical field of wellbore safety control, and in particular to a gas invasion risk quantitative evaluation method based on a controllable overflow warning value. Background Art

[0002] During the drilling process of fractured gas reservoirs, reservoir gas invades the drilling fluid column in the wellbore annulus due to low drilling fluid density or gravity displacement, resulting in overflow or even blowout, which seriously threatens the production safety of the drilling site. Timely and effective quantification of gas invasion risk and early warning are the primary measures to achieve safe well control.

[0003] The quantification of gas invasion risk requires the clarification of the possibility and intensity level of gas invasion well kick. At present, the research on gas invasion risk focuses on the monitoring and early warning of gas invasion, including acoustic monitoring, bottom hole pressure measurement while drilling, and theoretical calculation of gas invasion volume, but there is little research on the method of gas invasion intensity classification. Although some literatures have proposed that the gas invasion intensity classification method can be determined by referring to the underbalanced drilling risk classification method, this method does not take into account the impact of the actual early warning and control capabilities of the well control team on the one hand, and on the other hand, the bottom hole pressure drop value used to determine the classification amount is difficult to obtain accurately, and it is difficult to apply to the classification of gas invasion well kick intensity levels.

[0004] Therefore, it is urgent to propose a gas invasion intensity classification method based on the controllable overflow warning value criterion, which can accurately quantify the gas invasion risk, timely warn of the gas invasion risk, and guide the well site operators to take emergency response in time. Summary of the invention

[0005] In view of the problem that it is difficult to accurately determine the quantitative level of gas invasion well kick intensity at the current stage, the present invention proposes a gas invasion intensity grading method based on a controllable overflow warning value criterion. By accurately quantifying the gas invasion risk, timely warning of the gas invasion risk is achieved, which is conducive to the well site staff to take well control measures in time, effectively ensuring the safe production of the well site, and improving the oilfield enterprises' ability to prevent and control gas invasion risks.

[0006] The present invention specifically adopts the following technical solutions:

[0007] A gas intrusion intensity classification method based on a controllable overflow warning value criterion comprises the following steps:

[0008] Step 1: Select a target well and invert the gas invasion rate of the target well based on the data of its neighboring wells;

[0009] Step 2: construct a gas-liquid two-phase flow model for gas-invaded wellbore based on the drift flow model, and use the wellbore gas-liquid two-phase flow model to obtain the pressure, gas component position and overflow rate of the target well at different times after gas invasion, and draw a time-bottom hole pressure chart, a time-overflow chart and a well depth-gas position chart after gas invasion;

[0010] Step 3, determining the maximum allowable shut-in casing pressure according to the time-bottom hole pressure chart, the time-overflow chart and the well depth-gas position chart after gas invasion;

[0011] Step 4: Based on the time-bottom hole pressure chart, time-overflow chart and well depth-gas position chart after gas invasion, combined with the bottom hole pressure and formation pressure, a gas invasion and overflow risk level discrimination chart of comprehensive time-well depth-overflow-shut-in casing pressure is established;

[0012] Step 5: Based on the effective emergency response time of the well site staff, the maximum allowable overflow warning value considering the effective emergency response time is calculated. At the same time, combined with the actual minimum allowable warning time, the time-well depth-overflow-well shut-in casing pressure curve of the gas invasion overflow risk level discrimination chart is used, and combined with the well depth corresponding to the target layer, the maximum allowable overflow warning value considering the gas position is calculated. According to the maximum allowable overflow warning value considering the effective emergency response time and the maximum allowable overflow warning value considering the gas position, the maximum limit warning overflow of the target layer in the target well is determined;

[0013] Step 6: Based on the gas invasion and overflow risk level identification chart and the controllable gas invasion and overflow warning value classification criteria, combined with the maximum limit warning overflow value of the target layer in the target well, evaluate the gas invasion risk level of the target layer in the target well, and take corresponding well control measures.

[0014] Preferably, the step 1 specifically includes the following steps:

[0015] Step 1.1, select the target well, obtain the data of the neighboring wells of the target well, and obtain the production capacity data of each neighboring well;

[0016] Step 1.2, based on the production capacity data of each adjacent well and the type of the formation where the target well is located, a gas invasion calculation model is established to calculate the seepage characteristic index, which is used to characterize the gas invasion rate under unit thickness and unit pressure difference conditions. The gas invasion calculation model is used to calculate the seepage characteristic index of each adjacent well to obtain the seepage characteristic index of each adjacent well;

[0017] Step 1.3, based on the KNN weighted algorithm, the seepage characteristic index of all neighboring wells of the target well is used to inversely calculate the seepage characteristic index of the target layer of the target well, draw the gas invasion rate plate of the target well, and use the gas invasion rate plate to obtain the gas invasion rate under the conditions of the specified reservoir and bottom hole pressure difference.

[0018] Preferably, the capacity data includes capacity q SC , Wellhead nozzle pressure P bh , bottom hole pressure p w , reservoir thickness, reservoir depth, formation pressure, average reservoir radius re and the wellbore radius r W , where capacity refers to lost capacity or trial gas capacity.

[0019] Preferably, the conversion relationship between the wellhead nozzle pressure and the bottom hole flow pressure is:

[0020] P w =P bh ×e 1.1155×10-4 ρ s H s (1)

[0021] Where P w is the bottom hole flow pressure, in MPa; P bh is the wellhead flowing pressure, in MPa; ρ s is the wellbore gas density, in g / cm 3 ;H s is the height of the gas column in the wellbore, in meters.

[0022] Preferably, in step 1.2, when the target well is located in a homogeneous permeable formation, the gas invasion during the drilling process is regarded as a stable seepage flow, and the radial Darcy stable seepage flow in the reservoir plane is established, and the gas invasion amount calculation model is established as follows:

[0023]

[0024] In the formula, q SC is the gas well production under standard conditions, in m 3 / d; K is the effective permeability of the formation, in mD; h is the effective thickness of the formation, in m; p e is the original static pressure of the formation, in MPa; p w is the bottom hole flowing pressure, in MPa; T is the average temperature of the gas layer, in K; is the gas viscosity at average pressure and temperature, in mPa·s; is the gas deviation factor at average pressure and temperature; r w is the converted radius of the well, in m; r e is the converted radius of the reservoir, in m;

[0025] When the target well is located in a fractured formation, the gas changes dynamically during drilling. Based on the unsteady gas flow seepage model, the gas invasion calculation model is established as follows:

[0026]

[0027] in,

[0028]

[0029]

[0030] In the formula, μ g is the reference viscosity of the gas layer under average conditions, in mPa·s; S a is the apparent skin factor, dimensionless, S a =S+Dq SC , S is the true skin coefficient, dimensionless, D is the non-Darcy seepage coefficient, unit is (m 3 / d) -1 ;p SC is the standard pressure of gas; T sC is the standard temperature of the gas; C r is the comprehensive compression coefficient of the gas layer, MPa -1 ; A′, B′ are the calculation parameters of the gas intrusion calculation model, MPa -1 .

[0031] Preferably, the step 2 specifically includes the following steps:

[0032] Step 2.1, constructing a gas-liquid two-phase flow model for gas invasion wellbore based on the gas-liquid two-phase flow motion equations for gas invasion wellbore annulus, including the gas phase mass conservation equation, the liquid phase mass conservation equation and the gas-liquid two-phase momentum conservation equation;

[0033] In the gas-liquid two-phase flow model of gas invasion wellbore, the gas phase mass conservation equation is:

[0034]

[0035] The liquid mass conservation equation is:

[0036]

[0037] The momentum conservation equation for gas-liquid two phases is:

[0038]

[0039] Where t is time, unit is s; z is axial displacement, unit is m; A is annular flow area, unit is m 2 ρ g is the density of the gas phase, in kg / m 3 , ρ l is the density of drilling fluid, in kg / m 3 ; α g is the volume fraction of the gas phase, α l is the volume fraction of drilling fluid; v g is the actual flow rate of the gas phase, in m / s, v lis the actual flow rate of the drilling fluid, in m / s; g is the acceleration of gravity; θ is the well inclination, which is the angle between the wellbore direction and the horizontal direction; p is the pressure, p f is the pressure loss along the way, in Pa;

[0040] Step 2.2, solving the gas-liquid two-phase flow model of the gas-invasion wellbore based on the Roe format, and setting the initial conditions and boundary conditions of the gas-liquid two-phase flow model of the gas-invasion wellbore;

[0041] Step 2.3, discretize the gas-liquid two-phase flow model of the gas-invaded wellbore using a four-point difference display format to obtain a discretized wellbore pressure model, place the gas-liquid two-phase flow model of the gas-invaded wellbore in the divided space grid and time grid, set the space step and time step, and determine the space nodes and time nodes in the wellbore pressure model;

[0042] Step 2.4, solving the discretized wellbore pressure model to obtain the full transient pressure field of the wellbore gas-liquid two-phase flow;

[0043] Step 2.5, based on the calculated full transient pressure field of the gas-liquid two-phase flow in the wellbore, draw a time-bottomhole pressure chart, a time-overflow chart, and a well depth-gas position chart after gas invasion.

[0044] Preferably, in the process of solving the gas-liquid two-phase flow model of gas invasion wellbore, taking into account the slippage effect between the gas and liquid phases, the flow rate is set to:

[0045] v g =C0v m +v gr (9)

[0046] In the formula, v g is the flow rate; c0 is the gas phase distribution coefficient, dimensionless; v m is the velocity of the gas-liquid two-phase mixture in m / s, v gr is the gas phase slip velocity, in m / s;

[0047] In the process of solving the gas-liquid two-phase flow model of gas invasion wellbore, auxiliary solution equations are set, and the auxiliary solution equations include the wellbore pressure drop equation and the gas state equation control equation;

[0048] Since the pressure drop of the wellbore fluid along the way includes gravity pressure drop, friction pressure drop and acceleration pressure drop, the wellbore pressure drop equation is set as:

[0049]

[0050] in,

[0051]

[0052] ρm =ρ g α g +ρ l α l (12)

[0053] v m =v sg +v sl (13)

[0054] In the formula, p h is the gravity pressure drop, in Pa, p f is the friction pressure drop, in Pa, p a is the acceleration pressure drop, in Pa; f is the Fanning friction coefficient, dimensionless; ρ m is the mixed density of gas and liquid phases, d is the equivalent diameter, in m; v sg is the superficial velocity of the gas phase, in m / s, v sl is the superficial velocity of drilling fluid, in m / s;

[0055] The gas state equation is set to:

[0056]

[0057] Where R is the ideal gas constant, v0 is the molar volume, and a and b are Fan corrections.

[0058] Preferably, in step 2.2, the reservoir gas is taken as the gas phase and the drilling fluid is taken as the liquid phase, and the initial conditions of the gas-liquid two-phase flow model of the gas invasion wellbore are set, including the pressure of the annulus in the well at the initial moment of gas invasion, the volume fraction of each component in the drilling fluid, the volume fraction of each component in the gas phase, the gas phase velocity and the drilling fluid velocity;

[0059] Since the wellhead back pressure remains unchanged during drilling, the boundary conditions of the gas-liquid two-phase flow model of gas invasion wellbore are set as follows:

[0060] p(0,t)=pc(15)

[0061] Where pc is the wellhead back pressure, in Pa.

[0062] Preferably, in the step 2.3, the gas-liquid two-phase flow model of the gas invasion wellbore is discretized using a four-point difference display format, and then divided into a space grid and a time grid;

[0063] Set the unit space grid along the shaft axis to the step size on the space threshold, and set the space step size;

[0064] The division of the time step includes two stages. The first stage is the time before the gas phase migrates to the wellhead, and the second stage is the time in the quasi-steady state process after the gas phase migrates to the wellhead. For the first stage, the time step is in a changing state, and the time step is obtained by tracking the gas-liquid interface in the wellbore. For the second stage, the time step is preset to a constant value.

[0065] Preferably, the discretized wellbore pressure model is obtained by discretizing the gas-liquid two-phase flow model of the gas invasion wellbore. The gas phase in the discretized wellbore pressure model is:

[0066]

[0067] The liquid phase in the discretized wellbore pressure model is:

[0068]

[0069] The momentum conservation equation of the discretized wellbore pressure model is:

[0070]

[0071] in,

[0072] k=A j-1 / A j (19)

[0073] TS1=ρ g α g v g +ρ l α l v l (20)

[0074] TS2=ρ g α g v g 2 +ρ l α l v l 2 (twenty one)

[0075] TS3=ρ g α g +ρ l α l (twenty two)

[0076] In the formula, j is the number of the grid in the axis, n is the number of the time node, Δz is the axial spacing, Δt is the time interval, and A j-1 is the annular flow area corresponding to the j-1th grid in the axial direction, A j is the annular flow channel area corresponding to the jth grid in the axial direction, is the pressure of the jth grid in the axial direction at time node n, is the pressure of the j-1th grid in the axial direction at time node n, k, TS1, TS2, and TS3 are all calculation coefficients of the wellbore pressure model.

[0077] Preferably, in step 2.4, the process of solving the full transient pressure field of the wellbore gas-liquid two-phase flow specifically includes the following steps:

[0078] Step 2.4.1, obtain the preset initial conditions and boundary conditions and the discretized wellbore pressure model, and set the gas phase volume fraction accuracy value and pressure accuracy value;

[0079] Step 2.4.2: Use the discretized wellbore pressure model and the preset bottom hole pressure P H n+1 , calculate the bottom hole gas invasion, gas volume fraction, liquid volume fraction and flow rate corresponding to time n+1, and determine the initial pressure of the jth grid in the axial direction at time n+1 And according to the auxiliary solution equation, the physical parameters of the gas and liquid phases are used to determine the gas phase volume fraction in the wellbore. Recalculate and update the gas phase volume fraction in combination with the gas phase mass conservation equation;

[0080] Step 2.4.3, determine whether the updated gas phase volume fraction is greater than the preset gas phase volume fraction accuracy value, if it is greater than the preset gas phase volume fraction accuracy value, proceed to step 2.4.4, otherwise, return to step 2.4.2 to continue updating the phase volume fraction;

[0081] Step 2.4.4, calculate the pressure at the updated j-th grid according to the gas volume fraction of the j-th grid on the axis after the update And the initial pressure of the jth grid at time n+1 For comparison, if the pressure at the jth grid after update and the initial pressure of the jth grid at time n+1 If the difference between the two is less than the preset pressure accuracy value, go to step 2.4.5.

[0082] Step 2.4.5, move upward along the shaft axis to the upper space grid, update the position of the space grid, repeat steps 2.4.2 to 2.4.4 until all the space grids in the shaft axis are traversed, move to the wellhead, and then enter step 2.4.6;

[0083] Step 2.4.6, update the time node, move to the next time node, and repeat steps 2.4.2 to 2.4.5 until all time nodes are traversed to obtain the full transient pressure field of the wellbore gas-liquid two-phase flow.

[0084] Preferably, in step 3, the maximum allowable shut-in casing pressure is calculated as follows:

[0085] p j =min{p wh ,min(0.8p ci ),(p fmin -p j )×0.0098H c} (twenty three)

[0086] In the formula, p wh is the rated working pressure of the wellhead device, in MPa; p ci is the casing internal pressure resistance, in MPa; p fmin The minimum value of the equivalent density of the formation fracture pressure in the open hole section, in g / cm 3 ;H c is the depth of the weak part of the stratum, in meters; p j It is the maximum allowable shut-in casing pressure, in MPa.

[0087] Preferably, in step 4, according to the U-tube balance principle, the actual shut-in casing pressure calculation formula is:

[0088] P c =P f -P d (twenty four)

[0089] Where P c is the actual shut-in casing pressure, in MPa. f is the formation pressure, in MPa; P d is the bottom hole pressure, in MPa;

[0090] The time-bottomhole pressure curve is determined according to the time-bottomhole pressure chart after gas invasion, and the time-shut-in casing pressure curve is obtained. The time-shut-in casing pressure curve, the time-overflow curve determined by the time-overflow rate chart, and the well depth-gas position curve determined by the well depth-gas position chart are plotted on the same chart to obtain a gas invasion and overflow risk level judgment chart based on the comprehensive time-well depth-overflow rate-shut-in casing pressure.

[0091] Preferably, the step 5 specifically includes the following steps:

[0092] Step 5.1, according to the gas invasion overflow risk level discrimination chart, obtain the time-overflow volume-shut-in casing pressure curve of the target well, determine the overflow volume value Q and time t1 corresponding to the maximum allowable shut-in casing pressure value according to the time-overflow volume-shut-in casing pressure, comprehensively consider the effective emergency time for the well site staff to shut in or kill the well, and correct the warning time for correction;

[0093] The time-bottomhole pressure curve of the target well is obtained according to the time-bottomhole pressure chart after gas invasion. The overflow volume corresponding to the corrected warning time is determined by combining the time-overflow volume-well shut-in casing pressure curve, and the maximum allowable overflow volume warning value Q obtained based on the corrected warning time is obtained. max ;

[0094] Step 5.2: Obtain the time-depth-flow curve of the target well according to the gas invasion and overflow risk level identification chart, and use the time-depth-flow curve to determine the overflow flow and time t of the maximum gas reaching the specified well depth H0. 11 , the emergency response time Δt2 of the well site staff after the overflow warning is integrated to determine the actual minimum allowable warning time t 12 , the well depth-overflow-well shut-in casing pressure curve of the comprehensive gas invasion and overflow risk level discrimination chart is used to determine the overflow value corresponding to the shallowest allowable gas leakage position, and the maximum allowable overflow warning value Q based on the gas position is obtained. K ;

[0095] Step 5.3, based on the maximum allowable overflow warning value considering the effective emergency time and the maximum allowable overflow warning value considering the gas position, select the minimum value between the two as the maximum limit warning overflow, and determine the maximum limit warning overflow of the target layer.

[0096] Preferably, the corrected warning time is:

[0097] t2=t1-Δt (25)

[0098] Where t2 is the corrected warning time, t1 is the time corresponding to the maximum allowable shut-in casing pressure value determined by the time-overflow-shut-in casing pressure curve, and Δt is the effective emergency time of the well site staff.

[0099] Preferably, the maximum limit warning overflow calculation formula is:

[0100] Q W =min{Q max ,Q K} (26)

[0101] In the formula, Q W is the maximum limit warning overflow, Q max is the maximum allowable overflow warning value obtained based on the corrected warning time, Q K It is the maximum allowable overflow flow warning value based on the gas position.

[0102] Preferably, the controllable gas intrusion overflow warning value classification criteria are:

[0103] If the maximum limit warning overflow value of the target layer in the target well is greater than 2m 3, then the gas invasion intensity risk level of the target layer is judged to be low risk, and the gas invasion of the target layer is in a controllable state;

[0104] If the maximum limit warning overflow value of the target layer in the target well is greater than 1m 3 And not more than 2m 3 , then the gas invasion intensity risk level of the target layer is determined to be medium risk, and the gas invasion of the target layer is in a state that is difficult to control;

[0105] If the maximum limit warning overflow value of the target layer in the target well does not exceed 1m 3 , then the gas invasion intensity risk level of the target layer is judged to be high risk, and the gas invasion of the target layer is in a difficult-to-control state.

[0106] Preferably, the well control measures to be taken are determined according to the controllable gas intrusion and overflow warning value classification criteria:

[0107] If the gas invasion intensity risk level of the target layer in the target well is low risk, the overflow rate of the target layer is 1m 3 When observed, the overflow reaches 2m 3 Shut down the well for disposal;

[0108] If the gas invasion intensity risk level of the target layer in the target well is medium risk, the overflow rate of the target layer is 1m 3 Timely shut-in treatment, normal well pressure treatment;

[0109] If the gas invasion intensity risk level of the target layer in the target well is high risk, the overflow volume of the target layer should be paid attention to in real time, and the well shut-in plan, well killing plan and well killing materials should be formulated in advance, and overflow should be dealt with immediately.

[0110] The present invention has the following beneficial effects:

[0111] The present invention moves the time point based on which the gas invasion risk assessment is based to after the overflow warning and before the well crew takes effective measures. It integrates the influence of the well control reaction time of the well site operators for the first time, and is closer to the actual situation of the on-site gas invasion and well kick risk control operation.

[0112] At the same time, the present invention combines the controllable gas invasion overflow warning value classification criteria with the gas invasion intensity risk level, replacing the method of dividing the gas invasion risk intensity by referring to the underbalanced drilling risk level in the prior art, and establishing a gas invasion intensity classification method suitable for wellbore gas invasion based on the controllable overflow warning value criteria, which effectively ensures the safe production of the well site, improves the oilfield enterprise's ability to prevent and control gas invasion risks, and provides a guarantee for the safety of subsequent drilling and completion operations in the wellbore. BRIEF DESCRIPTION OF THE DRAWINGS

[0113] Figure 1 The present invention is a flow chart of a gas intrusion intensity classification method based on a controllable overflow warning value criterion.

[0114] Figure 2 Figure 2 is a gas invasion rate chart of different layers of the target well. In the figure, (a) is the gas invasion rate chart of layer 1, (b) is the gas invasion rate chart of layer 2, (c) is the gas invasion rate chart of layer 3, and (d) is the gas invasion rate chart of layer 4.

[0115] Figure 3 Figure 2 is a graph showing the relationship between the gas front migration position and time.

[0116] Figure 4 This is a graph showing the relationship between bottom hole pressure and time.

[0117] Figure 5 This is the relationship between the gas content at the annulus interface and the well depth when the gas migrates to the wellhead.

[0118] Figure 6 This is a graph showing the relationship between overflow rate and time.

[0119] Figure 7 This is a chart for distinguishing the risk levels of gas intrusion and overflow. DETAILED DESCRIPTION

[0120] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0121] Example 1

[0122] The present invention proposes a gas intrusion intensity classification method based on a controllable overflow warning value criterion, such as Figure 1 As shown, the following steps are included:

[0123] Step 1, select a target well, and invert the gas invasion rate of the target well based on the data of the neighboring wells of the target well, which specifically includes the following steps:

[0124] Step 1.1, select the target well, obtain the data of the neighboring wells of the target well, and obtain the production capacity data of each neighboring well, including the production capacity q of each neighboring well SC , Wellhead nozzle pressure P bh , bottom hole pressure p w , reservoir thickness, reservoir depth, formation pressure, average reservoir radius r e and the wellbore radius r W In this embodiment, the lost capacity or the test gas capacity can be used as the capacity data.

[0125] In the production capacity data, the conversion relationship between the wellhead nozzle pressure and the bottom hole flow pressure is:

[0126] P w =P bh ×e 1.1155×10-4 ρ s H s (1)

[0127] Where P w is the bottom hole flow pressure, in MPa; P bh is the wellhead flowing pressure, in MPa; ρ s is the wellbore gas density, in g / cm 3 ;H s is the height of the gas column in the wellbore, in meters.

[0128] If only the wellhead nozzle pressure P is known bh The bottom hole flow pressure p can be obtained by using the conversion relationship between the wellhead nozzle pressure and the bottom hole flow pressure w .

[0129] Step 1.2, based on the production capacity data of each adjacent well and the type of formation where the target well is located, a gas invasion calculation model is established to calculate the seepage characteristic index, which is used to characterize the gas invasion rate under unit thickness and unit pressure difference conditions. The seepage characteristic index of each adjacent well is calculated using the gas invasion calculation model to obtain the seepage characteristic index of each adjacent well.

[0130] Different gas invasion calculation models are constructed for different types of formations. When the target well is located in a homogeneous permeable formation, the gas invasion calculation model is established as follows:

[0131]

[0132] In the formula, q SC is the gas well production under standard conditions, in m 3 / d; K is the effective permeability of the formation, in mD; h is the effective thickness of the formation, in m; p e is the original static pressure of the formation, in MPa; p w is the bottom hole flowing pressure, in MPa; T is the average temperature of the gas layer, in K; is the gas viscosity at average pressure and temperature, in mPa·s; is the gas deviation factor at average pressure and temperature; r w is the converted radius of the well, in m; r e is the converted radius of the reservoir, in m.

[0133] When the target well is located in a fractured formation, the gas changes dynamically during drilling. Based on the unsteady gas flow seepage model, the gas invasion calculation model is established as follows:

[0134]

[0135] in,

[0136]

[0137]

[0138] In the formula, μ g is the reference viscosity of the gas layer under average conditions, in mPa·s; S a is the apparent skin factor, dimensionless, S a =S+Dq SC , S is the true skin coefficient, dimensionless, D is the non-Darcy seepage coefficient, unit is (m 3 / d) -1 ;p SC is the standard pressure of gas; T SC is the standard temperature of the gas; C r is the comprehensive compression coefficient of the gas layer, MPa -1 ; A′, B′ are the calculation parameters of the gas intrusion calculation model, MPa -1 .

[0139] Step 1.3, based on the known structural characteristics and well location parameters of the target well and its adjacent wells, combined with the seepage characteristic indexes of all adjacent wells of the target well, the seepage characteristic index of the target layer of the target well is calculated based on the KNN weighted algorithm, and the gas invasion rate map of the target well is drawn. The gas invasion rate map is used to obtain the gas invasion rate under the conditions of the specified reservoir and bottom hole pressure difference.

[0140] Step 2: construct a gas-liquid two-phase flow model for gas-invaded wellbore based on the drift flow model, use the wellbore gas-liquid two-phase flow model to obtain the pressure, gas component position and overflow rate of the target well at different times after gas invasion, and draw a time-bottom hole pressure chart, a time-overflow chart and a well depth-gas position chart after gas invasion, which specifically includes the following steps:

[0141] Step 2.1, constructing a gas-liquid two-phase flow model for gas invasion wellbore based on the gas-liquid two-phase flow motion equations for gas invasion wellbore annulus, including the gas phase mass conservation equation, the liquid phase mass conservation equation and the gas-liquid two-phase momentum conservation equation;

[0142] In the gas-liquid two-phase flow model of gas invasion wellbore, the gas phase mass conservation equation is:

[0143]

[0144] The liquid mass conservation equation is:

[0145]

[0146] The momentum conservation equation for gas-liquid two phases is:

[0147]

[0148] Where t is time, unit is s; z is axial displacement, unit is m; A is annular flow area, unit is m 2 ρ g is the density of the gas phase, in kg / m 3 , ρ l is the density of drilling fluid, in kg / m 3 ; α g is the volume fraction of the gas phase, α l is the volume fraction of drilling fluid; v g is the actual flow rate of the gas phase, in m / s, v l is the actual flow rate of the drilling fluid, in m / s; g is the acceleration of gravity; θ is the well inclination, which is the angle between the wellbore direction and the horizontal direction; p is the pressure, p f is the pressure loss along the way, in Pa;

[0149] In the process of solving the gas-liquid two-phase flow model of gas invasion wellbore in this embodiment, the slippage effect between the gas and liquid phases is taken into account. In order to better conform to the actual flow law of the gas-liquid two-phase flow and reduce the calculation error, the flow rate is set to:

[0150] v g =C0v m +v gr (9)

[0151] In the formula, v g is the flow rate; c0 is the gas phase distribution coefficient, dimensionless; v m is the velocity of the gas-liquid two-phase mixture in m / s, v gr is the gas phase slip velocity, in m / s;

[0152] In the process of solving the gas-liquid two-phase flow model of gas invasion wellbore, auxiliary solution equations are set, and the auxiliary solution equations include the wellbore pressure drop equation and the gas state equation control equation;

[0153] Among them, since the pressure drop of the wellbore fluid along the way includes gravity pressure drop, friction pressure drop and acceleration pressure drop, the wellbore pressure drop equation is set as:

[0154]

[0155] in,

[0156]

[0157] ρ m =ρ g α g +ρ l α l (12)

[0158] vm =v sg +v sl (13)

[0159] In the formula, p h is the gravity pressure drop, in Pa, p f is the friction pressure drop, in Pa, p a is the acceleration pressure drop, in Pa; f is the Fanning friction coefficient, dimensionless; ρ m is the mixed density of gas and liquid phases, d is the equivalent diameter, in m; v sg is the superficial velocity of the gas phase, in m / s, v sl is the superficial velocity of drilling fluid, in m / s;

[0160] The gas state equation is set to:

[0161]

[0162] In the formula, R is the ideal gas constant, v0 is the molar volume, and a and b are Fan's corrections;

[0163] Step 2.2, solve the gas-liquid two-phase flow model of the gas invasion wellbore based on the Roe format, and set the initial conditions and boundary conditions of the gas-liquid two-phase flow model of the gas invasion wellbore, where the initial conditions of the gas-liquid two-phase flow model of the gas invasion wellbore include the pressure of the annulus in the well at the initial moment of gas invasion, the volume fraction of each component in the drilling fluid, the volume fraction of each component in the gas phase, the gas phase velocity and the drilling fluid velocity.

[0164] At the same time, considering that the wellhead back pressure remains unchanged during drilling, the boundary conditions of the gas-liquid two-phase flow model of gas invasion wellbore are set as:

[0165] p(0,t)=p c (15)

[0166] In the formula, p c is the wellhead back pressure, in Pa.

[0167] Step 2.3, discretize the gas-liquid two-phase flow model of the gas-invasion wellbore using a four-point differential display format to obtain a discretized wellbore pressure model, place the gas-liquid two-phase flow model of the gas-invasion wellbore in the divided space grid and time grid, set the space step and time step, and determine the space nodes and time nodes in the wellbore pressure model.

[0168] In this embodiment, a four-point difference display format is used to discretize the gas-liquid two-phase flow model of the gas invasion wellbore, and then divide the space grid and the time grid;

[0169] Set the unit space grid along the shaft axis to the step size on the space threshold, and set the space step size;

[0170] The division of the time step includes two stages. The first stage is the time before the gas phase migrates to the wellhead, and the second stage is the time in the quasi-steady state process after the gas phase migrates to the wellhead. For the first stage, the time step is in a changing state, and the time step is obtained by tracking the gas-liquid interface in the wellbore. For the second stage, the time step is preset to a constant value.

[0171] In this embodiment, the gas-liquid two-phase flow model of gas invading the wellbore is discretized to obtain the discretized wellbore pressure model. The gas phase in the discretized wellbore pressure model is:

[0172]

[0173] The liquid phase in the discretized wellbore pressure model is:

[0174]

[0175] The momentum conservation equation of the discretized wellbore pressure model is:

[0176]

[0177] in,

[0178] k=A j-1 / A j (19)

[0179] TS1=ρ g α g v g +ρ l α l v l (20)

[0180] TS2=ρ g α g v g 2 +ρ l α l v l 2 (twenty one)

[0181] TS3=ρ g α g +ρ l α l (twenty two)

[0182] In the formula, j is the number of the grid in the axis, n is the number of the time node, Δz is the axial spacing, Δt is the time interval, and A j-1 is the annular flow area corresponding to the j-1th grid in the axial direction, A jis the annular flow channel area corresponding to the jth grid in the axial direction, is the pressure of the jth grid in the axial direction at time node n, is the pressure of the j-1th grid in the axial direction at time node n, k, TS1, TS2, and TS3 are all calculation coefficients of the wellbore pressure model.

[0183] Step 2.4, solving the discretized wellbore pressure model to obtain the full transient pressure field of the wellbore gas-liquid two-phase flow, specifically includes the following steps:

[0184] Step 2.4.1, obtain the preset initial conditions and boundary conditions and the discretized wellbore pressure model, and set the gas phase volume fraction accuracy value and pressure accuracy value;

[0185] Step 2.4.2: Use the discretized wellbore pressure model and the preset bottom hole pressure P H n+1 , calculate the bottom hole gas invasion, gas volume fraction, liquid volume fraction and flow rate corresponding to time n+1, and determine the initial pressure of the jth grid in the axial direction at time n+1 And according to the auxiliary solution equation, the physical parameters of the gas and liquid phases are used to determine the gas phase volume fraction in the wellbore. Recalculate and update the gas phase volume fraction in combination with the gas phase mass conservation equation;

[0186] Step 2.4.3, determine whether the updated gas phase volume fraction is greater than the preset gas phase volume fraction accuracy value, if it is greater than the preset gas phase volume fraction accuracy value, proceed to step 2.4.4, otherwise, return to step 2.4.2 to continue updating the phase volume fraction;

[0187] Step 2.4.4, calculate the pressure at the updated j-th grid according to the gas volume fraction of the j-th grid on the axis after the update And the initial pressure of the jth grid at time n+1 For comparison, if the pressure at the jth grid after update and the initial pressure of the jth grid at time n+1 If the difference between the two is less than the preset pressure accuracy value, go to step 2.4.5.

[0188] Step 2.4.5, move upward along the shaft axis to the upper space grid, update the position of the space grid, repeat steps 2.4.2 to 2.4.4 until all the space grids in the shaft axis are traversed, move to the wellhead, and then enter step 2.4.6;

[0189] Step 2.4.6, update the time node, move to the next time node, and repeat steps 2.4.2 to 2.4.5 until all time nodes are traversed to obtain the full transient pressure field of the wellbore gas-liquid two-phase flow.

[0190] Step 2.5, based on the calculated full transient pressure field of the gas-liquid two-phase flow in the wellbore, draw a time-bottomhole pressure chart, a time-overflow chart, and a well depth-gas position chart after gas invasion.

[0191] Step 3: Once gas invasion occurs during the drilling process of a gas reservoir, the risk assessment standard is whether the well can be successfully shut in or killed to prevent gas leakage to the ground, which includes two aspects: First, when shutting in or killing the well after an early warning, ensure that parameters such as casing pressure do not exceed the maximum allowable shut-in casing pressure; Second, take measures to prevent dangerous gases in acidic hazardous gas reservoirs from leaking to the ground through the wellhead.

[0192] According to the well control requirements, shut-in in any case must meet the minimum value of the three parameters: the maximum allowable shut-in casing pressure is less than the rated working pressure of the wellhead device, the internal pressure resistance of 80% of the casing weak points, and the maximum shut-in casing pressure allowed by the rupture pressure of the weak points of the formation in the wellbore. Therefore, it is necessary to determine the maximum allowable shut-in casing pressure.

[0193] The maximum allowable shut-in casing pressure is determined based on the time-bottomhole pressure chart, time-overflow chart and well depth-gas position chart after gas invasion.

[0194] In this embodiment, the maximum allowable shut-in casing pressure calculation formula is:

[0195] p j =min{p wh ,min(0.8p ci ),(p fmin -p j )×0.0098H c} (twenty three)

[0196] In the formula, p wh is the rated working pressure of the wellhead device, in MPa; p ci is the casing internal pressure resistance, in MPa; p fmin The minimum value of the equivalent density of the formation fracture pressure in the open hole section, in g / cm 3 ;H c is the depth of the weak part of the stratum, in meters; p j It is the maximum allowable shut-in casing pressure, in MPa.

[0197] Step 4: Based on the time-bottomhole pressure chart, time-overflow chart and well depth-gas position chart after gas invasion, combined with the bottomhole pressure and formation pressure, a gas invasion and overflow risk level judgment chart of comprehensive time-well depth-overflow-shut-in casing pressure is established.

[0198] According to the U-tube balance principle, the actual shut-in casing pressure is calculated using the bottom hole pressure and formation pressure, as shown in formula (24):

[0199] Pc=Pf-Pd(24)

[0200] Where P c is the actual shut-in casing pressure, in MPa. f is the formation pressure, in MPa; P d is the bottom hole pressure in MPa.

[0201] The time-bottomhole pressure curve is determined according to the time-bottomhole pressure chart after gas invasion, and the time-shut-in casing pressure curve is obtained. The time-shut-in casing pressure curve, the time-overflow curve determined by the time-overflow rate chart, and the well depth-gas position curve determined by the well depth-gas position chart are plotted on the same chart to obtain a gas invasion and overflow risk level judgment chart based on the comprehensive time-well depth-overflow rate-shut-in casing pressure.

[0202] Step 5, based on the effective emergency time of the well site staff, the maximum allowable overflow warning value considering the effective emergency time is calculated. At the same time, combined with the actual minimum allowable warning time, the time-well depth-overflow-well shut-in casing pressure curve of the gas invasion overflow risk level discrimination chart is used, and combined with the well depth corresponding to the target layer, the maximum allowable overflow warning value considering the gas position is calculated, and the maximum limit warning overflow of the target layer in the target well is determined according to the maximum allowable overflow warning value considering the effective emergency time and the maximum allowable overflow warning value considering the gas position, which specifically includes the following steps:

[0203] Step 5.1, according to the gas invasion overflow risk level discrimination chart, obtain the time-overflow volume-shut-in casing pressure curve of the target well, determine the overflow volume value Q and time t1 corresponding to the maximum allowable shut-in casing pressure value according to the time-overflow volume-shut-in casing pressure, comprehensively consider the effective emergency time for the well site staff to shut in or kill the well, and correct the warning time for correction.

[0204] The calculation formula for the corrected warning time is:

[0205] t2= t1-Δt (25)

[0206] Where t2 is the corrected warning time, t1 is the time corresponding to the maximum allowable shut-in casing pressure value determined by the time-overflow-shut-in casing pressure curve, and Δt is the effective emergency time of the well site staff.

[0207] The time-bottomhole pressure curve of the target well is obtained according to the time-bottomhole pressure chart after gas invasion. The overflow volume corresponding to the corrected warning time is determined by combining the time-overflow volume-well shut-in casing pressure curve, and the maximum allowable overflow volume warning value Q obtained based on the corrected warning time is obtained. max .

[0208] Step 5.2: Obtain the time-depth-flow curve of the target well according to the gas invasion and overflow risk level identification chart, and use the time-depth-flow curve to determine the overflow flow and time t of the maximum gas reaching the specified well depth H0. 11 , the emergency response time Δt2 of the well site staff after the overflow warning is integrated to determine the actual minimum allowable warning time t 12 , the well depth-overflow-well shut-in casing pressure curve of the comprehensive gas invasion and overflow risk level discrimination chart is used to determine the overflow value corresponding to the shallowest allowable gas leakage position, and the maximum allowable overflow warning value Q based on the gas position is obtained. K .

[0209] Step 5.3, based on the maximum allowable overflow warning value considering the effective emergency time and the maximum allowable overflow warning value considering the gas position, select the minimum value between the two as the maximum limit warning overflow, and determine the maximum limit warning overflow of the target layer.

[0210] The calculation formula for the maximum limit warning overflow is:

[0211] Q W =min{Q max ,Q K} (26)

[0212] In the formula, Q W is the maximum limit warning overflow, Q max is the maximum allowable overflow warning value obtained based on the corrected warning time, Q K It is the maximum allowable overflow flow warning value based on the gas position.

[0213] Step 6: Based on the gas invasion and overflow risk level identification chart and the controllable gas invasion and overflow warning value classification criteria, combined with the maximum limit warning overflow value of the target layer in the target well, evaluate the gas invasion risk level of the target layer in the target well, and take corresponding well control measures.

[0214] In this embodiment, according to the well control management regulations currently used in the well site, when the gas overflow rate is greater than 2m 3When the gas overflow rate is greater than 1m 3 And not more than 2m 3 When the gas overflow does not exceed 1m 3 When , the gas invasion intensity risk of the target layer is judged to be high risk, and the gas invasion of the target layer is in a difficult-to-control state.

[0215] Furthermore, when the gas invasion intensity risk of the target layer in the target well is low, the overflow rate of the target layer is 1m 3 When observed, the overflow reaches 2m 3 The well was shut down for disposal.

[0216] When the gas invasion intensity risk of the target layer in the target well is medium risk, the overflow rate of the target layer is 1m 3 Shut down the well in time for treatment and maintain normal well pressure.

[0217] When the gas invasion intensity risk of the target layer in the target well is high, the overflow volume of the target layer is paid attention to in real time, and the well closing plan, well killing plan and well killing materials are formulated in advance, and overflow is dealt with immediately once it occurs.

[0218] Example 2

[0219] In this embodiment, the gas invasion intensity classification method based on the controllable overflow volume warning value criterion proposed in Embodiment 1 is applied to Well A to verify the feasibility and effect of the gas invasion intensity classification method based on the controllable overflow volume warning value criterion of the present invention, which specifically includes the following steps:

[0220] Step 1: Select well A as the target well, invert the gas invasion rate of the target well based on the data of its adjacent wells, and obtain the data of well A and its adjacent wells, as shown in Table 1.

[0221] Table 1 Data of adjacent wells of Well A

[0222]

[0223] It can be seen from Table 1 that the formation fracture pressure at the second opening casing shoe of Well A (corresponding to the well depth of 4166m) is 1.45, the killing fluid density is 1.25, and the maximum allowable shut-in casing pressure is 10.41MPa.

[0224] Step 1.2, based on the production capacity data of each adjacent well and the type of formation where the target well is located, a gas invasion calculation model is established to calculate the seepage characteristic index, which is used to characterize the gas invasion rate under unit thickness and unit pressure difference conditions. The seepage characteristic index of each adjacent well is calculated using the gas invasion calculation model to obtain the seepage characteristic index of each adjacent well.

[0225] Step 1.3, based on the known structural characteristics and well location parameters of the target well and its adjacent wells, combined with the seepage characteristic indexes of all adjacent wells of the target well, the seepage characteristic index of the target layer of the target well is calculated based on the KNN weighted algorithm, and the gas invasion rate map of the target well is drawn. The gas invasion rate map is used to obtain the gas invasion rate under the conditions of the specified reservoir and bottom hole pressure difference.

[0226] In this embodiment, the geological design and engineering design data of well A are used, combined with the gas test data of the four layers of the adjacent wells of well A, to invert the gas invasion risk rate during the drilling process of the four layers corresponding to well A. Based on the well test production capacity data of different gas layers of the adjacent wells, the gas invasion volume calculation model is used, and the seepage characteristic index of the target layer is calculated based on the KNN weighted algorithm, and the gas invasion rate chart of the target well is drawn, as shown in FIG. Figure 2 shown.

[0227] Based on the gas invasion rate chart of each target layer, combined with the formation pressure and bottom hole pressure difference, the gas invasion rate range per unit thickness of each target layer is determined, as shown in Table 2.

[0228] Table 2 Inversion data of gas invasion in well A

[0229]

[0230] Step 2: construct a gas-liquid two-phase flow model for gas-invaded wellbores based on the drift flow model. Use the wellbore gas-liquid two-phase flow model to obtain the pressure, gas component position and overflow rate of the target well at different times after gas invasion. Calculate the full transient pressure field of the wellbore gas-liquid two-phase flow, and draw the time-bottomhole pressure chart, time-overflow chart and well depth-gas position chart after gas invasion.

[0231] In this embodiment, the gas-liquid two-phase flow model of the wellbore is used, combined with the gas-liquid two-phase flow parameters in the wellbore of well A, to calculate the corresponding relationship between the gas arrival position and the overflow volume in the wellbore after gas invasion occurs, where: Figure 3 is the relationship between the gas front migration position and time, Figure 4 is the relationship between bottom hole pressure and time, Figure 5 is the relationship between the gas content at the annular interface and the well depth when the gas migrates to the wellhead, Figure 6 is the relationship between overflow and time. Further, based on Figure 3 to Figure 6 The relationship between the migration position of the gas front and time, the relationship between the bottom hole pressure and time, the relationship between the gas content of the annulus interface and the well depth when the gas migrates to the wellhead, and the relationship between the overflow volume and time are calculated. The time-bottom hole pressure chart, time-overflow chart and well depth-gas position chart after gas invasion are drawn.

[0232] In this embodiment, the gas-liquid two-phase flow parameters in the borehole A include a drilling fluid density of 1.22 g / cm 3, the drilling fluid viscosity is 18.4 mPa·s, the yield value is 6.2 Pa, the drilling fluid displacement is 30 L / s, the gas relative density is 0.55, the gas viscosity is 0.018 mPa·s, and the gas compressibility coefficient is 6.16×10 -5 , the mechanical drilling speed is 2m / h.

[0233] Step 3, according to the time-bottomhole pressure chart, time-overflow chart and well depth-gas position chart after gas invasion, determine the maximum allowable shut-in casing pressure. In this embodiment, the wellhead equipment level of well A is 105 MPa, so the rupture pressure at the weak point of the formation (casing shoe) is selected to calculate the maximum allowable shut-in casing pressure. The maximum allowable shut-in casing pressure is calculated to be 10.41 MPa using formula (23).

[0234] Step 4: Based on the time-bottomhole pressure chart, time-overflow chart and well depth-gas position chart after gas invasion, combined with the bottomhole pressure and formation pressure, a comprehensive time-well depth-overflow-shut-in casing pressure gas invasion and overflow risk level judgment chart is established, such as Figure 7 shown.

[0235] Step 5, based on the effective emergency time of the well site staff, the maximum allowable overflow warning value considering the effective emergency time is calculated. At the same time, combined with the actual minimum allowable warning time, the time-well depth-overflow-well shut-in casing pressure curve of the gas invasion overflow risk level discrimination chart is used, and combined with the well depth corresponding to the target layer, the maximum allowable overflow warning value considering the gas position is calculated, and the maximum limit warning overflow of the target layer in the target well is determined according to the maximum allowable overflow warning value considering the effective emergency time and the maximum allowable overflow warning value considering the gas position, which specifically includes the following steps:

[0236] Step 5.1, according to the gas invasion overflow risk level discrimination chart, obtain the time-overflow volume-shut-in casing pressure curve of the target well, determine the overflow volume value Q and time t1 corresponding to the maximum allowable shut-in casing pressure value according to the time-overflow volume-shut-in casing pressure, comprehensively consider the effective emergency time for the well site staff to shut in or kill the well, and correct the warning time for correction.

[0237] The calculation formula for the corrected warning time is:

[0238] t2= t1-Δt (25)

[0239] Where t2 is the corrected warning time, t1 is the time corresponding to the maximum allowable shut-in casing pressure value determined by the time-overflow-shut-in casing pressure curve, and Δt is the effective emergency time of the well site staff.

[0240] The time-bottomhole pressure curve of the target well is obtained according to the time-bottomhole pressure chart after gas invasion. The overflow volume corresponding to the corrected warning time is determined by combining the time-overflow volume-well shut-in casing pressure curve, and the maximum allowable overflow volume warning value Q obtained based on the corrected warning time is obtained. max .

[0241] Step 5.2: Obtain the time-depth-flow curve of the target well according to the gas invasion and overflow risk level identification chart, and use the time-depth-flow curve to determine the overflow flow and time t of the maximum gas reaching the specified well depth H0. 11 , the emergency response time Δt2 of the well site staff after the overflow warning is integrated to determine the actual minimum allowable warning time t 12 , the well depth-overflow-well shut-in casing pressure curve of the comprehensive gas invasion and overflow risk level discrimination chart is used to determine the overflow value corresponding to the shallowest allowable gas leakage position, and the maximum allowable overflow warning value Q based on the gas position is obtained. K .

[0242] Step 5.3, based on the maximum allowable overflow warning value considering the effective emergency time and the maximum allowable overflow warning value considering the gas position, select the minimum value between the two as the maximum limit warning overflow, and determine the maximum limit warning overflow of the target layer, such as Figure 7 As shown in point B.

[0243] Step 6: Based on the gas invasion and overflow risk level identification chart and the controllable gas invasion and overflow warning value classification criteria, combined with the maximum limit warning overflow value of the target layer in the target well, evaluate the gas invasion risk level of the target layer in the target well, and take corresponding well control measures.

[0244] In this embodiment, in order to meet the safety requirements of gas well control, it is necessary to ensure that the wellbore treatment meets the two conditions of the maximum allowable shut-in casing pressure and the shallowest allowable gas leakage position. Figure 7 It can be seen from the casing pressure curve and gas invasion position curve shown in that the safest well depth area in this embodiment is area ③. Within a certain time range, the maximum allowable shut-in casing pressure condition must be met first.

[0245] The gas invasion of the target layer is at 2m of overflow 3 The shut-in casing pressure value at the early warning disposal line is A, which is greater than the maximum allowable shut-in casing pressure value B, and the overflow is 1m 3 The shut-in casing pressure value C during alarm treatment is less than the maximum allowable shut-in casing pressure value B; that is, the controllable overflow warning treatment threshold for gas invasion in the target layer is 1m 3 ~2m 3 , which is a medium risk, and the well crew needs to take it seriously according to the regulations and follow the 1m 3 Overflow well closure treatment and normal well pressure treatment.

[0246] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms used herein are only for describing specific embodiments, and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0247] In the present invention, the directions or positional relationships indicated by terms such as "upper", "lower", "bottom", "top", etc. are based on the directions or positional relationships shown in the accompanying drawings. They are relational words determined only for the convenience of describing the structural relationships of the various parts or elements of the present invention. They do not specifically refer to any part or element in the present invention and cannot be understood as limitations on the present invention.

[0248] In the present invention, terms such as "connected" and "connection" should be understood in a broad sense, indicating that the connection can be fixed, integral or detachable; it can be directly connected or indirectly connected through an intermediate medium. Relevant scientific research or technical personnel in this field can determine the specific meaning of the above terms in the present invention according to specific circumstances, and they should not be understood as limiting the present invention.

[0249] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A gas intrusion intensity classification method based on a controllable overflow warning value criterion, characterized in that: The following steps are involved: Step 1, select a target well and invert the gas invasion rate of the target well based on the data of its neighboring wells; Step 2: construct a gas-liquid two-phase flow model for gas-invaded wellbore based on the drift flow model, and use the wellbore gas-liquid two-phase flow model to obtain the pressure, gas component position and overflow rate of the target well at different times after gas invasion, and draw a time-bottom hole pressure chart, a time-overflow chart and a well depth-gas position chart after gas invasion; Step 3, determining the maximum allowable shut-in casing pressure according to the time-bottom hole pressure chart, the time-overflow chart and the well depth-gas position chart after gas invasion; Step 4: Based on the time-bottom hole pressure chart, time-overflow chart and well depth-gas position chart after gas invasion, combined with the bottom hole pressure and formation pressure, a gas invasion and overflow risk level discrimination chart of comprehensive time-well depth-overflow-shut-in casing pressure is established; Step 5: Based on the effective emergency response time of the well site staff, the maximum allowable overflow warning value considering the effective emergency response time is calculated. At the same time, combined with the actual minimum allowable warning time, the time-well depth-overflow-well shut-in casing pressure curve of the gas invasion overflow risk level discrimination chart is used, and combined with the well depth corresponding to the target layer, the maximum allowable overflow warning value considering the gas position is calculated. According to the maximum allowable overflow warning value considering the effective emergency response time and the maximum allowable overflow warning value considering the gas position, the maximum limit warning overflow of the target layer in the target well is determined; Step 6: Based on the gas invasion and overflow risk level identification chart and the controllable gas invasion and overflow warning value classification criteria, combined with the maximum limit warning overflow value of the target layer in the target well, evaluate the gas invasion risk level of the target layer in the target well, and take corresponding well control measures.

2. The gas intrusion intensity classification method based on the controllable overflow warning value criterion according to claim 1 is characterized in that: The step 1 specifically includes the following steps: Step 1.1, select the target well, obtain the data of the neighboring wells of the target well, and obtain the production capacity data of each neighboring well; Step 1.2, based on the production capacity data of each adjacent well and the type of the formation where the target well is located, a gas invasion calculation model is established to calculate the seepage characteristic index, which is used to characterize the gas invasion rate under unit thickness and unit pressure difference conditions. The gas invasion calculation model is used to calculate the seepage characteristic index of each adjacent well to obtain the seepage characteristic index of each adjacent well; Step 1.3, based on the KNN weighted algorithm, the seepage characteristic index of all neighboring wells of the target well is used to inversely calculate the seepage characteristic index of the target layer of the target well, draw the gas invasion rate plate of the target well, and use the gas invasion rate plate to obtain the gas invasion rate under the conditions of the specified reservoir and bottom hole pressure difference.

3. The gas intrusion intensity classification method based on the controllable overflow warning value criterion according to claim 2 is characterized in that: The capacity data includes capacity q SC , Wellhead nozzle pressure P bh , bottom hole pressure p w , reservoir thickness, reservoir depth, formation pressure, average reservoir radius r e and the wellbore radius r W , where capacity refers to lost capacity or trial gas capacity.

4. The gas intrusion intensity classification method based on the controllable overflow warning value criterion according to claim 3 is characterized in that: The conversion relationship between the wellhead nozzle pressure and the bottom hole flow pressure is: Where P w is the bottom hole flow pressure, in MPa; P bh is the wellhead flowing pressure, in MPa; ρ s is the wellbore gas density, in g / cm 3 ;H s is the height of the gas column in the wellbore, in meters.

5. The gas intrusion intensity classification method based on the controllable overflow warning value criterion according to claim 2 is characterized in that: In step 1.2, when the target well is located in a homogeneous permeable formation, the gas invasion during the drilling process is regarded as a stable seepage flow, and the radial Darcy stable seepage flow in the reservoir plane is established. The gas invasion calculation model is: In the formula, q SC is the gas well production under standard conditions, in m 3 / d; K is the effective permeability of the formation, in mD; h is the effective thickness of the formation, in m; p e is the original static pressure of the formation, in MPa; p w is the bottom hole flowing pressure, in MPa; T is the average temperature of the air layer, in K; is the gas viscosity at average pressure and temperature, in mPa·s; is the gas deviation factor at average pressure and temperature; r w is the converted radius of the well, in m; r e is the converted radius of the reservoir, in m; When the target well is located in a fractured formation, the gas changes dynamically during drilling. Based on the unsteady gas flow seepage model, the gas invasion calculation model is established as follows: in, In the formula, μ g is the reference viscosity of the gas layer under average conditions, in mPa·s; S a is the apparent skin factor, dimensionless, S a =S+Dq SC , S is the true skin coefficient, dimensionless, D is the non-Darcy seepage coefficient, unit is (m 3 / d) -1 ;p SC is the standard pressure of gas; T sC is the standard temperature of the gas; C r is the comprehensive compression coefficient of the gas layer, MPa -1 ; A′, B′ are the calculation parameters of the gas intrusion calculation model, MPa -1 .

6. The gas intrusion intensity classification method based on the controllable overflow warning value criterion according to claim 5 is characterized in that: The step 2 specifically includes the following steps: Step 2.1, constructing a gas-liquid two-phase flow model for gas invasion wellbore based on the gas-liquid two-phase flow motion equations for gas invasion wellbore annulus, including the gas phase mass conservation equation, the liquid phase mass conservation equation and the gas-liquid two-phase momentum conservation equation; In the gas-liquid two-phase flow model of gas invasion wellbore, the gas phase mass conservation equation is: The liquid mass conservation equation is: The gas-liquid two-phase momentum conservation equation is: Where t is time, unit is s; z is axial displacement, unit is m; A is annular flow area, unit is m 2 ρ g is the density of the gas phase, in kg / m 3 , ρ l is the density of drilling fluid, in kg / m 3 ; α g is the volume fraction of the gas phase, α l is the volume fraction of drilling fluid; v g is the actual flow rate of the gas phase, in m / s, v l is the actual flow rate of the drilling fluid, in m / s; g is the acceleration of gravity; θ is the well inclination, which is the angle between the wellbore direction and the horizontal direction; p is the pressure, p f is the pressure loss along the way, in Pa; Step 2.2, solving the gas-liquid two-phase flow model of the gas-invasion wellbore based on the Roe format, and setting the initial conditions and boundary conditions of the gas-liquid two-phase flow model of the gas-invasion wellbore; Step 2.3, discretize the gas-liquid two-phase flow model of the gas-invaded wellbore using a four-point difference display format to obtain a discretized wellbore pressure model, place the gas-liquid two-phase flow model of the gas-invaded wellbore in the divided space grid and time grid, set the space step and time step, and determine the space nodes and time nodes in the wellbore pressure model; Step 2.4, solving the discretized wellbore pressure model to obtain the full transient pressure field of the wellbore gas-liquid two-phase flow; Step 2.5, based on the calculated full transient pressure field of the gas-liquid two-phase flow in the wellbore, draw a time-bottomhole pressure chart, a time-overflow chart, and a well depth-gas position chart after gas invasion.

7. The gas intrusion intensity classification method based on the controllable overflow warning value criterion according to claim 6 is characterized in that: In the process of solving the gas-liquid two-phase flow model of gas invasion wellbore, the slippage effect between the gas and liquid phases is taken into account and the flow rate is set as: v g =C0v m +v gr (9) In the formula, v g is the flow rate; c0 is the gas phase distribution coefficient, dimensionless; v m is the velocity of the gas-liquid two-phase mixture in m / s, v gr is the gas phase slip velocity, in m / s; In the process of solving the gas-liquid two-phase flow model of gas invasion wellbore, auxiliary solution equations are set, and the auxiliary solution equations include the wellbore pressure drop equation and the gas state equation control equation; Since the pressure drop of the wellbore fluid along the way includes gravity pressure drop, friction pressure drop and acceleration pressure drop, the wellbore pressure drop equation is set as: in, r m =ρ g a g +r l a l (12) v m =v sg +v sl (13) In the formula, p h is the gravity pressure drop, in Pa, p f is the friction pressure drop, in Pa, p a is the acceleration pressure drop, in Pa; f is the Fanning friction coefficient, dimensionless; ρ m is the mixed density of gas and liquid phases, d is the equivalent diameter, in m; v sg is the superficial velocity of the gas phase, in m / s, v sl is the superficial velocity of drilling fluid, in m / s; The gas state equation is set to: Where R is the ideal gas constant, v0 is the molar volume, and a and b are Fan corrections.

8. The gas intrusion intensity classification method based on the controllable overflow warning value criterion according to claim 7 is characterized in that: In the step 2.2, the reservoir gas is taken as the gas phase and the drilling fluid is taken as the liquid phase, and the initial conditions of the gas-liquid two-phase flow model of the gas invasion wellbore are set, including the pressure of the annulus in the well at the initial moment of gas invasion, the volume fraction of each component in the drilling fluid, the volume fraction of each component in the gas phase, the gas phase velocity and the drilling fluid velocity; Since the wellhead back pressure remains unchanged during drilling, the boundary conditions of the gas-liquid two-phase flow model of gas invasion wellbore are set as follows: p(0,t)=p c (15) In the formula, p c is the wellhead back pressure, in Pa.

9. The gas intrusion intensity classification method based on the controllable overflow warning value criterion according to claim 8 is characterized in that: In the step 2.3, the gas-liquid two-phase flow model of the gas invasion wellbore is discretized using a four-point difference display format, and then divided into a space grid and a time grid; Set the unit space grid along the shaft axis to the step size on the space threshold, and set the space step size; The division of the time step includes two stages. The first stage is the time before the gas phase migrates to the wellhead, and the second stage is the time in the quasi-steady state process after the gas phase migrates to the wellhead. For the first stage, the time step is in a changing state, and the time step is obtained by tracking the gas-liquid interface in the wellbore. For the second stage, the time step is preset to a constant value.

10. The gas intrusion intensity classification method based on the controllable overflow warning value criterion according to claim 9 is characterized in that: By discretizing the gas-liquid two-phase flow model of gas invasion wellbore, the discretized wellbore pressure model is obtained. The gas phase in the discretized wellbore pressure model is: The liquid phase in the discretized wellbore pressure model is: The momentum conservation equation of the discretized wellbore pressure model is: in, k=A j-1 / A j (19) TS1=ρ g α g in g +ρ l α l in l (20) TS2=ρ g a g v g 2 +r l a l v l 2 (21) TS3=ρ g a g +r l a l (22) In the formula, j is the number of the grid in the axis, n is the number of the time node, Δz is the axial spacing, Δt is the time interval, and A j-1 is the annular flow area corresponding to the j-1th grid in the axial direction, A j is the annular flow channel area corresponding to the jth grid in the axial direction, is the pressure of the jth grid in the axial direction at time node n, is the pressure of the j-1th grid in the axial direction at time node n, k, TS1, TS2, and TS3 are all calculation coefficients of the wellbore pressure model.

11. The gas intrusion intensity classification method based on the controllable overflow warning value criterion according to claim 6 is characterized in that: In step 2.4, the process of solving the full transient pressure field of the gas-liquid two-phase flow in the wellbore specifically includes the following steps: Step 2.4.1, obtain the preset initial conditions and boundary conditions and the discretized wellbore pressure model, and set the gas phase volume fraction accuracy value and pressure accuracy value; Step 2.4.2: Use the discretized wellbore pressure model and the preset bottom hole pressure P H n+1 , calculate the bottom hole gas invasion, gas volume fraction, liquid volume fraction and flow rate corresponding to time n+1, and determine the initial pressure P of the jth grid in the axial direction at time n+1 j n+1(0) , and determine the gas phase volume fraction α in the wellbore based on the physical parameters of the gas-liquid two-phase auxiliary equation j n+1(0) , combined with the gas phase mass conservation equation, recalculate and update the gas phase volume fraction; Step 2.4.3, determine whether the updated gas phase volume fraction is greater than the preset gas phase volume fraction accuracy value, if it is greater than the preset gas phase volume fraction accuracy value, proceed to step 2.4.4, otherwise, return to step 2.4.2 to continue updating the phase volume fraction; Step 2.4.4, calculate the pressure P at the updated j-th grid according to the gas phase volume fraction of the j-th grid on the axis after the update j n+1 and the initial pressure P of the jth grid at time n+1 j n+1(0) For comparison, if the pressure P at the jth grid after update j n+1 and the initial pressure P of the jth grid at time n+1 j n+1(0) If the difference between the two is less than the preset pressure accuracy value, go to step 2.4.

5. Step 2.4.5, move upward along the shaft axis to the upper space grid, update the position of the space grid, repeat steps 2.4.2 to 2.4.4 until all the space grids in the shaft axis are traversed, move to the wellhead, and then enter step 2.4.6; Step 2.4.6, update the time node, move to the next time node, and repeat steps 2.4.2 to 2.4.5 until all time nodes are traversed to obtain the full transient pressure field of the wellbore gas-liquid two-phase flow.

12. The gas intrusion intensity classification method based on the controllable overflow warning value criterion according to claim 1 is characterized in that: In step 3, the maximum allowable shut-in casing pressure is calculated as follows: p j min{p wh ,min(0.8p ci ),(p fmin -p j )×0.0098H c } (23) In the formula, p wh is the rated working pressure of the wellhead device, in MPa; p ci is the casing internal pressure resistance, in MPa; p fmin The minimum value of the equivalent density of the formation fracture pressure in the open hole section, in g / cm 3 ; H c is the depth of the weak part of the stratum, in meters; p j It is the maximum allowable shut-in casing pressure, in MPa.

13. The gas intrusion intensity classification method based on the controllable overflow warning value criterion according to claim 1 is characterized in that: In step 4, according to the U-tube balance principle, the actual shut-in casing pressure calculation formula is: P c =P f -P d (24) Where P v is the actual shut-in casing pressure, in MPa. f is the formation pressure, in MPa; P d is the bottom hole pressure, in MPa; The time-bottomhole pressure curve is determined according to the time-bottomhole pressure chart after gas invasion, and the time-shut-in casing pressure curve is obtained. The time-shut-in casing pressure curve is plotted on the same chart with the time-overflow rate curve determined by the time-overflow rate chart and the well depth-gas position curve determined by the well depth-gas position chart, so as to obtain a gas invasion and overflow risk level judgment chart integrating time-well depth-overflow rate-shut-in casing pressure.

14. The gas intrusion intensity classification method based on the controllable overflow warning value criterion according to claim 1 is characterized in that: The step 5 specifically includes the following steps: Step 5.1, according to the gas invasion overflow risk level discrimination chart, obtain the time-overflow-shut-in casing pressure curve of the target well, determine the overflow value Q and time t1 corresponding to the maximum allowable shut-in casing pressure value according to the time-overflow-shut-in casing pressure, comprehensively consider the effective emergency time for the well site staff to shut in or kill the well, and correct the warning time for correction; The time-bottomhole pressure curve of the target well is obtained according to the time-bottomhole pressure chart after gas invasion. The overflow volume corresponding to the corrected warning time is determined by combining the time-overflow volume-well shut-in casing pressure curve, and the maximum allowable overflow volume warning value Q obtained based on the corrected warning time is obtained. max ; Step 5.2: Obtain the time-depth-flow curve of the target well according to the gas invasion and overflow risk level identification chart, and use the time-depth-flow curve to determine the overflow flow and time t of the maximum gas reaching the specified well depth H0. 11 , the emergency response time Δt2 of the well site staff after the overflow warning is integrated to determine the actual minimum allowable warning time t 12 , the well depth-overflow-well shut-in casing pressure curve of the comprehensive gas invasion and overflow risk level discrimination chart is used to determine the overflow value corresponding to the shallowest allowable gas leakage position, and the maximum allowable overflow warning value Q based on the gas position is obtained. K ; Step 5.3, based on the maximum allowable overflow warning value considering the effective emergency time and the maximum allowable overflow warning value considering the gas position, select the minimum value between the two as the maximum limit warning overflow, and determine the maximum limit warning overflow of the target layer.

15. The gas intrusion intensity classification method based on the controllable overflow warning value criterion according to claim 14 is characterized in that: The revised warning time is: t2=t1-Δt (25) Where t2 is the corrected warning time, t1 is the time corresponding to the maximum allowable shut-in casing pressure value determined by the time-overflow-shut-in casing pressure curve, and Δt is the effective emergency time of the well site staff.

16. The gas intrusion intensity classification method based on the controllable overflow warning value criterion according to claim 14 is characterized in that: The maximum limit warning overflow calculation formula is: Q W =min{Q max ,Q K } (26) In the formula, Q W is the maximum limit warning overflow, Q max is the maximum allowable overflow warning value obtained based on the corrected warning time, Q K It is the maximum allowable overflow flow warning value based on the gas position.

17. The gas intrusion intensity classification method based on the controllable overflow warning value criterion according to claim 14 is characterized in that: The controllable gas intrusion overflow warning value classification criteria are: If the maximum limit warning overflow value of the target layer in the target well is greater than 2m 3 , then the gas invasion intensity risk level of the target layer is judged to be low risk, and the gas invasion of the target layer is in a controllable state; If the maximum limit warning overflow value of the target layer in the target well is greater than 1m 3 And not more than 2m 3 , then the gas invasion intensity risk level of the target layer is determined to be medium risk, and the gas invasion of the target layer is in a state that is difficult to control; If the maximum limit warning overflow value of the target layer in the target well does not exceed 1m 3 , then the gas invasion intensity risk level of the target layer is judged to be high risk, and the gas invasion of the target layer is in a difficult-to-control state.

18. The gas intrusion intensity classification method based on the controllable overflow warning value criterion according to claim 17 is characterized in that: Determine the well control measures to be taken according to the controllable gas intrusion and overflow warning value classification criteria: If the gas invasion intensity risk level of the target layer in the target well is low risk, the overflow rate of the target layer is 1m 3 When observed, the overflow reaches 2m 3 Shut down the well for disposal; If the gas invasion intensity risk level of the target layer in the target well is medium risk, the overflow rate of the target layer is 1m 3 Timely shut-in treatment, normal well pressure treatment; If the gas invasion intensity risk level of the target layer in the target well is high risk, the overflow volume of the target layer should be paid attention to in real time, and the well shut-in plan, well killing plan and well killing materials should be formulated in advance, and overflow should be dealt with immediately.

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