A method and system for rapid identification of caves and fractures in a reservoir

Abstract

The application provides a method and system for quickly identifying caves and cracks in a reservoir, and belongs to the field of oil exploration and development. The method uses pressure data and production data collected by a pressure gauge and a flow meter to obtain a double logarithmic graph, and uses the double logarithmic graph to identify caves and cracks in the reservoir. The application establishes an oil and gas reservoir production data analysis model containing caves and cracks, and draws a typical graph for identifying caves, which can quickly identify caves and cracks in the reservoir. The application uses production data analysis technology to identify the existence and connectivity of caves and cracks, which can identify caves directly connected with the well and caves not connected with the well. The application has an important role in ensuring efficient development of oil and gas reservoirs, geothermal reservoirs, cave-type gas storage and the like containing caves and cracks, and improving economic benefits.

Description

Technical Field

[0001] This invention belongs to the field of petroleum exploration and development, and relates to a technology for describing the characteristics and analyzing the production dynamics of reservoirs such as oil and gas reservoirs, geothermal reservoirs, and cavernous gas storage facilities. Specifically, it relates to a method and system for rapid identification of caves and fractures in reservoirs. Background Technology

[0002] Caves and fractures are the main reservoir media in many oil and gas reservoirs, and are widely present in carbonate oil and gas reservoirs, tight oil and gas reservoirs, shale oil and gas reservoirs, geothermal reservoirs, and cavernous gas storage facilities. Taking carbonate reservoirs as an example, caves and fractures (hereinafter referred to as "fractures and caves") are the main oil storage spaces, directly determining the production capacity and production time of oil and gas wells. Therefore, determining whether caves exist in the near-wellbore zone and whether the caves in the near-wellbore zone communicate with the production well is of great importance.

[0003] Currently, the identification of fractures and cavities mainly relies on pressure recovery well test analysis. For example, the published literature "A New Model for Well Test Interpretation of Carbonate Cave-Type Reservoirs" (Special Oil and Gas Reservoirs, 2014, 21(2):98) discloses the use of shut-in pressure recovery data and well test analysis based on the pressure recovery data to identify and invert the existence and characteristics of cavities. The published literature "Well Test Model of Fractured-Void Reservoirs with Wells Drilled in Large-Scale Caves" (Acta Petrolei Sinica, 2009, 30(6):912-915) discloses the use of pressure recovery well test analysis technology to identify fractures and cavities, which can only identify cavities directly connected to the well. Chinese patent publication CN106599449B discloses a well test interpretation method for calculating the volume of cavities, which uses shut-in pressure recovery data and well test analysis based on the pressure recovery data to identify and invert the existence and characteristics of cavities. All of the above technologies use shut-in pressure recovery data and well test analysis based on the pressure recovery data to identify and invert the existence and characteristics of cavities. The problems with these systems are: for deep reservoirs, when shutting in the well for pressure recovery, test tubing and test tools need to be run. In the high temperature and high pressure downhole environment, the test tools are at high risk of failure, the test cycle is long, and the cost is high.

[0004] To overcome the difficulty of identifying caverns in deep carbonate salt reservoirs during pressure recovery testing, a production data testing analysis technique was attempted, which uses dynamic data from well production to identify fractures and caverns. The published document "Horizontal Well Production Data Analysis Model" (Petroleum Exploration and Development, 2010, 37(1): 99102) introduces a production data analysis method based on production-normalized pressure, but it only introduces the application of this method in conventional oil and gas reservoirs and does not establish an interpretation model and chart for cavern identification in production data, so it cannot be used to identify caverns and fractures in reservoirs. Chinese patent publication CN103995961A discloses a production data analysis method for test wells, which uses production data testing analysis technology. The above technologies all disclose a production data analysis method based on production-normalized pressure, but the problems with this method when used to identify caverns and fractures in reservoirs are: (1) Pressure and production are measured in days, and the data accuracy is insufficient; (2) The time of pressure and flow measurement is sometimes inconsistent, affecting the data quality; (3) There is currently no interpretation model and chart for cavern identification in production data. Summary of the Invention

[0005] The purpose of this invention is to solve the problems existing in the prior art and provide a method and system for rapid identification of caves and fractures in reservoirs. It establishes a reservoir production data analysis model containing caves and fractures and draws typical maps for identifying caves, which can quickly identify whether caves exist and whether caves are connected to the wellbore.

[0006] This invention is achieved through the following technical solution:

[0007] In a first aspect, the present invention provides a method for rapid identification of cavities and fractures in a reservoir, the method using pressure data and production data collected by a pressure gauge and a flow meter to obtain a double logarithmic chart, and using the double logarithmic chart to identify cavities and fractures in the reservoir.

[0008] A further improvement of the present invention is that the method includes:

[0009] S1, install pressure gauge and flow meter;

[0010] S2, set the pressure gauge and flow meter;

[0011] S3, estimate the time and duration of cave features, as well as the time of boundary features;

[0012] S4. Based on the estimated time of occurrence and duration of cave features and the time of occurrence of boundary features in step S3, set different timing frequencies.

[0013] S5. If the pressure gauge is installed at the wellhead, the pressure data it records is converted into bottom hole pressure data.

[0014] S6. Draw a double logarithmic chart based on the pressure data and production data measured by the pressure gauge and flow meter;

[0015] S7 uses a double logarithmic plot to identify cavities and fractures in reservoirs.

[0016] A further improvement of the present invention is that the operation of step S1 includes:

[0017] The pressure gauge and flow meter can be installed at the wellhead, or at the bottom of the well, or the pressure gauge can be installed at the bottom of the well and the flow meter at the wellhead.

[0018] A further improvement of the present invention is that the operation of step S2 includes:

[0019] Set the counting frequency of the pressure gauge and the flow meter to be the same, and also set the start counting time to be the same.

[0020] A further improvement of the present invention is that the operation of step S3 includes:

[0021] S31, collect formation permeability, porosity, saturation, reservoir thickness, formation temperature, and formation pressure;

[0022] S32, draw a curve, and preliminarily determine the time and duration of cave features and the time of boundary features on the curve.

[0023] A further improvement of the present invention is that the operation of drawing the curve in step S32 includes:

[0024] For oil wells, calculate the normalized pressure, normalized pressure derivative, normalized pressure integral, and normalized pressure integral derivative, and plot the corresponding four curves.

[0025] For a gas well, calculate the normalized pseudo-pressure, normalized pseudo-pressure derivative, normalized pseudo-pressure integral, and normalized pseudo-pressure integral derivative, and plot the corresponding four curves.

[0026] A further improvement of the present invention is that the operation of initially determining the time and duration of the appearance of cave features and the time of the appearance of boundary features on the curve in step S32 includes:

[0027] If a depression appears on the curve and the slope of the second half of the depression is 1, then the time corresponding to the start of the depression is determined to be the time when the cave feature appears, and the time between the start of the depression and the end of the depression is the duration of the cave feature.

[0028] If the slope at the end of the curve tends to be 1 or 0, then a boundary feature is determined to have appeared. The moment when the boundary feature appears is the moment when the boundary feature appears.

[0029] A further improvement of the present invention is that the operation of step S4 includes:

[0030] Set the timing frequency to record once per second or per minute during the initial well opening phase;

[0031] Set the timing frequency after the cave feature ends to record once per minute or hour;

[0032] Set the timing frequency after the boundary feature appears to be recorded once per hour or once per day.

[0033] A further improvement of the present invention is that the operation of step S6 includes:

[0034] For oil wells, based on the pressure data and production data measured by pressure gauges and flow meters, calculate the normalized pressure, normalized pressure derivative, normalized pressure integral, and normalized pressure integral derivative. Plot the normalized pressure and normalized pressure derivative curves on a double logarithmic plot, or plot the normalized pressure integral and normalized pressure integral derivative curves, or plot all four curves simultaneously.

[0035] For gas wells, based on the pressure data and production data measured by pressure gauges and flow meters, calculate the normalized pseudo-pressure, normalized pseudo-pressure derivative, normalized pseudo-pressure integral, and normalized pseudo-pressure integral derivative. Plot the normalized pseudo-pressure and normalized pseudo-pressure derivative curves on a double logarithmic plot, or plot the normalized pseudo-pressure integral and normalized pseudo-pressure integral derivative curves, or plot all four curves simultaneously.

[0036] A further improvement of the present invention is that the horizontal axis of the double logarithmic graph is the material equilibrium time.

[0037] A further improvement of the present invention is that the operation of step S7 includes:

[0038] If four flow stages appear on the curve, it is determined that the well and the cave are directly connected;

[0039] If six flow stages appear on the curve, it is determined that the well and the cave are connected through a crack;

[0040] If three flow stages appear on the curve, it is determined that the well and the cave are not connected or that the cave does not exist.

[0041] A further improvement of the present invention is that the four flow stages are sequentially connected wellbore storage section, transition section, cavern storage section, and formation boundary response section; wherein the slopes of the wellbore storage section and the cavern storage section are both 1.

[0042] The six flow stages are sequentially connected as follows: wellbore storage stage, skin effect stage, fracture flow stage, transition stage, cavern storage stage, and formation boundary response stage; wherein, the slope of the wellbore storage stage is 1, the slope of the fracture flow stage is 1 / 2 or 1 / 4, the slope of the cavern storage stage tends to be 1, and the slope of the formation boundary response stage tends to be 1 or 0.

[0043] The three flow stages are the wellbore storage section, the skin effect section, and the formation boundary response section, which are connected in sequence. The slope of the wellbore storage section 1 is 1, and the slope of the formation boundary response section 3 tends to be 1 or 0.

[0044] A second aspect of the present invention provides a rapid identification system for caverns and fractures in reservoirs, the system comprising:

[0045] Input unit: Used to input basic parameters and data from pressure gauges and flow meters;

[0046] Estimation unit: Connected to the input unit, it uses basic parameters and data from pressure gauges and flow meters to estimate the timing and duration of cave feature appearance, as well as the timing of boundary feature appearance;

[0047] Timing frequency adjustment unit: connected to the estimation unit, used to adjust the timing frequency of the pressure gauge and flow meter according to the time and duration of cave features and the time of boundary features.

[0048] Chart drawing unit: connected to the input unit, used to draw double logarithmic charts based on pressure data and production data measured by pressure gauges and flow meters;

[0049] Identification Unit: Connected to the plotting unit, it is used to identify caverns and fractures in reservoirs using a double logarithmic plot.

[0050] Compared with the prior art, the beneficial effects of the present invention are:

[0051] This invention establishes a reservoir production data analysis model containing caves and fractures, and draws typical maps for identifying caves, enabling rapid identification of caves and fractures in reservoirs.

[0052] This invention uses high-resolution pressure gauges and flow meters to synchronously and frequently record pressure and production. Based on an established model, simulation calculations are performed, with different timing frequencies set: recording once per second or minute during the initial well opening phase, once per minute or hour after the cavern feature is established, and once per hour or day after boundary features begin to appear. The measured pressure and production data are processed, and the production-normalized pressure and its derivative are plotted on a logarithmic chart. The chart shape is then compared to identify the presence of caverns and whether these caverns are connected to the wellbore.

[0053] This invention uses production data analysis technology to identify the existence and connectivity of caves and fissures. It can identify both caves that are directly connected to wells and caves that are not connected to wells.

[0054] Using this invention, complete cavern features can typically appear within a few days of well production. Therefore, the existence of caverns and their connection to the wellbore can be quickly identified, providing basic information for the dynamic evaluation of this type of oil and gas reservoir. This plays an important role in ensuring the efficient development of oil and gas reservoirs and improving economic benefits. Attached Figure Description

[0055] Figure 1 Double logarithmic charts of production normalization (quasi-)pressure, normalization (quasi-)pressure derivative, production normalization (quasi-)pressure integral, and production normalization (quasi-)pressure integral derivative;

[0056] Figure 2 The well is directly connected to the cave;

[0057] Figure 3 The well is connected to the cave through a fissure;

[0058] Figure 4 The well is not connected to the cave or the cave does not exist;

[0059] Figure 5 A flowchart illustrating the steps of the method of this invention;

[0060] Figure 6 A schematic diagram of the system composition of this invention. Detailed Implementation

[0061] The present invention will now be described in further detail with reference to the accompanying drawings:

[0062] (I) Establishing a flow model:

[0063] This invention makes the following assumptions:

[0064] (1) The formation is an isotropic oil reservoir with a variable production oil and gas well at the center.

[0065] (2) The outer part of the stratum is a homogeneous medium;

[0066] (3) Considering the slight compressibility of the fluid, we assume that the compressibility coefficient is very small and the velocity of the fluid during the motion is also very small.

[0067] Fluid flows from the cave into the well shaft and then out of the well shaft to the surface. This fluid flow process must satisfy the continuity equation, the momentum conservation equation, and the energy conservation equation:

[0068]

[0069]

[0070]

[0071] In the formula: ρ is the fluid density, kg / m³ 3 v is the fluid flow velocity, m / s; the x-axis is a one-dimensional coordinate axis established downwards from the center of the wellbore; p is the pressure, Pa; f is the coefficient of friction experienced by the fluid; D is the diameter of the wellbore, m; p wf and p v The pressures in the wellbore and the cavern, respectively, are in Pa; v wf The velocity of the fluid at the junction of the wellbore and the cavern is expressed in m / s.

[0072] Solving the simultaneous equations, the relationship between the pressure inside the wellbore and the pressure inside the cavern is obtained as follows:

[0073]

[0074] In the formula: C is the wave velocity in the oil pipe and fluid system, m / s; C v Let m be the storage constant of the cave. 3 / MPa; v0 is the initial velocity, m / s; r v Let be the radius of the cave, in meters (m).

[0075] In the flow model of fractured-vuggy oil and gas reservoirs, the flow equation consists of three parts: wellbore, vuggy reservoir, and formation. For the external formation, the seepage equation is still used:

[0076]

[0077] Where: k is the bedrock permeability, md; p1 is the pressure in the bedrock corresponding to the wellbore location, Pa; p is the pressure, Pa; C t φ is the bedrock compressibility coefficient, 1 / Pa; φ is the bedrock porosity, dimensionless.

[0078] Of course, depending on the different geological characteristics, equations such as dual-pore flow and dual-infiltration flow can also be used to characterize external geological flow.

[0079] By defining the skin of the wellbore and the cavern, the pressure p in the formation and the pressure p in the cavern can be compared. v Connecting them:

[0080]

[0081] In the formula: s v denoted as the surface coefficient of the cave; r is the distance from the center of the shaft or the center of the cave, in meters; r v Let be the radius of the cave, in meters (m).

[0082] Based on the storage constants of the wellbore and the cavern, and the constant production rate, the boundary conditions within the wellbore can be expressed as:

[0083]

[0084] In the formula: B is the fluid volume coefficient, dimensionless; q is the production rate, m 3 / s; t is time, s; r w r is the wellbore radius (m); h is the reservoir thickness (m); μ is the fluid viscosity (Pa·s); v C is the radius of the cave, in meters; v Let m be the cave storage constant. 3 / Pa;

[0085] Define the following dimensionless quantity:

[0086] In the formula: t D t is dimensionless time; hr is time.

[0087] In the formula: p D For dimensionless pressure; p i The original formation pressure is given in Pa.

[0088] In the formula: p vD Dimensionless cave pressure;

[0089] In the formula: q D Dimensionless output;

[0090] In the formula: r D r is the dimensionless distance; rw is the wellbore radius, in meters.

[0091] C vD The dimensionless cavern storage constant;

[0092] β is the dimensionless cave flow constant;

[0093] γ is the dimensionless cave fluctuation coefficient.

[0094] Combining equations (4) and (7) and performing dimensionless processing, the model of fluid flow in the coupled wellbore-cavity-formation is obtained as follows:

[0095]

[0096] Applying the Laplace transform to the formation seepage equation, wellbore and cavern equations, the equations in Laplace space are as follows:

[0097]

[0098] For an infinitely large stratum, the outer boundary condition in Laplace space can be expressed as:

[0099]

[0100] The solution to the system of equations (9) is:

[0101]

[0102] Of course, the stratigraphic boundary can be an infinitely large stratigraphic unit, a closed boundary, an isopyrostatic boundary, etc. When the stratigraphic boundary is a closed boundary or an isopyrostatic boundary, the establishment and solution process is similar.

[0103] By performing a Laplace numerical inversion on the dimensionless yield solution (11) in Laplace space, the true yield solution q can be obtained. D (t D ):

[0104]

[0105] Where N is an even number, generally between 8 and 16, and n and j are variables.

[0106] Substituting formulas (12) and (13) into formula (14) yields the actual output q(t).

[0107]

[0108]

[0109] Formula (14) represents the relationship between actual flow rate and dimensionless actual flow rate. In formula (14), q... D It is derived from formula (12), and formula (12) uses t. D , this t D It is obtained from formula (13).

[0110] (ii) Calculate the normalized (pseudo) pressure, normalized (pseudo) pressure derivative, normalized (pseudo) pressure integral, and normalized (pseudo) pressure integral derivative. For oil wells, it is called "pressure", for gas wells, it is called "pseudo pressure", and so on.

[0111] For oil and gas wells where daily production and pressure vary over time, the production-normalized (pseudo) pressure is calculated based on the obtained original formation pressure, bottom hole flowing pressure, and daily production. If bottom hole flowing pressure data is not measured, the casing pressure or oil pressure data measured at the wellhead is converted to bottom hole flowing pressure through pressure conversion.

[0112]

[0113] In the formula: RNP is the production normalization pressure (for oil wells), or the production normalization pseudo-pressure (for gas wells). i p represents the original formation pressure. wf Let q represent the bottom hole pressure, t represent time, and q represent the production rate. i ψ represents the original formation pseudo-pressure of the gas well. wf This indicates the simulated pressure at the bottom of the gas well.

[0114] For gas wells, simulated pressure is used instead of actual pressure:

[0115]

[0116] In the formula: ψ is the simulated pressure of the gas well, MPa 2 / cp; z is the gas compressibility factor; p is the pressure, Pa; p0 is the original pressure, Pa.

[0117] Calculation of material equilibrium time

[0118]

[0119] The derivative of the normalized (quasi-)pressure of output is obtained by differentiating the output normalization (quasi-)pressure with respect to cumulative output or material balance time:

[0120]

[0121] Where: RNP d This is the normalized (pseudo) pressure derivative for output.

[0122] Integrating the output normalization (pseudo) pressure yields the output normalization (pseudo) pressure integral:

[0123]

[0124] Where: RNP i The integral of the output normalization (pseudo) pressure.

[0125] Differentiating the obtained normalized (quasi-)pressure integral on a double logarithmic coordinate system yields the derivative of the normalized (quasi-)pressure integral:

[0126]

[0127] Where: RNP id The integral derivative of the normalized (quasi) pressure for output.

[0128] (III) Drawing of Double Logarithmic Charts

[0129] For a given oil and gas well type, oil and gas reservoir type, inner boundary type, outer boundary type, and fluid type, using the production-time relationship model established in Parts (I) and (II), with material balance time as the abscissa, four corresponding curves can be plotted on a double logarithmic coordinate system according to formulas (15), (18), (19), and (20). These curves are the production normalized (pseudo)pressure curve, the normalized (pseudo)pressure derivative curve, the production normalized (pseudo)pressure integral curve, and the production normalized (pseudo)pressure integral derivative curve, forming a double logarithmic chart, as shown below. Figure 1 As shown.

[0130] These four curves are the result calculated based on the flow model. The q used in formulas (15), (18), (19), and (20) is the q calculated using formula (14).

[0131] It can plot four curves: normalized (quasi-)pressure, normalized (quasi-)pressure derivative, normalized (quasi-)pressure integral, and normalized (quasi-)pressure integral derivative. While all four curves can be used simultaneously, plotting four curves on the same graph can be quite messy. Furthermore, two of these curves can already reflect the desired cave and crack features. Therefore, for convenience in practical applications, it is generally only necessary to use two curves simultaneously: normalized (quasi-)pressure and normalized (quasi-)pressure derivative, or normalized (quasi-)pressure integral and normalized (quasi-)pressure integral derivative.

[0132] (iv) Rapid identification methods for caves and fractures in reservoirs

[0133] like Figure 5 As shown, the rapid identification method for caverns and fractures in reservoirs according to the present invention includes:

[0134] S1, Install pressure gauge and flow meter:

[0135] Both the pressure gauge and flow meter can be installed at the wellhead, both at the bottom of the well, or one at the bottom and one at the wellhead. If conditions permit for lowering the pressure gauge to the bottom of the well when setting up the test string, it is recommended to lower the pressure gauge to the bottom of the well.

[0136] The pressure gauge and flow meter mentioned are existing pressure gauges and flow meters, as long as the sampling accuracy meets the requirements in S4.

[0137] S2, set the pressure gauge and flow meter so that their counting frequencies are the same and their start counting times are the same.

[0138] S3, Estimating the time and duration of cave features:

[0139] Input basic parameters such as formation permeability, porosity, saturation, reservoir thickness, formation temperature, and formation pressure, and calculate the production normalized (pseudo) pressure, normalized (pseudo) pressure derivative, production normalized (pseudo) pressure integral, and production normalized (pseudo) pressure integral derivative according to formulas (15), (18), (19), and (20). (In actual production, if there is no data from pressure gauges or flow meters, the input basic parameters can be used for estimation. After obtaining measured data from pressure gauges and flow meters, the input basic parameters are also used for calculation. The parameters can also be adjusted at any time using measured data, and then estimated.) Then, draw the corresponding four curves and estimate the time and duration of cave feature appearance and boundary feature appearance on the four curves, as follows:

[0140] If a depression appears on the curve and the slope of the second half of the depression is 1, then the time corresponding to the start of the depression is determined to be the time when the cave feature appears, and the time between the start of the depression and the end of the depression is the duration of the cave feature.

[0141] If the slope at the end of the curve tends to be 1 or 0, then a boundary feature is determined to have appeared. The moment when the boundary feature appears is the moment when the boundary feature appears.

[0142] S4 sets different timing frequencies based on the estimated times of cave feature appearance and boundary feature appearance in S3, as follows:

[0143] Record data once per second or per minute during the initial well-opening phase, and once cave features are established (judgment is made based on four curves, using...). Figure 2 For example, in the diagram, the end of point 3 indicates the end of the cave feature. After that, data can be recorded every minute or hour, and boundary features will begin to appear (using...). Figure 2 For example, Figure 2 Once the boundary features appear in the middle and late stages of stage 4, records can be made hourly or daily.

[0144] S5. If the pressure gauge is installed at the wellhead, the pressure data it records is converted to the bottom hole pressure data using the existing algorithm, which will not be elaborated here.

[0145] S6. Using pressure data and production data measured by pressure gauges and flow meters, and formulas (15), (18), (19), and (20), calculate the normalized (pseudo) pressure, normalized (pseudo) pressure derivative, normalized (pseudo) pressure integral, and normalized (pseudo) pressure integral derivative. Then, plot two curves on a logarithmic coordinate system based on formulas (15), (18), (19), and (20), namely, the normalized (pseudo) pressure curve and the normalized (pseudo) pressure derivative curve, or the normalized (pseudo) pressure integral curve and the normalized (pseudo) pressure integral derivative curve, or plot four curves simultaneously, to form a logarithmic chart, such as... Figure 1 As shown, Figure 1 This corresponds to the situation where there are no caves near the well.

[0146] S7, by identifying cave feature segments on the double logarithmic chart, determines whether there is a cave near the well, and whether the cave is directly connected to the well or connected to the well shaft through a crack.

[0147] The specific criteria for rapid identification of cavities and fractures in reservoirs are as follows:

[0148] On the double logarithmic plot of normalized (pseudo)pressure and normalized (pseudo)pressure derivative (or normalized (pseudo)pressure integral and normalized (pseudo)pressure integral derivative), the three cases of direct connection between the well and the cavern, connection between the well and the cavern through a fracture, and no connection between the well and the cavern or no cavern correspond to different flow regimes:

[0149] like Figure 2 As shown, when the well and the cavern are directly connected, four flow stages will appear on the logarithmic chart (all four curves will show four flow stages): wellbore storage segment 1 (characterized by a slope of 1), transition segment 2, cavern storage segment 3 (characterized by a slope of 1), and formation boundary response segment 4, which are connected sequentially. Wellbore storage segment 1 has a slope of 1 on the production normalized pressure derivative, and the flow stages of transition segment 2 and cavern storage segment 3 are caused by the presence of the cavern, so they can be used to determine the presence of the cavern. When using the curves for judgment, the first segment with a slope of 1 on the curve is wellbore storage segment 1, the second segment with a slope of 1 is cavern storage segment 3, the segment between the two is transition segment 2, and the segment after the cavern storage segment is formation boundary response segment 4.

[0150] When a well is directly connected to a cave, cave features usually begin to appear within seconds or minutes of well production and continue for about 1-2 days. Therefore, the cave connected to the well shaft can be identified within 1-2 days of well production.

[0151] like Figure 3 As shown, when the well and the cavern are connected through fractures, the double logarithmic chart will show 6 flow stages (all 4 curves mentioned above will show 6 flow stages), which are connected in sequence as follows: wellbore storage segment 1 (characterized by a slope of 1), skin effect segment 2, fracture flow segment 3 (characterized by a slope of 1 / 2 or 1 / 4), transition segment 4, cavern storage segment 5 (characterized by a slope tending towards 1), and formation boundary response segment 6 (characterized by a slope tending towards 1 or 0).

[0152] Wellbore storage section 1 has a slope of 1 on the normalized pressure derivative of production, and the two flow stages, transition section 4 and cavern storage section 5, are caused by the presence of caverns, thus they can be used to determine the presence of caverns. Fracture flow section 3 has a slope of 1 / 2 or 1 / 4 on the normalized pressure derivative of production, thus it can be identified that the wellbore connects to the cavern through fractures. When using curves for judgment, the first segment with a slope of 1 on the curve is wellbore storage section 1, the segment with a slope of 1 / 2 or 1 / 4 is fracture flow section 3, the segment between the two is skin effect section 2, the second segment with a slope of 1 is cavern storage section 5, the segment between fracture flow section 3 and cavern storage section 5 is transition section 4, and the segment after cavern storage section 5 is formation boundary response section 6.

[0153] Because fractures in carbonate rocks generally have a high conductivity, the flow characteristics of the fractures can end within a few days, thus entering the cave characteristic stage. Therefore, caves can be quickly identified within a few days.

[0154] like Figure 4 When the well and cavern are not connected or there is no cavern, the logarithmic plot will show three flow stages (all four curves will show three flow stages): wellbore storage segment 1 (characterized by a slope of 1), skin effect segment 2, and formation boundary response segment 3 (characterized by a slope tending towards 1 or 0). Wellbore storage segment 1 has a slope of 1, formation boundary response segment 3 has a slope tending towards 1 or 0, and the area between them is skin effect segment 2. Because there is no cavern flow characteristic (cavern flow characteristic is a depression with a slope of 1 in the latter half of the depression, such as...),... Figure 2 The combination of segments 2 and 3 in the text constitutes cave features (or, as in...) Figure 3 The combination of segments 4 and 5 in the curve represents cave features. Therefore, it can be determined that there is no cave, or although there is a cave, it is not connected to the wellbore. When using the curve for judgment, the first segment with a slope of 1 is the wellbore storage segment 1, the second segment with a slope of 1 or the first segment with a slope of 0 is the formation boundary response segment 3, and the segment in between is the skin effect segment 2.

[0155] Specifically, four curves are obtained through S6, and the changes in the slope of the curves are observed. If four flow stages appear as the material balance time progresses, it is determined that the well and the cave are directly connected. If six flow stages appear as the material balance time progresses, it is determined that the well and the cave are connected through a crack. If three flow stages appear as the material balance time progresses, it is determined that the well and the cave are not connected or that the cave does not exist.

[0156] This technology allows for the rapid identification of cavern features within a few days of well production, enabling quick assessment of cavern existence and its connection to the wellbore. This provides a basis for production dynamics prediction and development strategy formulation.

[0157] An embodiment of the method of the present invention is as follows:

[0158] Taking an oil well in a carbonate reservoir as an example, considering three scenarios—direct connection between the well and the cavern, connection between the well and the cavern through a fracture, and no connection between the well and the cavern or the absence of a cavern—double logarithmic plots of the production normalization pressure and the derivative of the production normalization pressure versus the material balance time were plotted.

[0159] ① When the well is directly connected to the cavern, four flow stages appear on the logarithmic plot: wellbore storage stage, transition stage, cavern storage stage, and formation boundary response stage. The cavern storage stage has a slope of 1 on the production-normalized pressure derivative, and the transition and cavern storage stages are caused by the presence of the cavern, thus they can be used to determine the presence of the cavern. Cavern characteristics begin to appear 5 seconds after well production begins, and cavern storage begins at 6 minutes, continuing until the end of 10 hours. Therefore, by continuously monitoring production and pressure data for 10 hours using this technique, caverns connected to the wellbore can be identified.

[0160] ② When the well and the cavern are connected through fractures, six flow stages appear on the double logarithmic plot: wellbore storage stage, skin effect stage, fracture flow stage, transition stage, cavern storage stage, and formation boundary response stage. The cavern storage stage has a slope of 1 on the production-normalized pressure derivative, and the transition and cavern storage stages are caused by the presence of the cavern, thus they can be used to determine its existence. The fracture flow stage has a slope of 1 / 2 on the production-normalized pressure derivative, thus indicating that the wellbore is connected to the cavern through fractures. Fracture flow characteristics appear approximately one hour after well production begins, and cavern characteristics appear after 50 hours of production, allowing for rapid identification of caverns within a few days.

[0161] ③ When the well and the cave are not connected or there is no cave, the logarithmic plot shows three flow stages: the wellbore storage stage, the skin effect stage, and the formation boundary response stage. Since no cave flow characteristics appear, it can be determined that there is no cave, or although there is a cave, it is not connected to the wellbore.

[0162] In summary, the existence of caverns and their connection to the wellbore can be quickly identified within 50 hours of well production, thus providing a basis for production dynamics prediction and development measures formulation.

[0163] After the above embodiments were implemented, the following effects were achieved: (1) The technology can reflect the complete flow stages in three situations: direct connection between the well and the cave, connection between the well and the cave through a crack, and no connection between the well and the cave or no cave. Therefore, it has good adaptability; (2) The existence of the cave can be determined by the transition flow section and the cave storage section, which provides a technical means for qualitatively judging the existence of the cave; (3) The connection between the cave and the well shaft can be quickly identified within 50 hours of well production.

[0164] This invention also provides a rapid identification system for caverns and fractures in reservoirs, such as... Figure 6 As shown, the system includes:

[0165] Input unit 10: Used to input basic parameters and data from pressure gauges and flow meters;

[0166] Estimation unit 20: Connected to input unit 10, it uses basic parameters and data from pressure gauges and flow meters to estimate the time and duration of cave feature appearance and the time of boundary feature appearance;

[0167] Timing frequency adjustment unit 30: connected to estimation unit 20, used to adjust the timing frequency of pressure gauge and flow meter according to the time and duration of cave feature appearance and the time of boundary feature appearance;

[0168] Chart drawing unit 40: connected to input unit 10, used to draw a double logarithmic chart based on pressure data and production data measured by pressure gauge and flow meter;

[0169] Identification unit 50: connected to the drawing unit 40, used to identify caverns and fractures in the reservoir using a double logarithmic drawing.

[0170] This invention presents a technology for rapidly identifying cavities and fractures in reservoirs. It establishes a data analysis model for reservoirs containing cavities and fractures and generates typical charts for cavity identification. High-resolution pressure gauges and flow meters are installed to synchronously record pressure and production at high frequency. Simulation calculations are performed based on the established model, with different timing frequencies set: recording once per second or minute during the initial well opening phase, once per minute or hour after cavity characteristics are established, and once per hour or day after boundary features begin to appear. The measured pressure and production data are processed, and the production-normalized pressure and its derivative are plotted on a logarithmic chart. The chart morphology is then compared to identify the presence of cavities and whether they are connected to the wellbore. This technology can reflect the complete flow stages in three scenarios: direct connection between the well and the cavity, connection through fractures, and no connection or absence of cavities. The presence of cavities can be determined by the transition flow section and the cavity storage section. It can quickly identify the connection between cavities and the wellbore within a few days of well opening, providing fundamental information for the dynamic evaluation of this type of reservoir. This plays a crucial role in ensuring efficient oil and gas reservoir development and improving economic benefits.

[0171] This invention can be applied to the field of reservoir evaluation and dynamic analysis of carbonate oil and gas reservoirs, tight oil and gas reservoirs, shale oil and gas reservoirs, geothermal reservoirs, and cavernous gas storage facilities.

[0172] This invention can provide a basis for evaluating the volume and geological reserves of oil and gas reservoirs, geothermal reservoirs, and cavernous gas storage facilities containing caves and fractures, optimizing the design of measures, deploying production capacity construction and adjustment plans, and evaluating economic benefits. It provides basic information for the dynamic evaluation of such reservoirs and plays an important role in ensuring efficient development and improving economic benefits.

[0173] Finally, it should be noted that the above technical solution is only one embodiment of the present invention. For those skilled in the art, based on the application methods and principles disclosed in the present invention, it is easy to make various types of improvements or modifications, and not limited to the methods described in the above specific embodiments of the present invention. Therefore, the methods described above are only preferred and have no limiting significance.

Claims

1. A method for rapid identification of caves and fractures in a reservoir, characterized in that: The method obtains a double logarithmic graph by pressure data and production data collected by the pressure gauge and the flow meter, and identifies the cave and the fracture in the reservoir by the double logarithmic graph; The method comprises: S1, installing a pressure gauge and a flow meter; S2, setting the pressure gauge and the flow meter; S3, estimating the appearing time and the duration of the cave feature and the appearing time of the boundary feature; S4, setting different timing frequencies according to the appearing time and the duration of the cave feature and the appearing time of the boundary feature estimated in step S3; S5, if the pressure gauge is installed at the wellhead, converting the pressure data recorded by the pressure gauge into bottom hole pressure data; S6, drawing a double logarithmic graph according to the pressure data and the production data measured by the pressure gauge and the flow meter; S7, identifying the cave and the fracture in the reservoir by the double logarithmic graph; The operation of step S3 comprises: S31, collecting the permeability, the porosity, the saturation, the reservoir thickness, the formation temperature and the formation pressure of the stratum; S32, drawing a curve, and preliminarily determining the appearing time and the duration of the cave feature and the appearing time of the boundary feature on the curve; The operation of preliminarily determining the appearing time and the duration of the cave feature and the appearing time of the boundary feature on the curve in step S32 comprises: If a concave appears on the curve, and the slope of the latter half of the concave is 1, it is determined that the appearing time corresponding to the starting point of the concave is the appearing time of the cave feature, and the time between the starting point of the concave and the ending point of the concave is the duration of the cave feature; If the slope of the rear end of the curve becomes 1 or 0, it is determined that the boundary feature appears, and the appearing time of the boundary feature is the appearing time of the boundary feature; The operation of step S6 comprises: For an oil well, calculating the production normalized pressure, the normalized pressure derivative, the production normalized pressure integral and the production normalized pressure integral derivative according to the pressure data and the production data measured by the pressure gauge and the flow meter, and drawing two curves of the production normalized pressure and the normalized pressure derivative, or drawing two curves of the production normalized pressure integral and the production normalized pressure integral derivative, or drawing four curves on the double logarithmic graph; For a gas well, calculating the production normalized pseudo pressure, the normalized pseudo pressure derivative, the production normalized pseudo pressure integral and the production normalized pseudo pressure integral derivative according to the pressure data and the production data measured by the pressure gauge and the flow meter, and drawing two curves of the normalized pseudo pressure and the normalized pseudo pressure derivative, or drawing two curves of the production normalized pseudo pressure integral and the production normalized pseudo pressure integral derivative, or drawing four curves on the double logarithmic graph; The operation of step S7 comprises:

2. The method for rapid identification of caves and fractures in a reservoir according to claim 1, characterized in that: If four flow stages appear on the curve, it is determined that the well is directly connected with the cave; If six flow stages appear on the curve, it is determined that the well is connected with the cave through the fracture; 3. The method for rapid identification of caves and fractures in a reservoir according to claim 1, characterized in that: If three flow stages appear on the curve, it is determined that the well is not connected with the cave or the cave does not exist. The operation of step S1 comprises: Installing the pressure gauge and the flow meter at the wellhead, or installing the pressure gauge and the flow meter at the bottom hole, or installing the pressure gauge at the bottom hole and installing the flow meter at the wellhead. The operation of step S2 comprises: The counting frequencies of the pressure gauge and the flow meter are set to be the same, and the starting counting time is also set to be the same.

4. The method for rapid identification of caves and fractures in a reservoir according to claim 1, characterized in that: The operation of drawing curves in the step S32 comprises: For oil wells, the normalized pressure, the derivative of the normalized pressure, the integral of the normalized pressure, and the derivative of the integral of the normalized pressure are calculated, and four corresponding curves are drawn; For gas wells, the normalized pseudo-pressure, the derivative of the normalized pseudo-pressure, the integral of the normalized pseudo-pressure, and the derivative of the integral of the normalized pseudo-pressure are calculated, and four corresponding curves are drawn.

5. The method for rapid identification of caves and fractures in a reservoir according to claim 1, characterized in that: The operation of the step S4 comprises: The counting frequency at the initial stage of opening the well is set to be recorded once per second or once per minute; The counting frequency after the end of the cave feature is set to be recorded once per minute or once per hour; The counting frequency after the appearance of the boundary feature is set to be recorded once per hour or once per day.

6. The method for rapid identification of caves and fractures in a reservoir according to claim 1, wherein: The horizontal coordinate of the double logarithmic graph is the material balance time.

7. The method for rapid identification of caves and fractures in a reservoir according to claim 1, wherein: The four flow stages are connected in sequence as a wellbore storage section, a transition section, a cave storage section, and a formation boundary response section; the slopes of the wellbore storage section and the cave storage section are both 1; The six flow stages are connected in sequence as a wellbore storage section, a skin effect section, a fracture flow section, a transition section, a cave storage section, and a formation boundary response section; the slope of the wellbore storage section is 1, the slope of the fracture flow section is 1 / 2 or 1 / 4, the slope of the cave storage section tends to 1, and the slope of the formation boundary response section tends to 1 or 0; The three flow stages are connected in sequence as a wellbore storage section, a skin effect section, and a formation boundary response section; the slope of the wellbore storage section is 1, and the slope of the formation boundary response section tends to 1 or 0.

8. A system for rapid identification of caves and fractures in a reservoir based on the method of any one of claims 1-7, characterized in that: The system comprises: an input unit for inputting basic parameters and data of the pressure gauge and the flow meter; an estimation unit connected with the input unit, which estimates the appearance time and duration of the cave feature and the appearance time of the boundary feature by using the basic parameters and the data of the pressure gauge and the flow meter; a counting frequency adjustment unit connected with the estimation unit, which adjusts the counting frequency of the pressure gauge and the flow meter according to the appearance time and duration of the cave feature and the appearance time of the boundary feature; a graph drawing unit connected with the input unit, which draws a double logarithmic graph according to the pressure data and the production data measured by the pressure gauge and the flow meter; an identification unit connected with the graph drawing unit, which identifies the cave and the fracture in the reservoir by using the double logarithmic graph.

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