Method for monitoring pore pressure of high-CO2-content carbonate rock in deep well

Abstract

The invention discloses a method for monitoring pore pressure of high-CO2-content carbonate rocks in a deep well. The method comprises the following steps: establishing a calibrated formation pressure set; calculating the pore pressure of the carbonate rock by using a DC index method and a sigma method; different weight coefficients are given to the carbonate rock pore pressure value, and the carbonate rock pore pressure at the well depth is calculated; obtaining a Pareto solution set of the weight coefficient by using a particle swarm algorithm, and taking the Pareto solution set as a reasonable interval of the weight coefficient; inverting a weight coefficient by using a least square method and updating the weight coefficient; and judging whether the weight coefficient is in a reasonable interval, and selecting a calculation strategy. According to the method, the DC index method and the sigma method are optimized, the pore pressure is comprehensively monitored from the two aspects of the drilling speed and the stratum strength through the weight coefficient, the Pareto solution set is obtained through the particle swarm algorithm to serve as the reasonable weight interval, the weight coefficient is determined in combination with the least square method, the carbonate rock pore pressure is monitored in real time, and the pore pressure calculation precision is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of drilling engineering in oil exploration and development, and particularly relates to a method for monitoring pore pressure of deep wells with high CO2 content in carbonate rocks. Background Art

[0002] Accurately predicting the pore pressure of carbonate rocks is a difficult problem in the industry. If the density of the drilling fluid is too low, it will lead to complex accidents such as gas invasion, overflow, well kick, well collapse, and even blowout. If the density of the drilling fluid is too high, it will increase the risk of drilling fluid loss, and the formation is easily contaminated, which is not conducive to oil and gas discovery. Managed pressure drilling is a commonly used technology when drilling carbonate rock formations. In the industry, pore pressure monitoring methods are often used in combination with managed pressure drilling devices to achieve safe drilling of carbonate rock formations. The widely used pore pressure monitoring methods are mainly divided into two categories: ① Drilling rate type: Using the direct relationship between drilling rate and pore pressure to monitor pore pressure, such as the standard drilling rate method, DC index method, etc. ② Formation strength type: Since abnormal pore pressure will reduce rock strength and improve rock drillability, rock strength is used to monitor pore pressure, such as the sigma method, rock strength method, etc. However, the formation mechanism of pore pressure in carbonate rocks is complex, and the accuracy of using only drilling rate type or formation strength type pore pressure monitoring methods is limited.

[0003] The patent with the publication number CN202210721290.3 discloses a method for monitoring formation pressure under managed pressure drilling conditions, which establishes a relationship model between gas logging values and swabbing pressure using an RNN neural network model based on a swarm optimization algorithm. When the gas suction volume is zero, the swabbing pressure is the pressure difference in the wellbore, and the formation pore pressure is the bottom hole pressure minus the pressure difference in the wellbore. However, the neural network model relied on by this method has high requirements for the amount of data and data validity, and the calculation accuracy cannot be guaranteed. The patent with the publication number CN109577969A discloses a method for calculating the pore pressure of carbonate rock formations based on the rock compressibility, which establishes a relationship model between the rock compressibility and the pore pressure through experiments, and realizes the prediction of pore pressure by analyzing the rock compressibility of carbonate rocks. However, the model of this method mainly obtains the relationship model through experiments, has a strong dependence on experimental samples, and has limitations in popularization and application. Summary of the Invention

[0004] The present invention is proposed to solve the problems existing in the prior art, and its purpose is to provide a method for monitoring pore pressure of deep wells with high CO2 content in carbonate rocks.

[0005] The present invention is realized through the following technical solutions:

[0006] A method for monitoring pore pressure of deep wells with high CO2 content in carbonate rocks, comprising the following steps:

[0007] S1. Take the formation depth and the pore pressure of the supercritical CO2 formation as the calibrated formation pressure set P;

[0008] S2. Collect the drilling data of the target well, and calculate the carbonate pore pressure by using the DC index method and the sigma method respectively;

[0009] S3. Assign different weight coefficients to the carbonate pore pressure values calculated by the DC index method and the sigma method, and calculate the carbonate pore pressure at the well depth; it can be understood that the two weight coefficients are obtained from the pore pressure monitoring methods of the drilling rate type and the formation strength type respectively, and the formation pressure is the carbonate pore pressure at the well depth;

[0010] S4. Take the calibrated formation pressure set P obtained in step S1 as the training data. By simplifying the weight coefficients into particles, use the particle swarm algorithm to obtain the weight coefficients that meet the algorithm termination conditions, and form the Pareto solution set of all possible weight coefficients as the reasonable weight interval Q;

[0011] S5. Take the latest calibrated two sets of formation pressures as the inversion data, and use the least squares method to invert P dc and P sigma of the weight coefficient Q dc 、Q sigma and update;

[0012] S6. Judge whether the weight coefficients Q dc 、Q sigma updated in step S5 are within the reasonable interval Q of the weight coefficients;

[0013] If Q dc 、Q sigma ∈Q, use the weight coefficient Q dc and P sigma to calculate the carbonate pore pressure P hi ;

[0014] If decide by expert.

[0015] In the above technical solution, the determination method of the supercritical CO2 formation in step S1 is: collect the gas logging value at the wellhead of the target well to calculate the partial pressure of CO2, and select the formation with the partial pressure of CO2 greater than 7.38 MPa as the supercritical CO2 formation; the calculation method of the partial pressure of O2 is a conventional method in the art, and the detailed calculation method can be found in the reference document "Real-time Monitoring Method for CO2 Volume Fraction in Gas Reservoirs during Gas Drilling".

[0016] In the above technical solution, the method for determining the pore pressure of the supercritical CO2 formation in step S1 is as follows: Observe the relationship between the flow rate difference at the inlet and outlet of the target wellhead and the density of the drilling fluid, and select the bottom hole pressure when the flow rate difference at the inlet and outlet is approximately zero as the pore pressure of the supercritical CO2 formation.

[0017] In the above technical solution, the expression of the calibrated formation pressure set P is:

[0018]

[0019] In the formula:

[0020] P is the calibrated formation pressure set;

[0021] h is the well depth set; h i is the formation depth, with the unit of m;

[0022] P h is the carbonate rock pore pressure set at the well depth h; P hi is the pore pressure at the well depth hi, with the unit of MPa.

[0023] In the above technical solution, the drilling data includes the drilling rate, the weight on bit, the rotational speed, the bit diameter, and the density of the drilling fluid.

[0024] In the above technical solution, the formula for calculating the carbonate rock pore pressure P dc using the DC exponent method in step S2 is:

[0025]

[0026] In the formula:

[0027] P dc is the carbonate rock pore pressure calculated using the DC exponent method, with the unit of MPa;

[0028] P v is the overburden pressure, with the unit of MPa;

[0029] n is the regional coefficient, dimensionless;

[0030] ROP is the mechanical drilling rate, with the unit of m / h;

[0031] RPM is the rotational speed, with the unit of revolutions per minute;

[0032] WOB is the weight on bit, with the unit of t;

[0033] D is the bit diameter, with the unit of mm;

[0034] ρ is the density of the drilling fluid, with the unit of g / cm 3 ;

[0035] dc is a parameter calculated using drilling parameters, dimensionless;

[0036] dcn is the normal trend line of dc, obtained by fitting the dc exponent of the normal pressure formation.

[0037] In the above technical solution, the carbonate rock pore pressure P is calculated using the sigma method in step S2 sigma The calculation formula is:

[0038]

[0039] In the formula:

[0040] P sigma is the carbonate rock pore pressure calculated using the sigma method, with the unit of MPa;

[0041] ρ is the density of the drilling fluid, with the unit of g / cm 3 ;

[0042] J, N, and F are intermediate calculation parameters of the model, dimensionless;

[0043] h i is the formation depth, with the unit of m;

[0044] WOB is the weight on bit, with the unit of t;

[0045] RPM is the rotational speed, with the unit of revolutions per minute;

[0046] D is the bit diameter, with the unit of mm;

[0047] ROP is the rate of penetration, with the unit of m / h.

[0048] In the above technical solution, the carbonate rock pore pressure at the well depth in step S3 is as follows:

[0049]

[0050] In the formula:

[0051] h i is the well depth, with the unit of m;

[0052] P hi is the carbonate rock pore pressure at the well depth h i with the unit of MPa;

[0053] P dc is the carbonate rock pore pressure calculated using the DC exponent method, with the unit of MPa;

[0054] P sigma is the carbonate rock pore pressure calculated using the sigma method, with the unit of MPa;

[0055] Q dc is the weight coefficient of carbonate pore pressure calculated by the DC index method, with an initial value of 0.5, dimensionless;

[0056] Q sigma is the weight coefficient of carbonate pore pressure calculated by the sigma method, with an initial value of 0.5, dimensionless.

[0057] In the above technical solution, the expression of the reasonable interval Q of the weight in step S4 is:

[0058] Q = [min(Q sigma ), max(Q sigma )]

[0059] In the formula: min(Q sigma ) is the minimum value of the weight coefficient Q of the carbonate pore pressure calculated by the sigma method, dimensionless; max(Q sigma ) is the maximum value of the weight coefficient Q of the carbonate pore pressure calculated by the sigma method, dimensionless. sigma ) is the minimum value of the weight coefficient Q of the carbonate pore pressure calculated by the sigma method, dimensionless; max(Q sigma ) is the maximum value of the weight coefficient Q of the carbonate pore pressure calculated by the sigma method, dimensionless.

[0060] In the above technical solution, the two groups of newly calibrated formation pressures in step S5 are P hi-1 , P hi .

[0061] In the above technical solution, the decision made by the expert in step S6 is decision plan one or decision plan two;

[0062] The specific content of decision plan one is: randomly select a subset P1 of the calibrated formation pressure set P, use the particle swarm optimization algorithm to obtain a new Pareto solution set of weight coefficients as the reasonable interval Q of the weight coefficients. If Q dc , then repeat decision plan one. If Q dc , Q sigma ∈Q, execute step S5;

[0063] The number of elements in the subset P1 is not less than 3;

[0064] The specific content of decision plan two is: do not update the weight coefficients and execute step S5.

[0065] The beneficial effects of the present invention are:

[0066] The present invention provides a method for monitoring pore pressure of deep well high-CO2 carbonate rock. Relying on the characteristic that CO2 presents a supercritical state under high temperature and high pressure conditions, pore pressure calibration is achieved. On this basis, according to the complex pressure-forming mechanisms of chemistry, mechanics, and biology in carbonate rock formations, the DC index method and the sigma method are preferably selected, and the pore pressure is comprehensively monitored from two aspects of drilling speed and formation strength by using a weight coefficient. The particle swarm algorithm is used to obtain the Pareto solution set as a reasonable weight interval, and the least squares method is combined to determine the weight coefficient, thereby forming a method for monitoring pore pressure of carbonate rock. Description of the Drawings

[0067] Figure 1 is a flow chart of the method of the present invention;

[0068] Figure 2 is a schematic diagram of formation calibration pore pressure in Embodiment 1 of the present invention;

[0069] Figure 3 is a schematic diagram of a reasonable weight interval and weight coefficient in Embodiment 1 of the present invention;

[0070] Figure 4 is a diagram of the monitoring result of formation pore pressure in Embodiment 1 of the present invention.

[0071] For those of ordinary skill in the art, without creative efforts, other related drawings can be obtained based on the above drawings. Detailed Embodiments

[0072] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be further described below with reference to the drawings in the specification and through specific embodiments.

[0073] Embodiment 1

[0074] Taking Well H2 in the South Yellow Sea Basin as an example, as Figure 1 shown, a method for monitoring pore pressure of deep well high-CO2 carbonate rock includes the following steps:

[0075] S1. Take the formation depth and the pore pressure of the supercritical state CO2 formation as the calibration formation pressure set P;

[0076] The determination method of the supercritical state CO2 formation in step S1 is: collect the gas logging value at the wellhead of the target well to calculate the partial pressure of CO2, and select the formation with the partial pressure of CO2 greater than 7.38 MPa as the supercritical state CO2 formation;

[0077] The determination method of the pore pressure of the supercritical state CO2 formation in step S1 is: observe the relationship between the flow difference at the inlet and outlet of the wellhead of the target well and the density of the drilling fluid, and select the bottom hole pressure when the flow difference at the inlet and outlet is approximately zero as the pore pressure of the supercritical state CO2 formation, asFigure 2 as shown;

[0078] The expression of the calibrated formation pressure set P is:

[0079]

[0080] In the formula:

[0081] P is the calibrated formation pressure set;

[0082] h is the well depth set; h i is the formation depth, with the unit of m;

[0083] P h is the carbonate rock pore pressure set at well depth h; P hi is the pore pressure at well depth hi, with the unit of MPa.

[0084] S2. Collect the drilling data of the target well, and calculate the carbonate rock pore pressure by using the DC index method and the sigma method respectively;

[0085] The drilling data includes drilling speed, drilling pressure, rotation speed, bit diameter and drilling fluid density;

[0086] The calculation formula for calculating the carbonate rock pore pressure P by using the DC index method dc is:

[0087]

[0088] In the formula:

[0089] P dc is the carbonate rock pore pressure calculated by using the DC index method, with the unit of MPa;

[0090] P v is the overburden pressure, with the unit of MPa;

[0091] n is the regional coefficient, dimensionless;

[0092] ROP is the mechanical drilling speed, with the unit of m / h;

[0093] RPM is the rotation speed, with the unit of revolutions per minute;

[0094] WOB is the drilling pressure, with the unit of t;

[0095] D is the bit diameter, with the unit of mm;

[0096] ρ is the drilling fluid density, with the unit of g / cm 3 ;

[0097] dc is the parameter calculated by using the drilling parameters, dimensionless;

[0098] The DCN is the normal trend line of DC, which is obtained by fitting the DC index of the normal pressure formation.

[0099] Calculate the carbonate pore pressure P using the sigma method sigma The calculation formula is:

[0100]

[0101] In the formula:

[0102] P sigma is the carbonate pore pressure calculated using the sigma method, with the unit of MPa;

[0103] ρ is the density of the drilling fluid, with the unit of g / cm 3 ;

[0104] J, N, and F are intermediate calculation parameters of the model, dimensionless;

[0105] h i is the formation depth, with the unit of m;

[0106] WOB is the weight on bit, with the unit of t;

[0107] RPM is the rotational speed, with the unit of revolutions per minute;

[0108] D is the bit diameter, with the unit of mm;

[0109] ROP is the rate of penetration, with the unit of m / h.

[0110] S3. Assign different weight coefficients to the carbonate pore pressure values calculated using the DC index method and the sigma method, and calculate the carbonate pore pressure at the well depth;

[0111] The carbonate pore pressure at the well depth is shown in the following formula:

[0112]

[0113] In the formula:

[0114] h i is the well depth, with the unit of m;

[0115] P hi is the carbonate pore pressure at the well depth h i with the unit of MPa;

[0116] P dc is the carbonate pore pressure calculated using the DC index method, with the unit of MPa;

[0117] P sigma is the carbonate pore pressure calculated using the sigma method, with the unit of MPa;

[0118] Q dc is the weight coefficient of carbonate pore pressure calculated by the DC index method, with an initial value of 0.5, dimensionless;

[0119] Q sigma is the weight coefficient of carbonate pore pressure calculated by the sigma method, with an initial value of 0.5, dimensionless.

[0120] S4. Use the calibrated formation pressure set P obtained in step S1 as training data, and use the particle swarm optimization algorithm to obtain the Pareto solution set of the weight coefficients, and use the Pareto solution set as the reasonable interval Q of the weight coefficients;

[0121] The expression of the reasonable weight interval Q is:

[0122] Q = [min(Q sigma ), max(Q sigma )]

[0123] where: min(Q sigma ) is the minimum value of the weight coefficient Q of the carbonate pore pressure calculated by the sigma method, dimensionless; max(Q sigma ) is the maximum value of the weight coefficient Q of the carbonate pore pressure calculated by the sigma method, dimensionless. sigma ) for the weight coefficient Q of the carbonate pore pressure calculated by the sigma method sigma is dimensionless.

[0124] S5. Use the latest calibrated two sets of formation pressures as inversion data, and use the least squares method to invert the weight coefficients Q dc of P sigma and P dc and update them, as shown in sigma ; Figure 3 shown;

[0125] The latest calibrated two sets of formation pressures are P hi-1 , P hi ;

[0126] S6. Judge whether the weight coefficients Q dc , Q sigma updated in step S5 are within the reasonable interval Q of the weight coefficients;

[0127] If Q dc , Q sigma ∈Q, use the weight coefficient Q dc and P sigma to calculate the carbonate pore pressure P hi , as shown in Figure 4 shown;

[0128] If Q dc , Decided by experts.

[0129] The experts make a decision for Decision Plan 1 or Decision Plan 2;

[0130] Specifically, Decision Plan 1 is as follows: randomly select a subset P1 of the calibrated formation pressure set P, use P1 as training data, and use the particle swarm algorithm to obtain a new Pareto solution set of weight coefficients as the reasonable interval Q of the weight coefficients. If Q dc 、 Then repeat Decision Plan 1. If Q dc 、Q sigma ∈Q, execute step S5; the number of elements in the subset P1 is not less than 3;

[0131] Decision Plan 2 is as follows: do not update the weight coefficients and execute step S5.

[0132] The present invention combines the drilling rate type and formation strength type pore pressure monitoring methods, can monitor the formation pressure under different pressure formation mechanisms of carbonate rocks; the main calculation parameters are all parameters that can be obtained through on-site conventional operations, and have strong popularization; a new weight coefficient calculation method is provided, which can correct the carbonate rock pore pressure calculation results in real time, improve the accuracy of pore pressure calculation, has the characteristics of real-time and quantitative evaluation.

[0133] The applicant declares that the above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and public scope of the present invention.

Claims

1. A method for monitoring pore pressure of carbonate rock with high CO2 content in deep wells, characterized by: The following steps are involved: S1, taking the formation depth and the pore pressure of the supercritical CO2 formation as the calibration formation pressure set P; S2, collecting drilling data of the target well, and calculating the carbonate pore pressure using the DC index method and the sigma method respectively; S3, assigning different weight coefficients to the carbonate rock pore pressure values ​​calculated by the DC index method and the sigma method to calculate the carbonate rock pore pressure at the depth of the well; S4, using the calibrated formation pressure set P obtained in step S1 as training data, using the particle swarm algorithm to obtain the Pareto solution set of the weight coefficient, and using the Pareto solution set as the reasonable interval Q of the weight coefficient; S5. Use the two most recently calibrated formation pressures as inversion data and use the least squares method to invert P dc With P sigma The weight coefficient Q dc , Q sigma and update it; S6: Determine the weight coefficient Q after the update in step S5 dc , Q sigma Whether it is within the reasonable range Q of the weight coefficient; If Q dc , Q sigma ∈Q, using the weight coefficient Q dc With P sigma Calculation of carbonate rock pore pressure P hi ; If Q dc , Decisions made by experts.

2. The method for monitoring pore pressure of carbonate rock with high CO2 content in deep well according to claim 1 is characterized by: The method for determining the supercritical CO2 formation in step S1 is: collecting the gas measurement value at the wellhead of the target well to calculate the CO2 partial pressure, and selecting the formation with a CO2 partial pressure greater than 7.38 MPa as the supercritical CO2 formation.

3. The method for monitoring pore pressure of deep well high CO2 carbonate rock according to claim 1 is characterized by: The method for determining the pore pressure of the supercritical CO2 formation in step S1 is: observing the relationship between the inlet and outlet flow rate difference of the target well and the drilling fluid density, and selecting the bottom hole pressure when the inlet and outlet flow rate difference is approximately zero as the pore pressure of the supercritical CO2 formation.

4. The method for monitoring pore pressure of deep well high CO2 carbonate rock according to claim 1 is characterized in that: The expression of the calibration formation pressure set P is: Where: P is the set of calibrated formation pressures; h is the well depth set; h i is the formation depth, in m; P h is the carbonate rock pore pressure at the well depth h; P hi is the pore pressure at the well depth hi, in MPa.

5. The method for monitoring pore pressure of deep well high CO2 carbonate rock according to claim 1 is characterized in that: The drilling data includes drilling speed, drilling pressure, rotation speed, drill bit diameter and drilling fluid density.

6. The method for monitoring pore pressure of deep well high CO2 carbonate rock according to claim 1 is characterized by: In step S2, the DC index method is used to calculate the carbonate rock pore pressure P dc The calculation formula is: Where: P dc is the carbonate rock pore pressure calculated using the DC index method, in MPa; P v is the overburden pressure, in MPa; n is the area coefficient, dimensionless; ROP is the mechanical drilling rate, in m / h; RPM is the rotation speed, in revolutions per minute; WOB is the bit weight, in t; D is the drill bit diameter, in mm; ρ is the drilling fluid density, in g / cm 3 ; dc is the parameter calculated using drilling parameters and is dimensionless; dcn is the normal trend line of dc, obtained by fitting the dc exponential of normal pressure formation; In step S2, the sigma method is used to calculate the carbonate rock pore pressure P sigma The calculation formula is: Where: P sigma is the pore pressure of carbonate rock calculated by sigma method, in MPa; ρ is the drilling fluid density, in g / cm 3 ; J, N, and F are intermediate calculation parameters of the model and are dimensionless; h i is the formation depth, in m; WOB is the bit weight, in t; RPM is the rotation speed, in revolutions per minute; D is the drill bit diameter, in mm; ROP is the mechanical drilling rate, measured in m / h.

7. The method for monitoring pore pressure of deep well high CO2 carbonate rock according to claim 1 is characterized by: The carbonate rock pore pressure at the depth of the well in step S3 is as shown in the following formula: Where: h i is the well depth, in m; P hi is the well depth h i The carbonate rock pore pressure at , in MPa; P dc is the carbonate rock pore pressure calculated using the DC index method, in MPa; P sigma is the pore pressure of carbonate rock calculated by sigma method, in MPa; Q dc is the weight coefficient of carbonate pore pressure calculated by DC index method, with an initial value of 0.5 and dimensionless; Q sigma is the weight coefficient of carbonate rock pore pressure calculated by sigma method, with an initial value of 0.5 and dimensionless.

8. The method for monitoring pore pressure of deep well high CO2 carbonate rock according to claim 1 is characterized by: The expression of the reasonable weight interval Q in step S4 is: Q=[min(Q sigma ),max(Q sigma )] Where: min(Q sigma ) is the minimum value of the weight coefficient Qsigma of carbonate rock pore pressure calculated by the sigma method, which is dimensionless; max(Q sigma ) is the weight coefficient Q of carbonate rock pore pressure calculated by sigma method sigma The maximum value of , dimensionless.

9. The method for monitoring pore pressure of carbonate rock with high CO2 content in deep well according to claim 1, characterized in that: The two groups of formation pressures most recently calibrated in step S5 are P hi-1 , P hi .

10. The method for monitoring pore pressure of deep well high CO2 carbonate rock according to claim 1, characterized in that: In step S6, the expert makes a decision as decision plan 1 or decision plan 2; The first decision-making scheme is specifically as follows: randomly select a subset P1 of the calibrated formation pressure set P, use the subset P1 as training data, and use the particle swarm algorithm to obtain a new Pareto solution set of weight coefficients as a reasonable interval Q of weight coefficients. If Q dc , Then repeat decision plan 1. If Q dc , Q sigma ∈Q, execute step S5; The number of elements in the subset P1 is not less than 3; The second decision-making scheme is: do not update the weight coefficient and execute step S5.

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