Early and mid-term production prediction methods for coalbed methane wells in medium and high-rank coal reservoirs

Abstract

This invention relates to a method for predicting the early and mid-stage production of coalbed methane wells in medium- to high-rank coal reservoirs. The method includes: determining whether the coalbed methane well is located in a medium- to high-rank coal reservoir based on the average random reflectance of the vitrinite group; obtaining reservoir parameters of the medium- to high-rank coal reservoir where the well is located, including the well point gas content, reservoir stratigraphic coefficient, and well structural location; establishing a geological potential evaluation model for the well based on these parameters; denoising the gas production data; obtaining the critical analytical pressure of the reservoir and the bottomhole flowing pressure after the well production has stabilized; calculating the apparent analytical coefficient of the well; and establishing a drainage potential evaluation model for the well; and using the denoised production data from the geological potential evaluation model and the drainage potential evaluation model, a comprehensive early and mid-stage production prediction model is established. This method can adjust and update the fitting coefficients in real time based on field production data, and is simple, convenient, fast, and has high prediction accuracy.

Description

Technical Field

[0001] This invention relates to the field of coalbed methane development, and more specifically, to a method for predicting the early and mid-stage production of coalbed methane wells in medium- and high-rank coal reservoirs. Background Technology

[0002] Coalbed methane (CBM) production prediction is highly challenging due to numerous factors, including geology, engineering conditions, and development timeline. Taking the Panhe Block, China's first CBM demonstration project, as an example, the target formations in this block are primarily concentrated in medium- and high-rank coal seams, and development is still in its early stages. Conventional prediction methods, mainly designed for the later stages of development with stable decline, are less applicable to this block. Therefore, it is necessary to establish a production prediction method for the early to mid-stages of medium- to high-rank coal reservoirs to analyze the production potential of gas wells and formulate reasonable development plans.

[0003] Currently, domestic and international methods for predicting coalbed methane production mainly include decline analysis, numerical simulation, and statistical methods. Decline analysis and statistical methods primarily rely on the data itself and are mainly applicable to wells with stable declines in the later stages of development, without considering the influence of geological, engineering, and other intrinsic factors, thus their prediction accuracy needs improvement. Numerical simulation requires long modeling times and demands high accuracy and completeness of reservoir data. When fitting historical gas production data, parameter adjustments are limited by experience, resulting in multiple solutions. Kang Yuanyuan, Zhang Hairu, Ren Jianhua, Cao Tengfei, and others have successively analyzed factors affecting gas production profiles and proposed corresponding prediction models, but these production capacity evaluation methods are mostly limited to the later stages of development. Kang Yongshang proposed a production prediction method for the early and mid-stages; however, this method does not subdivide coal rank and does not consider the influence of structural location on the gas production profile. In the same main coal seam in the Panzhuang block, influenced by factors such as stress environment and gravity migration of water and gas, structural location and gas well production capacity show a significant correlation, leading to limitations in this method for gas well production prediction in the Panzhuang block. Therefore, it is necessary to analyze the internal aspects such as gas reservoir geology and drainage to establish a method for predicting the early and mid-term production of coalbed methane wells in medium- to high-rank coal reservoirs. Summary of the Invention

[0004] To address the aforementioned problems, the purpose of this invention is to provide a method for predicting the early and mid-stage production of coalbed methane wells. This method is applicable to the production prediction of newly commissioned gas wells or gas wells in the early and mid-stages of development.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for predicting the early and mid-stage production of coalbed methane wells in medium- and high-rank coal reservoirs includes:

[0007] The average random reflectance of the vitrinite group is used to determine whether the coalbed methane reservoir is a medium- to high-rank coal reservoir.

[0008] Obtain the reservoir parameters of the medium-to-high-rank coal reservoir where the gas well is located. The reservoir parameters include the gas content at the well point, the gas reservoir formation coefficient, and the structural location of the gas well. Establish a gas well geological potential evaluation model based on the reservoir parameters of the medium-to-high-rank coal reservoir where the gas well is located.

[0009] Denoising gas well production data;

[0010] Obtain the critical analytical pressure of the reservoir where the gas well is located and the bottom hole flowing pressure after the gas well production is relatively stable, calculate the apparent analytical coefficient of the gas well, and establish a gas well drainage potential evaluation model;

[0011] A comprehensive production prediction model for the early and mid-term stages is established using production data after multiple regression denoising from gas well geological potential evaluation model and gas well drainage potential evaluation model.

[0012] A gas well geological potential evaluation model is established using the following formula:

[0013]

[0014] in,

[0015] P g Parameters for characterizing the geological potential of gas wells;

[0016] C g This refers to the gas content at the well point.

[0017] K represents the penetration rate;

[0018] H is the formation thickness; and

[0019] D represents the structural location of the main coal seam where the gas well is located.

[0020] The gas well production data denoising process uses a local weighted regression analysis method. First, gas well profile data is obtained, and the data is checked to see if it is continuous and stable. If the gas well data has poor continuity due to factors such as well opening / closing or power outages, the local weighted method is used to denoise the data.

[0021] The following formula is used to determine the stable production status of a gas well at a certain stage, and to obtain the corresponding bottom hole flowing pressure and production values: Stable Production Status Judgment Conditions

[0022] Gas well production fluctuation rate r over ten consecutive days q Less than 10% and the corresponding bottom hole flowing pressure fluctuation rate Less than 5%, which is manifested as:

[0023]

[0024]

[0025] in,

[0026] r q This represents the production fluctuation rate of a gas well over a continuous 10-day period.

[0027] q max This represents the maximum gas production of a gas well over 10 consecutive days.

[0028] q min This represents the minimum gas production rate of a gas well over 10 consecutive days.

[0029] q i This represents the gas production of the gas well on the i-th day out of a continuous 10-day period.

[0030] The bottomhole flowing pressure fluctuation rate of the gas well over 10 consecutive days;

[0031] This represents the maximum bottom-hole pressure of the gas well over a continuous 10-day period.

[0032] This represents the minimum bottom hole pressure of a gas well over a continuous 10-day period.

[0033] The bottom pressure of the gas well is on the i-th day out of 10 consecutive days.

[0034] Once the conditions for judging stable production are met, the stable gas production and bottom hole flowing pressure of the gas well are calculated using the following formula.

[0035]

[0036]

[0037] q represents the stable gas production of the gas well;

[0038] P wf This refers to the bottom flow pressure of the gas well.

[0039] The apparent resolution coefficient of a gas well is calculated using the following formula:

[0040]

[0041] in,

[0042] I is the apparent resolution coefficient of the gas well;

[0043] P cd For critical analytical pressure; and

[0044] P wf This refers to the bottom flow pressure of the gas well.

[0045] A gas well drainage potential evaluation model is established based on the following formula:

[0046] P d =emI

[0047] in,

[0048] P d Parameters characterizing the gas well drainage potential; and

[0049] m is a coefficient.

[0050] Using multiple regression analysis and denoised data, the geological potential evaluation model P is comprehensively considered according to the following formula. g 1. Extraction potential evaluation model P d A comprehensive prediction model for gas production q was established, and the model coefficients were fitted, where:

[0051] q=aP g +bP d +c

[0052] in:

[0053] q represents the stable gas production of the gas well;

[0054] P g Parameters for characterizing the geological potential of gas wells;

[0055] P d Parameters characterizing the gas well drainage potential;

[0056] a, b, and c are coefficients.

[0057] To predict the early and mid-term production of gas wells using the established production prediction model, the formation coefficient, structural location, and gas content of the gas well are first statistically analyzed. Then, given arbitrary bottom hole pressure data for the prediction stage, the apparent resolution coefficient is calculated, and the relatively stable gas production under the bottom hole pressure is predicted using the comprehensive early and mid-term production prediction model.

[0058] When the bottom pressure is close to 0, that is, when the apparent resolution coefficient approaches 1, the corresponding gas production is the peak gas production.

[0059] The present invention has the following advantages due to the adoption of the above technical solutions:

[0060] For early and mid-term production prediction of coalbed methane wells, under the condition of stable bottom hole flowing pressure, the comprehensive model proposed in this patent can be used to analyze the production increase pattern and predict the gas production potential of the well. This method fully considers the influence of geological, engineering and other factors on the gas production profile and solves the problem of production prediction for newly commissioned gas wells.

[0061] This avoids the uncertainties caused by unclear reservoir understanding in numerical simulation prediction of gas reservoirs, as well as the problems of complex, costly, and long-term numerical simulation methods.

[0062] The method of this invention can update and adjust the fitting coefficients in real time according to on-site production data. It is simple, convenient, fast and has high prediction accuracy. Attached Figure Description

[0063] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts. In the drawings:

[0064] Figure 1 This is a schematic flowchart of a method for predicting the early and mid-stage production of coalbed methane wells in medium- and high-rank coal reservoirs, according to an embodiment of this application.

[0065] Figure 2 This is a schematic diagram of the changes in bottom hole flowing pressure and gas production during a relatively stable phase according to an embodiment of this application.

[0066] Figure 3 This is a schematic diagram showing the variation of the apparent resolution coefficient with bottom hole flowing pressure according to an embodiment of this application.

[0067] Figure 4 This is a schematic diagram comparing the actual gas production of a gas well with the gas production calculated by the model according to an embodiment of this application. Detailed Implementation

[0068] Exemplary embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art.

[0069] According to some embodiments of this application, a method for predicting the early and mid-stage production of coalbed methane wells is provided, mainly including the following steps:

[0070] Step 1. Determine whether the coal seam containing the coalbed methane is of medium to high rank: the average random reflectance Ro of the vitrinite group should be ≥0.65%.

[0071] Step 2. Determine the geological potential P of coalbed methane wells g .

[0072] 2.1 Obtaining reservoir parameters where the gas well is located.

[0073] a. Determine the gas content C at the well point of the gas well. g Unit m 3 / t. This parameter is mainly obtained through indoor experiments. If the gas content at this well point is abnormal due to coring issues, the average gas content of the surrounding neighboring gas wells is taken as the gas content at this well point.

[0074] b. Determine the formation coefficient KH of the gas reservoir, in mD·m. The permeability K is obtained through laboratory core experiments, and the formation thickness H is obtained through well logging interpretation curves.

[0075] c. Determine the structural location D of the gas well, in meters (m). For gas wells with well logging interpretation results, this parameter is primarily obtained from those results. For gas wells without well logging interpretation results, the structural location is determined by drawing a map using known data.

[0076] 2.2 Establish a gas well geological potential evaluation model using equation (1):

[0077]

[0078] in:

[0079] P g Parameters for characterizing the geological potential of gas wells;

[0080] C g Gas content at well point, m 3 / t;

[0081] KH is the gas reservoir formation coefficient, mD·m;

[0082] K represents permeability, in mD;

[0083] H is the formation thickness, in meters;

[0084] D represents the structural location of the main coal seam where the gas well is located, in meters (m).

[0085] Step 3. Noise removal processing of gas well production data.

[0086] First, obtain gas well profile data and check whether the data is continuous and stable. If the gas well data has poor continuity due to factors such as well opening / closing or power outages, then use a local weighting method to denoise the data.

[0087] Step 4. Determine the stable production status of a gas well at a certain stage and obtain the corresponding stable gas production and bottom hole flowing pressure.

[0088] 4.1 Determine the stable production status of gas wells at a certain stage.

[0089] A gas well exhibits a gas production fluctuation rate of less than 10% for ten consecutive days and a corresponding bottomhole flowing pressure fluctuation rate of less than 5%, which is characterized by:

[0090]

[0091]

[0092] in,

[0093] r q This represents the production fluctuation rate of a gas well over a continuous 10-day period.

[0094] q max The maximum gas production of a gas well over 10 consecutive days, m 3 / d;

[0095] q min The minimum gas production of a gas well over 10 consecutive days, m 3 / d;

[0096] q i Let m be the gas production on day i out of a continuous 10-day period. 3 / d;

[0097] The bottomhole flowing pressure fluctuation rate of the gas well over 10 consecutive days;

[0098] The maximum bottom hole pressure of the gas well over 10 consecutive days, in MPa;

[0099] The minimum bottom hole pressure of the gas well over 10 consecutive days, in MPa;

[0100] Let be the bottom pressure of the gas well on the i-th day out of 10 consecutive days, in MPa.

[0101] 4.2 Calculate the stable gas production and bottom hole flowing pressure.

[0102] Once the conditions for determining stable production are met, the stable gas production and bottom hole flowing pressure are calculated using the following formula:

[0103]

[0104]

[0105] Step 5. Determine the evaluation model for the drainage potential of coalbed methane wells.

[0106] 5.1 Calculate the apparent resolution coefficient I of the gas well according to equation (6):

[0107]

[0108] in,

[0109] I is the apparent resolution coefficient of the gas well;

[0110] P cd The critical analytical pressure is given in MPa; and

[0111] P wf The bottom pressure of the gas well is MPa.

[0112] 5.2 Establish a gas well drainage potential evaluation model based on equation (7):

[0113] Pd = e mI (7)

[0114] in,

[0115] P d Parameters characterizing the gas well drainage potential; and

[0116] m is a coefficient.

[0117] Step 6. Establish a comprehensive gas production prediction model.

[0118] Using multiple regression analysis and combined with denoised data, a comprehensive gas production prediction model was established based on equation (8), taking into account both the geological potential evaluation model and the drainage potential evaluation model, and the model coefficients were fitted:

[0119] q = nP g +bP d +c (8)

[0120] in:

[0121] q represents gas production, m 3 / d;

[0122] P g Parameters for characterizing the geological potential of gas wells;

[0123] P d Parameters characterizing the gas well drainage potential;

[0124] a, b, and c are coefficients.

[0125] Step 7. Use the established production prediction model to predict the early and mid-term production of the gas well.

[0126] First, the formation coefficient, structural location, and gas content of the gas well are statistically analyzed. Then, given arbitrary bottom-hole pressure data for the prediction stage, the apparent resolution coefficient I is calculated. The model in step 6 is used to predict the relatively stable gas production under that bottom-hole pressure. Furthermore, when the bottom-hole pressure approaches 0, i.e., when the apparent resolution coefficient approaches 1, the corresponding gas production is the peak gas production.

[0127] Application Examples

[0128] The A coalbed methane block has an average coal seam thickness of 9.4 m and an average burial depth of 425 m. The vitrinite reflectance (Ro,max) of the main coal seam ranges from 1.20% to 4.25%. The average reservoir pressure is 2.45 MPa, and the average measured saturation is 115%, indicating a high gas storage capacity. Well W1 in block A is located in a coal seam with a reservoir thickness of 6.93 m, a permeability around the well of 1.21 mD, and a gas cut of 20.38 m³ / h. 3 / t, the main coal seam structure is located at 320m.

[0129] According to step 1, the reflectance Ro of the vitrinite group of the main coal seam is between 1.20% and 4.25%, which is greater than 0.65%, and belongs to medium- to high-rank coalbed methane.

[0130] Based on step 2, evaluate the geological potential of single well W1 in the block: input the data into the gas well geological potential evaluation model to calculate P. g = 9.48, the geological potential evaluation model satisfies:

[0131]

[0132] in,

[0133] P g Parameters for characterizing the geological potential of gas wells;

[0134] C g Gas content at well point, m 3 / t;

[0135] KH is the gas reservoir formation coefficient, mD·m;

[0136] K represents permeability, in mD;

[0137] H is the formation thickness, in meters; and

[0138] D represents the structural location of the main coal seam where the gas well is located, in meters (m).

[0139] Based on step 3, gas well production data denoising: First, obtain gas well profile data and check whether the data is continuous and stable. If the gas well data has poor continuity due to factors such as well opening and closing, power outages, etc., then use a local weighting method to denoise the data.

[0140] Based on step 4, the stable production status of the gas well at different stages was determined, and the corresponding bottom hole flowing pressure and production values ​​were obtained. By analyzing the gas well production data, the relationship between relatively stable gas production and bottom hole flowing pressure changes at each stage was plotted, such as... Figure 1 .

[0141] (1) Criteria for judging stable production

[0142] Gas well gas production fluctuation rate r over ten consecutive days qLess than 10% and the corresponding bottom hole flowing pressure fluctuation rate Less than 5%, which is manifested as:

[0143]

[0144]

[0145] in,

[0146] r q This represents the production fluctuation rate of a gas well over a continuous 10-day period.

[0147] q max The maximum gas production of a gas well over 10 consecutive days, m 3 / d;

[0148] q min The minimum gas production of a gas well over 10 consecutive days, m 3 / d;

[0149] q i Let m be the gas production on day i out of a continuous 10-day period. 3 / d;

[0150] The bottomhole flowing pressure fluctuation rate of the gas well over 10 consecutive days;

[0151] The maximum bottom hole pressure of the gas well over 10 consecutive days, in MPa;

[0152] The minimum bottom hole pressure of the gas well over 10 consecutive days, in MPa;

[0153] Let be the bottom pressure of the gas well on the i-th day out of 10 consecutive days, in MPa.

[0154] (2) Stable gas production and bottom hole flowing pressure values

[0155] Once the conditions in step (1) are met, calculate the gas production and bottom hole pressure as follows.

[0156]

[0157]

[0158] Based on step 5.1, the apparent resolution coefficient I for different stable stages in step 4 was calculated, and the curves showing the variation of the apparent resolution coefficient with bottom hole pressure were plotted, as follows. Figure 2 .

[0159]

[0160] in,

[0161] I is the apparent resolution coefficient of the gas well;

[0162] P cd The critical analytical pressure is given in MPa; and

[0163] P wf The bottom pressure of the gas well is MPa.

[0164] Based on step 5.2, a gas well drainage potential evaluation model is established. Combined with the geological potential evaluation model calculated in step 2, a multiple regression is performed on the stable gas production obtained in step 4. A comprehensive prediction model is then established according to step 6. For well W1 in this block, the fitted comprehensive prediction model for gas production q is as follows:

[0165] q = 249.6P g +643.3e 4.24I -1876

[0166] A comparison between the calculation results of the comprehensive prediction model and the actual gas production results is shown below. Figure 3 The last point was used as a verification point, and calculations showed that the actual daily gas production at that point was 11,895 m³. 3 The model calculates the daily gas production to be 12962 m³. 3 The error was 8.9%, indicating high prediction accuracy.

[0167] Based on step 7, any bottom hole flowing pressure P of well W1 can be given. wf The apparent resolution coefficient is calculated, and then the stable gas production under the bottom hole flowing pressure is calculated. When the bottom hole flowing pressure is 0.1 MPa, the apparent resolution coefficient can be obtained as 0.96 according to step 4, and the peak gas production is calculated according to the comprehensive prediction model, which is approximately 37,999 cubic meters per day.

[0168] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for early to mid-life production prediction of a coalbed methane well for a medium to high rank coal reservoir, characterized in that, The application relates to a method for early and medium-term production prediction of a gas well. The method comprises the following steps: According to the vitrinite average random reflectivity, it is determined whether the coal reservoir where the coalbed gas is located is a medium-high rank coal reservoir; Reservoir parameters of the medium-high rank coal reservoir where the gas well is located are obtained, the reservoir parameters comprising well point gas content, gas reservoir formation coefficient and gas well structure position of the gas well, and a gas well geological potential evaluation model is established according to the reservoir parameters of the medium-high rank coal reservoir where the gas well is located; The gas well production data are denoised; The critical desorption pressure of the reservoir where the gas well is located and the bottom hole flowing pressure after the gas well production is relatively stable are obtained, the apparent desorption coefficient of the gas well is calculated, and a gas well drainage potential evaluation model is established; By using the multivariate regression analysis method, combining the denoised gas well production data, using the gas well geological potential evaluation model and the gas well drainage potential evaluation model, an early and medium-term production comprehensive prediction model is established; The denoising of the gas well production data adopts the local weighted regression analysis method, first, the gas well profile data are obtained, and it is checked whether the gas well profile data are continuous and stable, if the gas well profile data are poor in continuity due to well opening and closing and power failure, the local weighted regression analysis method is used to denoise the gas well production data; 2. The method for early to mid-life production prediction of a coalbed methane well for a medium to high rank coal reservoir according to claim 1, wherein, The early and medium-term production of the gas well is predicted by using the established early and medium-term production prediction model, first, the formation coefficient, structure position and gas content of the gas well are counted, then, any bottom hole pressure data in the prediction stage are given, the apparent desorption coefficient is calculated, and the early and medium-term production comprehensive prediction model is used to predict the relatively stable gas production under the bottom hole pressure. The gas well geological potential evaluation model is established by the following formula: P g is a parameter for characterizing the geological potential of a gas well; C g For well point gas content; K is the permeability, H is the formation thickness, and D is the structure position of the main coal seam where the gas well is located.

3. The method for early to mid-life production prediction of a coalbed methane well for a medium to high rank coal reservoir according to claim 2, wherein, The gas well stable production condition in a stage is judged by the following formula, and the stable production condition judging condition is obtained: The gas well continuous ten-day gas production fluctuation rate is less than 10% and the corresponding bottom hole flowing pressure fluctuation rate is less than 5%, which is shown by the following formula: The corresponding stable gas production and bottom hole flowing pressure of the gas well are obtained: the rate of fluctuation of the gas well's production for 10 consecutive days; Maximum gas rate for a gas well for a 10-day period; Minimum gas production for 10 consecutive days for a gas well; the gas production rate for the 10th consecutive day of the gas well the gas production rate for the 10th consecutive day of the gas well is the rate of fluctuation of the bottom-hole flowing pressure for the gas well for 10 consecutive days; Maximum bottom hole pressure for 10 consecutive days for gas wells; Minimum bottom hole pressure for 10 consecutive days for gas wells; is the bottom hole pressure for the 10th day of the gas well. is the bottom hole pressure for the 10th day of the gas well.

4. The method for early to mid-life production prediction of a coalbed methane well targeting a medium to high rank coal reservoir according to claim 3, wherein, When the stable production condition judging condition is met, the stable gas production and bottom hole flowing pressure are calculated according to the following formula: In the formula, The apparent desorption coefficient of the gas well is calculated according to the following formula: q To stabilize gas production from a gas well; Pwf is the flowing bottomhole pressure.

5. The method for early to mid-life production prediction of a coalbed methane well targeting a medium to high rank coal reservoir according to claim 4, wherein, I is the apparent desorption coefficient of the gas well, The gas well drainage potential evaluation model is established according to the following formula: By using the multivariate regression analysis method, combining the denoised gas well production data, the early and medium-term gas production comprehensive prediction model is established by comprehensively considering the gas well geological potential evaluation model and the gas well drainage potential evaluation model according to the following formula, and the model coefficient is fitted: Pc is the critical resolution pressure; and Pwf is the flowing bottomhole pressure.

6. The method for early to mid-life production prediction of a coalbed methane well targeting a medium to high rank coal reservoir according to claim 5, wherein, When the bottom hole pressure approaches 0, that is, the apparent desorption coefficient approaches 1, the corresponding gas production is the peak gas production. ​ characterizing parameters for potential production of the gas well; and m is a coefficient.

7. The method for early to mid-life production prediction of a coalbed methane well targeting a medium to high rank coal reservoir according to claim 6, wherein, ​ ​ To stabilize gas production from a gas well; to characterize the geological potential of a gas well; Characterize parameters for gas well drainage potential; a , b , c are coefficients.

8. The method for early to mid-life production prediction of a coalbed methane well targeting a medium to high rank coal reservoir of claim 1, wherein, ​

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