Reservoir testing method for determining well opening time and stable production time of shale gas

Abstract

The invention discloses a reservoir testing method for determining shale gas well opening time and stable production time. The reservoir testing method comprises the following steps that M-day data of a sample single well or a well group in a research area is collected according to field oil and gas testing data; acquiring chloride ion concentration data of the flowback fluid; summarized drawing is carried out on the obtained chloride ion concentration, oil nozzle size and instantaneous yield data on the premise of time development; determining a stage transition point of the instantaneous yield curve and the chloride ion concentration curve; performing regional division according to stage transition points of an instantaneous yield curve and a chloride ion concentration curve in the summary graph curve; the well opening production time is determined; and obtaining the stable production time of the target well group. In the actual production work, crack distribution analysis can be carried out simply based on the change trend of chloride ions to determine the well opening time and the stable production time.

Description

Technical Field

[0001] The present invention relates to shale gas reservoir testing technology, and in particular to a reservoir testing method for determining shale gas well opening time and stable production time. Background Art

[0002] Shale gas reservoirs are unconventional, self-generating and self-storing gas reservoirs with dense formations that require extensive hydraulic fracturing to start production. Most pristine shale gas reservoirs are characterized by abnormally high pressure, abundant formation energy, and limited initial formation water within the shale, often devoid of free water. Mainstream research suggests that shutting in shale gas wells for a period after fracturing promotes hydration through shale imbibition, replenishing reservoir energy and promoting fracture propagation and development. However, some researchers suggest that residual fracturing fluid in the reservoir induces hydration reactions that weaken the fracturing effect. The demand for rapid production launches necessitates shortening reservoir testing time. Therefore, determining the economically appropriate time to start production, obtaining sufficient reservoir testing data, and calculating the time to stable production are crucial. Current conventional reservoir testing methods rely on pressure funnel calculations based on constant-volume, constant-pressure, and composite reservoir models. Therefore, a rapid and accurate method for determining the start-up time of individual wells is needed. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a reservoir testing method for determining the shale gas well opening time and stable production time in response to the defects in the existing technology.

[0004] The technical solution adopted by the present invention to solve the technical problem is: a reservoir testing method for determining the shale gas well opening time and stable production time, comprising the following steps:

[0005] 1) Based on the field oil and gas test data, collect M days of data for a single well or well group in the study area, with M ≥ 60. The collected data include nozzle size, instantaneous production and pressure;

[0006] 2) Analyze the flowback fluid samples from a single well or a group of wells at the same time to obtain the chloride ion concentration data of the flowback fluid;

[0007] 3) summarizing the chloride ion concentration, nozzle size, and instantaneous production data obtained in steps 1) and 2) over time and plotting the graph; the graph includes an instantaneous production curve and a chloride ion concentration curve;

[0008] 4) comparing the instantaneous yield curve and the chloride ion concentration curve in step 3), identifying the characteristics of the instantaneous yield curve and the chloride ion concentration curve, and determining the stage transition point between the instantaneous yield curve and the chloride ion concentration curve;

[0009] Among them, the instantaneous production curve is divided into three stages: disturbance, rise, and stability; the chloride ion concentration curve is divided into three stages: rapid rise, slow rise or stability, and stability or slight rise;

[0010] 5) Based on the stage transition points of the instantaneous production curve and the chloride ion concentration curve in the summary graph, the regions are divided into: rapid rise region t1, slow rise region t2, and stable fluctuation region t3;

[0011] 6) Determine the time to start production;

[0012] The reservoir test is terminated when half of the duration of the stable fluctuation zone t3 is determined as the time point for starting production of shale gas wells in the study area.

[0013] 7) Obtain the average value of chloride ions in the stable fluctuation area t3 of a single structural subunit in the study area;

[0014] 8) Determine the upper specification limit based on the average value of chloride ions in the stable fluctuation zone t3 in a single structural subunit, and perform stability calculations using the stability calculation model;

[0015] 9) Calculate the stable period of the wells in a single structural subunit and merge it into the stable period diagram of all batches to obtain the stable production time of the target well group.

[0016] According to the above solution, in step 4), the feature identification is that the change value of the rising slope of the curve within the set time range or the change value per unit time exceeds the set threshold and lasts for more than the set time.

[0017] According to the above solution, in step 5), when determining the stable fluctuation area t3, the nozzle size in the area remains unchanged.

[0018] According to the above scheme, in step 8), in the stability calculation model, the confidence level is 95, and the AlPha value of the merged batch is 0.25.

[0019] The beneficial effects produced by the present invention are:

[0020] In actual production work, the present invention can determine the well opening time and the stable production time by simply analyzing the fracture distribution based on the chloride ion change trend. The method is easy to implement and operate, has low cost, and has strong practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0022] Figure 1 It is a structural diagram of an embodiment of the present invention;

[0023] Figure 2 This is a chloride ion change curve of the flowback fluid after fracturing in the JY71-4 well in the study area of ​​the embodiment of the present invention;

[0024] Figure 3This is a chloride ion change curve of the flowback fluid after fracturing of three wells in the JY69 well group in the study area of ​​the embodiment of the present invention;

[0025] Figure 4 2. It is a chloride ion data fitting residual test diagram of an embodiment of the present invention;

[0026] Figure 5 This is a schematic diagram of the stable production period of all single wells in an embodiment of the present invention. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0028] like Figure 1 As shown, a reservoir testing method for determining the shale gas well opening time and stable production time includes the following steps:

[0029] Step 1: Screen 60 days of data for a single well or well group based on field oil and gas test data to select key parameters such as nozzle size, instantaneous production, and pressure;

[0030] Step 2: Analyze the 60-day flowback fluid samples of a single well or a well group to obtain chloride ion concentration data;

[0031] Step 3: Make a summary map of the 60-day chloride ion concentration, nozzle size, and instantaneous production data of a single well or well group under the premise of time development; Figure 2 ;

[0032] Step 4: Compare the instantaneous yield curve and the chloride ion concentration curve in step 3 to identify the characteristics of the instantaneous yield curve (perturbation, rise, stability) and the chloride ion concentration curve (rapid rise, slow rise or stability, stability or slight rise), and draw regional demarcation lines at the stage transition points;

[0033] Step 5: Define and divide each area according to the development trend of the summary graph curve: fast rising area t1, slow rising area t2, and stable fluctuation area t3, to determine the time to start well production;

[0034] Step 6: Collect multiple sets of single-well partition curves in a well group or a single structural subunit in the study area to form a chart, and finally determine the time point when half of the duration of the stable fluctuation zone t3 is to end the reservoir test and start well production;

[0035] Step 7: Based on the conclusion of step 2, calculate the average value of chloride ions in the stable fluctuation zone t3 of a single structural subunit in the study area;

[0036] Step 8: Preset the platform well study boundaries and construct a 9-month stability study worksheet for 3 wells (3 batches). Measure chloride ion concentrations regularly according to the worksheet requirements and enter them into the worksheet.

[0037] In step 9, based on the results calculated in step 7, set the average chloride ion value (average of the three wells) in the stable fluctuation zone t3 as the upper specification limit, the confidence level is 95, and the AlPha value of the combined batch is 0.25. Substitute the mathematical model and perform the stability calculation;

[0038] Step 10: Calculate the stable period of the three wells and merge them into the stable period graph for all batches. A residual graph is also generated to facilitate data verification. The stable production time of the target well group is obtained.

[0039] In step 9, the stability calculation model is as follows:

[0040] The general form of a mixture model is:

[0041] Y=Xβ+Z1μ1+Z2μ2+K+Z i μ i +ε

[0042] Where: Y is the n×1 vector of response values; X is the n×p design matrix of fixed effects, p≤n; Z1 is the n×m vector of random effects in the model i Design matrix; β is the p×1 vector of unknown parameters; μ i for The independent variable m in i ×1 vector; ε is is the n×1 vector of independent variables in ; i is the number of random effects in the model;

[0043] The general variance-covariance matrix of the response vector Y is:

[0044]

[0045] in:

[0046] Further decomposing the variance, we get the expression of H(θ):

[0047] V(σ 2 )=σ 2 H(θ)=σ 2 [ln+θ1Z1Z1'+K+θ i Z i Z i ']

[0048] When batch is a random factor, the unknown parameter estimates are obtained by minimizing the inverse of the restricted log-likelihood function twice. Finding the minimum is equivalent to maximizing the restricted log-likelihood function. The function that achieves the minimization is:

[0049] Where n is the number of observations; p is the number of parameters in β, and there are 2 parameters in the stability study; σ 2 are the error variance components; X is the design matrix - for fixed terms, constants, and time; ln is the identity matrix with n rows and columns; θ i is the ratio of the variance of the i-th random term to the error variance; Z i is the known code of the i-th random effect in the model n×m i matrix; m i is the number of levels of the i-th random effect; i is the number of random effects in the model; |H(θ)| is the determinant of H(θ); X' is the transpose of X; H -1 (θ) is the inverse of H(θ);

[0050] The Box-Cox transformation selects the value of lambda that minimizes the residual sum of squares, where Y' is the transformation of the data Y (Table 1):

[0051] Table 1 Data transformation

[0052]

[0053] Random Batch Model Selection. Model selection determines whether shelf life depends on batch and whether the time effect depends on batch. Minitab considers the following three models in order:

[0054] 1. Time + Batch + Batch * Time (the slope and intercept of the batch are not equal)

[0055] 2. Time + Batch (Batch slopes are equal, intercepts are not equal)

[0056] 3. Time (the slope and intercept of the batch are equal)

[0057] If the Batch*Time interaction term is significant, the analysis will fit the first model. If the interaction term is not significant, but the batch term is significant in the second model, the analysis will fit the second model. Otherwise, the analysis will fit the third model.

[0058] This embodiment gives a specific example, screening the formation test data of JY71-4 well and summarizing the chloride ion concentration data Figure 2 ;

[0059] Will Figure 2Determine the trend of the curve change, as shown in the figure, and divide it into a rapid rise area t1, a slow rise area t2, and a stable fluctuation area t3;

[0060] Analysis revealed that peak production occurred in the stable fluctuation zone t3. With the nozzle unchanged, production began to decline significantly on the 22nd day of testing. This suggests that after entering the stable fluctuation zone t3, bottomhole pressure reached microfractures and the matrix. Gas accumulated in these microfractures during the shut-in period was displaced into the main fractures and ultimately discharged through the wellbore, resulting in maximum production. The optimal end-of-test and start-up time for Well JY71-4 was 22 days, within the predicted 20-day timeframe.

[0061] Select the data of three wells in adjacent platforms ( Figure 3 ), it can be seen that the regional characteristics of the platform well data are not obvious, but the overall change trend of chloride ion concentration is small, which is convenient for calculating the stable production time;

[0062] Data from three wells on adjacent platforms were selected, and a 9-month stabilization period study worksheet was constructed based on actual project conditions. Chloride ion concentrations were measured regularly (Table 2):

[0063] Table 2 Stability Study Worksheet

[0064] Run sequence moon hashtag Chloride ion content 1 0 JY69-3 13283 2 0 JY69-1 12984 3 0 JY69-2 13875 4 3 JY69-2 13876 5 3 JY69-3 14092 6 3 JY69-1 14024 7 6 JY69-3 13982 8 6 JY69-2 13746 9 6 JY69-1 13920 10 9 JY69-2 13872 11 9 JY69-1 14012 12 9 JY69-3 13904

[0065] Based on the average chloride ion value of the study well group, set the upper specification limit to 18,000, the confidence level to 95, and the AlPha value of the merged batch to 0.25. Perform the stable production time calculation;

[0066] First, an interaction analysis was performed by calculation to verify whether the model was reliable ( Table 3 );

[0067] Table 3 Interaction analysis of chloride ion content

[0068] source degrees of freedom Seq SS Seq MS F-number P-value moon 1 351747 351747 3.72 0.102 batch 2 24896 12448 0.13 0.879 Month × Batch 2 246889 123445 1.30 0.339 error 15 567763 94627 total 20 1191295

[0069] As can be seen from Table 3, the P values ​​in the source items are all less than the significance level of 0.25, indicating that they are all statistically significant;

[0070] Further calculations show that Figure 4 This is the residual test graph of the chloride ion data fitting. Figure 5 This is the conclusion diagram of the stable production period of all single wells;

[0071] The analytical results show that the regression equation is: chloride ion = 13568 + 51.0 months. The stable production period is 48 months.

[0072] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all such improvements and changes should fall within the scope of protection of the appended claims of the present invention.

Claims

1. A reservoir testing method for determining shale gas well opening time and stable production time, characterized in that: The following steps are involved: 1) Based on the field oil and gas test data, collect M days of data for a single well or well group in the study area, with M ≥ 60. The collected data includes the nozzle size and instantaneous production; 2) Analyze the flowback fluid samples from a single well or a group of wells at the same time to obtain the chloride ion concentration data of the flowback fluid; 3) summarizing the chloride ion concentration, nozzle size, and instantaneous production data obtained in steps 1) and 2) over time and plotting the graph; the graph includes an instantaneous production curve and a chloride ion concentration curve; 4) comparing the instantaneous yield curve and the chloride ion concentration curve in step 3), identifying the characteristics of the instantaneous yield curve and the chloride ion concentration curve, and determining the stage transition point between the instantaneous yield curve and the chloride ion concentration curve; Among them, the instantaneous production curve is divided into three stages: disturbance, rise, and stability; the chloride ion concentration curve is divided into three stages: rapid rise, slow rise or stability, and stability or slight rise; 5) Based on the stage transition points of the instantaneous production curve and the chloride ion concentration curve in the summary graph, the regions are divided into: rapid rise region t1, slow rise region t2, and stable fluctuation region t3; 6) Determine the time to start production; The reservoir test is terminated when half of the duration of the stable fluctuation zone t3 is determined as the time point for starting production of shale gas wells in the study area. 7) Obtain the average value of chloride ions in the stable fluctuation area t3 of a single structural subunit in the study area; 8) Determine the upper specification limit based on the average value of chloride ions in the stable fluctuation zone t3 in a single structural subunit, and perform stability calculations using the stability calculation model; 9) Calculate the stable period of the wells in a single structural subunit and merge it into the stable period diagram of all batches to obtain the stable production time of the target well group.

2. A reservoir testing method for determining shale gas well opening time and stable production time according to claim 1, characterized in that: In step 4), the feature identification is that the change value of the rising slope of the curve within the set time range or the change value per unit time exceeds the set threshold and lasts for more than the set time.

3. A reservoir testing method for determining shale gas well opening time and stable production time according to claim 1, characterized in that: In step 5), when determining the stable fluctuation area t3, the nozzle size in the area remains unchanged.

4. A reservoir testing method for determining shale gas well opening time and stable production time according to claim 1, characterized in that: In step 8), in the stability calculation model, the confidence level is 95, and the AlPha value of the merged batch is 0.

25.

5. A server comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the computer program, the reservoir testing method for determining the shale gas well opening time and stable production time according to any one of claims 1 to 4 is implemented.

6. A computer-readable storage medium, characterized in that The computer-readable storage medium stores computer instructions, and the computer instructions are used to enable a processor to implement the reservoir testing method for determining the shale gas well opening time and stable production time according to any one of claims 1 to 4 when executed.

Images