Production allocation method for shale gas wells based on quantitative relationship between decline rate and production allocation ratio

Abstract

The present invention discloses a shale gas well production allocation method based on the quantitative relationship between decline rate and production allocation ratio, comprising the following steps: establishing the wellbore structure and three-dimensional geological model of the shale gas well, and completing the fitting of historical production data; setting the bottom hole flow pressure to 0.1MPa, performing production simulation calculation of the shale gas well, and taking the average daily gas production of the first n months as the early production capacity of the shale gas well; taking the early production capacity as the standard, setting several groups of production allocation ratios to perform production dynamic numerical simulation of the shale gas well, and obtaining the maximum decline rate of production and the change rate of economically recoverable reserves under different production allocation ratios; and drawing curves based on the maximum decline rate and the change rate of economically recoverable reserves with the change of the production allocation ratio to form a production allocation chart. The present invention solves the problem of lack of theoretical support and technical guidance for shale gas horizontal well production allocation, can reduce stress-sensitive damage and economically recoverable reserve losses under high production allocation ratio conditions, and lays a foundation for maximizing the production capacity of shale gas well infill wells.

Description

Technical Field

[0001] The invention relates to the technical field of shale gas development, and in particular to a shale gas well production allocation method based on a quantitative relationship between decline rate and production allocation ratio. Background Art

[0002] The development of shale gas usually adopts the production increase method of long horizontal wells and large-scale volume fracturing. Due to the extremely low permeability of shale, the gas reservoir reserves controlled by the production wells are mostly fracture-controlled reserves. In the process of shale gas production, the early high-yield method is usually adopted. After 1-2 years of production, the gas well production declines rapidly. Usually, the stable production after 2 years is only 10% to 20% of the initial production. Current research has shown that the stress sensitivity of fractures and microfractures in shale is strong, and studies have shown that the closure of shale fractures is not only related to the pressure drop amplitude, but also to the pressure drop rate. Early rapid production will obviously lead to higher fracture closure, resulting in a reduction in economically recoverable reserves. The decline rate is an important parameter to describe the degree of gas well decline and pressure exhaustion, but the current production allocation method does not take into account the decline relationship of gas wells. Therefore, it is necessary to clarify the production capacity of shale gas wells and optimize the production allocation ratio of gas wells based on the decline rate of gas wells, appropriately reduce the fracture closure rate, and delay the decline in production. Due to the extremely low permeability of shale and the extremely slow pressure propagation, a large number of production capacity tests and interpretations cannot be carried out. As it is difficult to stabilize production and directly calculate production capacity through numerical simulation methods, the current production allocation for shale gas wells is usually based on empirical methods, which have low accuracy. Summary of the invention

[0003] In order to solve at least one of the above problems, the present invention proposes a shale gas well production allocation method based on the quantitative relationship between decline rate and production allocation ratio.

[0004] The technical solution of the present invention is: a shale gas well production allocation method based on the quantitative relationship between decline rate and production allocation ratio, comprising the following steps:

[0005] Collect data from a certain block and establish the wellbore structure and three-dimensional geological model of the shale gas well in the block, and complete the fitting of historical production data;

[0006] The bottom hole flow pressure is set to 0.1 MPa, and the production simulation calculation of the shale gas well is performed, and the average daily gas production in the first n months is taken as the early production capacity of the shale gas well, where n is not greater than 6;

[0007] Taking the early production capacity as the standard, several groups of production allocation ratios are set to perform the production dynamic numerical simulation of the shale gas well, and the maximum production decline rate and economically recoverable reserves under different production allocation ratios are obtained, and the economically recoverable reserves change rate is obtained according to the economically recoverable reserves calculation;

[0008] Based on the maximum decline rate and the change rate of economically recoverable reserves versus the change of the production allocation ratio, curves are drawn to form a production allocation chart. The first drop point of the curve of the change rate of economically recoverable reserves versus the production allocation ratio is taken as the starting point, and the intersection of the two curves is taken as the end point to form a production allocation range. This production allocation range is the reasonable production allocation range for shale gas wells in this block.

[0009] One implementation of the present invention is that the data includes well data, formation parameters, seismic data, logging information and interpretation data, reservoir transformation parameters, geomechanical parameters, and production data.

[0010] An implementation manner of the present invention is that the production allocation ratio is calculated by the following formula: production allocation ratio=output / early production capacity.

[0011] In one embodiment of the present invention, the decline rate is calculated by the following formula: Where D is the decline rate, q g is the gas production, and t is the production time.

[0012] In one implementation of the present invention, the economically recoverable reserves change rate is calculated by the following formula: Where α is the change rate of economically recoverable reserves under each production allocation condition; EUR is the economically recoverable reserves under each production allocation condition; EUR γmin Economically recoverable reserves extracted for all simulation cases with the smallest production allocation ratio.

[0013] Beneficial effects: The present invention solves the problem of lack of theoretical support and technical guidance for shale gas horizontal well production allocation, can reduce stress-sensitive damage and economically recoverable reserve losses under high production allocation ratio conditions, and lays a foundation for maximizing the production capacity of shale gas well infill wells. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The wellbore structure and three-dimensional geological model diagram of the shale gas well in the embodiment;

[0015] Figure 2 It is the fitting result figure in the embodiment;

[0016] Figure 3 This is the simulated production diagram when the bottom hole flowing pressure is 0.1MPa;

[0017] Figure 4 The yield curve under different production ratio conditions

[0018] Figure 5 This is the calculation result diagram of the decline rate under different production allocation ratios;

[0019] Figure 6 This is the economic recoverable reserves change rate diagram under different production allocation ratios;

[0020] Figure 7 It is the production plate of this embodiment;

[0021] Figure 8 It is the matching relationship between the maximum monthly decline rate and the production allocation ratio and the actual production process. DETAILED DESCRIPTION

[0022] The specific implementation modes of the present invention will be described clearly and completely below with reference to examples and drawings. Obviously, the described examples are only some embodiments of the present invention, rather than all embodiments.

[0023] A shale gas well production allocation method based on the quantitative relationship between decline rate and production allocation ratio comprises the following steps:

[0024] Collect data from a certain block and establish the wellbore structure and three-dimensional geological model of the shale gas well in the block, and complete the fitting of historical production data;

[0025] Specifically, in this embodiment, the data includes well data, formation parameters, seismic data, logging data and interpretation data, reservoir transformation parameters, geomechanical parameters, and production data. Among them, the well data include: structural location, core filling altitude, well depth, wellbore trajectory, wellbore structure, completed drilling layer, horizontal section length and oil and casing size; formation parameters include: porosity, permeability, TOC, adsorption and desorption parameters, gas saturation, etc., fluid PVT parameters and Class I reservoir continuous thickness; seismic data include: depth domain, time domain three-dimensional seismic data body, structural interpretation results, fracture and natural fracture prediction attribute body and artificial fracture inversion attribute parameters; logging data and interpretation data include: conventional and special logging data, interpretation data include Small layer division, reservoir physical parameters and natural fractures; reservoir transformation parameters include: fracturing design parameters and fracturing construction parameters, including segmented liquid volume, segmented sand volume, proppant particle size, liquid viscosity, gel breaking method, liquid viscosity after gel breaking, fracturing and pump-off curves of segmented construction and engineering anomalies and treatment conditions; geomechanical parameters include: Young's modulus, Poisson's ratio, tensile strength, minimum horizontal principal stress, maximum horizontal principal stress and stress direction; production data include: single well production data, including daily gas production, daily liquid production, casing pressure, oil pressure and bottom hole flowing pressure.

[0026] Using the above parameters to establish the wellbore structure and three-dimensional geological model of a shale gas well is a routine operation in this field. For example, the modeling can be completed directly through the Petrel-intersect geological modeling and numerical simulation technology platform, and its specific parameters are not described here. Those skilled in the art can also use other methods and modeling software in this field for modeling.

[0027] After the model is established, the above model can be used to fit the production data so that the simulation results of the model can better reflect the actual production situation.

[0028] In this embodiment, a shale gas well in Changning area is selected as an example. Since the initial data is large and difficult to reflect in the patent text, this embodiment only gives the final model and the fitting of historical data. The wellbore structure of the final shale gas well and the three-dimensional geological model are shown in Figure 1. Figure 1 The fitting is shown in Figure 2 shown.

[0029] The bottom hole flow pressure is set to 0.1 MPa, and the production simulation calculation of the shale gas well is performed, and the average daily gas production in the first n months is taken as the early production capacity of the shale gas well, where n is not greater than 6;

[0030] A bottom hole flow pressure of 0.1MPa indicates an absolute unobstructed production, which represents the maximum production of the gas well. For shale gas and other gas wells, it takes at least 3 to 6 months for the flow to stabilize. There is no way to conduct a production capacity test, and even if a test is performed, a stable production capacity cannot be obtained: the initial production of shale gas wells is extremely high, reaching millions of cubic meters per day, but its decline rate is extremely fast, so it is not appropriate to take the production of any day as the early production capacity. Combining long-term field work experience, the inventor proposes to use the average production of the first n months as the early production capacity of shale gas; the specific value of n in each gas well needs to be determined based on the production decline rate and initial production of the gas well.

[0031] In this embodiment, the simulation results are as follows: Figure 3 As shown, according to the production characteristics of shale gas in Changning area, the n value of the selected gas well is 3, and the early production capacity is 414,300 cubic meters per day.

[0032] Taking the early production capacity as the standard, the number of production allocation ratio groups can be set to 8 to 15 groups, which can be set according to the actual situation; based on the set multiple production allocation ratios, the production dynamic numerical simulation of shale gas wells is carried out to obtain the maximum production decline rate and economically recoverable reserves under different production allocation ratios, and the economically recoverable reserves change rate is obtained based on the economically recoverable reserves calculation;

[0033] Specifically, the production ratio is calculated by the following formula: production ratio = output / early production capacity; the decline rate is calculated by the following formula: Where D is the decline rate, q gis the gas production, t is the production time; economically recoverable reserves refer to the maximum economic gas production that can be obtained from the gas reservoir under the existing well network and process technology conditions; under some conditions, although there is still a small amount of natural gas in the reservoir, the cost of exploiting it is higher than the income from obtaining natural gas. In this case, it is necessary to stop exploitation. In this embodiment, combined with the actual situation in Changning area, the calibration standard of economically recoverable reserves is set to gas well production less than 5000 cubic meters / day.

[0034] The economically recoverable reserves change rate is calculated by the following formula: Where α is the change rate of economically recoverable reserves under each production allocation condition; EUR is the economically recoverable reserves under each production allocation condition; EUR γmin Economically recoverable reserves extracted for all simulation cases with the smallest production allocation ratio.

[0035] The number of production allocation ratios can be set according to actual conditions: the more the number of settings, the more accurate the final calculation result, but the longer the simulation calculation time. Those skilled in the art can set it according to actual conditions. In this embodiment, twelve groups of production allocation ratios are set: 0.15, 0.2, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65 and 0.70.

[0036] After setting up twelve groups of production allocation ratios, the above model was used to conduct a 20-year production dynamic numerical simulation under fixed production allocation conditions to obtain the corresponding production curve. Based on the production curve, the real-time decline rate and economically recoverable reserves were calculated.

[0037] The final result is Figure 4-6 As shown, Figure 4 It represents the yield curve under different production ratio conditions; Figure 5 A graph showing the calculation results of the decline rate under different production allocation ratios; Figure 6 It represents the change rate of economically recoverable reserves under different production allocation ratios.

[0038] Based on the maximum decline rate and the change rate of economically recoverable reserves versus the change of the production allocation ratio, curves are drawn to form a production allocation chart. The first drop point of the curve of the change rate of economically recoverable reserves versus the production allocation ratio is taken as the starting point, and the intersection of the two curves is taken as the end point to form a production allocation range. This production allocation range is the reasonable production allocation range for shale gas wells in this block.

[0039] In the above steps, the maximum decline rate under different production allocation ratios and the economic recoverable reserves change rate under different production allocation ratios have been obtained. After a large number of experiments by the inventors, it was found that for unconventional oil and gas, such as shale gas and coalbed methane, the overall trend of the curve of the change rate of economic recoverable reserves with the change of production allocation ratio is first rising and then falling, and there is a peak point in the test process; while for conventional gas reservoirs, there is usually no peak point.

[0040] In order to further guide the production on site, in this step, two curves are combined to draw the production allocation plate: with the production allocation ratio as the horizontal axis, the maximum decline rate and the economic recoverable reserves change rate as the vertical axis, and the corresponding curve graph is drawn. In this figure, the maximum decline rate is rising with the change trend of the production allocation ratio, and the economic recoverable reserves change rate is rising first and then falling with the overall change trend of the production allocation ratio. The inventor combines the actual production process in Changning area, takes the initial decline point of the economic recoverable reserves change rate with the production allocation ratio change curve as the starting point, and forms the production allocation interval with the intersection of the two curves as the end point. In this interval, the production allocation ratio is reasonable: this is mainly due to the fact that when the production allocation ratio is less than the production allocation ratio corresponding to the starting point, the production allocation is relatively low, and it is difficult to exert production capacity; when the production allocation ratio is greater than the production allocation ratio corresponding to the end point, the rising speed of the maximum decline rate and the decline ratio of the economic recoverable reserves are relatively large, which will affect the development of the reservoir and cause the reservoir to be difficult to be fully developed.

[0041] like Figures 7-8 As shown in the figure, Figure 7 It is the production plate of this embodiment; Figure 8 It is the matching relationship between the maximum monthly decline rate and the production allocation ratio and the actual production process.

[0042] from Figure 7 It can be seen that in this embodiment, in the block in Changning area, when the production ratio is set to 0.2-0.4, its economically recoverable reserves are relatively high, the maximum monthly decline rate is low, and stable production can be maintained for a long time. Combined with the existing technology, it can be seen that the damage to the reservoir is small, so its economically recoverable reserves are higher; Figure 8 It can be seen that when the production allocation chart of this embodiment is compared with the production conditions of the other three wells in the block in Changning area, it is found that the change pattern of the maximum monthly decline rate of the three wells with the production allocation ratio is consistent with the production allocation chart obtained in this embodiment, which illustrates the accuracy of the embodiment of the present invention.

[0043] Through the above-mentioned production allocation chart, the production of shale gas wells in the block can be allocated.

[0044] The above description is only a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention is disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A shale gas well production allocation method based on the quantitative relationship between decline rate and production allocation ratio, characterized in that: The following steps are involved: Collect data from a certain block and establish the wellbore structure and three-dimensional geological model of the shale gas well in the block, and complete the fitting of historical production data; The bottom hole flow pressure is set to 0.1 MPa, and the production simulation calculation of the shale gas well is performed, and the average daily gas production in the first n months is taken as the early production capacity of the shale gas well, where n is not greater than 6; Taking the early production capacity as the standard, several groups of production allocation ratios are set to carry out the production dynamic numerical simulation of the shale gas well, and the maximum production decline rate and economically recoverable reserves under different production allocation ratios are obtained, and the economically recoverable reserves change rate is calculated based on the economically recoverable reserves; the economically recoverable reserves change rate is calculated by the following formula: Where α is the change rate of economically recoverable reserves under each production allocation condition; EUR is the economically recoverable reserves under each production allocation condition; EUR γmin The economically recoverable reserves extracted from all simulation cases with the smallest production allocation ratio; the production allocation ratio is calculated by the following formula: production allocation ratio = production / early production capacity; Based on the maximum decline rate and the change rate of economically recoverable reserves versus the change of the production allocation ratio, curves are drawn to form a production allocation chart. The first drop point of the curve of the change rate of economically recoverable reserves versus the production allocation ratio is taken as the starting point, and the intersection of the two curves is taken as the end point to form a production allocation range. This production allocation range is the reasonable production allocation range for shale gas wells in this block.

2. The method according to claim 1, characterized in that The data include well data, formation parameters, seismic data, logging information and interpretation data, reservoir transformation parameters, geomechanical parameters, and production data.

3. The method according to claim 1, characterized in that The decline rate is calculated by the following formula: Where D is the decline rate, q g is the gas production, and t is the production time.

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