A method for exploiting shallow adsorbed shale gas

Abstract

This invention discloses a method for exploiting shallow adsorbed shale gas, comprising the following steps: S101, based on core and well logging data, determining the shale gas occurrence characteristics, reservoir type, and main exploitation targets; S102, based on isothermal adsorption-desorption experiments, determining the adsorption-desorption law of the adsorbed gas and the sensitive desorption pressure P. 敏感 Based on the production characteristics, S103 selected the adsorption pneumatic drainage process to achieve large-scale production of shallow adsorbed shale gas.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of shale gas exploration and development, and particularly relates to a method for mining shallow adsorbed shale gas. BACKGROUND

[0002] According to the shale burial depth, the shale gas in China can be divided into shallow shale gas (burial depth is 2000m or less), medium-deep shale gas (burial depth is 2000-3500m), deep-ultra-deep shale gas (burial depth is 3500m or more) and the like. The medium-deep shale gas, the deep-ultra-deep shale gas has realized a major breakthrough, and large shale gas fields such as Fuling, Changning and Weiyuan have been discovered. The shallow shale gas is widely distributed in the complex tectonic area outside the basin, and the resource amount reaches several hundred trillion cubic meters, and the exploration and development prospect is broad, and is expected to become an important field of increasing reserves and production. At present, the exploration and understanding degree is still low.

[0003] The shale gas mainly exists in dark shale in two forms of free state and adsorbed state. Under different geological conditions, the occurrence state of the shale gas has great difference. The shale gas fields such as Fuling, Changning and Weiyuan which have realized commercial development in China have good shale gas preservation conditions, and the occurrence state of the shale gas is mainly in the free state. The preservation condition of the shallow shale gas is poor, the free gas escaping amount is relatively larger than that of the medium-deep shale gas and the deep-ultra-deep shale gas, and the occurrence state of the shale gas is mainly in the adsorbed state, and the adsorbed gas is the main mining object. Therefore, it is important to carry out research on the adsorption and desorption law of the adsorbed gas, and to develop the corresponding adsorbed gas mining technology, so as to realize commercial mining of the shallow adsorbed shale gas.

[0004] Domestic and foreign experts have carried out a large amount of research work on shale gas mining and shale adsorption characteristics, but the following problems exist.

[0005] Firstly, the main mining object of the gas reservoir is not determined to be free gas or adsorbed gas through the occurrence state research of the shale gas, but free gas and adsorbed gas are mixed together as the mining object.

[0006] Secondly, the desorption mechanism and sensitive desorption pressure of the adsorbed gas under the formation condition lack in-depth research.

[0007] Thirdly, the mining method of the adsorbed gas cannot be developed in a targeted manner. In fact, due to the different characteristics of the free gas and the adsorbed gas, the mining methods should also have great difference. The free gas has good fluidity, and the mainstream mining method in the industry has good adaptability. The adsorbed gas is adsorbed on the surface of the organic matter and the mineral particles, and has poor fluidity, and needs to reach a certain reservoir condition to realize large-scale desorption mining.

[0008] Therefore, it is necessary to provide a method for mining shallow adsorbed shale gas to solve the problems in the background. SUMMARY

[0009] To achieve the above object, the present application provides the following technical solutions: a shallow adsorption state shale gas exploitation method, comprising the following steps:

[0010] S101, based on core and logging data, determining shale gas occurrence characteristics, gas reservoir type and main exploitation object;

[0011] S102, based on isothermal adsorption and desorption experiment, determining adsorbed gas adsorption and desorption rule and sensitive desorption pressure P 敏感 ;

[0012] S103, according to production characteristics, selecting adsorbed gas dynamic displacement process to realize large-scale output of shallow adsorption state shale gas.

[0013] Further, as preferred, in the step S101, in the preset area, a vertical well is implemented, and the system obtains shale gas layer core, logging and other data to determine shale gas occurrence characteristics, specifically including determining shale total gas content, adsorbed gas content and its proportion, free gas content and its proportion, etc.

[0014] And according to the shale gas occurrence characteristics, the gas reservoir type and the main exploitation object are determined.

[0015] Further, as preferred, in the step S102, isothermal adsorption and desorption experiment of shale gas layer core sample in different sections is carried out to determine the adsorption and desorption rule of shale under the condition of reservoir temperature and different pressure, and the sensitive desorption pressure P 敏感 of adsorbed gas is determined.

[0016] When the formation pressure is less than or equal to P 敏感 , the shale gas is rapidly desorbed, the desorption rate is fast, the desorbed gas amount is large, and the single well production rapidly increases.

[0017] When the formation pressure is higher than P 敏感 , the shale gas is slowly desorbed, the desorption rate is low, the desorbed gas amount is small, and the single well production is low.

[0018] Further, as preferred, in the step S103, in the preset area, shale gas horizontal well is implemented, and hydraulic sand fracturing is carried out on the horizontal section, according to different production characteristics, adsorbed gas dynamic displacement process is selected to realize large-scale output of shallow adsorption state shale gas.

[0019] Further, as preferred, when the shale gas horizontal well cannot self-flow production at the initial production stage, the following adsorbed gas dynamic displacement process is selected to rapidly reduce the downhole pressure to the sensitive desorption pressure P 敏感 , strengthen liquid discharge and reduce flow pressure, and promote the large desorption and output of adsorbed gas from the reservoir.

[0020] When it is detected that the gas well production is significantly increased, the above drainage production process can be closed after self-flowing liquid-carrying production, and a suitable drainage production system is selected to promote long-term stable desorption production of adsorbed gas and maintain high and stable production of the gas well.

[0021] Further, as preferred, when the shale gas horizontal well can be self-flowing produced at the initial production stage and the production reaches the expected production, a suitable drainage production system is selected to prolong the self-flowing production period and increase the cumulative production during the self-flowing production period.

[0022] When it is detected that the gas well is different from self-flowing production or the production is less than the expected production, the desorption production of adsorbed gas is realized according to the method of step S103.

[0023] Compared with the prior art, the present application provides a shallow adsorbed shale gas production method, which has the following beneficial effects:

[0024] In the present application, a shallow adsorbed shale gas production method is provided, which aims at the problem that the adsorbed gas resource amount in the shallow shale gas area is large but difficult to exploit, determines the shale gas occurrence characteristics, gas reservoir type and main exploitation object based on core and logging data, determines the adsorbed gas adsorption and desorption law and sensitive desorption pressure P 敏感 based on isothermal adsorption and desorption experiment, and selects the adsorbed gas production drainage process according to the production characteristics to realize the large-scale production of shallow adsorbed gas.

[0025] The present application helps to realize the large-scale production of shallow adsorbed shale gas, significantly improves the single well production, can provide important reference for the exploitation of shallow shale gas resources in China, can provide reference for the exploitation of medium-deep layer-super-deep layer adsorbed shale gas resources, and has great popularization and application value. BRIEF DESCRIPTION OF DRAWINGS

[0026] Fig. 1 The present application is a main flow diagram;

[0027] Fig. 2 The present application is an isothermal adsorption curve and isothermal desorption curve diagram of the embodiment. DETAILED DESCRIPTION

[0028] Embodiment: Please refer to Figs. 1-2 In the present embodiment, a shallow adsorbed shale gas production method comprises the following steps:

[0029] S101, based on core and logging data, determine the shale gas occurrence characteristics, gas reservoir type and main exploitation object;

[0030] Specifically, in the preset area, a vertical well is implemented, and core, logging and other data of the shale gas layer are obtained, which specifically includes determining the total shale gas content, adsorbed gas content and its proportion, free gas content and its proportion, etc.

[0031] In addition, determining the shale gas reservoir type based on its occurrence characteristics specifically includes classifying shale gas reservoir types according to the proportion of adsorbed gas:

[0032] When the proportion of adsorbed gas is greater than 60%, it is an adsorbed gas reservoir, and adsorbed gas is the main target for exploitation.

[0033] When the proportion of adsorbed gas is between 50% and 60%, it is a free-adsorbed gas reservoir, where adsorbed gas is the main target for exploitation, followed by free gas.

[0034] When the proportion of adsorbed gas is between 40% and 50%, it is an adsorbed-free gas reservoir, with free gas being the main target for exploitation, followed by adsorbed gas.

[0035] If the adsorbed gas content is less than 40%, it is a free gas reservoir, and free gas is the main target for exploitation.

[0036] S102. Based on isothermal adsorption-desorption experiments, the adsorption-desorption law of the adsorbed gas and the sensitive desorption pressure P are determined.

[0037] Specifically, isothermal adsorption-desorption experiments were conducted on core samples from different sections of the shale gas reservoir to simulate the adsorption and desorption behavior of shale under reservoir temperature and pressure conditions. Isothermal adsorption and desorption data were obtained, and isothermal adsorption curves and isothermal desorption curves were plotted to determine the adsorption and desorption behavior of the adsorbed gas.

[0038] In addition, based on the obtained isothermal desorption curves, the desorption rate curves and the derivative curves of the desorption rate curvature were obtained, and the adsorbed gas-sensitive desorption pressure P was determined. 敏感 The adsorbed gas sensitive desorption pressure P 敏感 This is the formation pressure at which the adsorbed gas begins to desorb and be produced in large quantities. When the formation pressure is less than or equal to P... 敏感 At this time, shale gas undergoes rapid desorption, with a fast desorption rate, large desorbed gas volume, and a rapid increase in single-well production; when the formation pressure is higher than P... 敏感 At that time, shale gas desorbs slowly, with a low desorption rate, small desorbed gas volume, and low production per well.

[0039] S103. Based on the production characteristics, select the adsorption pneumatic drainage process to achieve large-scale production of shallow adsorbed shale gas.

[0040] Specifically, in the designated area, horizontal shale gas wells are implemented. The horizontal section mainly traverses high-quality shale reservoirs. Casing is installed and cemented in the horizontal well. Hydraulic fracturing with proppant is carried out on the horizontal section to create a large stirred volume and a complex artificial fracture network. Gas testing and trial production are conducted on the fracturing shale gas horizontal wells. Different drainage processes are selected according to different production characteristics.

[0041] When a shale gas horizontal well cannot produce gas automatically in the early stages of production, a method that can quickly reduce downhole pressure to the sensitive desorption pressure P should be selected.敏感 The following adsorbed gas production process can strengthen liquid discharge and reduce flow pressure, promote adsorbed gas to be massively desorbed and produced from the reservoir, and after detecting that the gas well production is significantly increased, the above production process can be closed, and a suitable production system can be selected to promote long-term stable desorption and production of adsorbed gas and maintain high and stable production of the gas well.

[0042] When the shale gas horizontal well can be self-flowing produced in the initial production period and the production reaches the expected production, a suitable production system is selected to prolong the self-flowing production cycle and improve the cumulative production in the self-flowing production period, and after detecting that the gas well is in different self-flowing production or the production is less than the expected production, a suitable production system is selected to quickly reduce the downhole pressure to the sensitive desorption pressure P 敏感 The following adsorbed gas production process can strengthen liquid discharge and reduce flow pressure, promote adsorbed gas to be massively desorbed and produced from the reservoir, and after detecting that the gas well production is significantly increased, the above production process can be closed, and a suitable production system can be selected to promote long-term stable desorption and production of adsorbed gas and maintain high and stable production of the gas well.

[0043] Please refer to Fig. 2 Taking the L anticline as an example, the process of realizing the exploitation of shallow adsorbed shale gas by using the method of the present application is described in detail.

[0044] The L anticline is located in the complex structure belt outside the basin in the southeast of Chongqing, and the shale gas target layer is the Wufeng Group of the Upper Ordovician to the Longmaxi Group of the Lower Silurian. The structure has experienced multiple tectonic movements since the Caledonian period, and the tectonic action is strong. The uplift amplitude is large, and the target layer is widely eroded. The strata of the Silurian to the Sinian are exposed in the core of the anticline, and the strata above the Upper Permian have been almost eroded. The shale of the Wufeng Group is buried at a depth of 0-1200m in the two wings, and the shale of the Wufeng Group is buried at a depth of 1200-2000m. The pressure coefficient of the strata is 0.9-1.0. It is a typical shallow shale gas area. In the early stage, the traditional shale gas exploitation method is used in this area, and the single well production is low, and the economic benefit is poor. Through the method provided by the present application, the shale gas occurrence mode and the adsorption and desorption law are studied, and the adsorbed gas production technology is strengthened. The commercial exploitation of shallow adsorbed shale gas in this area is realized, the single well production is greatly improved, and the economic benefit is remarkable.

[0045] In the implementation, the step S101 is performed. In the preset area of the L anticline, a straight well A is implemented, and the system obtains shale gas layer core, logging and other data.

[0046] According to the logging data of the A well, the shale gas occurrence characteristics are determined. The total gas content of the high-quality shale section is 3.46m3 / t, the adsorbed gas content is 2.78m3 / t, the adsorbed gas content accounts for 80.3%, and the free gas content accounts for 19.7%.

[0047] According to the shale gas occurrence characteristics, the gas reservoir type of the L anticline is determined as an adsorbed gas reservoir, and the adsorbed gas is the main exploitation object.

[0048] The step S102 is performed, isothermal adsorption and desorption experiments of core samples of different sections of the shale gas layer of the A well are carried out, adsorption and desorption rules of the shale under the conditions of reservoir temperature and different pressures are simulated, isothermal adsorption and desorption data are obtained, isothermal adsorption and desorption curves are drawn, and the adsorption and desorption rules of the shale gas are determined.

[0049] The isothermal adsorption curve of the shale of the A well shows three-stage characteristics: the first stage is a rapid adsorption stage, the corresponding pressure is generally 0-5 MPa, the shale adsorbed gas amount increases rapidly with the increase of the pressure, and the adsorption rate is high; the second stage is a slow adsorption stage, the corresponding pressure is generally 5-10 MPa, the shale adsorbed gas amount increases slowly with the increase of the pressure, and the adsorption rate is reduced; the third stage is a flat adsorption stage, the corresponding pressure is generally greater than 10 MPa, with the increase of the pressure, the shale adsorbed gas amount tends to be saturated, and the adsorption rate is low.

[0050] According to the isothermal desorption curve of the A well, a desorption rate curve and a desorption rate curvature derivative curve are obtained, and the sensitive desorption pressure P 敏感 of the high-quality shale of the A well in different sublayers is determined.

[0051] When the formation pressure is less than or equal to P 敏感 , the shale gas is rapidly desorbed, the desorption rate is fast, the desorbed gas amount is large, and the single-well production rapidly increases; when the formation pressure is higher than P 敏感 , the shale gas is slowly desorbed, the desorption rate is low, the desorbed gas amount is small, and the single-well production is low.

[0052] The step S103 is performed, a shale gas horizontal well B well is implemented in a preset area of the L anticline, the horizontal section of the well mainly passes through the high-quality shale reservoir, casing is run in the B well and cementing is carried out, hydraulic sand fracturing is carried out on the horizontal section to form a larger reconstruction volume and a complex artificial fracture network, and gas testing and production testing are carried out on the shale gas horizontal well after the fracturing is completed, different drainage and production processes are selected according to different production characteristics.

[0053] The B well cannot self-flow production in the early production stage, and the daily gas production of the jet pump is only 0.7×104 m3, according to the researches of the steps S101 and S102, it is realized that the sensitive desorption pressure of the shallow adsorbed shale gas is low, the downhole pressure is reduced to below the sensitive desorption pressure, and therefore, the rapid desorption and seepage of the adsorbed gas can be realized, therefore, researches on the adsorbed gas development technology are carried out, and the downhole pressure is quickly reduced to the sensitive desorption pressure P 敏感The hydraulic rodless pump drainage and production process enhances the drainage and reduces the flow pressure, and promotes the large desorption and production of the adsorbed gas from the reservoir. After using the drainage and production process for a period of time, it is detected that the gas well production rapidly increases to more than 45,000 cubic meters per day, and after the liquid production is carried by the self-suction, the above drainage and production process is closed, the appropriate drainage and production system is selected, the long-term stable desorption and production of the adsorbed gas is promoted, the high and stable production of the gas well is maintained, at present, the test production effect of the B well is good, the shallow normal pressure shale gas exploration breakthrough is achieved, and the commercial production of the shallow adsorbed shale gas is realized.

[0054] The above is only the preferred specific implementation of the present application, but the protection scope of the present application is not limited to this, any skilled person in the art can make equivalent replacement or change according to the technical scheme and the inventive concept of the present application within the technical range disclosed by the present application, which should be covered in the protection scope of the present application.

Claims

1. A method for the exploitation of shallow adsorbed shale gas, characterized in that: The method comprises the following steps: S101, based on core and logging data, determining shale gas occurrence characteristics, gas reservoir type and main exploitation object; In S102, based on the isothermal adsorption and desorption experiment, the adsorption gas adsorption and desorption rule and the adsorption gas sensitive desorption pressure P are determined. 敏感 The adsorption gas sensitive desorption pressure P 敏感 is the corresponding formation pressure when the adsorption gas starts to be massively desorbed. S103, according to the production characteristics, selecting the adsorbed gas dynamic displacement production process to realize the large-scale production of shallow adsorbed shale gas; The step S102 carries out the isothermal adsorption and desorption experiment of the core sample of different sections of the shale gas layer, determines the adsorption and desorption rule of the shale under the reservoir temperature and different pressure conditions, and determines the sensitive desorption pressure P 敏感 ; When the formation pressure is less than or equal to P 敏感 When the formation pressure is less than or equal to P 敏感 When the formation pressure is less than or equal to P 敏感 When the formation pressure is less than or equal to P 敏感 When the formation pressure is less than or equal to P 敏感 When the formation pressure is less than or equal When the formation pressure is higher than P 敏感 When the formation pressure is higher than P 敏感 When the formation pressure is higher than P 敏感 When the formation pressure is higher than P 敏感 When the formation pressure is higher than P 敏感 When the formation pressure is higher than P 敏感 When the In the step S103, in the preset area, shale gas horizontal wells are implemented, and hydraulic sand fracturing is carried out on the horizontal section, according to different production characteristics, the adsorbed gas dynamic displacement production process is selected to realize the large-scale production of shallow adsorbed shale gas; When the shale gas horizontal well cannot be produced by itself at the initial stage of production, the pressure at the bottom of the well is quickly reduced to the sensitive desorption pressure P 敏感 The following adsorbed gas drainage technology can strengthen liquid drainage, reduce flow pressure, and promote the desorption and production of adsorbed gas from the reservoir. When the gas well production is detected to be significantly increased, after self-flowing liquid-carrying production, the above displacement production process is closed, a suitable displacement production system is selected to promote the long-term stable desorption production of adsorbed gas and maintain the high and stable production of the gas well; When the shale gas horizontal well can produce self-flowing at the initial production stage and the production reaches the expected production, a suitable displacement production system is selected to prolong the self-flowing production cycle and improve the cumulative production during the self-flowing production period; When the gas well is detected to produce self-flowing or the production is less than the expected production, according to the specific operation method when the shale gas horizontal well cannot produce self-flowing at the initial production stage, the desorption exploitation of adsorbed gas is realized.

2. The method of claim 1, wherein: In the step S101, in the preset area, straight wells are implemented, the system obtains shale gas layer core and logging data, and determines shale gas occurrence characteristics, specifically including determining shale total gas content, adsorbed gas content and its proportion, free gas content and its proportion; And according to the shale gas occurrence characteristics, the gas reservoir type and the main exploitation object are determined.

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