CN113530511B - Method for developing natural gas reservoir - Google Patents
Method for developing natural gas reservoir Download PDFInfo
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- CN113530511B CN113530511B CN202010319236.7A CN202010319236A CN113530511B CN 113530511 B CN113530511 B CN 113530511B CN 202010319236 A CN202010319236 A CN 202010319236A CN 113530511 B CN113530511 B CN 113530511B
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/25—Methods for stimulating production
- E21B43/26—Methods for stimulating production by forming crevices or fractures
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/16—Enhanced recovery methods for obtaining hydrocarbons
- E21B43/164—Injecting CO2 or carbonated water
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/50—Improvements relating to the production of bulk chemicals
- Y02P20/54—Improvements relating to the production of bulk chemicals using solvents, e.g. supercritical solvents or ionic liquids
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P90/00—Enabling technologies with a potential contribution to greenhouse gas [GHG] emissions mitigation
- Y02P90/70—Combining sequestration of CO2 and exploitation of hydrocarbons by injecting CO2 or carbonated water in oil wells
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Abstract
The present disclosure provides a method for developing a natural gas reservoir, which belongs to the technical field of oil and gas reservoir development. Hydraulic fracturing development is performed on natural gas reservoirs. Most of free gas in the natural gas reservoir is extracted from the gas well, the formation pressure in the gas well is reduced, and the productivity of the gas well is continuously reduced to a more stable value, and the productivity value of the gas well is obtained at the moment. If the vertical well pipe of the gas well is in a normal state, the fracture length of the horizontal well pipe is smaller than the fracture length threshold value, the productivity of the gas well is larger than the productivity threshold value, the natural gas reservoir has enough stratum pressure, and the oil pipe in the gas well is stable, so that the secondary fracturing condition is met. And (3) converting the injected supercritical carbon dioxide into gaseous carbon dioxide in the gas well to replace the adsorbed gas, converting the adsorbed gas into free gas to be extracted, improving the output capacity of the gas well with reduced productivity, and finally improving the overall output of the natural gas reservoir.
Description
Technical Field
The present disclosure relates to the field of oil and gas reservoir development technologies, and in particular, to a method for developing a natural gas reservoir.
Background
The natural gas reservoir is an aggregated natural gas resource which is reserved in a shale layer for exploitation, shale gas is reserved in organic shale and an interlayer thereof, and the occurrence state of the shale gas comprises free gas, adsorption gas and a small amount of dissolved gas. Free gas exists in natural cracks and pores, adsorbed gas exists in adsorbed state on the surface between organic matter and mineral crystals, and a very small amount is stored in dissolved state in kerogen and asphaltenes.
In the development of natural gas reservoirs, it is common to use hydraulic fracturing to allow a significant amount of the gas present as free gas in the shale formation to escape to the well and to recover natural gas from the well. However, as the development of free gas in the shale layer is gradually completed, the formation pressure of the natural gas reservoir is gradually reduced, the development of shale gas existing in the natural gas reservoir in the form of adsorbed gas is difficult to extract and develop, and even if secondary hydraulic fracturing is performed, the output effect of the gas existing in the natural gas reservoir in the form of adsorbed gas is low, and the overall output of the natural gas reservoir is low.
Disclosure of Invention
The embodiment of the disclosure provides a development method of a natural gas reservoir, which can improve the overall output of the natural gas reservoir. The technical scheme is as follows:
the embodiment of the disclosure provides a method for developing a natural gas reservoir, which comprises the following steps:
performing primary fracturing development on a gas well in the natural gas reservoir, wherein the primary fracturing development is hydraulic fracturing development;
acquiring the state of a vertical well pipe of the gas well and the fracture length of a horizontal well pipe of the gas well, wherein the state of the vertical well pipe comprises a fracture state and a normal state;
after the productivity of the gas well gradually decreases to a stable range, acquiring the productivity of the gas well;
and if the state of the vertical well pipe is the normal state, the fracture length of the horizontal well pipe is not more than a fracture length threshold value, and the productivity of the gas well is not less than a productivity threshold value, performing secondary fracturing development on the natural gas reservoir by using supercritical carbon dioxide.
Optionally, the using supercritical carbon dioxide for secondary fracturing development of the natural gas reservoir comprises:
obtaining the flowback rate of the natural gas reservoir in the primary fracturing development;
if the flow back rate is not greater than the flow back rate threshold, pumping strength is 800-1200 m 3 Carrying out secondary fracturing development on the natural gas reservoir by supercritical carbon dioxide of/km; if the flow back rate is larger than the flow back rate threshold, pumping strength is 600-800 m 3 Supercritical carbon dioxide/km secondary fracturing development was performed on the natural gas reservoir.
Optionally, the pumping strength is 600-800 m 3 Supercritical carbon dioxide per km for the daySecondary fracturing development is performed on the natural gas reservoir, and the secondary fracturing development comprises the following steps:
and mixing slickwater in the supercritical carbon dioxide to perform secondary fracturing development on the natural gas reservoir.
Optionally, the amount of slickwater is equal to or less than the difference between the amount of flowback from the natural gas reservoir and the amount of supercritical carbon dioxide in the hydraulic fracturing.
Optionally, the flowback rate threshold is 20-40%.
Optionally, the using supercritical carbon dioxide for secondary fracturing development of the natural gas reservoir further comprises:
closing the gas well;
opening the gas well when the formation pressure in the gas well is not less than the critical pressure of carbon dioxide and the temperature in the gas well is not less than the critical temperature of carbon dioxide;
injecting supercritical carbon dioxide into the gas well for fracturing, closing the gas well for 7-14 days, and opening the gas well for production.
Optionally, the method for developing a natural gas reservoir further comprises:
obtaining the ratio of free gas in the natural gas reservoir before using supercritical carbon dioxide to perform secondary fracturing and splitting on the natural gas reservoir;
and if the state of the vertical well pipe is the normal state, the fracture length of the horizontal well pipe is not more than a fracture length threshold value, the productivity of the gas well is not less than a productivity threshold value, the ratio of free gas in the natural gas reservoir is not more than a free gas ratio threshold value, and the supercritical carbon dioxide is used for carrying out secondary fracturing development on the natural gas reservoir.
Optionally, the free gas ratio threshold is 60-70%.
Optionally, the capacity threshold is 2×10 4 ～3×10 4 m 3 /d。
Optionally, the fracture length threshold is 5-10%.
The technical scheme provided by the embodiment of the disclosure has the beneficial effects that at least:
when the natural gas reservoir is developed, the gas well in the natural gas reservoir is firstly subjected to primary fracturing development, and the primary fracturing development is hydraulic fracturing development. And acquiring the state of the vertical well pipe of the gas well and the fracture length of the horizontal well pipe of the gas well, wherein the state of the vertical well pipe comprises the fracture state and the normal state. After a period of development, most of free gas in the natural gas reservoir is extracted from the gas well, the formation pressure in the gas well is continuously reduced along with the extraction of most of free gas in the natural gas reservoir, the productivity of the gas well is continuously reduced to a stable value, and the productivity value of the gas well is obtained at the moment. If the vertical well pipe of the gas well is in a normal state, the fracture length of the horizontal well pipe is not more than the fracture length threshold value, and the productivity of the gas well is more than the productivity threshold value, the natural gas well is provided with a certain stratum pressure reserved in the natural gas reservoir, so that the natural gas can be produced, and the oil pipe in the gas well is stable, so that the secondary fracturing condition is met. And then the supercritical carbon dioxide is used for carrying out secondary pressure cracking development on the natural gas reservoir, after the supercritical carbon dioxide enters the gas well, the pressure in the gas well is usually lower than that of the supercritical carbon dioxide, the temperature is usually higher than that of the supercritical carbon dioxide, the supercritical carbon dioxide is converted into gaseous carbon dioxide in the gas well after being kept in a critical state for a period of time to flush out a stratum, and the adsorption capacity of the gaseous carbon dioxide is higher than that of natural gas (the main component of the gaseous carbon dioxide is methane), so that most of adsorption gas adsorbed between organic matters and mineral crystals can be replaced by the gaseous carbon dioxide, so that the adsorption gas is converted into free gas and can be extracted, the output capacity of the gas well with reduced productivity is improved, and the integral output of the natural gas reservoir is finally improved.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings needed in the description of the embodiments will be briefly introduced below, it will be apparent that the drawings in the following description are only some embodiments of the present disclosure, and other drawings may be obtained according to these drawings without inventive effort to a person of ordinary skill in the art,
FIG. 1 is a flow chart of a method of developing a natural gas reservoir provided by an embodiment of the present disclosure;
fig. 2 is a flow chart of another method of developing a natural gas reservoir provided by an embodiment of the present disclosure.
Detailed Description
For the purposes of clarity, technical solutions and advantages of the present disclosure, the following further details of the embodiments of the present disclosure will be described with reference to the accompanying drawings.
To enhance the overall production of the natural gas reservoir, fig. 1 is provided herein. Fig. 1 is a flowchart of a method for developing a natural gas reservoir according to an embodiment of the present disclosure, and as can be seen with reference to fig. 1, the embodiment of the present disclosure provides a method for developing a natural gas reservoir, where the method for developing a natural gas reservoir includes:
s101: and carrying out primary fracturing development on a gas well in the natural gas reservoir, wherein the primary fracturing development is hydraulic fracturing development.
S102: the method comprises the steps of obtaining the state of a vertical well pipe of a gas well and the fracture length of a horizontal well pipe of the gas well, wherein the state of the vertical well pipe comprises a fracture state and a normal state.
S103: and after the productivity of the gas well gradually decreases to a stable range, acquiring the productivity of the gas well.
S104: if the state of the vertical well section well pipe is a normal state, the fracture length of the horizontal well section well pipe is not more than the fracture length threshold value, and the productivity of the gas well is not less than the productivity threshold value, performing secondary fracturing development on the natural gas reservoir by using supercritical carbon dioxide.
When the natural gas reservoir is developed, the gas well in the natural gas reservoir is firstly subjected to primary fracturing development, and the primary fracturing development is hydraulic fracturing development. And acquiring the state of the vertical well pipe of the gas well and the fracture length of the horizontal well pipe of the gas well, wherein the state of the vertical well pipe comprises the fracture state and the normal state. After a period of development, most of free gas in the natural gas reservoir is extracted from the gas well, the formation pressure in the gas well is continuously reduced along with the extraction of most of free gas in the natural gas reservoir, the productivity of the gas well is continuously reduced to a stable value, and the productivity value of the gas well is obtained. If the vertical well pipe of the gas well is in a normal state, the fracture length of the horizontal well pipe is not more than the fracture length threshold value, and the productivity of the gas well is more than the productivity threshold value, the natural gas well is provided with a certain stratum pressure reserved in the natural gas reservoir, so that the natural gas can be produced, and the oil pipe in the gas well is stable, so that the secondary fracturing condition is met. And then the supercritical carbon dioxide is used for carrying out secondary pressure cracking development on the natural gas reservoir, after the supercritical carbon dioxide enters the gas well, the pressure in the gas well is usually lower than that of the supercritical carbon dioxide, the temperature is usually higher than that of the supercritical carbon dioxide, the supercritical carbon dioxide is converted into gaseous carbon dioxide in the gas well after being kept in a critical state for a period of time to flush out a stratum, and the adsorption capacity of the gaseous carbon dioxide is higher than that of natural gas (the main component of the gaseous carbon dioxide is methane), so that most of adsorption gas adsorbed between organic matters and mineral crystals can be replaced by the gaseous carbon dioxide, so that the adsorption gas is converted into free gas and can be extracted, the output capacity of the gas well with reduced productivity is improved, and the integral output of the natural gas reservoir is finally improved.
In the method, the hydraulic fracturing is performed for the first time in the gas well, so that the cost is low, the fracturing effect is good, and most of free gas in the natural gas reservoir can be released. The secondary fracturing of the supercritical carbon dioxide mainly aims at the adsorbed gas, the replacement effect is good, most of the adsorbed gas can be replaced, and because the supercritical carbon dioxide is the secondary fracturing, the supercritical carbon dioxide which needs to be put into is relatively less on the basis that the gas well is fractured once, and the final benefit of the natural gas reservoir is relatively larger.
The normal state of the well casing of the gas well means a position where the well casing of the gas well is not broken, and if the vertical well casing of the gas well is broken and the broken length of the horizontal well casing is greater than the broken length threshold, it is described that the state of the well casing in the gas well is difficult to support the development of the secondary fracturing of carbon dioxide. And when the productivity of the gas well is smaller than the productivity threshold value, the formation pressure of the gas well is too low, and even if a certain amount of natural gas exists in the gas well, the natural gas is difficult to produce from the gas well. Therefore, in both cases, the development of secondary fracturing using supercritical carbon dioxide is not possible.
Fig. 2 is a flowchart of another method for developing a natural gas reservoir according to an embodiment of the present disclosure, and as can be seen with reference to fig. 2, the embodiment of the present disclosure provides another method for developing a natural gas reservoir, where the method for developing a natural gas reservoir includes:
s201: the ratio of free gas in the natural gas reservoir is obtained.
Before the primary fracturing exploitation of the natural gas reservoir, the gas content in the natural gas reservoir can be detected and the data can be recorded, so that the development of the subsequent natural gas reservoir can be guided.
The ratio of free gas in the natural gas reservoir may be calculated according to the following formula:
in the formula (1), R 1 The free gas ratio in the natural gas reservoir is expressed in units of; b (B) f 、B a The unit is m, and the free air amount and the adsorption air amount are respectively 3 /t。
Alternatively, the free gas occupancy can also be calculated according to the following formula:
subtracting R in equation (2) from 100% 2 Obtaining the free gas ratio in the natural gas reservoir, wherein R in the formula (2) 2 The unit is the adsorption gas ratio in the natural gas reservoir; b (B) f 、B a The unit is m, and the free air amount and the adsorption air amount are respectively 3 /t。
It should be noted that B in the above formula f 、B a Can be obtained by geophysical measurement techniques.
S202: and carrying out primary fracturing development on a gas well in the natural gas reservoir, wherein the primary fracturing development is hydraulic fracturing development.
In step S202, when the primary fracturing development is hydraulic fracturing development, the hydraulic fracturing development includes two steps of hydraulic fracturing and development, the hydraulic fracturing is performed on the gas well in the natural gas reservoir, and after the internal environment of the gas well is stable after the hydraulic fracturing, the natural gas is exploited.
Alternatively, in hydraulically fracturing a gas well within a natural gas reservoir, construction parameters that need to be involved in hydraulic fracturing may be set, such as: total fluid volume of fracturing pump injection L o Intensity Δl of use solution o Pumping strength q o And recording the flowback rate eta.
Recording these construction parameters may facilitate the performance and adjustment of subsequent gas well development.
Total fluid volume of fracturing pump injection L o Intensity Δl of use solution o Average pumping displacement q o The flowback rate eta can be measured when hydraulic fracturing is carried out.
S203: the method comprises the steps of obtaining the state of a vertical well pipe of a gas well and the fracture length of a horizontal well pipe of the gas well, wherein the state of the vertical well pipe comprises a fracture state and a normal state.
And whether the vertical well pipe and the horizontal well pipe are broken or not is collected, and the broken length can be used as a judging standard for judging whether the secondary fracturing development of the supercritical carbon dioxide is implemented subsequently or not.
The vertical well leg in step S203 refers to a well leg of which axis is parallel to the local gravitational acceleration of the gas well, and the horizontal well leg refers to a well leg of which axis is perpendicular to the local gravitational acceleration of the gas well.
Optionally, in the case that no blockage exists in the gas well, the instrument is lowered into the gas well to monitor and check the well pipe in the gas well, and whether the well pipe of the gas well is broken or not and the breaking length are judged according to the condition of the wall of the well pipe and whether rock and sand exist in the well pipe or not. The method is convenient for detecting the state of the well pipe in the gas well and acquiring the fracture length.
S204: and after the productivity of the gas well gradually decreases to a stable range, acquiring the productivity of the gas well.
After the gas well works for a long time, natural gas in the gas well is gradually extracted, the formation pressure of the natural gas reservoir is gradually reduced, free natural gas overflowed from the gas well under pressure is also reduced, the productivity of the gas well is gradually reduced, and finally, the productivity value is kept to be stable. At this time, the productivity of the gas well is obtained again, and the productivity can be used as a judging standard for judging whether the supercritical carbon dioxide is subjected to secondary fracturing or not.
Alternatively, after the production of the gas well is measured, a coiled tubing string operation may be performed on the gas well if the production of the gas well is greater than the production threshold.
And the coiled tubing well-dredging operation is implemented on the gas well, so that the occurrence of blockage in the gas well can be avoided, and the stable implementation of the secondary supercritical carbon dioxide fracturing is ensured.
S205: if the vertical well pipe of the gas well is in a normal state, the fracture length of the horizontal well pipe is smaller than the fracture length threshold, the productivity of the gas well is larger than the productivity threshold, and if the free gas ratio in the natural gas reservoir is lower than the free gas ratio threshold, the supercritical carbon dioxide is used for carrying out secondary fracturing development on the natural gas reservoir.
After meeting the conditions for performing the supercritical carbon dioxide secondary fracturing required in step S205, step S205 may include:
closing a gas well; opening the gas well when the formation pressure in the gas well is not less than the critical pressure of carbon dioxide and the temperature in the gas well is not less than the critical temperature of carbon dioxide; injecting supercritical carbon dioxide into the gas well for fracturing, closing the gas well for 7-14 days, and opening the gas well for production.
The method comprises the steps of closing the gas well before injecting the supercritical carbon dioxide, so that the pressure in the gas well is increased, and when the formation pressure and temperature in the gas well are equal to or higher than the critical pressure and critical temperature of the carbon dioxide, the supercritical carbon dioxide is opened to inject the supercritical carbon dioxide into the gas well, and after the supercritical carbon dioxide enters the gas well, the pressure and the temperature in the gas well are kept at the critical pressure and the critical temperature, the supercritical carbon dioxide can be kept in a liquid state for a period of time, and formation cracks are flushed, so that the natural gas in an adsorption state can be replaced and extracted more easily. After injecting the supercritical carbon dioxide, closing for 7-14 days, so that the pressure and the temperature in the gas well can be maintained, and the supercritical carbon dioxide can be converted into a gaseous state and the natural gas in the natural gas reservoir can be replaced.
It should be noted that after the supercritical carbon dioxide is injected into the gas well, the wellhead temperature of the gas well is generally affected by the supercritical carbon dioxide to be rapidly reduced, but the temperature of the bottom layer of the gas well is generally higher than the critical temperature of the carbon dioxide, after the gas well is closed for 7-14 days, the whole temperature in the gas well becomes relatively uniform, and most of the supercritical carbon dioxide is converted into a gaseous state and natural gas is replaced.
Illustratively, after the first step of closing the gas well, the gas well may be re-opened when the formation pressure in the gas well is 7Mpa and the temperature in the gas well is 35 ℃. The natural gas replacement effect is better.
Illustratively, in step S205, a soluble bridge plug may be inserted into the gas well through the coiled tubing during secondary fracturing using supercritical carbon dioxide.
The soluble bridge plug can help the layering in the gas well, and is convenient for the stable progress of the supercritical carbon dioxide secondary fracturing.
The flowback rate of the natural gas reservoir in the hydraulic fracturing obtained in step S202 can be referred to;
if the flow back rate is not greater than the flow back rate threshold, pumping strength is 800-1200 mm 3 Carrying out secondary fracturing development on the natural gas reservoir by supercritical carbon dioxide of/km; if the flow back rate is larger than the flow back rate threshold, pumping strength is 600-800 mm 3 Supercritical carbon dioxide/km secondary fracturing development was performed on natural gas reservoirs.
When the flowback rate of the gas well is smaller than the flowback rate threshold value, the seam net in the natural gas reservoir is better in development, supercritical carbon dioxide can enter into the seams of the stratum more easily to replace the natural gas, and pumping strength is 800-1200 m 3 The supercritical carbon dioxide with larger discharge capacity per km is used for carrying out secondary fracturing development on the natural gas reservoir, the development degree is high, the natural gas yield is high, and the overall benefit is good. When the flowback rate of the gas well is larger than the flowback rate threshold value, the gas well can be regarded as poor in development of an internal fracture network of the natural gas reservoir, poor in primary hydraulic fracturing effect, poor in reformation property by using supercritical carbon dioxide, less in stratum cracks, less in replaceable natural gas and 600-800 m in pumping strength 3 Supercritical carbon dioxide to natural gas with small/km displacementThe reservoir is subjected to secondary fracturing development, the investment is relatively low, and the productivity of natural gas can be improved to a certain extent.
The pumping strength refers to the pumping fracturing fluid amount or supercritical carbon dioxide amount required to be used per unit fracturing length, and the unit is m 3 /m or m 3 /km. The pumping strength may be obtained from empirical values, such as with reference to pumping strength and returns of other gas wells.
Illustratively, in step S205, the flowback rate threshold may be 20-40%.
When the flowback rate threshold is 20-40%, the flowback rate threshold can be used as a standard for judging the development condition of the internal joint network of the natural gas reservoir, when the flowback rate is lower than or in the range of 20-40%, the joint network in the natural gas reservoir is better in development, supercritical carbon dioxide can enter stratum gaps more easily to replace natural gas, and the supercritical carbon dioxide with larger discharge capacity can be used for carrying out secondary fracturing development on the natural gas reservoir, so that the development degree is high, the natural gas output is high, and the overall benefit is good. When the flowback rate of the gas well is larger than the upper limit value of 40%, the gas well can be regarded as poor in development of an internal joint network of the natural gas reservoir, poor in primary hydraulic fracturing effect and poor in reformation property of using supercritical carbon dioxide, secondary fracturing development can be carried out on the natural gas reservoir by using the supercritical carbon dioxide with small discharge capacity, the investment is relatively low, and the productivity of the natural gas can be improved to a certain extent.
Alternatively, pumping strength of 600-800 m is used 3 The supercritical carbon dioxide/km for secondary fracturing and splitting of natural gas reservoirs may comprise:
and mixing slickwater in supercritical carbon dioxide to perform secondary fracturing development on the natural gas reservoir.
The pumping strength is 600-800 m 3 When the supercritical carbon dioxide of/km carries out secondary fracturing development on the natural gas reservoir, the supercritical carbon dioxide can be mixed with slick water to carry out secondary fracturing development on the natural gas reservoir, the slick water can replace the supercritical carbon dioxide to flush out stratum cracks, the supercritical carbon dioxide can be ensured to smoothly enter a stratum fracture network, the natural gas recovery effect is ensured, and meanwhile, the development cost of a gas well can be properly reduced.
Illustratively, the amount of slickwater may be equal to or less than the difference between the amount of flowback from the natural gas reservoir and the amount of supercritical carbon dioxide in the hydraulic fracturing.
The consumption of the slickwater is equal to or less than the difference between the flow-back liquid amount of the natural gas reservoir and the consumption of the supercritical carbon dioxide in the hydraulic fracturing, so that the defect that the pressure of the supercritical carbon dioxide is insufficient can be guaranteed to be exactly supplemented by the slickwater, the conversion and replacement of the supercritical carbon dioxide cannot be influenced due to the fact that the ratio of the slickwater is too large, the relative cost is low, and the output of the natural gas reservoir can be greatly improved.
Alternatively, the capacity threshold may be 2×10 4 ～3×10 4 m 3 /d。
Capacity threshold of 2×10 4 ～3×10 4 m 3 And/d, can be used as a basis for judging the output condition in the natural gas reservoir. Gas wells with a capacity of less than 2 x 10 4 ～3×10 4 m 3 When the production capacity of the gas well is too low, the content of the natural gas which can be produced is small even if the development is carried out; gas wells with capacities greater than 2 x 10 4 ～3×10 4 m 3 And/d, the formation pressure in the gas well is enough, more natural gas can be produced from the gas well after transformation, and the overall production amount and final income of the natural gas are effectively improved.
Illustratively, the burst length threshold in step S205 may be 5-10%.
The fracture length threshold value is 5-10%, and whether the condition of the well pipe in the gas well can support the implementation of secondary fracturing development can be judged. When the fracture length of the horizontal well pipe is less than or in the range of 5-10%, the well pipe in the gas well has better condition, and can support the impact caused by secondary fracturing development and carry out natural gas exploitation after fracturing. When the fracture length of the horizontal section of well pipe is greater than the fracture length threshold, namely greater than the upper limit value of 10%, the condition of the well pipe in the gas well is poor, the forced secondary fracturing fracture can cause the accelerated damage of the well pipe, and the gas well is difficult to maintain the normal natural gas production function.
In step S205, the free gas ratio threshold may be 60 to 70%.
The free gas ratio threshold is 60-70%, if the free gas ratio in the natural gas reservoir is smaller than or within the range of 60-70%, the natural gas reservoir is provided with more adsorbed gas, the probability of the adsorbed gas being replaced can be effectively improved by carrying out secondary fracturing on the gas well, the production efficiency of the gas well of the natural gas reservoir is improved, and the final overall benefit is higher. When the ratio of free gas in the natural gas reservoir is larger than the upper limit value of 70%, the ratio of adsorbed gas is relatively small, and even if the supercritical carbon dioxide is used for secondary fracturing, the income of the adsorbed gas obtained by final replacement is difficult to offset the investment of the supercritical carbon dioxide for fracturing development, and the benefit is insufficient.
The method shown in fig. 2 is newly added with step S201, before judging whether to perform the secondary fracturing of the supercritical carbon dioxide, the ratio of free gas in the natural gas reservoir is obtained to roughly judge the final yield of the gas well if the secondary fracturing of the supercritical carbon dioxide is performed, and the final yield of the gas well can be used as a judging basis to ensure that the finally developed gas well can effectively improve the yield of the gas well and maintain positive yields, so that the situation that the cost is higher than the yield is not easy to occur.
The method shown in fig. 2 is further described in detail with respect to the method shown in fig. 1, with the steps of fig. 2.
In the implementation manner provided in the present disclosure, the value is not greater than a certain threshold, and the value is not greater than an upper limit value of the threshold, is not less than a certain threshold, and is not less than a lower limit value of the threshold.
To facilitate an understanding of the present disclosure, one implementation of the method may be described herein, the present disclosure being in the context of the development of natural gas reservoirs:
the free gas fraction of natural gas from a gas well within a natural gas reservoir is measured and recorded by geophysical measurements.
If the free gas ratio of the natural gas in the natural gas reservoir is more than 70%, the gas adsorption in the natural gas reservoir is smaller, the development value is low, and the supercritical carbon dioxide can be not used for carrying out secondary fracturing and cracking treatment on the gas well.
If the free gas ratio of the natural gas in the natural gas reservoir is less than 70%, a certain amount of adsorbed gas remains in the natural gas reservoir; further determining the capacity of the gas well when the capacity of the gas well is less than 2-3 x 10 4 m 3 At/d, the formation pressure of the gas well is insufficient to support continued development of the gas well, and the gas well may be subjected to secondary fracturing and initiation treatments without using supercritical carbon dioxide.
When the productivity of the gas well is not less than 2X 10 4 ～3×10 4 m 3 And (d) further judging the relation between the flowback rate of the gas well and the flowback rate threshold value.
When the flowback rate is lower than 40% of the flowback rate threshold, the seam net in the natural gas reservoir is better in development, supercritical carbon dioxide can enter gaps of the stratum more easily to replace the natural gas, and the supercritical carbon dioxide with the pumping strength of 800-1200 m3/km can be used for carrying out secondary fracturing development on the natural gas reservoir, so that the development degree is high, the natural gas output is high, and the overall benefit is good.
When the flowback rate of the gas well is greater than 40% of the flowback rate threshold, the gas well can be regarded as poor in development of an internal joint network of the natural gas reservoir, poor in primary hydraulic fracturing effect and poor in reformation property by using supercritical carbon dioxide, the supercritical carbon dioxide with pumping strength of 600-800 m3/km can be used for secondary fracturing development of the natural gas reservoir, the investment is relatively low, and the productivity of the natural gas can be improved to a certain extent.
And finally closing the wellhead of the gas well, wherein the supercritical carbon dioxide entering the gas well partially breaks formation cracks under the conditions of pressure in the gas well and environment, part of the supercritical carbon dioxide is converted into gaseous carbon dioxide, and the gaseous carbon dioxide can replace the natural gas on the surface of the adsorbed organic matters or mineral crystals due to the relation that the adsorption capacity is larger than that of the natural gas, so that the replaced natural gas is recovered.
The present invention will be described in further detail by taking a gas well X from the aust Tao Tong five peak group on the basin of si-chu to a certain block of the campaigns group of the down-log system as an example. The method comprises the following steps:
first, the gas content in the gas well X is clarified, and whether or not to perform the supercritical operation is determinedAnd (5) secondary fracturing of carbon dioxide. Total gas content of gas well X4.5 m 3 And/t, the adsorption gas accounts for 37 percent, the free gas accounts for 63 percent, and the free gas accounts for less than 70 percent, thereby meeting the implementation conditions of supercritical carbon dioxide secondary fracturing.
Further, determining whether to implement supercritical carbon dioxide secondary fracturing or not by defining gas well drainage conditions. The initial production pressure of X production of the gas well is 45MPa, and the initial yield is about 36 multiplied by 10 4 m 3 And/d, the yield is reduced to 2.5X10 after 3 years of production 4 m 3 And the pressure of production is 4.5MPa, the capacity requirement of carrying out supercritical carbon dioxide secondary fracturing is met, and the supercritical carbon dioxide secondary fracturing can be carried out.
Referring to the construction parameters and the reconstruction effect of the X initial hydraulic fracturing of the gas well, and designing a supercritical carbon dioxide secondary fracturing fluid system and displacement according to the construction parameters and the reconstruction effect of the X initial hydraulic fracturing. The construction period of the gas well X is smooth, the well pipe in the gas well is not seriously broken, and the total injection liquid amount is 36505m 3 After 3 years, the flowback rate is 33.6%, and the flowback rate is lower than 40%, so that no pre-slick water injection measures are adopted.
Finally, supercritical carbon dioxide secondary fracturing is implemented, so that yield increase is realized. Closing the well at the beginning of the production in the 3 rd year, soaking the well, recovering the construction pressure to 7MPa, and opening the well for construction. The soluble bridge plug is put into the toe end of the coiled tubing to carry out fracturing construction, and supercritical CO is pumped 2 Pumping supercritical CO into stratum by fracturing truck 2 Injection displacement of 6m 3 /min, injection intensity 1000m 3 /km. Supercritical CO at wellhead and pump 2 Sealing between fracturing trucks, and maintaining supercritical CO at wellhead 2 The required pressure and temperature conditions ensure CO 2 The injection is always in a supercritical state when the injection is carried out to the bottom of the well. Closing the well after construction is finished, and ensuring CO 2 The supercritical state is converted into the gaseous state to form a gap net and replace the adsorption gas among organic matters and mineral crystals, thereby achieving the purpose of increasing yield. And (5) soaking the well for 7-14 days, and restarting the well to produce.
The present invention is not limited to the above embodiments, but is not limited to the above embodiments, and any simple modification, equivalent changes and modification of the above embodiments according to the technical principles of the present invention can be made by those skilled in the art without departing from the scope of the technical aspects of the present invention.
Claims (8)
1. A method of developing a natural gas reservoir, the method comprising:
performing primary fracturing development on a gas well in the natural gas reservoir, wherein the primary fracturing development is hydraulic fracturing development;
acquiring the state of a vertical well pipe of the gas well and the fracture length of a horizontal well pipe of the gas well, wherein the state of the vertical well pipe comprises a fracture state and a normal state;
after the productivity of the gas well gradually decreases to a stable range, acquiring the productivity of the gas well;
if the state of the vertical well pipe is the normal state, the fracture length of the horizontal well pipe is not more than a fracture length threshold value, and the productivity of the gas well is not less than a productivity threshold value, performing secondary fracturing development on the natural gas reservoir by using supercritical carbon dioxide;
the use of supercritical carbon dioxide for secondary fracturing development of the natural gas reservoir comprises:
obtaining the flowback rate of the natural gas reservoir in the primary fracturing development;
if the flowback rate is larger than the flowback rate threshold, mixing slick water in supercritical carbon dioxide, and pumping with the strength of 600-800 m 3 And (3) carrying out secondary fracturing development on the natural gas reservoir by using supercritical carbon dioxide of/km, wherein the consumption of slickwater is equal to or less than the difference between the flow-back liquid amount of the natural gas reservoir and the consumption of the supercritical carbon dioxide in hydraulic fracturing.
2. The method of claim 1, wherein the secondary fracturing development of the natural gas reservoir using supercritical carbon dioxide comprises:
if the flow back rate is not greater than the flow back rate threshold, pumping strength is 800-1200 m 3 Supercritical carbon dioxide/km secondary fracturing development was performed on the natural gas reservoir.
3. The method of claim 2, wherein the flowback rate threshold is 20-40%.
4. A method of developing a natural gas reservoir according to any one of claims 1 to 3, wherein the secondary fracturing development of the natural gas reservoir using supercritical carbon dioxide further comprises:
closing the gas well;
opening the gas well when the formation pressure in the gas well is not less than the critical pressure of carbon dioxide and the temperature in the gas well is not less than the critical temperature of carbon dioxide;
injecting supercritical carbon dioxide into the gas well for fracturing, closing the gas well for 7-14 days, and opening the gas well for production.
5. A method of developing a natural gas reservoir according to any one of claims 1 to 3, further comprising:
obtaining the ratio of free gas in the natural gas reservoir before using supercritical carbon dioxide to perform secondary fracturing and splitting on the natural gas reservoir;
and if the state of the vertical well pipe is the normal state, the fracture length of the horizontal well pipe is not more than a fracture length threshold value, the productivity of the gas well is not less than a productivity threshold value, the ratio of free gas in the natural gas reservoir is not more than a free gas ratio threshold value, and the supercritical carbon dioxide is used for carrying out secondary fracturing development on the natural gas reservoir.
6. A method of developing a natural gas reservoir as defined in claim 5, wherein the free gas fraction threshold is between 60 and 70%.
7. A method of developing a natural gas reservoir according to any one of claims 1 to 3, wherein the capacity threshold is 2 x 10 4 ～3×10 4 m 3 /d。
8. A method of developing a natural gas reservoir according to any one of claims 1 to 3, wherein the fracture length threshold is in the range 5 to 10%.
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