CN112943185A - Composite fracturing process based on supercritical carbon dioxide pre-fracturing - Google Patents
Composite fracturing process based on supercritical carbon dioxide pre-fracturing Download PDFInfo
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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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- C09K8/00—Compositions for drilling of boreholes or wells; Compositions for treating boreholes or wells, e.g. for completion or for remedial operations
- C09K8/60—Compositions for stimulating production by acting on the underground formation
- C09K8/62—Compositions for forming crevices or fractures
- C09K8/66—Compositions based on water or polar solvents
- C09K8/68—Compositions based on water or polar solvents containing organic compounds
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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K8/00—Compositions for drilling of boreholes or wells; Compositions for treating boreholes or wells, e.g. for completion or for remedial operations
- C09K8/60—Compositions for stimulating production by acting on the underground formation
- C09K8/84—Compositions based on water or polar solvents
- C09K8/86—Compositions based on water or polar solvents containing organic compounds
- C09K8/88—Compositions based on water or polar solvents containing organic compounds macromolecular compounds
- C09K8/90—Compositions based on water or polar solvents containing organic compounds macromolecular compounds of natural origin, e.g. polysaccharides, cellulose
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- 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
- E21B43/166—Injecting a gaseous medium; Injecting a gaseous medium and a liquid medium
- E21B43/168—Injecting a gaseous medium
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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
- E21B43/25—Methods for stimulating production
- E21B43/26—Methods for stimulating production by forming crevices or fractures
- E21B43/267—Methods for stimulating production by forming crevices or fractures reinforcing fractures by propping
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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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- Y02P20/00—Technologies relating to chemical industry
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Abstract
The embodiment of the application provides a composite fracturing process based on supercritical carbon dioxide pre-fracturing, and relates to the technical field of geological resource exploration. The composite fracturing process is mainly characterized in that supercritical carbon dioxide is injected into a stratum for pre-fracturing to form a complex fracture network; then injecting different types of fracturing fluid carrying proppant into the gap net in sequence for hydraulic sand-carrying fracturing to expand, support and polish the gap net, and in the hydraulic sand-carrying fracturing process, stirring the liquid state N in the whole process2(ii) a Slickwater is then injected to perform a displacement operation to displace the fracturing fluid into the formation. Examples of the present applicationThe composite fracturing process based on the supercritical carbon dioxide pre-fracturing realizes the effects of modifying the volume of a complex fracture network of a stratum, particularly a shale reservoir, effectively supporting the fracture network, increasing the energy of the stratum and the like.
Description
Technical Field
The application relates to the technical field of geological resource exploration, in particular to a composite fracturing process based on supercritical carbon dioxide pre-fracturing.
Background
The oil and gas reserves in the shale reservoir of the earth are huge, the shale reservoir has the characteristics of ultralow porosity and ultralow permeability, oil and gas cannot flow in the shale reservoir, and the industrial capacity is difficult to obtain by adopting the conventional development technology. Therefore, in the field of development of compact shale reservoirs, a volume fracturing process capable of forming large-scale complex fracture networks is a key core technology for obtaining high yield of shale oil and gas.
In particular, a plurality of sets of organic-rich shale series with large deposition thickness and wide distribution range are developed in continental facies basins of China, the geological resource amount of continental facies oil is about 500 hundred million tons, the geological resource amount of continental facies shale gas is about 100000 hundred million square, and the exploration potential is huge. However, the clay mineral content of the continental facies shale is high, and the continental facies shale has strong heterogeneity, and a complex fracture network cannot be formed by adopting the conventional large-scale hydraulic fracturing technology.
Related researches are carried out on the land shale stratum volume fracturing, wherein the research on a supercritical carbon dioxide dry method and a foam fracturing process is the hottest, and the method is to inject liquid carbon dioxide with the proportion of 100 percent or liquid carbon dioxide mixed solution with the proportion of 50 percent into the stratum so as to achieve the effects of resisting water sensitivity, deeply penetrating and increasing energy. But of the typeThe method is still not good in use effect, and the reason may be that: firstly, the construction displacement is low, generally 2m3Min, the total dosage is low, and the hydraulic fracturing volume transformation effect cannot be achieved; secondly, the sand carrying capacity is poor, so that the sand carrying agent can not be carried almost, and the seam net can not be effectively supported; thirdly, the liquid carbon dioxide is very easy to combine with water to form carbonic acid after entering the stratum, and the carbonic acid is consumed by the carbonate mineral reaction in the stratum, so that the consumption rate can reach 95 percent, and the energy increasing effect cannot be achieved; fourthly, the requirements on ground and underground equipment are high, the construction risk is large, and the cost is high. Therefore, the supercritical carbon dioxide dry method and the foam fracturing process are not mature, and are difficult to popularize and apply in a large range.
Therefore, the volume fracturing process of the normal-pressure strong-heterogeneity continental-facies shale reservoir is still a bottleneck technical problem, and the continental-facies shale reservoir volume fracturing technology needs to be researched and developed urgently.
Disclosure of Invention
The composite fracturing process based on the supercritical carbon dioxide pre-fracturing aims to achieve the effects of modifying the volume of a complex fracture network of a stratum, particularly a shale reservoir, effectively supporting the fracture network, energizing the stratum and the like.
In a first aspect, an embodiment of the present application provides a composite fracturing process based on supercritical carbon dioxide pre-fracturing, which includes the following steps:
s1, injecting supercritical carbon dioxide into the stratum for pre-fracturing to form a seam network;
s2, injecting different types of fracturing fluids carrying proppant into the fracture network in sequence to carry out hydraulic sand-carrying fracturing for expanding, supporting and polishing the fracture network, and in the hydraulic sand-carrying fracturing process, stirring the fluid state N in the whole process2；
And S3, injecting slickwater to perform displacement operation so as to drive the fracturing fluid into the stratum.
In the technical scheme, firstly, pre-fracturing is carried out on the stratum by using supercritical carbon dioxide, and a complex fracture network is formed in the stratum by using the extremely strong fluidity, diffusivity and penetrability of the supercritical carbon dioxide; then, different types of fracturing fluids are utilized to perform hydraulic sand-carrying fracturing, namelyExpanding complex seam nets formed in the early stage and forming effective supports; liquid N is injected in a mixing way in the whole process of hydraulic fracturing2Liquid state N2After entering the formation, it will change to a gaseous state with increasing temperature, increasing in volume by several thousand times, and N2Inert gas is adopted, and the chemical reaction with stratum rock is avoided, so that the stratum energizing effect can be realized; and finally, injecting slick water to replace the fracturing fluid, so that the fracturing fluid completely enters the stratum, and the effect is ensured.
In one possible implementation, in step S2, the liquid state N is fully mixed2The discharge capacity of (A) is 150 to 200L/min.
In the technical scheme, the liquid state N is mixed and injected according to a certain displacement2The formation energizing and pressure maintaining device is beneficial to formation energizing and pressure maintaining in the later period of flowback, and meanwhile, the density of the flowback liquid is reduced, the flowback is accelerated, and the flowback rate is improved.
In one possible implementation mode, the supercritical carbon dioxide is obtained by heating and boosting liquid carbon dioxide to a supercritical state, wherein the critical temperature is 31.1 ℃, and the critical pressure is 7.38 MPa;
and/or the injection discharge capacity of the supercritical carbon dioxide is 3-4 m3/min。
In the technical scheme, the supercritical carbon dioxide refers to carbon dioxide fluid with the temperature and the pressure reaching or exceeding the critical temperature and the critical pressure at the same time, the supercritical carbon dioxide has unique physical and chemical properties, the cracking pressure of rocks can be reduced by about 45 percent by the supercritical carbon dioxide, meanwhile, the crack-forming efficiency is 3 times higher than that of hydraulic fracturing, a complex crack network is easily formed, and the complex crack network in a certain range is easily formed in a stratum with high clay mineral content and strong heterogeneity by utilizing the extremely strong fluidity, diffusivity and penetrability of supercritical carbon dioxide, and the supercritical carbon dioxide can be combined with formation water in the formation to form an acidic solution, so that the formation is further corroded, particularly carbonate cement and the like in the shale reservoir, a seepage channel of the shale reservoir is opened, and favorable conditions are provided for subsequent fracturing and oil gas flowback.
In one possible implementation, in step S2, the hydraulic sand-carrying fracturing includes the following steps:
sequentially sewing the net according to the length of 14-18 m3Injecting high-viscosity gel fracturing fluid carrying coarse-particle-size propping agent into the fracturing fluid at a delivery rate of/min to enlarge a gap net according to the length of 12-14 m3Injecting low-viscosity slick water fracturing fluid carrying small-particle-size proppant into the fracturing fluid at a delivery rate of/min to support all seam meshes according to the length of 14-16 m3Injecting medium-viscosity linear gel fracturing fluid carrying medium-particle size proppant into the per min discharge capacity to polish the seam net;
wherein the viscosity of the high-viscosity gel fracturing fluid is more than 50 mPa.s, the coarse-grain-size propping agent is 30-50 meshes of ceramsite, and the sand adding proportion is 4-6 wt%;
the low-viscosity slickwater fracturing fluid has the viscosity of 3-5 mPa & s, the small-particle-size propping agent is 70-140 meshes of ceramsite, and the sand adding proportion is 10-15 wt%;
the viscosity of the medium-viscosity linear fracturing fluid is 10-30 mPa.s, the medium-particle-size propping agent is 40-70 meshes of ceramsite, and the sand adding proportion is 8-10 wt%.
In the technical scheme, the fracturing fluid systems with different viscosities are respectively used for carrying proppants with different particle sizes to perform large-scale hydraulic fracturing, so that the complex fracture net, the supporting fracture net and the near-well fracture net are sequentially expanded. Specifically, a small amount of high-viscosity jelly is adopted to carry a coarse-particle-size propping agent, so that on one hand, the maximum range of the complex seam net formed in the early stage is enlarged, the height and the length of an artificial crack are increased, on the other hand, the liquid filtration is reduced, the seam forming efficiency is improved, and meanwhile, the complex seam net formed in the early stage is supported, so that an effective channel is provided for the extension of subsequent fracturing fluid; then, a large amount of low-viscosity slickwater is adopted to carry small-particle-size propping agents to further improve the complexity of the cracks, natural micro cracks and secondary cracks are opened to the maximum extent, and a large amount of carried silt enters the stratum to form effective support for middle and far end micro cracks formed in the fracturing process; and finally, carrying the medium-particle-size propping agent by using the medium-viscosity linear adhesive for rear-end tracking, so that the medium-viscosity linear adhesive carrying the medium-particle-size propping agent flows in the seam net to play a polishing role, and the artificial crack is smoother and straighter and has larger width, thereby further improving the flow conductivity of the crack.
In a possible implementation mode, the high-viscosity gel fracturing fluid mainly comprises 0.5-0.8% of carboxymethyl hydroxypropyl guar gum, 1-2% of KCL anti-swelling agent, 0.3-0.5% of fluorocarbon cleanup additive, 0.5-0.7% of cross-linking agent, 0.1-0.2% of resistance reducing agent and 95-98% of clear water in percentage by mass; the anti-swelling rate of the high-viscosity gel fracturing fluid is more than 85 percent, the gel breaking time at 90 ℃ is less than 1 hour, and the resistance reduction rate is more than 70 percent;
the low-viscosity slickwater fracturing fluid mainly comprises 0.1-0.2 percent of carboxymethyl hydroxypropyl guar gum, 1-2 percent of KCL anti-swelling agent, 0.3-0.5 percent of fluorocarbon cleanup additive, 0.1-0.2 percent of drag reducer and 96-98 percent of clear water in percentage by mass; the anti-swelling rate of the low-viscosity slickwater fracturing fluid is more than 85 percent, and the resistance reducing rate is more than 70 percent;
the medium-viscosity linear gel fracturing fluid mainly comprises 0.2-0.4% of carboxymethyl hydroxypropyl guar gum, 1-2% of KCL anti-swelling agent, 0.3-0.5% of fluorocarbon cleanup additive, 0.3-0.5% of cross-linking agent, 0.1-0.2% of drag reducer and 95-98% of clear water in percentage by mass; the anti-swelling rate of the medium-viscosity linear gel fracturing fluid is more than 85 percent, the gel breaking time at 90 ℃ is less than 1 hour, and the resistance reduction rate is more than 70 percent;
and/or the compression strength of the ceramsite is more than 70Mpa, and the density of the ceramsite is less than 1.6g/cm3。
In a possible implementation mode, the cluster is selected in a segmented mode, the setting position of the bridge plug and the position of each segment of perforation are determined, and then the composite fracturing process is carried out on each single segment according to the steps S1-S3.
According to the technical scheme, the cluster is selected in a segmented mode, and then the composite fracturing process is carried out on each single segment, so that the volume transformation of the complex seam network of the whole stratum can be rapidly and efficiently realized.
In one possible implementation mode, the length of each single section is controlled to be 20-40 m;
and/or the selection principle of the perforation position comprises the following steps: selecting a part with the brittle mineral content of more than 50 percent; the rupture pressure of the perforation points in the same section is lower than 50% of the average value, and the rupture pressure difference amplitude of each perforation point is less than 20%; the total porosity of the reservoir is more than 4 percent, and the permeability is more than 0.01 md; gas measuring total hydrocarbon > 0.8%, TOC > 1.0%, S1A fraction greater than 0.3 mg/g; the part with the logging sound amplitude less than 20 percent;
and/or the number of single-section clusters is 3-5 clusters, the cluster length is 1-2 m, and the cluster spacing is 10-20 clusters/m.
In a possible implementation manner, before the step S1, a step of performing a perforating operation according to the bridge plug setting position and the perforation position is further included, and in the steps S1 to S3, materials are injected through a wellbore formed by perforation.
In a possible implementation mode, the bridge plug is a soluble bridge plug, the temperature resistance of the bridge plug and the soluble ball is more than 130 ℃, the compressive strength of the bridge plug and the soluble ball is more than 90MPa, and the dissolving time of the bridge plug and the soluble ball in an electrolyte solution with the mass concentration of 1% is less than 20 d;
and/or the penetration depth of the perforating charge adopted by perforating is larger than 1m, the perforating charge arrangement positions are spirally arranged at equal intervals of 360 degrees, the perforating charge arrangement interval is controlled to be 8-12 holes/m, and the total number of single-section perforating holes is not more than 40 holes.
In a possible implementation mode, the total consumption of the single-stage fracturing fluid is controlled to be 1000-1800 m3A/stage;
and/or the injection amount of the single-stage supercritical carbon dioxide is controlled to be 200-400 m3。
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are required to be used in the embodiments of the present application will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered as limiting the scope, and that those skilled in the art can also obtain other related drawings based on the drawings without inventive efforts.
Fig. 1 is a process flow diagram of a composite fracturing process based on supercritical carbon dioxide pre-fracturing provided in an embodiment of the present application;
FIG. 2 is a comprehensive interpretation and segmentation cluster selection plot for a Geiger oil 1HF well of example 1;
FIG. 3 is a graph of a typical shale section fracturing construction for a Jipag oil 1HF well of example 1;
FIG. 4 is a graph comparing microseismic events after pressure of a Geiger oil 1HF well of example 1 to conventional hydraulic wells;
FIG. 5 is a plot of open-flow production after a Jipag oil 1HF well pressure of example 1;
FIG. 6 is a comprehensive explanation and sectional cluster selection diagram of Ji pear leaf oil 1 well of example 2;
FIG. 7 is a graph of a typical shale section fracturing construction of a Ji pear page oil 1 well of example 2;
FIG. 8 is a plot of open flow production after 1 well pressure for Ji pear leaf oil of example 2.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions of the embodiments of the present application will be clearly and completely described below. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
The composite fracturing process based on supercritical carbon dioxide pre-fracturing in the embodiment of the present application is specifically described below.
Referring to fig. 1, an embodiment of the present application provides a composite fracturing process based on supercritical carbon dioxide pre-fracturing, which includes the following steps:
the method comprises the following steps: and performing segmented cluster selection on the shale reservoir based on a geological-engineering integrated dessert evaluation method, determining the setting position of the bridge plug and the perforation position of each segment, and realizing the dense cutting of the shale reservoir.
The evaluation parameters mainly fall into two categories, namely the geological dessert evaluation parameters mainly evaluating the oil-gas-containing property and the reservoir physical property of the shale reservoir, and the evaluation parameters mainly comprise logging gas logging total hydrocarbon and S1TOC, well logging interpretation porosity, permeability, neutron density, resistivity, acoustic time difference and other parameters; and the other is an engineering dessert evaluation parameter which is mainly used for evaluating the compressibility of the shale reservoir and mainly comprises the parameters of mineral composition, Poisson's ratio, Young modulus, horizontal stress difference, fracture pressure, crack development condition and the like. And establishing a single-well comprehensive rating map of the target well according to the evaluation of the parameters, and then performing segmented cluster selection according to the following principle.
(I) segmentation principle: the semi-quantitative principle is adopted, and the method specifically comprises the following steps:
1) reservoir property homogeneity principle: lithology, rock density, brittle mineral content, porosity and gas measurement uniformity should be kept as much as possible in the same fracturing section, and the homogeneity in the section is ensured to be good;
2) the mechanical and ground stress characteristics of the rock are similar: the Young modulus, Poisson ratio, ground stress, horizontal stress difference, fracture pressure and other parameters of the rock in the same section are made to be similar as much as possible, and overlarge difference between the mechanical property of the rock in the section and the ground stress is avoided;
3) considering well drilling construction parameters such as well trajectory, well cementation quality, casing coupling, dog leg degree, well completion mode and the like;
4) and encrypting and segmenting the well section with better reservoir quality.
According to the volume fracturing concept, the shale reservoir stratum which is continuously distributed needs to be subjected to integrated volume transformation, the section length is controlled to be 20-40 m according to the segmentation principle, the well section with good shale reservoir stratum condition is continuously segmented, and the well section with poor shale reservoir stratum quality is not segmented.
(II) selecting a perforating position: the quantitative principle is adopted, and the method specifically comprises the following steps:
1) a relatively high brittle mineral content site, the brittle mineral content being greater than 50%;
2) the fracture pressure of the perforation points in the same section is lower than 50% of the average value according to the actual condition of the stratum, and the amplitude of the fracture pressure difference of each perforation point is less than 20%;
3) well logging explains the parts with higher porosity and permeability, the total porosity of the reservoir is more than 4 percent, and the permeability is more than 0.01 md;
4) well logging gas measurement shows good and high geological index part, gas measurement total hydrocarbon > 0.8%, TOC > 1.0%, S1Greater than 0.3 mg/g;
5) the well cementation position with good quality avoids the position of the coupling, and the logging sound amplitude is less than 20 percent. According to the close cutting idea, the number of single-section clusters is 3-5, the cluster length is 1-2 m, and the cluster spacing is 10-20 clusters/m.
Step two: and (4) carrying out the ball throwing and perforating operation of the pumping cable on the single-section shale reservoir according to the bridge plug setting position and the perforating position determined in the step one. As an implementation mode, the parameters of the lower depth of a bridge plug and the depth of perforation are input into a control system of a cable downhole operation vehicle, clear water is pumped by a fracturing pump vehicle, a pipe column with the bridge plug and a perforating gun is lowered to a specified position, ignition and setting of the bridge plug and ignition of perforating bullets are controlled through cable signal transmission to excite multiple clusters of perforation, and close cutting operation of a shaft before fracturing is completed.
In the embodiment of the application, the bridge plug can be a drill-free large-drift-diameter soluble bridge plug, the bridge plug and the soluble ball can be made of MgAl composite alloy, the temperature resistance of the bridge plug and the soluble ball is required to be more than 130 ℃, the compressive strength of the bridge plug and the soluble ball is required to be more than 90MPa, and the dissolving time of the bridge plug and the soluble ball in electrolyte solutions of KCl and the like with the mass concentration of 1% is less than 20 d.
In the embodiment of the application, the perforating bullets can adopt deep penetrating bullets, the penetrating depth is required to be larger than 1m, the perforating bullet arrangement positions are arranged at equal intervals in a 360-degree spiral mode, in order to prevent the casing from being cut too densely and causing deformation of the casing, the perforating bullet arrangement intervals are controlled to be 8-12 holes/m, and the total number of single-section perforating is not more than 40 holes.
Step three: and injecting supercritical carbon dioxide into the shale reservoir to perform pre-fracturing of the supercritical carbon dioxide, thereby realizing the volume transformation of the complex fracture network of the shale reservoir. Specifically, the liquid carbon dioxide can be heated and pressurized to a supercritical state by a temperature-increasing booster pump to obtain supercritical carbon dioxide, wherein the critical temperature is 31.1 ℃, and the critical pressure is 7.38 MPa; then according to the length of 3-4 m3And (4) discharging at a/min rate, and injecting supercritical carbon dioxide into the shaft through the anti-freezing high-pressure manifold by a fracturing pump truck.
Step four: carrying out hydraulic sand-carrying fracturing construction on the formed complex fracture network, generally injecting different types of fracturing fluid carrying proppant into a target well in sequence, and mixing and injecting N in the whole process2The mixing injection specifically comprises the following steps:
s401: according to the length of 14-18 m3And (4) discharging at a/min rate, and injecting the prepared high-viscosity gel fracturing fluid carrying a coarse-particle size proppant such as coarse sand into a target wellbore through a fracturing pump truck. Wherein the viscosity of the high-viscosity gel fracturing fluid is more than 50 mPa.s, the anti-swelling rate is more than 85 percent, the gel breaking time at 90 ℃ is less than 1h, the resistance reduction rate is more than 70 percent, and the high-viscosity gel fracturing fluid is used as a componentIn one embodiment, the high viscosity gel fracturing fluid is prepared from 0.5-0.8% of carboxymethyl hydroxypropyl guar gum, 1-2% of KCL anti-swelling agent, 0.3-0.5% of fluorocarbon cleanup additive, 0.5-0.7% of cross-linking agent, 0.1-0.2% of resistance reducing agent and 95-98% of clear water in percentage by mass; wherein the coarse grain size proppant is low-density ceramsite with the grain size of 30-50 meshes, and the compression strength of the ceramsite is required to be more than 70Mpa, and the density of the ceramsite is required to be less than 1.6g/cm3(ii) a The sand adding proportion is 4 wt% -6 wt%. In the step, a small amount of cross-linked jelly is adopted to carry the coarse-grain proppant to enlarge the complex seam network formed in the third step in the largest range, so that the height and the length of the artificial crack are increased, the liquid filtration is reduced, the seam making efficiency is improved, and meanwhile, the complex seam network formed in the early stage is supported, so that an effective channel is provided for the extension of the follow-up fracturing liquid.
S402: according to the length of 12-14 m3And (4) discharging at a/min rate, injecting the prepared low-viscosity slickwater fracturing fluid carrying small-particle-size propping agent, such as silt, into a target wellbore through a fracturing pump truck. The low-viscosity slickwater fracturing fluid is 3-5 mPa & s in viscosity, the anti-swelling rate is more than 85%, the resistance reduction rate is more than 70%, and as an implementation mode, the low-viscosity slickwater fracturing fluid consists of 0.1-0.2% of carboxymethyl hydroxypropyl guar gum, 1-2% of KCL anti-swelling agent, 0.3-0.5% of fluorocarbon cleanup additive, 0.1-0.2% of resistance reduction agent and 96-98% of clear water in percentage by mass; wherein the small-particle-size propping agent is low-density powder ceramic with 70-140 meshes, and the compression strength is required to be more than 70Mpa, and the density of the ceramic is required to be less than 1.6g/cm3(ii) a The sand adding proportion is 10 wt% -15 wt%. In the step, a large amount of low-viscosity slickwater is adopted to carry small-particle-size propping agents to further improve the complexity of the cracks, natural micro cracks and secondary cracks are communicated in the largest range, and a large amount of powder ceramic is carried to enter the stratum to effectively support middle and far end micro cracks formed in the fracturing process.
S403: according to the length of 14-16 m3And (4) discharging at a/min rate, and injecting the prepared medium-viscosity linear fracturing fluid carrying medium-particle size proppant, such as medium sand, into the target well bore through a fracturing pump truck. Wherein the viscosity of the medium-viscosity linear gel fracturing fluid is 10-30 mPa.s, the anti-swelling rate is more than 85%, the gel breaking time at 90 ℃ is less than 1h, the resistance reduction rate is more than 70%, as an implementation mode,the formula of the medium-viscosity linear gel fracturing fluid comprises 0.2-0.4% of carboxymethyl hydroxypropyl guar gum, 1-2% of KCL anti-swelling agent, 0.3-0.5% of fluorocarbon cleanup additive, 0.3-0.5% of cross-linking agent, 0.1-0.2% of drag reducer and 95-98% of clear water in percentage by mass; wherein the medium-particle-size propping agent is low-density ceramsite of 40-70 meshes, the compressive strength is required to be more than 70Mpa, and the ceramsite density is required to be less than 1.6g/cm3The sand adding proportion is 8 wt% -10 wt%. The medium-viscosity linear adhesive carrying medium-particle-size propping agent is used for performing rear-end tracking, a near well seam network is polished, and the near well zone fracture conductivity is further improved.
In the process of hydraulic sand-carrying fracturing of the steps S401 to S403, the liquid state N is fully mixed2Realizing normal pressure stratum energization, specifically according to the discharge capacity of 150-200L/min, adding liquid N2And injecting the mixture into a shaft through an anti-freezing high-pressure manifold by a fracturing pump truck, wherein the whole-process mixing injection is carried out.
Step five: and injecting slick water for replacing operation. After all the main fracturing procedures in the third step are finished, low-viscosity acidic slickwater is adopted for displacement and acidification, and 5% -15% of HCL solution is added into the formula of the low-viscosity slickwater in the step S3, namely the low-viscosity acidic slickwater consists of 0.1% -0.2% of carboxymethyl hydroxypropyl guar gum, 1% -2% of KCL anti-swelling agent, 0.3% -0.5% of fluorocarbon drainage aid, 0.1% -0.2% of resistance reducing agent, 5% -15% of HCL and 96% -98% of clear water in mass fraction, and the using amount is 1-2 volume of the shaft volume.
And respectively operating each single section of the shale reservoir according to the steps one to three until the composite fracturing of the whole shale reservoir is completed.
In the embodiment of the present application, in the third step, supercritical carbon dioxide is injected into the reactor in a single stage with a volume of 200-400 m3。
In the hydraulic sand-carrying fracturing process of the step four, because the shale reservoir is compact, the sand adding difficulty is very high, in order to prevent sand blocking and further improve the complexity of the fracture, the sand adding can be completed by adopting a spacing block type sand adding mode. The slug sand adding is as follows: and after all the proppant added into the stratum by the previous slug enters the stratum, adding sand into the next slug, sequentially adding sand into each slug gradually, and adjusting in real time according to the difficult and easy condition of adding sand into the stratum.
In the three stages S401-S403 of the hydraulic sand-carrying fracturing of the fourth step, the total fracturing fluid consumption of a single stage is controlled to be 1000-1800 m3The dosage proportion of each type of fracturing fluid is that high-viscosity jelly glue/low-viscosity slickwater/medium-viscosity linear glue is controlled between 10 percent to 30 percent/40 percent to 80 percent/10 percent to 30 percent; the dosage of the single-section ceramsite is controlled to be 80-150 m3The dosage proportion of each type of propping agent is controlled between 10-20%/50-70%/20-30% of the coarse grain diameter/the small grain diameter/the medium grain diameter, and the volume transformation effects of dense cutting, large discharge capacity, large scale and high sand ratio are realized.
Blending N in step four2In-process, single stage injection of liquid N2The amount increases and decreases according to the time of hydraulic fracturing.
The features and properties of the present application are described in further detail below with reference to examples.
The method is successfully implemented in fracturing of shale oil wells and shale gas wells of 2 mouths in Songliao basin in northeast, has obvious effect, and is further illustrated by line and plane in combination with specific embodiments, but the following embodiments do not limit the invention at all.
Example 1
The embodiment is used for modifying a shale oil reservoir of a green hill group of a sunken Jiye 1HF well in the long ridge of the Songliao basin, the Jiye 1HF well is positioned in a deep safe and favorable area of the depression of the long ridge of the south of the Songliao basin, a target layer is a shale stratum of the green hill group of the Chalk system, the clay mineral content of the shale oil reservoir is high, the clay mineral content is concentrated to be about 40-60%, the average clay mineral content is 46.7%, the stratum has strong plasticity, the brittleness index (static modulus calculation) is more than 40% -60%, and the shale oil reservoir belongs to a strong water-sensitive stratum; the longitudinal stress difference is large due to the development of longitudinal sand interlayers and bedding seams of the reservoir, the horizontal stress difference is concentrated between 9 MPa and 14MPa, and the heterogeneity is strong.The content of brittle minerals such as green section shale quartz, feldspar and the like is 43 percent averagely, the content of clay minerals is 47 percent averagely, illite and illite/montmorillonite mixed layers are taken as main materials, the content of carbonate minerals is about 10 percent, and the carbonate minerals are mainly cements such as calcite and the like. The average value of the porosity of the green-stage shale is 4.5 percent; the mean permeability is 0.07X 103μm2An ultra-low pore permeability shale reservoir; the formation pressure coefficient is 0.9-1.1, and the method belongs to a normal pressure formation. The transformation of the atmospheric high clay mineral content strong heterogeneous continental facies shale reservoir is a world-level problem, and a targeted fracturing process must be used.
In the embodiment, the composite fracturing technology is adopted to perform 21-stage/1431 m fracturing construction on the horizontal well, and the concrete steps are as follows:
the method comprises the following steps: according to the geological-engineering integrated evaluation standard and method, the horizontal section of the Jipage oil 1HF well is divided into sections according to the section cluster optimization mode of 'three-property uniform section selection, four-high-one-low cluster fixation', namely, according to the lithology, the rock mechanical property and the ground stress which are uniform as the section dividing basis, the perforation section is selected according to the principles of high gas logging, high porosity, high resistance, high brittleness index and low density, and meanwhile, a casing collar and an interval with poor well cementation quality are avoided, and the comprehensive explanation and the sectional cluster selection diagram of the Jipage oil 1HF well are shown in figure 2. Through optimized design, 1431m horizontal segment of a Jipp oil 1HF well, 21 segments in total, 82 clusters of perforation, the average segment length of 68 m and the average cluster spacing of 15.8m are in accordance with the close cutting concept.
Step two: and (4) performing pumping bridge plug setting and perforating operation on one section of the shale reservoir according to the bridge plug setting position and the perforating position determined in the step one. The bridge plug is a drill-free large-drift-diameter soluble bridge plug, and the stratum water chlorine root of the well is completely dissolved in 15d under the environment according to prediction of about 3952 mg/L; perforating by using large-aperture deep-penetrating perforating gun charges (89 guns, super 2-generation charges), wherein the arrangement interval of the perforating charges is controlled to be 8-12 holes/m, and the total number of single-section perforating is 34-40 holes.
Step three: heating liquid carbon dioxide to supercritical state at 31.1 deg.C under 7.38MPa at 4m3The discharge amount is/min, supercritical carbon dioxide is injected into a shaft, and the amount of the supercritical carbon dioxide injected into a single section is 200-400 m3。
Step four: injecting different types of fracturing fluid carrying proppant into the target well in sequence, and mixing and injecting N in the whole process2The mixing and pouring method comprises the following specific steps:
carrying coarse particle size proppant with the prepared high-viscosity gel fracturing fluid according to the size of 16m3Injecting the mixture into a shaft at a delivery rate of/min, wherein the formula of the high-viscosity jelly glue comprises 0.8 percent of carboxymethyl hydroxypropyl guar gum, 2 percent of KCL anti-swelling agent, 0.5 percent of fluorocarbon cleanup additive, 0.5 percent of cross-linking agent, 0.2 percent of resistance reducing agent and 96 percent of clear water in percentage by mass, the coarse-particle-diameter propping agent is 30/50-mesh low-density ceramsite, and the density of the ceramsite is 1.58g/cm3And the sand adding proportion is 5 percent.
Carrying small-particle size proppant by using the prepared low-viscosity slickwater fracturing fluid according to the proportion of 12m3Injecting the mixed solution into a shaft at a discharge rate of/min, wherein the formula of the low-viscosity slickwater consists of 0.1 percent of carboxymethyl hydroxypropyl guar gum, 1.5 percent of KCL anti-swelling agent, 0.3 percent of fluorocarbon cleanup additive, 0.1 percent of resistance reducing agent and 98 percent of clear water in percentage by mass; the proppant with small particle size is 70/140-mesh low-density powder pottery, and the density of the ceramsite is 1.58g/cm3The sand adding proportion is 12 percent.
Carrying middle-particle-size propping agent by the prepared middle-viscosity linear gel fracturing fluid according to the length of 14m3Injecting the mixture into a shaft at a discharge rate of/min, wherein the formula of the medium-viscosity linear adhesive comprises 0.2 percent of carboxymethyl hydroxypropyl guar gum, 1.5 percent of KCL anti-swelling agent, 0.3 percent of fluorocarbon cleanup additive, 0.3 percent of cross-linking agent, 0.2 percent of resistance reducing agent and 97.5 percent of clear water in percentage by mass, the medium-particle-diameter proppant is low-density ceramsite with the mesh of 40/70, and the density of the ceramsite is 1.58g/cm3The sand adding proportion is 10 percent.
In the hydraulic sand-carrying fracturing process, the liquid state N is stirred and injected in the whole process2The liquid N is discharged according to the discharge capacity of 180L/min2And mixing and injecting the mixture into a shaft in the whole process.
A typical shale section fracturing construction graph for a Jipag oil 1HF well is shown in FIG. 3.
Step five: and replacing by using low-viscosity acidic slickwater, wherein the low-viscosity acidic slickwater is used for adding 15% of HCL solution into the slickwater formula in the third step, and the amount of the HCL solution is 1.5 volumes of the volume of the shaft, and the low-viscosity acidic slickwater is used for completely jacking the fracturing fluid and the proppant into the stratum.
And completing the first-stage fracturing construction through the second-fifth steps.
And step six, repeating the step two to the step five to complete the 21-section fracturing construction in sequence. In the hydraulic sand-carrying fracturing process, sand adding is completed in a spacing segment plug type sand adding mode. Gibber oil 1HF well main fracturing fluid volume 34808.17m3Wherein the high-viscosity jelly accounts for 15 percent, the low-viscosity slippery water accounts for 70 percent, and the medium-viscosity linear jelly accounts for 15 percent; the dosage of liquid carbon dioxide is 3265m3(ii) a Total sand addition amount 1978.56m3Wherein 70-140 meshes of ceramsite accounts for 31%, 40-70 meshes of ceramsite accounts for 55%, and 30-50 meshes of ceramsite accounts for 14%; liquid state N2The dosage is 600m3。
A comparison graph of microseismic events of the Geiger oil 1HF well and a conventional hydraulic well after being pressed is shown in figure 4, so that the Geiger oil 1HF well after being modified by the complex seam network can resist the microseismic.
After the test after the pressure, the open flow production curve after the pressure of the Jipu oil 1HF well is shown in figure 5, and the Jipu oil 1HF well obtains the highest daily oil production of 36m3Daily stable yield of oil 16.4m3The high-yield industrial oil flow realizes the major strategic breakthrough of atmospheric continental facies shale oil exploration in Songliao basin for the first time.
Example 2
The method is used for modifying a shale oil reservoir of Jili leaf oil 1, the Jili leaf oil 1 well is located in a beneficial region of a broken mountain ash house in a pear tree in a rising region in the southeast of Songliao basin, a target layer is a shale stratum of a lower chalky river sub-group, the shale oil reservoir has high clay mineral content, the clay mineral content is concentrated to about 30-50%, the average clay mineral content is 36%, the stratum has strong plasticity, and the brittleness index (static modulus calculation) is more than 50-70%, and belongs to a strong water sensitivity stratum; the longitudinal stress difference is large due to the development of longitudinal sand interlayers and bedding seams of the reservoir, the horizontal stress difference is concentrated between 5MPa and 10MPa, and the heterogeneity is strong. The content of brittle minerals such as shale quartz, feldspar and the like in the sand river subgroup is 32 percent on average, the content of clay minerals is 36 percent on average, the content of carbonate minerals is about 32 percent, and the shale is mixed shale. The average value of the porosity of the shale is 5.4 percent; the mean permeability is 0.12X 103μm2A low pore permeability shale reservoir; the formation pressure coefficient is 1.02-1.18, and the method belongs to the normal pressure formation。
In the embodiment, the composite fracturing process of the application is adopted to implement 5-section/221 m fracturing construction on the well, and the concrete steps are as follows:
the method comprises the following steps: according to the geological-engineering integrated evaluation standard and method, the principle is the same as that of example 1, the comprehensive explanation and the segmented cluster selection diagram of the Jierye oil 1 well are shown in fig. 6, a 221m vertical well section is segmented into 5 sections, the perforation is 20 clusters, the average section length is 44 meters, and the average cluster spacing is 11.1 m.
The typical shale section fracturing construction curve diagram of the Ji pear page oil 1 well in the same fracturing mode as the example 1 in the second step, the third step, the fourth step and the fifth step is shown in FIG. 7.
And step six, completing the first-stage fracturing construction through the steps two to five, and repeating the steps two to five to sequentially complete the 5-stage fracturing construction. Gill pear leaf oil 1 well main fracturing fluid amount 7304.25m3Wherein the high-viscosity jelly accounts for 10 percent, the low-viscosity slippery water accounts for 75 percent, and the medium-viscosity linear jelly accounts for 15 percent; liquid carbon dioxide dosage of 698m3(ii) a Total sand addition amount 449.44m3Wherein 70-140 meshes of ceramsite accounts for 10%, 40-70 meshes of ceramsite accounts for 75%, and 30-50 meshes of ceramsite accounts for 15%; liquid nitrogen 77.4m3。
After the test after the pressure, the open flow yield curve after the pressure of the Ji pear leaf oil in the 1 well is shown in figure 8, and the highest daily yield of the Ji pear leaf oil in the 1 well is 17 ten thousand meters3Fixed yield 7.6 ten thousand meters3The method for high-yield shale gas flow realizes the major strategic breakthrough of atmospheric continental facies shale gas exploration in Songliao basin for the first time.
As can be seen from examples 1 and 2, the examples of the present application mainly employ supercritical CO2Large displacement pre-preshrunk + liquid N2The proposal of the combination of stirring water injection force sand-carrying composite fracturing improves the advantages and avoids the disadvantages, overcomes the technical problems of normal pressure, high clay content and strong heterogeneity of continental shale stratum, and overcomes the defects of CO2Low discharge capacity, high sand carrying difficulty, high equipment requirement and the like in dry method/foam fracturing construction. And the fracturing fluid can be successfully practiced and applied in fracturing practices of shale gas of Jiye oil 1HF well Qingshan Kou group and Jili Jiye 1 well Shahe subgroup, and the effect is obvious. By seismic monitoring, unstable well testing, tracer tracing, oil and gasBy means of source comparison and the like, evaluation shows that the process is utilized to form a complex volume seam network in the continental facies shale stratum, the longitudinal expansion height of the seam network can reach 70m, the plane extension length can reach 900m, the continental facies shale reservoir is fully improved, engineering accidents such as clay expansion, casing deformation and the like do not occur, and the purpose of large-scale volume improvement of the continental facies shale reservoir is achieved. The process provided by the embodiment of the application is novel in principle, convenient to implement and strong in operability, can realize commercial exploitation of the atmospheric high-clay-mineral-content strong-heterogeneity continental facies shale oil and shale gas, and has good innovation, economy and application values.
To sum up, the composite fracturing process based on the supercritical carbon dioxide pre-fracturing of the embodiment of the application realizes the effects of volume transformation of complex fracture networks of stratums, particularly shale reservoirs, effective support of the fracture networks, stratum energization and the like.
The above description is only an example of the present application and is not intended to limit the scope of the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.
Claims (10)
1. A composite fracturing process based on supercritical carbon dioxide pre-fracturing is characterized by comprising the following steps:
s1, injecting supercritical carbon dioxide into the stratum for pre-fracturing to form a seam network;
s2, injecting different types of fracturing fluids carrying proppant into the fracture net in sequence to carry out hydraulic sand-carrying fracturing for expanding, supporting and polishing the fracture net, wherein in the hydraulic sand-carrying fracturing process, the liquid N is injected in a stirring manner in the whole process2；
And S3, injecting slickwater for displacement operation to push the fracturing fluid into the stratum.
2. The composite fracturing process based on supercritical carbon dioxide pre-fracturing of claim 1, wherein in step S2Full-course liquid mixing and injecting state N2The discharge capacity of (A) is 150 to 200L/min.
3. The composite fracturing process based on the supercritical carbon dioxide pre-fracturing, which is characterized in that the supercritical carbon dioxide is obtained by heating and boosting liquid carbon dioxide to a supercritical state, the critical temperature is 31.1 ℃, and the critical pressure is 7.38 MPa;
and/or the injection discharge capacity of the supercritical carbon dioxide is 3-4 m3/min。
4. The supercritical carbon dioxide pre-fracturing based composite fracturing process of claim 1, wherein in step S2, the hydraulic sand-laden fracturing comprises the steps of:
sequentially sewing the net according to the length of 14-18 m3Injecting high-viscosity gel fracturing fluid carrying coarse-particle-size propping agent into the fracturing fluid at a delivery rate of/min to enlarge a gap net according to the length of 12-14 m3Injecting low-viscosity slick water fracturing fluid carrying small-particle-size proppant into the fracturing fluid at a delivery rate of/min to support all seam meshes according to the length of 14-16 m3Injecting medium-viscosity linear gel fracturing fluid carrying medium-particle size proppant into the per min discharge capacity to polish the seam net;
wherein the viscosity of the high-viscosity gel fracturing fluid is more than 50mPa & s, the coarse-particle-size propping agent is 30-50 meshes of ceramsite, and the sand adding proportion is 4-6 wt%;
the low-viscosity slickwater fracturing fluid is 3-5 mPa & s in viscosity, the small-particle-size propping agent is 70-140-mesh ceramsite, and the sand adding proportion is 10-15 wt%;
the viscosity of the medium-viscosity linear gel fracturing fluid is 10-30 mPa · s, the medium-particle-size propping agent is ceramsite with 40-70 meshes, and the sand adding proportion is 8-10 wt%.
5. The composite fracturing process based on supercritical carbon dioxide pre-fracturing, which is characterized in that the high-viscosity jelly fracturing fluid mainly comprises 0.5-0.8% of carboxymethyl hydroxypropyl guar gum, 1-2% of KCL anti-swelling agent, 0.3-0.5% of fluorocarbon cleanup additive, 0.5-0.7% of cross-linking agent, 0.1-0.2% of friction reducer and 95-98% of clear water in percentage by mass; the anti-swelling rate of the high-viscosity gel fracturing fluid is more than 85 percent, the gel breaking time at 90 ℃ is less than 1 hour, and the resistance reduction rate is more than 70 percent;
the low-viscosity slickwater fracturing fluid mainly comprises 0.1-0.2% of carboxymethyl hydroxypropyl guar gum, 1-2% of KCL anti-swelling agent, 0.3-0.5% of fluorocarbon cleanup additive, 0.1-0.2% of drag reducer and 96-98% of clear water in percentage by mass; the anti-swelling rate of the low-viscosity slickwater fracturing fluid is more than 85 percent, and the resistance reduction rate is more than 70 percent;
the medium-viscosity linear gel fracturing fluid mainly comprises 0.2-0.4% of carboxymethyl hydroxypropyl guar gum, 1-2% of KCL anti-swelling agent, 0.3-0.5% of fluorocarbon cleanup additive, 0.3-0.5% of cross-linking agent, 0.1-0.2% of resistance reducing agent and 95-98% of clear water in percentage by mass; the anti-swelling rate of the medium-viscosity linear gel fracturing fluid is more than 85 percent, the gel breaking time at 90 ℃ is less than 1 hour, and the resistance reduction rate is more than 70 percent;
and/or the compression strength of the ceramsite is more than 70Mpa, and the density of the ceramsite is less than 1.6g/cm3。
6. The composite fracturing process based on supercritical carbon dioxide pre-fracturing, as claimed in claim 1, wherein the cluster is selected by stages, the bridge plug setting position and each stage of perforation position are determined, and then the composite fracturing process is performed on each single stage according to steps S1-S3.
7. The composite fracturing process based on supercritical carbon dioxide pre-fracturing, which is characterized in that the length of each single section is controlled to be 20-40 m;
and/or the selection principle of the perforation positions comprises the following steps: selecting a part with the brittle mineral content of more than 50 percent; the rupture pressure of the perforation points in the same section is lower than 50% of the average value, and the rupture pressure difference amplitude of each perforation point is less than 20%; the total porosity of the reservoir is more than 4 percent, and the permeability is more than 0.01 md; gas measuring total hydrocarbon > 0.8%, TOC > 1.0%, S1A fraction greater than 0.3 mg/g; the part with the logging sound amplitude less than 20 percent;
and/or the number of single-section clusters is 3-5 clusters, the cluster length is 1-2 m, and the cluster spacing is 10-20 clusters/m.
8. The composite fracturing process based on supercritical carbon dioxide pre-fracturing, according to claim 6, further comprising a step of performing a perforating operation according to the bridge plug setting position and the perforation position before step S1, wherein the step S1-S3 is to inject materials through the perforated wellbore.
9. The composite fracturing process based on supercritical carbon dioxide pre-fracturing, according to claim 8, characterized in that the bridge plug is selected from soluble bridge plugs, the temperature resistance of the bridge plug and soluble ball is more than 130 ℃, the compressive strength is more than 90MPa, and the dissolution time in the electrolyte solution with the mass concentration of 1% is less than 20 d;
and/or the penetration depth of the perforating charge adopted by perforating is larger than 1m, the perforating charge arrangement positions are spirally arranged at equal intervals of 360 degrees, the perforating charge arrangement interval is controlled to be 8-12 holes/m, and the total number of single-section perforating holes is not more than 40 holes.
10. The composite fracturing process based on supercritical carbon dioxide pre-fracturing, as claimed in claim 6, wherein the total amount of single stage fracturing fluid is controlled to be 1000-1800 m3A/stage;
and/or the injection amount of the single-stage supercritical carbon dioxide is controlled to be 200-400 m3。
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