CN115126461A - Composite fracturing method for continental shale oil reservoir - Google Patents
Composite fracturing method for continental shale oil reservoir Download PDFInfo
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Images
Classifications
-
- 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
-
- 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
- C09K8/62—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
-
- 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
- C09K8/80—Compositions for reinforcing fractures, e.g. compositions of proppants used to keep the fractures open
-
- 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
-
- 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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- Engineering & Computer Science (AREA)
- Life Sciences & Earth Sciences (AREA)
- Mining & Mineral Resources (AREA)
- Geology (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Environmental & Geological Engineering (AREA)
- Fluid Mechanics (AREA)
- Physics & Mathematics (AREA)
- Geochemistry & Mineralogy (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Soil Conditioners And Soil-Stabilizing Materials (AREA)
Abstract
The invention provides a composite fracturing method for a continental facies shale oil reservoir, which comprises the following steps: pretreating a reservoir by using acid liquor; injecting liquid carbon dioxide into the pretreated reservoir stratum; adopting acid gel liquid to make main cracks; opening and expanding a micro-crack and branch crack system by adopting slickwater; adopting a first propping agent to prop the micro-fracture system and the branch fracture system; propping the primary fracture system with a second proppant and a third proppant; displacing the proppant to the fracture seam. In the process of shale oil exploration and development, low-damage fracturing fluid is preferably selected according to the characteristics of a reservoir stratum; and put forwardThe high-flow-guide complex volume slotted net is formed by using slickwater and acid gel mixed fracturing fluid, multi-scale small-particle size proppant and fiber sand, so that the modification volume of a reservoir is increased; with pre-liquid CO 2 Increasing energy to increase the back-flow rate of the high pressure.
Description
Technical Field
The invention belongs to the technical field of oil and gas field fracturing, and particularly relates to a composite fracturing method for a continental facies shale oil reservoir.
Background
The recoverable and storable amount of the Chinese shale (compact) oil is 44.1 hundred million tons, occupies the third position in the world, accounts for about 10 percent of the petroleum resource amount, and is mainly distributed in Songliao basin, Bohai Bay basin, Ordors basin, Nanxiang cave, Subei basin, three-pond lake basin, QusongEr basin, Sichuan basin and the like. The domestic continental facies shale oil is mainly formed in the continental facies depressed lake basin front delta and the semi-deep lake facies, the burial depth is 2200-3500 m, the organic carbon content is 1.2-2.6%, the brittle mineral content is lower (40-50%), the thermal evolution degree is lower (R) 0 0.5% -1.1%), poor flowability of crude oil, permeability of 0.01-0.3 mD, porosity of 3.4-8.9%, formation pressure coefficient of 1.05-1.15, and normal pressure coefficient. The reservoir space mainly develops shale matrix pores, organic pores, a small amount of microcracks and the like.
In recent years, shale oil exploration tests performed by medium petrochemicals and medium petroleum have a not ideal effect, and the phenomena of 'no pressure open, no support, low flowback and difficult stable production' which are poor in compressibility commonly exist in domestic continental shale oil fracturing; the specific fracturing reconstruction difficulty is as follows: the mud quality is high, and the reservoir is easily damaged when meeting fracturing fluid; secondly, the stratum has partial plasticity, great sand adding difficulty, high embedding degree of the propping agent and low fracture flow conductivity; thirdly, the low-pore low-permeability low-pressure stratum is difficult to flow back after being pressed; fourthly, the horizontal stress difference is large, natural cracks are underdeveloped, and a volume seam network formed by changing the conventional shale is difficult to form.
Therefore, how to solve the problems of reservoir damage, easy proppant embedding, low flow conductivity and difficult backflow of fracturing fluid and how to form a complex seam network to realize volume fracturing become problems to be solved by technical personnel in the field.
Disclosure of Invention
In view of the above, the invention aims to provide a composite fracturing method for a continental shale oil reservoir, which can solve the problems that the reservoir is easily damaged, a proppant is easily embedded, the flow conductivity is low, and the fracturing fluid is difficult to flow back, and can realize volume fracturing reformation of a complex fracture network.
The invention provides a composite fracturing method for a continental facies shale oil reservoir, which comprises the following steps:
pretreating a reservoir by using acid liquor;
injecting liquid carbon dioxide into the pretreated reservoir stratum;
adopting acid gel liquid to make main cracks;
opening and expanding a micro-crack and branch crack system by adopting slick water;
adopting a first propping agent to prop the micro-fracture system and the branch fracture system;
propping the primary fracture system with a second proppant and a third proppant;
displacing the proppant to the fracture seam;
the granularity of the first proppant is 70-140 meshes;
the granularity of the second proppant is 40-70 meshes;
the granularity of the third proppant is 30-50 meshes;
the second proppant and/or the third proppant contains degradable fibers therein.
Preferably, the acid solution comprises hydrochloric acid and/or earth acid.
Preferably, the discharge capacity of the injected liquid carbon dioxide is 1.0-1.5 m 3 /min。
Preferably, the slickwater comprises the following components:
0.06 to 0.08 wt% of a resistance reducing agent;
0.08-0.12 wt% of a cleanup additive;
0.1-0.3 wt% of an anti-swelling agent;
the balance being water.
Preferably, the resistance reducing agent is a polyacrylamide substance;
the cleanup additive is a complex of polyoxyethylene amine ether and fluorocarbon surfactant;
the anti-swelling agent is a poly N-hydroxymethyl acrylamide substance.
Preferably, the acid jelly liquid comprises the following components:
0.3-0.4 wt% of a thickening agent;
0.4-0.6 wt% of a clay stabilizer;
0.04-0.06 wt% of a demulsifier;
0.08-0.12 wt% of a cleanup additive;
0.08-0.12 wt% of a bactericide;
0.5 to 0.7 wt% of a crosslinking agent;
0.5-0.7% of a pH regulator;
0.01-0.15 wt% of a gel breaker;
the balance being water.
Preferably, the thickening agent is carboxymethyl hydroxypropyl guar gum;
the clay stabilizer is one or a combination of ammonium chloride and quaternary ammonium salt;
the demulsifier is one or two of alkyl phosphate and alkoxy carboxylate;
the cleanup additive is one or two of fatty alcohol polyether substance and fatty alcohol polyether cation compound;
the bactericide is one or more of formaldehyde, glutaraldehyde and quaternary ammonium salt;
the cross-linking agent is an organic zirconium salt substance;
the pH regulator is an acetic acid substance;
the gel breaker is ammonium persulfate.
Preferably, the first proppant is a ceramsite proppant;
the second propping agent is a resin coated quartz sand propping agent;
and the third proppant is a resin-coated quartz sand proppant.
Preferably, the viscosity of the slickwater is 2-6 mPa.s;
the viscosity of the acid jelly liquid is 100-150 mPa.s.
Preferably, the degradable fiber is a polyester fiber.
The composite fracturing method provided by the invention is a fracturing process of a preposed liquid carbon dioxide energizing, a slick water and acid gel liquid mixed fracturing fluid system, a multi-scale small-particle-size proppant, degradable fibers and sand. In the process of shale oil exploration and development, low-damage fracturing fluid is preferably selected according to the characteristics of a reservoir stratum; and the slickwater and acid jelly mixed fracturing fluid, the multi-scale small-particle size proppant and the fiber sand are provided to form a high-flow-guide complex volume seam net, so that the modification volume of the reservoir is increased; with pre-liquid CO 2 Increasing energy to increase the back-flow rate of the high pressure. The invention solves the problems of damage to the domestic continental facies shale oil reservoir, easy embedding of a propping agent, low flow conductivity and difficult flowback of fracturing fluid, and has very important significance for guiding the exploration and development of the domestic continental facies shale oil.
Drawings
FIG. 1 is a fracture profile obtained by the method provided in the examples;
fig. 2 is a fracture modification volume distribution diagram obtained by the method provided in the example.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other examples, which may be modified or appreciated by those of ordinary skill in the art based on the examples given herein, are intended to be within the scope of the present invention. It should be understood that the embodiments of the present invention are only for illustrating the technical effects of the present invention, and are not intended to limit the scope of the present invention. In the examples, the methods used were all conventional methods unless otherwise specified.
The invention provides a composite fracturing method for a continental facies shale oil reservoir, which comprises the following steps:
pretreating a reservoir by using acid liquor;
injecting liquid carbon dioxide into the pretreated reservoir stratum;
adopting acid gel liquid to make main cracks;
opening and expanding a micro-crack and branch crack system by adopting slickwater;
adopting a first propping agent to prop the micro-fracture system and the branch fracture system;
propping the primary fracture system with a second proppant and a third proppant;
displacing the proppant to the fracture seam;
the granularity of the first proppant is 70-140 meshes;
the granularity of the second proppant is 40-70 meshes;
the granularity of the third proppant is 30-50 meshes;
the second proppant and/or the third proppant contains degradable fibers therein.
In the invention, the type and injection parameters of the acid liquor are preferably selected according to the conditions of the reservoir; the conditions of the reservoir preferably include the mineral composition of the reservoir; the acid solution preferably comprises hydrochloric acid and/or earth acid; the injection parameters preferably comprise the discharge capacity and the dosage of the acid liquor, and the discharge capacity of the acid liquor is preferably 0.5-1.0 m 3 A/min, more preferably 0.6 to 0.8m 3 Min; the preferable dosage of the acid liquor is 10-20 m 3 More preferably 12 to 18m 3 Most preferably 14 to 16m 3 。
In the invention, the acid solution comprises the following components:
12-18 wt% of industrial hydrochloric acid;
1-2 wt% of corrosion inhibitor;
1-2 wt% of an iron ion stabilizer;
0.2 to 0.8 wt% of a clay stabilizer;
0.08-0.12 wt% of a cleanup additive.
In the invention, the mass content of the industrial hydrochloric acid is preferably 13-17%, more preferably 14-16%, and most preferably 15%.
In the invention, the mass content of the corrosion inhibitor is preferably 1.2-1.8%, more preferably 1.4-1.6%, and most preferably 1.5%; the corrosion inhibitor is preferably one or a combination of more of quaternary pyridinium salt, Mannich base and aromatic amine.
In the invention, the mass content of the iron ion stabilizer is preferably 1.2-1.8%, more preferably 1.4-1.6%, and most preferably 1.5%; the iron ion stabilizer is preferably ethylenediamine tetraacetic acid, nitrilotriacetic acid complexing agent, thiourea or isoascorbic acid reducing agent.
In the invention, the mass content of the clay stabilizer (clay stabilizer in the acid solution) is preferably 0.3 to 0.7%, more preferably 0.4 to 0.6%, and most preferably 0.5%; the clay stabilizer (clay stabilizer in acid solution) is preferably one or two of ammonium chloride and quaternary ammonium salt.
In the invention, the mass content of the cleanup additive (cleanup additive in the acid solution) is preferably 0.09-0.11%, and more preferably 0.1%; the discharge assistant (discharge assistant in acid liquor) is preferably one or a combination of alcohols, ethers and fluorocarbon surfactants.
In the invention, the injection discharge capacity of the injected liquid carbon dioxide is preferably 1.0-1.5 m 3 A concentration of 1.1 to 1.4 m/min 3 Min, most preferably 1.2-1.3 m 3 And/min. In the invention, the liquid carbon dioxide is mainly used for energizing and promoting the flowback of the fracturing fluid after pressing, and the dosage of the liquid carbon dioxide is preferably 80-120 m 3 More preferably 90 to 110m 3 Most preferably 100m 3 。
The invention adopts preposed liquid carbon dioxide for energizing, and CO is used for energizing before formal fracturing construction 2 The pump truck adopts small displacement (1.0-2.0 m) 3 Min) injecting liquid carbon dioxide into the stratum, and calculating the injection amount of liquid CO according to the principle of material balance 2 Volume and formation pressureAscending relationship when liquid CO is reached 2 At miscible pressure with crude oil, optimum liquid CO is present 2 Dosage; when CO is in liquid state 2 After the oil is injected into the stratum, the water in the oil layer is combined for the first time to generate carbonic acid with stable form, and the carbonic acid is quickly dissolved in the crude oil to achieve the purpose of reducing the viscosity of the crude oil and reduce CO in a saturated state 2 The acid-base value of the water is within the range of 3-3.7, the acid characteristic is obvious, the acid characteristic has certain corrosion capacity on the cementing material of rock particles, the corrosion material can be discharged along with the flow-back fluid, the oil-gas seepage space is enlarged, and the expansibility of clay minerals in the stratum can be effectively controlled under the acid environment. With CO 2 Extended residence time in the reservoir and gradual recovery of its temperature CO 2 Faster vaporization, 1m 3 Liquid CO 2 Can produce 546 standard square gaseous CO 2 Generating great flow-back power in the limited space of the reservoir; the method provided by the invention is suitable for the fracturing transformation of the continental facies shale oil low-pressure reservoir, reduces the damage to the reservoir and improves the flowback rate of the fracturing fluid.
In the present invention, the method for creating a main fracture by using an acid jelly solution preferably includes:
injecting 5-7 acid gel liquid with the volume of the shaft to obtain a main crack system; and injecting a gel breaker at the same time.
In the invention, the discharge capacity of the acid frozen glue solution in the main seam making process is preferably in a stepped rise; the initial displacement of the stepwise increasing displacement is preferably 2m 3 /min～3m 3 Min; particularly preferably, the discharge capacity is increased in a stepped manner for 2-3 times, and the discharge capacity of the stepped increase is 1.5-2.0 m in sequence 3 The quantity of the discharge is increased gradually until the discharge capacity is increased to 10-12 m 3 And/min. In the invention, the optimal dosage of the acidic jelly liquid is 100-150 m 3 More preferably 110 to 140m 3 Most preferably 120 to 130m 3 。
In the invention, the viscosity of the acid jelly liquid is preferably 100-150 mPa.s, more preferably 110-140 mPa.s, and most preferably 120-130 mPa.s.
In the present invention, the acidic jelly solution preferably has the following components:
0.3-0.4 wt% of a thickening agent;
0.4-0.6 wt% of a clay stabilizer;
0.04-0.06 wt% of a demulsifier;
0.08-0.12 wt% of a cleanup additive;
0.08-0.12 wt% of a bactericide;
0.5 to 0.7 wt% of a crosslinking agent;
0.5-0.7 wt% of a pH regulator;
0.01-0.15 wt% of a gel breaker;
the balance being water.
In the invention, the mass content of the thickening agent is preferably 0.35%; the mass content of the clay stabilizer (the clay stabilizer in the acid jelly liquid) is preferably 0.5%; the mass content of the demulsifier is preferably 0.05%; the mass content of the cleanup additive (the cleanup additive in the acid jelly solution) is preferably 0.1%; the mass content of the bactericide is preferably 0.1%; the mass content of the cross-linking agent is preferably 0.6%; the mass content of the pH regulator is preferably 0.6%; the mass content of the gel breaker (gel breaker in the acid gel liquid) is preferably 0.05-0.1%, and more preferably 0.06-0.08%.
In the present invention, the thickener is preferably carboxymethyl hydroxypropyl guar gum; the clay stabilizer (the clay stabilizer in the acid jelly liquid) is one or the combination of ammonium chloride and quaternary ammonium salt; the demulsifier is preferably one or two of alkyl phosphate and alkoxy carboxylate; the cleanup additive (the cleanup additive in the acid jelly solution) is preferably one or two of fatty alcohol polyether substance and fatty alcohol polyether cation compound; the bactericide is preferably one or more of formaldehyde, glutaraldehyde and quaternary ammonium salt; the cross-linking agent is preferably an organic zirconium salt substance; the pH regulator is preferably an acetic acid substance; the gel breaker (the gel breaker in the acid gel liquid) is preferably an ammonium persulfate substance, and the gel breaker is preferably added from a sand mixing truck during fracturing construction; the water is preferably clear water.
In the invention, the crosslinking time of the acid jelly liquid is preferably 30-180 s, more preferably 50-150 s, more preferably 80-120 s, and most preferably 100 s.
In the invention, the acidic jelly liquid is crosslinked in an acidic environment (pH is 3-5), so that the acidic jelly liquid has the advantages of good temperature resistance and shearing resistance, low residue, easiness in breaking and flowing back and small damage. The acid gel solution provided by the invention has a low-damage effect, and the acid fracturing fluid system-carboxymethyl hydroxypropyl guanidine gum fracturing fluid is adopted, so that the clay mineral expansion and migration caused by the electronegativity of the clay surface can be effectively inhibited, and the effect of stabilizing the clay is achieved; thereby effectively reducing the damage of the fracturing fluid to the reservoir.
In the present invention, the breaker is preferably an ammonium persulfate.
In the invention, the discharge capacity of the slickwater is preferably 12-14 m 3 Min, more preferably 13m 3 Min; the preferable dosage of the slickwater is 600-800 m 3 More preferably 650 to 750m 3 Most preferably 700m 3 。
In the present invention, the ingredients of the slickwater are preferably:
0.06-0.08 wt% of a resistance reducing agent;
0.08-0.12 wt% of a cleanup additive;
0.1-0.3 wt% of an anti-swelling agent;
the balance being water.
In the invention, the mass content of the resistance reducing agent is preferably 0.07%; the mass content of the cleanup additive (cleanup additive in slick water) is preferably 0.1%; the mass content of the anti-swelling agent is preferably 0.2%.
In the invention, the resistance reducing agent is preferably a polyacrylamide substance; the discharge aiding agent (discharge aiding agent in the slick water) is preferably a compound of polyoxyethylene amine ether and fluorocarbon surfactant; the anti-swelling agent is preferably a composite anti-swelling agent, and more preferably a poly N-hydroxymethyl acrylamide substance.
In the invention, the viscosity of the slickwater is preferably 2-6 mPa.s, more preferably 3-5 mPa.s, and most preferably 4 mPa.s; the density is preferably 1.0 to 1.05g/cm 3 (ii) a The anti-swelling rate is preferably 75-85%, more preferably 78-82%, and most preferably 80%; the surface tension is preferably 25 to 28mN/m, more preferably 26 to 27 mN/m; the interfacial tension is preferably 2.5 to 3.0mN/m, more preferably 2.6 to 2.8 mN/m; has the advantages of effectively inhibiting the expansion of clay and reducing the damage to stratum.
In the present invention, the method of filling the microcracks and the branched cracks preferably includes:
the first propping agent with 3-12% sand ratio carried by slickwater is injected into the micro-cracks and the branch cracks in a slug type sand adding mode.
In the present invention, the method of filling the microcracks and the branched fractures more preferably comprises:
the sand slug (first sand slug) and the liquid slug (first liquid slug) were injected alternately.
In the invention, the first sand adding slug is preferably a sand carrying liquid which is obtained by carrying a first supporting agent in slickwater with the volume of 2-3 mineshafts.
In the invention, the first liquid slug is preferably slickwater with 2-3 shaft volumes.
In the invention, in the process of alternately injecting the first sand adding slug and the first liquid slug, the first propping agent is preferably added from the sand adding slug with the sand ratio of 3-5%; in the alternating process, the sand ratio of the later sand adding slug is improved to a certain extent compared with that of the former sand adding slug, and the sand ratio is preferably improved by 1-2%; the number of the first sand adding slugs is preferably 5-7.
In the invention, the first propping agent is preferably a ceramsite propping agent with 70-140 meshes, more preferably 80-120 meshes, and most preferably 100 meshes.
In the present invention, the propping the primary fracture system with the second proppant and the third proppant preferably further comprises:
injecting acid jelly liquid to make main seam again.
In the invention, the discharge capacity of the acidic jelly liquid in the secondary main sewing process is preferably 10-12 m 3 The dosage of the acid jelly liquid is preferably 600-700 m 3 More preferably 620 to 680m 3 Most preferably 640 to 660m 3 。
In the present invention, the method of propping a primary fracture system preferably comprises:
and injecting a second proppant and a third proppant which carry 6-20% of sand ratio by using acid jelly liquid in a slug type sand adding mode.
In the present invention, the method of propping a primary fracture system more preferably comprises:
sand slug (second sand slug) and liquid slug (second liquid slug) were injected alternately.
In the invention, the second sand adding slug is preferably an acid gel liquid carrying a second proppant and a third proppant and having 2-3 shaft volumes.
In the invention, the second sand adding slug preferably further contains degradable fibers; the invention preferably adopts a fiber adding device to add a certain amount of degradable fibers into the second sand adding slug. In the invention, the degradable fiber is added with a second sand adding slug, preferably in the middle and later stages of fracturing, after the sand ratio of the second sand adding slug is increased to 10%, the degradable fiber with the mass concentration of 0.08-0.12% is added in the sand adding stage; the mass content of the degradable fibers in the sand-added slug is preferably 0.08-0.12%, more preferably 0.09-0.11%, and most preferably 0.1%.
In the invention, the degradable fiber is preferably a polyester fiber material, and the length of the degradable fiber is preferably 6-9 mm, and more preferably 7-8 mm; the degradable fiber is preferably automatically degraded after being soaked for 45-55 hours at the temperature of 75-85 ℃; the temperature is preferably 78-82 ℃, and more preferably 80 ℃; the soaking time is preferably 48 to 50 hours.
After the degradable fibers are added, damage to fracture flow conductivity caused by proppant crushing, embedding and the like due to closing pressure can be reduced, the degradable fibers have good sand carrying capacity, the proppant can be conveyed to deep parts, and the fracture flow conductivity is improved. The addition of the degradable fibers can reduce the settling speed of the proppant, so that the fracture efficiency reduction caused by proppant settling can not occur in the fracture closing process; the sand-carrying capacity is good, the propping agent can be conveyed to the deep part, and the flow conductivity of the crack is high; the damage to the flow guiding capacity of the crack caused by proppant crushing, embedding and the like due to closing pressure is reduced.
In the invention, the second liquid section plug is preferably acid gel liquid with 1-2 shaft volumes.
In the invention, in the process of alternately injecting the second sand adding slug and the second liquid slug, a second proppant and a third proppant are preferably added from the sand adding slug with the sand ratio of 6-8%; in the alternating process, the sand ratio of the later sand adding slug is improved to a certain extent compared with the sand ratio of the former sand adding slug, and the sand ratio is preferably improved by 1-2%; the number of sand adding sections added with the second proppant is preferably 8-10; the sand adding slug number of the third propping agent is preferably 3-4.
In the invention, the second propping agent is preferably a 40-70 mesh resin-coated quartz sand propping agent, more preferably a 50-60 mesh propping agent, and most preferably a 55 mesh propping agent; the second proppant is preferably added with a sand adding slug with a sand ratio of 6-18%, more preferably 8-16%, more preferably 10-14%, and most preferably 12-13%.
In the invention, the third propping agent is preferably a resin-coated quartz sand propping agent with 30-50 meshes, more preferably 35-45 meshes, and most preferably 40 meshes; and preferably adding a sand adding slug with the sand ratio of 18-20% into the third proppant.
In the invention, the total addition of the first proppant, the second proppant and the third proppant in fracturing of each interval is preferably 60-80 m 3 More preferably 65 to 75m 3 Most preferably 70m 3 (ii) a The adding mass ratio of the first proppant, the second proppant and the third proppant is preferably (2-4): (5-7): 1, more preferably 3: 6: 1.
in the invention, the second proppant and the third proppant are made of resin-coated quartz sand, and compared with the common proppant, the resin-coated quartz sand can effectively prevent the resin-coated quartz sand from being embedded in the stratum and has higher pressure-bearing capacity. According to the invention, a combined segment sand adding mode of 70/140-mesh powder pottery, 40/70-mesh resin-coated quartz sand and 30/50-mesh resin-coated quartz sand with multiple scales and small particle sizes is adopted; the 70/140-mesh powder pottery is used for polishing the friction of pores at the early stage, reducing the filtration loss and supporting micro cracks and secondary cracks; supporting branch seams and main cracks by using 40/70-mesh resin-coated quartz sand; and in the later period, 30/50-mesh resin-coated quartz sand is added into the high sand ratio, and a high-flow-guide main crack is formed at the crack opening, so that a branch crack net and a high-flow-guide main crack are realized.
In the present invention, the method of displacing proppant to the fracture seam preferably comprises:
and replacing the last section of proppant in the shaft to the crack gap by using slickwater.
In the invention, the time for replacing the last section of proppant in the shaft to the crack gap by using slickwater is preferably the time when the sand adding amount of the fracturing design is reached; the last section of proppant is preferably the second proppant or the third proppant described in the above technical scheme; the slickwater is preferably used in an amount equal to the sum of the volume of the wellbore and the volume of the surface pipeline.
The invention adopts a fracturing fluid system of mixing slick water and acid gel liquid, the fracturing fluid system adopted by fracturing is slick water and acid gel liquid, the mass ratio of the slick water to the acid gel liquid in the total injected fracturing fluid is preferably 1: (0.8 to 1.2), more preferably 1: (0.9 to 1.1), most preferably 1: 1.
in the present invention, the process of making the main slit, initiating and propagating the micro-cracks and the branch cracks, and filling the main slit preferably includes:
after formal fracturing is started, firstly injecting 100-150 m of acid gel liquid 3 The injection displacement is 10-12 m 3 Min, promoting the formation of effective main seams; then injecting the slippery water with the thickness of 600-800 m 3 The injection displacement is 12-14 m 3 Min, forming a complex seam net by utilizing the good communication capacity of slick water; then injecting 600-700 m of acid jelly liquid 3 The injection displacement is 10-12 m 3 And/min, improving the sand-liquid ratio and filling the main crack by utilizing the good crack forming and sand carrying capacity of the material.
In the present invention, the composite fracturing method for a continental facies shale oil reservoir preferably comprises:
pretreating a reservoir by using acid liquor;
injecting liquid carbon dioxide
Making a main crack by using an acid jelly solution;
injecting slickwater carrying 70-140 meshes of ceramsite propping agents with the sand ratio of 3% -12% respectively to support a micro-crack system and a branch crack system, wherein the concentration of each section of propping agent is different;
injecting acidic gel liquid carrying 40-70 meshes plus 30-50 meshes of resin coated quartz sand propping agents with a sand ratio of 6-20% respectively to support a main fracture system, wherein the concentration of each section of propping agent is different, and injecting degradable fibers with a certain concentration in a later high sand ratio stage;
and completely displacing the last section of proppant in the shaft to the fracture seam by using slick water.
In the present invention, the composite fracturing method for a continental facies shale oil reservoir more preferably comprises:
pretreating a reservoir by using acid liquor;
injecting liquid carbon dioxide with the injection discharge capacity of 1.0-1.5 m 3 /min；
Injecting 5-7 wellbore volumes of preposed acid gel liquid to make a main fracture to obtain a main fracture system, and injecting a gel breaker, wherein the viscosity of the acid gel liquid is 100-150 mPa.s;
injecting slickwater to start and expand a system of the micro-cracks and the branch cracks, adding a first propping agent into the slickwater to fill the micro-cracks and the branch cracks, alternately injecting a liquid slug (a first liquid slug) with 2-3 shaft volume sand carrying liquid (slickwater carrying the first propping agent) and a liquid slug (a first liquid slug) with 1-2 shaft volume slickwater, starting adding the first propping agent by using a 3-5% sand ratio slug, wherein the sand ratio of the latter sand feeding slug is improved to a certain extent compared with the former sand feeding slug by 1-2%, and the number of the sand feeding slugs is 5-7; the viscosity of the slickwater is 2-6 mPa.s;
injecting acid gel liquid to make a main crack and carry a second propping agent and a third propping agent to prop the main crack, alternately injecting sand carrying liquid amounts (acid gel liquid carrying the second propping agent and the third propping agent) with 2-3 shaft volumes as a sand adding slug (second sand adding slug) and acid gel liquid amounts with 1-2 shaft volumes as a liquid slug (second liquid slug), adding a certain amount of degradable fibers in the sand adding slug along with a fiber adding device, and sequentially adding the second propping agent and the third propping agent from a slug with a sand ratio of 6% -8%, wherein the sand ratio of the next sand adding slug is improved by a certain amount and is improved by 1-2% compared with the previous sand adding slug; the number of sand adding sections of the second propping agent is 8-10, the number of sand adding sections of the third propping agent is 3-4, and a gel breaker is injected at the same time, wherein the viscosity of the acid gel liquid is 100-150 mPa.s;
and when the sand adding amount of the fracturing design is reached, completely replacing the second proppant or the third proppant in the well casing to the crack joint by using slickwater, wherein the using amount of the slickwater is the sum of the volume of the well casing and the volume of the ground pipeline.
In the process of shale oil exploration and development, the low-damage fracturing fluid is adopted according to the characteristics of a reservoir stratum; and the slickwater and acid jelly mixed fracturing fluid, the multi-scale small-particle size proppant and the fiber sand are provided to form a high-flow-guide complex volume seam net, so that the modification volume of the reservoir is increased; with pre-liquid CO 2 Increasing energy to increase the back-flow rate of the high pressure. The invention solves the problems of damage to the domestic continental facies shale oil reservoir, easy embedding of a propping agent, low flow conductivity and difficult flowback of fracturing fluid, and has very important significance for guiding the exploration and development of the domestic continental facies shale oil.
The acid formula adopted in the following embodiments of the invention comprises: 15 wt% of industrial hydrochloric acid, 1.5 wt% of corrosion inhibitor, 1.5 wt% of iron ion stabilizer, 0.5 wt% of clay stabilizer and 0.1 wt% of cleanup additive, and is provided for Beijing Hongyaoen Enze energy technology Limited company. The formula of the acid jelly liquid is as follows: 0.35 wt% of carboxymethyl hydroxypropyl guar gum, 0.5 wt% of clay stabilizer, 0.05 wt% of demulsifier, 0.1 wt% of cleanup additive, 0.1 wt% of bactericide, 0.6 wt% of cross-linking agent, 0.6 wt% of pH conditioner, 0.01-0.15 wt% of gel breaker and the balance of water, and is provided by Beijing Baofengchun oil technology Co. The formula of the slick water comprises: 0.07 wt% of resistance reducing agent, 0.1 wt% of cleanup additive, 0.2 wt% of composite anti-swelling agent and the balance of water, and is provided by Beijing Baofengchun oil technology Co. The ceramsite with 70-140 meshes is a ceramsite product with the size of 0.112-0.224 mm, which is provided by Zhengzhou Shaolin filter materials Co. The 40-70-mesh resin-coated quartz sand is a resin-coated quartz sand product with the particle size of 0.224-0.45 mm, which is provided by Beijing wonderland new material company Limited. The resin-coated quartz sand with the particle size of 0.35-0.6 mm is provided by Beijing wonderland new material company Limited and is a resin-coated quartz sand product with the particle size of 30-50 meshes. The degradable fiber is a polyester fiber, is provided by Beijing Hongyao Enze energy technology Limited company, and is a polyester fiber product with the length of 6-8 mm.
Examples
A shale oil horizontal well is arranged in a depression at the north part of a Songliao basin, 10 sections of fracturing construction are smoothly completed by adopting the method provided by the invention, industrial oil flow is obtained after the fracturing, and the specific implementation steps of each section of fracturing construction are shown in the table 1:
TABLE 1 construction procedure for each stage of fracturing
The well is divided into 10 sections for fracturing, and acid liquor is injected into the well in total of 100m 3 8551m of slick water 3 8448m of acid jelly liquid 3 Front-mounted liquid carbon dioxide 600m 3 Adding 70/140 mesh pottery 165m 3 481m of 40/70 mesh resin-coated quartz sand 3 30/50 mesh resin-coated quartz sand 75m 3 Degradable fiber 2320m 3 。
The accumulated amount of the flowback fracturing fluid after the well pressure is 3185.3m 3 The flow-back rate is 18.63 percent, and the daily oil 14.37m is obtained by the self-spraying production 3 The stable production time is long, and the fracturing effect is obvious; the method is characterized in that the fracturing fractures are distributed in a complex network shape by ground microseism monitoring, and are shown in figure 1; the total rebuild volume (SRV) was found to be 1253.61X 10 4 m 3 As shown in fig. 2.
The invention is used in the process of shale oil exploration and developmentAiming at the characteristics of the reservoir stratum, low-damage fracturing fluid is adopted; and the slickwater and acid jelly mixed fracturing fluid, the multi-scale small-particle size proppant and the fiber sand are provided to form a high-flow-guide complex volume seam net, so that the modification volume of the reservoir is increased; with pre-liquid CO 2 Increasing energy to increase the back-flow rate of the high pressure. The invention solves the problems of damage to the domestic continental facies shale oil reservoir, easy embedding of propping agent, low flow conductivity and difficult flowback of fracturing fluid, and has very important significance for guiding the exploration and development of the domestic continental facies shale oil.
While only the preferred embodiments of the present invention have been described, it should be understood that various modifications and adaptations thereof may occur to one skilled in the art without departing from the spirit of the present invention and should be considered as within the scope of the present invention.
Claims (10)
1. A composite fracturing method for a continental shale oil reservoir, comprising:
pretreating a reservoir by using acid liquor;
injecting liquid carbon dioxide into the pretreated reservoir stratum;
adopting acid gel liquid to make main cracks;
opening and expanding a micro-crack and branch crack system by adopting slick water;
adopting a first propping agent to prop the micro-fracture system and the branch fracture system;
propping the primary fracture system with a second proppant and a third proppant;
displacing the proppant to the fracture seam;
the granularity of the first proppant is 70-140 meshes;
the granularity of the second proppant is 40-70 meshes;
the granularity of the third proppant is 30-50 meshes;
the second proppant and/or the third proppant comprises degradable fibers.
2. A process according to claim 1, wherein the acid solution comprises hydrochloric acid and/or earth acid.
3. The method according to claim 1, wherein the discharge amount of the injected liquid carbon dioxide is 1.0-1.5 m 3 /min。
4. The method of claim 1, wherein the slickwater has the composition:
0.06 to 0.08 wt% of a resistance reducing agent;
0.08-0.12 wt% of a cleanup additive;
0.1-0.3 wt% of an anti-swelling agent;
the balance being water.
5. The method according to claim 4, wherein the friction reducer is a polyacrylamide substance;
the cleanup additive is a complex of polyoxyethylene amine ether and fluorocarbon surfactant;
the anti-swelling agent is a poly N-hydroxymethyl acrylamide substance.
6. The method according to claim 1, wherein the acidic jelly solution comprises the following components:
0.3-0.4 wt% of a thickening agent;
0.4-0.6 wt% of a clay stabilizer;
0.04-0.06 wt% of a demulsifier;
0.08-0.12 wt% of a cleanup additive;
0.08-0.12 wt% of a bactericide;
0.5 to 0.7 wt% of a crosslinking agent;
0.5-0.7% of a pH regulator;
0.01-0.15 wt% of a gel breaker;
the balance being water.
7. The method of claim 6, wherein the thickener is carboxymethyl hydroxypropyl guar;
the clay stabilizer is one or a combination of ammonium chloride and quaternary ammonium salt;
the demulsifier is one or two of alkyl phosphate and alkoxy carboxylate;
the cleanup additive is one or two of fatty alcohol polyether substance and fatty alcohol polyether cation compound;
the bactericide is one or more of formaldehyde, glutaraldehyde and quaternary ammonium salt;
the cross-linking agent is an organic zirconium salt substance;
the pH regulator is an acetic acid substance;
the gel breaker is ammonium persulfate.
8. The method of claim 1, wherein the first proppant is a ceramsite proppant;
the second propping agent is a resin coated quartz sand propping agent;
the third propping agent is resin coated quartz sand propping agent.
9. The method according to claim 1, wherein the viscosity of the slickwater is 2-6 mpa.s;
the viscosity of the acid jelly liquid is 100-150 mPa.s.
10. The method of claim 1, wherein the degradable fiber is a polyester fiber.
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