CN109736767B - Supercritical carbon dioxide fracturing production increasing process - Google Patents
Supercritical carbon dioxide fracturing production increasing process Download PDFInfo
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Abstract
The invention relates to a supercritical carbon dioxide fracturing production increasing process, which comprises the following steps: s1: construction preparation, including preparation of carbon dioxide fracturing fluid and preparation of fracturing equipment; s2: connecting a ground pipeline; s3: ground circulation detection; s4: testing pressure of a wellhead and a ground pipeline; s5: filling a shaft to prepare fracturing construction; s6: performing primary fracturing test; s7: performing fracturing construction, namely enabling carbon dioxide to reach a supercritical state, increasing the fracture degree of a fractured stratum at the moment, further extending the fracture and extending the fracture by using carbon dioxide fracturing fluid, and then starting sand mixing equipment to inject a propping agent until the propping agent completely enters the stratum; s8: closing the well for at least 120min, and then performing step S9; s9: and (5) releasing pressure, and controlling the release of carbon dioxide until the crack is closed. The invention effectively improves the fracturing yield-increasing transformation effect, solves the fracturing problem of sensitive strata, is easier to produce wide and long seams, and simultaneously reduces the damage of fracturing fluid to the matrix of the reservoir.
Description
Technical Field
The invention relates to the technical field of oil and gas development, in particular to a supercritical carbon dioxide fracturing yield-increasing process.
Background
Hydrocarbon resource reservoirs exist in the pores, caverns and fractures of subterranean rocks and flow in these reservoir spaces. If the storage space and the pore space of the underground reservoir are large, oil and gas are easy to produce by seepage after drilling. The fracturing technology is a common technology that in the oil extraction process, liquid with certain viscosity is squeezed into an oil layer, and after a plurality of cracks are formed in the oil layer, a propping agent is added to fill the cracks, so that the permeability of the oil-gas layer is improved, and the oil yield is increased.
In recent years, the fracturing scale is developed towards the direction of large sand volume and large liquid volume (industrialization), the development of unconventional oil and gas reservoirs (condensate) poses a serious challenge to large-scale volume (fracture network) fracturing, and the fracturing meets the technical bottleneck and is not favorable for popularization. At present, many fracturing production increasing technologies are tried at home and abroad aiming at low-porosity, low-permeability and sensitive oil-gas reservoirs, for example: fracture network fracturing, conventional carbon dioxide fracturing, coiled tubing drag fracturing with bottom seal, soluble bridge plug fracturing and the like, but the yield increase transformation effect is not obvious.
Therefore, how to improve the fracturing yield-increasing transformation effect on low-porosity, low-permeability and sensitive oil-gas layers, solve the fracturing problem of the sensitive stratum, make wide seams and long seams easier, and reduce the damage of fracturing fluid to reservoir matrixes is a technical problem to be solved by the technical personnel in the field.
Disclosure of Invention
The invention aims to provide a supercritical carbon dioxide fracturing production-increasing process, which can effectively improve the fracturing production-increasing transformation effect on low-porosity, low-permeability and sensitive oil-gas layers, solve the fracturing problem of sensitive strata, be easier to produce wide seams and long seams and reduce the damage of fracturing fluid to reservoir matrixes.
In order to solve the technical problems, the supercritical carbon dioxide fracturing production increasing process provided by the invention comprises the following steps:
s1: construction preparation, including preparation of supercritical carbon dioxide fracturing fluid and preparation of fracturing equipment;
s2: connecting a surface pipeline, including connecting the fracturing truck to the surface pipeline between the wellheads;
s3: ground circulation detection is carried out, whether the puncture and connection conditions are qualified or not is detected, and if the puncture and connection conditions are qualified, the step S4 is carried out;
s4: testing the pressure of the wellhead and the ground pipeline, and if the pressure is qualified, performing step S5;
s5: filling a shaft to prepare fracturing construction;
s6: performing a preliminary fracturing test, and if the preliminary fracturing test result meets the requirement, performing step S7;
s7: performing fracturing construction, namely injecting supercritical carbon dioxide fracturing fluid to a fractured stratum, enabling the carbon dioxide to reach a supercritical state, increasing the fracture degree of the fractured stratum at the moment, further extending cracks and extending the cracks by the supercritical carbon dioxide fracturing fluid, and then starting sand mixing equipment to inject proppant until the proppant completely enters the stratum;
s8: closing the well for at least 120min, and then performing step S9;
s9: and (5) releasing pressure, and controlling the release of carbon dioxide until the crack is closed.
The invention mainly improves the fracturing yield-increasing transformation effect on low-porosity, low-permeability and sensitive oil-gas layers, solves the fracturing difficult problem of the sensitive stratum, achieves certain achievements on the development of unconventional oil-gas reservoirs, is more suitable for fracturing transformation of reservoirs with outstanding internal contradictions, and improves the fracturing sweep volume and the oil-driving (sweeping) efficiency.
Optionally, the preparation of the supercritical carbon dioxide fracturing fluid in step S1 includes the following steps:
s11: preheating a preparation instrument to a preset temperature, adding 5.0-7.0 mass percent of dispersing agent and 0.5-2 mass percent of tackifier into the preparation instrument under the condition of continuous stirring, introducing carbon dioxide, and continuously stirring until the dispersing agent is completely dissolved to obtain base liquid;
s12: under continuous stirringUnder the condition, 2.0-4.0% of cross-linking agent is added into clear water according to the mass percentage, the stirring is continued until the cross-linking agent is completely dissolved to obtain cross-linking liquid, and the shear rate is 170s at room temperature-1Detecting the cross-linking viscosity of the cross-linking liquid through a viscometer, and if the cross-linking viscosity is greater than 50mPa & s, finishing the preparation of the cross-linking liquid;
s13: adding the crosslinking liquid obtained in S12 to the base liquid obtained in step S11;
s14: and adjusting the pressure of a preparation instrument to a preset pressure, and continuously stirring until the system is clear and transparent to obtain the supercritical carbon dioxide fracturing fluid.
Optionally, the preparation of the fracturing equipment in step S1 includes: placing a first fracturing fluid tank, a booster pump truck, a first fracturing pump truck, a second fracturing fluid tank, a sand mixing device, a second fracturing pump truck and an instrument truck at preset positions, arranging a recovery device below the position where the second fracturing fluid tank is connected with a manifold connected with the second fracturing fluid tank, and arranging impermeable cloth below a sand hopper of the sand mixing device; connecting a ground pipeline in the step S2 includes sequentially communicating the carbon dioxide pipe, the booster pump truck and the first fracturing pump truck, communicating the second fracturing fluid tank, the sand mulling equipment and the second fracturing pump truck, and communicating the first fracturing pump truck and the second fracturing pump truck with a spraying pipeline of a wellhead; the instrument vehicle is respectively connected with the booster pump truck, the sand mixing equipment, the first fracturing pump truck and the second fracturing pump truck and is used for monitoring the working states of the booster pump truck, the sand mixing equipment, the first fracturing pump truck and the second fracturing pump truck; anchoring the fracturing pipeline and the blow-off pipeline.
Optionally, the preparation of the fracturing equipment in step S1 further comprises: and (2) assembling a blowout prevention controller at the wellhead, lowering a fracturing string after flushing the oil pipe, installing a Christmas tree at the wellhead, wherein the oil pipe of the fracturing string is made of P110 steel grade material, the outer diameter is phi 88.9mm, the lowering speed of the fracturing string is not more than 24m/min, and the fracturing string is lowered into the wellhead to a preset depth for at least 2 hours before fracturing construction in the step S7.
Optionally, the preparation of the fracturing equipment in step S1 further comprises: a cleaning vehicle equipped with a hose is prepared for backwashing the well when plugging occurs during the fracturing construction.
Optionally, in step S7, the fracturing construction includes the following steps:
s71: the fracturing fluid of the first fracturing fluid tank is pressurized by the booster pump truck, conveyed to the first fracturing pump truck and injected into an oil pipe from a wellhead 7 to manufacture a crack;
s72: closing the first fracturing pump truck, opening the second fracturing pump truck, mixing the fracturing fluid and the proppant in the second fracturing fluid tank in the sand mulling equipment, conveying the mixture to the second fracturing pump truck, and pumping the mixture into an oil pipe of the wellhead so that the proppant is filled in the fracture manufactured in the step S71;
s73: and closing the second fracturing pump truck, opening the first fracturing pump truck, and introducing the fracturing fluid of the first fracturing fluid tank into the wellhead for displacement.
Optionally, in step S7, the fracturing construction is performed by layer-by-layer fracturing: and after fracturing each layer, opening a gate of the well mouth, throwing a sealing ball, and fracturing the next layer after plugging the modified layer section when the detection pressure shows that the displacement of the sealing ball is not changed.
Optionally, the proppant is at least one of quartz sand and ceramsite, and the particle size of the proppant is a combination of at least two adjacent particle sizes of 20 meshes, 40 meshes, 70 meshes and 100 meshes.
Optionally, before step S6, a fluid loss additive is pumped into the well and the well is shut in for at least 30 min.
Optionally, in step S4, the pressure testing of the wellhead and the surface pipeline includes: and (3) injecting clear water into the ground pipeline, keeping for at least 10min under the pressure condition of 70MPa, observing whether the ground pipeline and the gate are punctured, and if not, testing the pressure to be qualified.
Drawings
FIG. 1 is a flow diagram of a supercritical carbon dioxide fracturing stimulation process of an embodiment of the present invention;
FIG. 2 is a diagram of equipment connections for a supercritical carbon dioxide fracturing stimulation process;
fig. 3 is a schematic diagram of the structure of the fracturing string.
In the accompanying fig. 1-3, the reference numerals are illustrated as follows:
1-a first fracturing fluid tank; 2-a booster pump truck; 3-a first fracturing pump truck; 4-a second fracturing fluid tank; 5-sand mixing equipment; 6-a second fracturing pump truck; 7-well head; 8-fracturing string, 81 tubing.
Detailed Description
In order to make the technical solutions of the present invention better understood by those skilled in the art, the present invention will be further described in detail with reference to the accompanying drawings and specific embodiments.
Referring to fig. 1-3, fig. 1 is a flow chart of a supercritical carbon dioxide fracturing stimulation process according to an embodiment of the present invention; FIG. 2 is a diagram of equipment connections for a supercritical carbon dioxide fracturing stimulation process; fig. 3 is a schematic diagram of the structure of the fracturing string.
The embodiment of the invention provides a supercritical carbon dioxide fracturing stimulation process, which comprises the following steps of:
s1: construction preparation, including preparation of supercritical carbon dioxide fracturing fluid and preparation of fracturing equipment;
s2: connecting a surface pipeline, including connecting the fracturing truck to the surface pipeline between the wellheads;
s3: ground circulation detection is carried out, whether the puncture and connection conditions are qualified or not is detected, and if the puncture and connection conditions are qualified, the step S4 is carried out;
s4: testing the pressure of the wellhead and the ground pipeline, and if the pressure is qualified, performing step S5;
s5: filling a shaft to prepare fracturing construction;
s6: performing a preliminary fracturing test, and if the preliminary fracturing test result meets the requirement, performing step S7;
s7: performing fracturing construction, namely injecting supercritical carbon dioxide fracturing fluid to a fractured stratum, enabling the carbon dioxide to reach a supercritical state, increasing the fracture degree of the fractured stratum at the moment, further extending cracks and extending the cracks by the supercritical carbon dioxide fracturing fluid, and then starting sand mixing equipment to inject proppant until the proppant completely enters the stratum;
s8: closing the well for at least 120min, and then performing step S9;
s9: and (5) releasing pressure, and controlling the release of carbon dioxide until the crack is closed.
In the embodiment of the invention, the supercritical carbon dioxide fracturing fluid (namely the carbon dioxide with the temperature higher than 31.1 ℃ and the pressure higher than 7.38 MPa) is used, and the viscosity and the surface tension of the supercritical carbon dioxide are low, so that the supercritical carbon dioxide fracturing fluid is high in fluidity, is beneficial to flowing and diffusing in a stratum, has stronger rock breaking capacity than a conventional water-based system, can form a more complex fracture system, and increases the effective reconstruction volume.
Specifically, the stimulation mechanism by the fracturing of the supercritical carbon dioxide fracturing fluid mainly comprises the following contents:
(1) expanding crude oil, the solubility of carbon dioxide in oil is higher than that in water, for example, at 49 deg.C and 10.34MPa, the solubility of carbon dioxide in oil is 4.4 times that in water. 660m in oil3/m3In water at 150m3/m3And the carbon dioxide can realize the expansion of crude oil after being dissolved in the oil.
(2) Viscosity reduction, when carbon dioxide is saturated in crude oil, the viscosity of the crude oil can be reduced by 1/10-1/100, and the viscosity of the crude oil is reduced more when the crude oil is more viscous, so that the fluidity of the crude oil can be effectively increased.
(3) Lowering the interfacial tension, typically between 30 and 35mN/m between oil and water, reduces the interfacial tension by 30% to 40% when the water is saturated with carbon dioxide at 750 lb/in 2(5.2MPa), and reduces the capillary force, which is desirable for crude oil flowing in the pores.
(4) The expansion-proof blockage-relieving function, the carbon dioxide reacts with the formation water to generate carbonic acid, and the pH value of the saturated carbonated water is 3.3-3.7, so that the expansion of clay minerals can be reduced. (generally, clay mineral swelling is reduced below pH 4.5-5.0, and aluminum and iron ions precipitate and clog flow channels above pH 4.0. Low pH carbonate helps prevent such clogging)
(5) The wettability of the rock is converted into hydrophilicity, the water-wetting capacity of the rock can be improved by higher soaking pressure, the rock is developed towards the hydrophilicity direction, water displacement is facilitated, and the recovery ratio of crude oil is improved.
Molecules of the supercritical carbon dioxide can enter pores with small radius, weak faces with small opening degree and natural cracks, so that rocks are broken more easily and longer and more complex cracks are formed, the supercritical carbon dioxide fracturing fluid can realize large-range penetration in a stratum and large effective sweep range, and the complexity of a crack system is increased. And the supercritical carbon dioxide fracturing fluid is injected into the stratum with larger discharge capacity through the fracturing pump truck, and a complex dynamic fracture system is formed by controlling the phase change of carbon dioxide at different stages and utilizing the extremely strong fluidity and rock breaking capacity of the supercritical carbon dioxide, so that the generated rock fragments and the added propping agent act together to support complex fractures. Meanwhile, after the fracturing construction of the supercritical carbon dioxide fracturing fluid is finished, carbon dioxide is changed into a gaseous state and dissolved in oil water, no residue is generated, and no damage is caused to a reservoir. Specifically, after fracturing construction is finished, a 7-gate of an oil casing wellhead is closed in time, the well is closed for at least 120min, and a 10mm oil nozzle is used for controlling open flow of carbon dioxide until a crack is closed (diffusion pressure time and an open flow process are determined by field technicians). Compared with the conventional fracturing process, the method has obvious effect of increasing the yield of the water-sensitive reservoir.
The supercritical carbon dioxide fracturing fluid has the following advantages:
(1) the supercritical carbon dioxide has stronger rock breaking capacity than that of a conventional water-based system, a more complex crack system can be formed, and the effective modification volume is increased;
(2) the fracturing fluid has no residues and low damage;
(3) reducing damage of the fracturing fluid to the reservoir matrix;
(4) the cold injury effect is low;
(5) wide and long seams are easier to manufacture.
For example, by comparing the supercritical carbon dioxide fracturing fluid with the vegetable gum fracturing fluid, the effect is shown in the table (one), and the table (one) shows that the performance advantage of the supercritical carbon dioxide fracturing fluid is obvious, which is beneficial to crack formation and yield increase.
Table (I) fracturing fluid system performance comparison chart
Before construction, according to characteristic parameters such as reservoir conditions, well body conditions and the like of an oil-gas well needing yield increase, a proper gas phase fracturing device is selected, an adaptive technical scheme is compiled, construction discharge capacity is optimized, stable construction net pressure is maintained, the height of a supporting seam is accurately predicted, reasonable construction discharge capacity is controlled, the problem that the seam width and the seam length are reduced directly due to the fact that the height of the seam is out of control caused by large construction discharge capacity is avoided, and a large amount of propping agents are filled inefficiently.
The invention mainly improves the fracturing yield-increasing transformation effect on low-porosity, low-permeability and sensitive oil-gas layers, solves the fracturing difficult problem of the sensitive stratum, achieves certain achievements on the development of unconventional oil-gas reservoirs, is more suitable for fracturing transformation of reservoirs with outstanding internal contradictions, and improves the fracturing sweep volume and the oil-driving (sweeping) efficiency.
In addition, before the fracturing construction step S7, a preliminary fracturing test step S6 is performed, so as to further detect whether the preparation before the fracturing construction is sufficient, such as the connection between the pipelines, whether there is leakage, and the like.
In the above embodiment, the preparation of the supercritical carbon dioxide fracturing fluid in step S1 includes the following steps:
s10: before injecting the carbon dioxide fracturing fluid in batches, determining the temperature of the carbon dioxide fracturing fluid injected into a wellhead by combining a specific construction scheme and geological conditions; the injection temperature of the well head is different due to different seasons and geological conditions (including different well depths, different residence time of the carbon dioxide fracturing fluid in a well bore).
S11: preheating a preparation instrument to a determined preset temperature, adding 5.0-7.0% by mass of a dispersing agent and 0.5-2% by mass of a tackifier into the preparation instrument under the condition of continuous stirring, and continuously stirring until the dispersing agent is completely dissolved to obtain a base solution;
s12: under the condition of continuous stirring, 2.0-4.0 percent of cross-linking agent is added according to the mass percentageStirring in clear water until the crosslinking agent is completely dissolved to obtain a crosslinking solution, and shearing at room temperature for 170s-1Detecting the cross-linking viscosity of the cross-linking liquid through a viscometer, and finishing the preparation of the cross-linking liquid if the cross-linking viscosity is greater than 50mPa & s;
s13: adding the crosslinking liquid obtained in S12 to the base liquid obtained in step S11;
s14: and adjusting the pressure of the preparation instrument to a preset pressure, and continuously stirring until the system is clear and transparent to obtain the fracturing fluid.
Specifically, when the base solution is prepared, under the condition of continuous stirring, the dispersing agent and the tackifier of 1 percent are added according to the proportion of 6.0 percent, and the mixture is continuously stirred for more than one week to ensure that no insoluble substances exist in the solution; when preparing the cross-linking liquid: under the condition of continuous stirring, 3.0 percent of cross-linking agent is added according to the mass percentage, dissolved in clear water and continuously stirred for more than one week to form uniform and stable liquid. For the crosslinking experiments, a Fann35 viscometer was used at room temperature with a shear rate of 170s-1When the viscosity of the crosslinking solution is more than 50 mPas, the crosslinking solution is qualified. Specifically, in each preparation step of the fracturing fluid, the time for continuous stirring is not limited, and can be set according to specific conditions, for example, when no insoluble matter exists in the solution.
The dispersing agent is a fluorine-containing surfactant, the tackifier is selected from hydroxy fatty acid, and the crosslinking agent is selected from potassium chloride, and the like, which is not limited specifically herein.
The viscosity of the fracturing fluid is improved by adding the tackifier, so that the settling speed of the proppant in the fracturing fluid is reduced, the sand carrying capacity of the fracturing fluid is improved, and meanwhile, the filtration loss of the fracturing fluid in the construction process can be reduced by increasing the viscosity.
When the liquid is prepared on site, the discharge capacity is more than 1.0m3The circulation liquid preparation of the min cement truck is realized by that a stirring barrel with a stirring function can realize continuous stirring for more than 90min, or 2 jet pumps with a negative pressure suction function can continuously circulate for more than 90 min; additionally, a crane is needed to be matched with and hoist the dispersing agent transportation barrel and other medicaments; before construction, preparing liquid, preparing corresponding equipment and clear water for liquid preparation in advance, wherein the pH value of the clear water for liquid preparation is 6.5-7.5, and all liquid storage tanks, liquid preparation pools and liquid preparation pipesThe line is cleaned, no residue of the last liquid preparation is obtained, and hydrocarbon chemicals such as crude oil, kerosene, gasoline and the like are not generated, so that adverse reaction is avoided; the operation is strictly carried out according to the formula and the preparation requirement, the measurement is accurate, and the liquid loss in the construction process is reserved for the preparation liquid amount. The liquid preparation personnel should prepare protective articles, prepare a barrel of clear water on a tank car, and prevent the strong alkali from burning.
The following table (two) shows the damage rate of the conventional water-based fracturing fluid to the reservoir, and the following table (three) shows the damage rate of the supercritical carbon dioxide fracturing fluid prepared by the steps S11-S14 to the reservoir under the same conditions:
as is obvious from the table (II) and the table (III), after the fracturing construction is carried out by the supercritical carbon dioxide fracturing fluid in the embodiment, the damage rate to the reservoir is obviously reduced to a great extent, and the damage to the stratum is greatly reduced.
TABLE (II) injury rate of conventional water-based fracturing fluid to reservoir
TABLE (III) injury rate of supercritical carbon dioxide fracturing fluid of this example to reservoir
In the above embodiment, the preparation of the fracturing equipment in step S1 includes: placing a first fracturing fluid tank 1, a booster pump truck 2, a first fracturing pump truck 3, a second fracturing fluid tank 4, a sand mulling device 5, a second fracturing pump truck 6 and an instrument truck at preset positions, arranging a recovery device below the position where the second fracturing fluid tank 4 is connected with a manifold connected with the second fracturing fluid tank 4, and arranging impermeable cloth below a sand hopper of the sand mulling device 5; the step S2 of connecting a ground pipeline comprises the steps of sequentially communicating a carbon dioxide pipe, a booster pump truck 2, a first fracturing pump truck 3, a second fracturing fluid tank 4, a sand mixing device 5 and a second fracturing pump truck 6, and communicating the first fracturing pump truck 3 and the second fracturing pump truck 6 with a spraying pipeline of a wellhead 7; the instrument vehicle is respectively connected with the booster pump truck 2, the sand mulling equipment 5, the first fracturing pump truck 3 and the second fracturing pump truck 6 and is used for monitoring the working states of the booster pump truck 2, the sand mulling equipment 5 and the fracturing pump truck; anchoring the fracturing pipeline and the blow-off pipeline.
Specifically, ground and in-environment tools such as gates, short joints, variable-port joints and the like must withstand pressure of 70MPa, and each screw thread needs to be coated with sealing grease, tightened, filled and not leaked.
As shown in fig. 2, each device (including a first fracturing fluid tank 1, a booster pump truck 2, a first fracturing pump truck 3, a second fracturing fluid tank 4, a sand mulling device 5, a second fracturing pump truck 6 and an instrument truck) is placed at a preset position, each device is provided with a corresponding low-pressure manifold and a corresponding high-pressure manifold, pipelines between the devices and between wellheads 7 are connected in step S2, and in step S3, each manifold, that is, an interface between the manifold and the device, is detected. In the fracturing process, a recovery device is arranged at the joint between the low-pressure manifold and the second fracturing fluid tank 4 to prevent the fracturing fluid from falling to the ground, and an impermeable cloth is arranged below a sand hopper of the sand mixing equipment 5 to prevent the propping agent from falling to the ground. In addition, the fracturing pipeline and the spraying pipeline are anchored, so that the phenomenon that the internal gas or liquid is shaken to contact the ground to cause abrasion is avoided when the internal gas or liquid flows.
Specifically, the number of the first fracturing fluid tanks 1, the second fracturing fluid tanks 4, the first fracturing pump trucks 3 and the second fracturing pump trucks 6 is not required, and the number can be specifically set according to field needs and construction requirements.
Further, the preparation of the fracturing equipment in step S1 further includes: the blowout prevention controller is assembled at the wellhead 7, the fracturing string 8 is placed after the oil pipe is washed, the Christmas tree is installed, wherein the fracturing string 8 is structurally shown in figure 3, the fracturing string 8 is made of P110 steel grade materials, and the outer diameter of the outer thickening oil pipe 81 is phi 88.9mm, the placing speed of the fracturing string 8 is not more than 24m/min, the operation is stable, the emergency placing and stopping are strictly forbidden, and the fracturing string is placed into the wellhead 7 to the preset depth for at least 2h before the fracturing construction of the step S7, so that the later-period preparation time is sufficient.
In addition, when the oil pipe is pulled out and lowered, the wellhead 7 must be provided with a non-well-killing controller for placing underground falling objects and blowout. In step S6, if the pressure test is qualified, step S7 is performed, and if the pressure test is not qualified, the sealability of each fracturing equipment and the christmas tree tubing valve is detected.
Further, the preparation of the fracturing equipment in step S1 further includes: a cleaning vehicle equipped with a hose is prepared for backwashing the well when clogging occurs in the fracturing construction process, and in step S2, a backwashing line is connected so that the clogging can be solved in time.
In step S7 in the above embodiment, the fracturing work includes the following steps:
s71: the fracturing fluid of the first fracturing fluid tank is pressurized by a sand mixer truck and carbon dioxide by a booster pump truck, is conveyed to the first fracturing pump truck after passing through a ground high-pressure manifold, and is injected into an oil pipe from a wellhead 7 to manufacture a crack; preferably after passing through the surface high pressure manifold, after being foamed by the foaming device, to the first fracturing pump truck, or directly to the wellhead 7.
S72: closing the first fracturing pump truck, opening the second fracturing pump truck, mixing fracturing fluid and proppant in a second fracturing fluid tank in sand mixing equipment, conveying the mixture to the second fracturing pump truck, and pumping the mixture into an oil pipe at a wellhead to fill the proppant into the crack manufactured in the step S71;
s73: and closing the second fracturing pump truck, opening the first fracturing pump truck, and replacing the fracturing fluid introduced into the first fracturing fluid tank into the wellhead.
That is to say, in this embodiment, the formation is fractured and the fracture is extended by the supercritical carbon dioxide fracturing fluid of the first fracturing fluid tank 1, and then the supercritical carbon dioxide fracturing fluid of the second fracturing fluid tank 4 carries the proppant to fill the fracture until the proppant completely enters the formation, and then the addition of the proppant is stopped, and only the supercritical carbon dioxide fracturing fluid is introduced into the wellhead 7 for replacement, and the replacement fluid volume needs to be larger than the oil pipe internal volume from the perforation section to the wellhead 7.
Further, in step S7, the fracturing construction is performed by layer-by-layer fracturing: and after fracturing each layer, opening a 7-gate of the well mouth, throwing a sealing ball, and fracturing the next layer after plugging the modified layer section when the detection pressure shows that the displacement of the sealing ball is not changed.
In detail, the fracturing construction steps are as follows: firstly fracturing a first layer according to the steps S71-S73, opening a gate of a well mouth 7, throwing a sealing ball A (checking the well mouth 7 to see whether a solid sealing ball A is thrown into the well or not on the premise of ensuring safety), after opening control, when seeing that a pressure display of opening a control switch for blocking the first layer is performed (observing whether the displacement of the sealing ball A is kept unchanged during the pressure display period or not), after blocking a modified layer section (the first layer), fracturing a second layer according to the steps S71-S73, opening the gate of the well mouth 7, throwing a sealing ball B (checking the well mouth 7 and the solid sealing ball B are thrown into the well or not on the premise of ensuring safety), when seeing that the pressure display of opening the control switch for blocking the second layer is performed (observing whether the displacement of the sealing ball B is kept unchanged during the pressure display period or not), after blocking is modified (the second layer), fracturing the third layer as per steps S71-S73 above, and so on. The layer-by-layer fracturing can ensure the fracturing effect of each layer and the overall fracturing quality.
In the above embodiment, the proppant added in step S7 includes at least one of quartz sand and ceramsite, that is, the proppant may be quartz sand, ceramsite or a mixture of quartz sand and ceramsite. Specifically, the proppant includes a combination of at least two adjacent particle sizes of 20 mesh, 40 mesh, 70 mesh and 100 mesh, that is, the particle size of the proppant may be a mixture of 20 mesh and 40 mesh, a mixture of 40 mesh and 70 mesh, a mixture of 70 mesh and 100 mesh, or may be three sizes, such as a mixture of 20 mesh, 40 mesh and 70 mesh or a mixture of 40 mesh, 70 mesh and 100 mesh, and is not particularly limited herein. The proppants with different particle size specifications can better pass through fractures with different widths to the deep part of a stratum, when the supercritical carbon dioxide fracturing fluid obtains wider propped fractures, conditions are created for the proppants with large particle sizes, all the fractures are correspondingly propped, and the sanding range is large.
Research shows that the optimal laying of 5-7 layers of propping agents cannot realize the purpose of adding large-particle-size propping agents to obtain high-conductivity propped cracks under the condition of narrow crack width, so that the propping agents with different particle sizes are adopted to obtain the high-conductivity cracks conveniently.
In the above embodiment, before step S6, fluid loss additive is pumped into the well and the well is shut in for at least 30 min. The fluid loss additive is added to maintain higher net bottom hole pressure, so that a seam net design is realized, and a bifurcation seam (or a communication natural fracture) is formed.
The fluid loss agent is pumped into a stratum before fracturing construction for sand fracturing, and can further increase the viscosity of the supercritical carbon dioxide fracturing fluid, improve the sand carrying capacity of the fluid loss agent, effectively reduce the fluid loss of the fracturing fluid, avoid the damage of water phase invading into an oil-gas layer and basically have no damage to the reservoir.
TABLE (IV) fracturing fluid filtration coefficient comparison table
The fluid loss coefficients of the supercritical carbon dioxide fracturing fluid and the existing fracturing fluids in the embodiment are compared as shown in the fourth table, and it can be seen that the fluid loss coefficient of the supercritical carbon dioxide fracturing fluid in the embodiment is obviously smaller than that of other fracturing fluids, so that the fluid loss of carbon dioxide to a stratum through a well wall is reduced, the viscosity of the supercritical carbon dioxide fracturing fluid can be further improved due to the addition of the fluid loss reducer, and the sand carrying capacity of the supercritical carbon dioxide fracturing fluid is improved while the fluid loss is reduced.
Specifically, the fluid loss additive may be carboxymethyl cellulose, a resin fluid loss additive, or modified starch, and the like, which is not specifically limited herein.
In the above embodiment, in step S4, the pressure testing of the wellhead 7 and the surface pipeline includes: and (3) injecting clear water into the ground pipeline, keeping for at least 10min under the pressure condition of 70MPa, observing whether the ground pipeline and the gate are punctured, and if not, testing the pressure to be qualified. The clean water pressure test can avoid the pipeline from leaking and polluting the ground.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that it is obvious to those skilled in the art that various modifications and improvements can be made without departing from the principle of the present invention, and these modifications and improvements should also be considered as the protection scope of the present invention.
Claims (1)
1. A supercritical carbon dioxide fracturing production increase process is characterized by comprising the following steps:
s1: construction preparation, including preparation of supercritical carbon dioxide fracturing fluid and preparation of fracturing equipment;
s2: connecting a surface pipeline, including connecting the fracturing truck to the surface pipeline between the wellheads;
s3: ground circulation detection is carried out, whether the puncture and connection conditions are qualified or not is detected, and if the puncture and connection conditions are qualified, the step S4 is carried out;
s4: testing the pressure of the wellhead and the ground pipeline, and if the pressure is qualified, performing step S5;
s5: filling a shaft to prepare fracturing construction;
s6: performing a preliminary fracturing test, and if the preliminary fracturing test result meets the requirement, performing step S7;
s7: performing fracturing construction, namely injecting supercritical carbon dioxide fracturing fluid to a fractured stratum, enabling the carbon dioxide to reach a supercritical state, increasing the fracture degree of the fractured stratum at the moment, further extending cracks and extending the cracks by the supercritical carbon dioxide fracturing fluid, and then starting sand mixing equipment to inject proppant until the proppant completely enters the stratum;
s8: closing the well for at least 120min, and then performing step S9;
s9: releasing pressure, and controlling the release of carbon dioxide until the crack is closed;
wherein the preparation of the supercritical carbon dioxide fracturing fluid in the step S1 comprises the following steps:
s11: preheating a preparation instrument to a preset temperature, adding 5.0-7.0 mass percent of dispersing agent and 0.5-2 mass percent of tackifier into the preparation instrument under the condition of continuous stirring, introducing carbon dioxide, and continuously stirring until the dispersing agent is completely dissolved to obtain base liquid;
s12: under the condition of continuous stirring, adding 2.0-4.0% of cross-linking agent into clear water according to the mass percentage, and continuously stirring until the cross-linking agent is completely stirredDissolving to obtain a crosslinking solution with a shear rate of 170s at room temperature-1Detecting the cross-linking viscosity of the cross-linking liquid through a viscometer, and if the cross-linking viscosity is greater than 50mPa & s, finishing the preparation of the cross-linking liquid;
s13: adding the crosslinking liquid obtained in S12 to the base liquid obtained in step S11;
s14: adjusting the pressure of a preparation instrument to a preset pressure, and continuously stirring until a system is clear and transparent to obtain the supercritical carbon dioxide fracturing fluid;
wherein the preparation of the fracturing equipment in step S1 includes: placing a first fracturing fluid tank, a booster pump truck, a first fracturing pump truck, a second fracturing fluid tank, a sand mixing device, a second fracturing pump truck and an instrument truck at preset positions, arranging a recovery device below the position where the second fracturing fluid tank is connected with a manifold connected with the second fracturing fluid tank, and arranging impermeable cloth below a sand hopper of the sand mixing device;
connecting a ground pipeline in the step S2 includes sequentially communicating a carbon dioxide pipe, the booster pump truck and the first fracturing pump truck, communicating the second fracturing fluid tank, the sand mulling equipment and the second fracturing pump truck, and communicating the first fracturing pump truck and the second fracturing pump truck with a spraying and releasing pipeline of a wellhead;
the instrument vehicle is respectively connected with the booster pump truck, the sand mixing equipment, the first fracturing pump truck and the second fracturing pump truck and is used for monitoring the working states of the booster pump truck, the sand mixing equipment, the first fracturing pump truck and the second fracturing pump truck;
anchoring the fracturing pipeline and the blow-off pipeline;
the preparation of the fracturing equipment in step S1 further includes: assembling a blowout prevention controller at a wellhead, putting a fracturing string down after flushing an oil pipe, installing a Christmas tree at the wellhead, wherein the oil pipe of the fracturing string is made of P110 steel grade material, the outer diameter is phi 88.9mm, the putting-down speed of the fracturing string is not more than 24m/min, and the fracturing string is put down to the wellhead to a preset depth at least 2 hours before fracturing construction in step S7;
the preparation of the fracturing equipment in step S1 further includes: preparing a cleaning vehicle provided with a hose and used for backwashing a well when blockage occurs in the fracturing construction process;
in step S7, the fracturing construction includes the following steps:
s71: the fracturing fluid of the first fracturing fluid tank is pressurized by the booster pump truck, conveyed to the first fracturing pump truck and injected into an oil pipe from a wellhead (7) to manufacture a crack;
s72: closing the first fracturing pump truck, opening the second fracturing pump truck, mixing the fracturing fluid and the proppant in the second fracturing fluid tank in the sand mulling equipment, conveying the mixture to the second fracturing pump truck, and pumping the mixture into an oil pipe of the wellhead so that the proppant is filled in the fracture manufactured in the step S71;
s73: closing the second fracturing pump truck, opening the first fracturing pump truck, and introducing the fracturing fluid of the first fracturing fluid tank into the wellhead for replacement;
in step S7, the fracturing construction is performed as a layer-by-layer fracturing: opening a gate of a well mouth after fracturing each layer, throwing a sealing ball, and fracturing the next layer after plugging the modified layer section when the detection pressure shows that the displacement of the sealing ball is not changed;
the proppant is at least one of quartz sand and ceramsite, and the grain size is the combination of at least two adjacent grain sizes of 20 meshes, 40 meshes, 70 meshes and 100 meshes;
pumping fluid loss additive into the well and closing the well for at least 30min before step S6;
in step S4, the pressure test of the wellhead and the ground pipeline comprises: and (3) injecting clear water into the ground pipeline, keeping for at least 10min under the pressure condition of 70MPa, observing whether the ground pipeline and the gate are punctured, and if not, testing the pressure to be qualified.
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| CN110424937A (en) * | 2019-07-15 | 2019-11-08 | 河南理工大学 | A kind of coal bed gas low yield well nitrogen-carbon dioxide joint transformation method for increasing |
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