CN117468908A - Novel method for improving recovery ratio of pressure flooding of medium-low permeability reservoir - Google Patents
Novel method for improving recovery ratio of pressure flooding of medium-low permeability reservoir Download PDFInfo
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- 239000010410 layer Substances 0.000 claims abstract description 16
- 238000000605 extraction Methods 0.000 claims abstract description 11
- 238000009826 distribution Methods 0.000 claims abstract description 8
- 239000003129 oil well Substances 0.000 claims abstract description 8
- 238000004088 simulation Methods 0.000 claims abstract description 8
- 239000011229 interlayer Substances 0.000 claims abstract description 5
- 238000012544 monitoring process Methods 0.000 claims abstract description 5
- 238000011160 research Methods 0.000 claims abstract description 5
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- ZRALSGWEFCBTJO-UHFFFAOYSA-N Guanidine Chemical compound NC(N)=N ZRALSGWEFCBTJO-UHFFFAOYSA-N 0.000 claims description 8
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- CHJJGSNFBQVOTG-UHFFFAOYSA-N N-methyl-guanidine Natural products CNC(N)=N CHJJGSNFBQVOTG-UHFFFAOYSA-N 0.000 claims description 4
- 238000009435 building construction Methods 0.000 claims description 4
- SWSQBOPZIKWTGO-UHFFFAOYSA-N dimethylaminoamidine Natural products CN(C)C(N)=N SWSQBOPZIKWTGO-UHFFFAOYSA-N 0.000 claims description 4
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- 229920000647 polyepoxide Polymers 0.000 description 2
- 238000005086 pumping Methods 0.000 description 2
- 238000009491 slugging Methods 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- BDHFUVZGWQCTTF-UHFFFAOYSA-M sulfonate Chemical compound [O-]S(=O)=O BDHFUVZGWQCTTF-UHFFFAOYSA-M 0.000 description 2
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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
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A10/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE at coastal zones; at river basins
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Abstract
The invention provides a novel method for improving recovery ratio of pressure flooding of a medium-low permeability reservoir, which comprises the following steps: step one, re-dividing the reservoir according to the research result of fine geological data of oil extraction plants and the longitudinal small layer distribution and interlayer evaluation result; step two, optimizing crack parameters by combining well pattern well spacing conditions; step three, determining the displacement of the pressure-driving construction; step four, determining the total consumption of the pressure flooding agent; step five, selecting a pressure flooding agent injection mode; step six, determining the optimal well-stewing time by a numerical simulation method; and step seven, aiming at the layer section re-divided in the step one, performing pressure flooding construction on the target well according to the pressure flooding agent injection mode selected in the step five by using the total consumption and the construction displacement of the pressure flooding agent determined in the step three and the step four, performing well soaking according to the optimal well soaking time determined in the step six, performing subsequent well opening production after well soaking is finished, and monitoring the production dynamics of the oil well. The invention achieves the purpose of improving the recovery ratio.
Description
Technical Field
The invention belongs to the technical field of oilfield development, and particularly relates to a novel method for improving recovery ratio of pressure flooding of a medium-low permeability reservoir.
Background
At present, most of the petroleum in China is still produced from old oil fields, and the residual oil of the old oil fields has huge diving space, so that the old oil fields are still the main sources of petroleum supply in the next decades. However, after the old oil field is subjected to long-term water injection scouring in the enhanced oil recovery stage and synergistic flooding of various chemical agents in the tertiary oil recovery stage, most of the old oil fields enter the double-high (high extraction degree and high water content) stage at present, and how to overcome the double-high problem of the oil field and improve the yield is a huge problem to be solved in the current stage of China.
The development difficulty of low permeability reservoirs in ultra-high water-containing old oil fields is that the reservoir characteristics of low permeability, low average pore throat radius, high drainage and driving pressure, high mud content and high clay content of the low permeability reservoirs are that 'water injection is not advanced and oil production is not carried out', which clearly increases the difficulty of further improving the recovery ratio, so that development of a reservoir efficient acquisition technology capable of improving the utilization degree of the reservoir and effectively utilizing scattered residual oil is urgently needed.
Disclosure of Invention
The invention aims to provide a novel method for improving recovery ratio by combining fracturing, seepage and oil displacement into a whole, which uses a low-viscosity chemical agent as fracturing fluid (namely, the low-viscosity chemical agent is petroleum sulfonate solution with the mass fraction of 0.3 percent, guanidine gum is not added, sand is not added, and the subsequent stage of fracturing fluid flowback of the conventional fracturing technology is not supported), pumps a large amount of the chemical agent directly to deep parts of upper and lower reservoirs along the fracture path by means of hydraulic fracturing, changes the "crack extension promotion" of the conventional hydraulic fracturing into "crack extension retardation", inhibits the early breakthrough of the front edge of an aqueous phase caused by the rapid extension of the fracture, realizes the expansion of effective wave and volume, simultaneously changes "normal-speed injection" into "high-pressure injection", reduces the loss along the stratum of the chemical agent, rapidly supplements stratum energy, greatly increases the contact area of the chemical agent and the stratum, drives scattered residual oil to be enriched, realizes high-efficiency exploitation, and achieves the purpose of high-efficiency ultra-high-permeability reservoir oil-old reservoir.
The construction of the pressure driving technology has two modes: (1) injecting a pressure driving agent from an injection end at high pressure, pressing open cracks in the stratum, collecting scattered residual oil by the pressure driving agent along the displacement direction, and continuously displacing to a production end; after the pressure, the crack is gradually closed, the well is opened for production after the well is closed for a period of time, and the injection end is restored to conventional water injection; this approach is called "forward pressure driving"; (2) injecting a pressure driving agent from the extraction end under high pressure, fracturing cracks in the stratum, and collecting scattered residual oil in the area near the extraction end by the pressure driving agent under the action of displacement pressure difference; after the pressure, the crack is gradually closed, the well is opened for production after the well is closed for a period of time, and meanwhile, the injection end resumes conventional water injection; this approach is called "reverse pressure flooding".
The technical scheme of the invention is as follows:
a new method for enhanced oil recovery for pressure flooding of medium and low permeability reservoirs, the method comprising:
step one, re-dividing the reservoir according to the research result of fine geological data of oil extraction plants and the longitudinal small layer distribution and interlayer evaluation result;
step two, optimizing fracture parameters by optimizing the optimal ratio between half length of the fracture and the injection and production well spacing in combination with well pattern well spacing conditions so that the fracture can effectively communicate with the residual oil enrichment part; wherein the fracture parameters include fracture half length;
thirdly, establishing a relation chart of the displacement of the pressure-driven construction and the friction of the system, and a relation chart of the displacement of the pressure-driven construction and the crack parameters, and determining the displacement of the pressure-driven construction by combining the geological parameters of the oil layer;
step four, building construction scale optimization plates with different pore filling coefficients according to the stratum thickness, the porosity, the permeability, the pore filling degree and the residual oil distribution condition, and comprehensively considering the reservoir transformation range, the sand control area and the effective porosity to determine the total consumption of the pressure flooding agent;
step five, in order to ensure that more pressure-driving agent percolates into the stratum under the condition of controllable crack extension, a pressure-driving agent injection mode is selected;
step six, determining the optimal well-stewing time through a numerical simulation method, so that the pressure flooding agent is fully contacted with the stratum crude oil, the oil-water two-phase imbibition and displacement effects are fully exerted, the oil saturation in the cracks is improved, and scattered residual oil is enriched;
step seven, aiming at the layer section re-divided in the step one, performing pressure driving construction on the target well according to the pressure driving agent injection mode selected in the step five by using the total consumption and the construction displacement of the pressure driving agent determined in the step three and the step four, wherein the joint making length is the optimal joint length calculated in the step two; closing the well after the pressure driving construction is completed, performing well logging according to the optimal well logging time determined in the step six, performing subsequent well logging production after well logging is completed, and monitoring the production dynamics of the oil well.
Furthermore, the fracturing fluid is not added with guanidine gum, sand and support in the follow-up process, and is not only used as a pre-fluid, but also does not pass through a fracturing fluid flowback stage of the conventional fracturing technology.
Further, the calculation formula of the half length of the split seam is as follows:
L f ＝d×r
wherein L is f Is half-length of the split seam, and the unit is m; d is the injection well spacing and the unit m; r is the optimal ratio between the half length of the fracture and the injection and production well spacing.
Further, the geological parameters of the oil layer in the third step comprise reservoir physical properties, oiliness and lithology.
Further, the calculation formula of the total consumption of the medium-pressure flooding agent in the fourth step is as follows:
Q＝π×r 2 ×H×φ×C
wherein Q is the total consumption of the pressure driving agent, and the unit is m 3 The method comprises the steps of carrying out a first treatment on the surface of the r is the transformation radius, and the unit is m; h is the thickness of sandstone, and the unit is m; phi is the porosity in units; c is the pore fullness in%.
Further, the injection mode of the pressure driving agent in the fifth step is divided into two modes of continuous injection of the pressure driving agent after fracture fracturing and intermittent injection of the pressure driving agent in a slug type after fracture fracturing.
Further, the step seven medium-pressure driving construction includes: forward and reverse pressure drives;
the forward pressure driving is to perform pressure driving construction on the injection well; and the reverse pressure driving is to perform pressure driving construction on the production well.
The invention has the technical effects that:
the invention provides a novel method for improving recovery ratio by combining fracturing, seepage and oil displacement into a whole by means of a hydraulic fracturing means, which directly pumps a large amount of flooding agent (namely fracturing fluid, wherein guanidine gum is not added, sand is not added, follow-up is not supported, the flooding agent is not only used as a pre-fluid, but also does not pass through a flowback stage of the fracturing fluid) to deep parts of upper and lower reservoirs along a fracture path, the 'crack extension' of the traditional hydraulic fracturing is changed into 'crack extension slow', the crack extension is characterized by 'crack edge seepage', the crack formation process is 'slow extension', long cracks are formed, the early breakthrough of the front edge of an aqueous phase caused by rapid extension of the cracks is inhibited, the expansion of effective swept volume is realized, meanwhile, the 'constant speed injection' is changed into 'high pressure injection', the loss of the flooding agent along the way is reduced, the energy is rapidly supplemented, the contact area of the flooding agent and the stratum is greatly increased, scattered residual oil is driven to be enriched, and finally the purpose of improving the recovery ratio is achieved.
Drawings
The accompanying drawings illustrate various embodiments by way of example in general and not by way of limitation, and together with the description and claims serve to explain the inventive embodiments. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. Such embodiments are illustrative and not intended to be exhaustive or exclusive of the present apparatus or method.
FIG. 1 is a schematic illustration of the technical principle of two construction modes of the invention;
FIG. 2 is a schematic view of a core according to a first embodiment of the present invention;
fig. 3 is a schematic flow chart of a press-driving experimental device in the first embodiment of the invention.
Detailed Description
It should be noted that, in the case of no conflict, the embodiments and features in the embodiments may be combined with each other. The present application will be described in detail below with reference to the accompanying drawings in conjunction with embodiments.
The invention is further illustrated by the following examples.
Example 1
And (3) performing comparison evaluation on the effects of the conventional fracturing process and the pressure flooding process by adopting a physical simulation method to bond the artificial homogeneous rock core with the quartz sand epoxy resin.
1. Experimental materials
Pressure driving agent: petroleum sulfonate (mass fraction is 0.3%), oil-water interfacial tension is 0.34mN/m.
The experimental water is reinjection water of a development area in Daqing oilfield sa, and the mineralization degree is 3681mg/L; the experimental oil is simulated oil, which is prepared by mixing degassed and dehydrated crude oil extracted from a low-permeability reservoir in a development area in Daqing oilfield Sasa with kerosene, and has a viscosity of 9.75 mPa.s (45 ℃).
The experimental core is an artificial homogeneous core glued by quartz sand epoxy resin, and the appearance geometrical dimension of the core is as follows: parallel connection of length, width and height=30.0 cm, 30.0cm, 4.5cm, and core permeability of 100×10 -3 μm 2 The method comprises the steps of carrying out a first treatment on the surface of the In the experiment, according to construction parameters of a pressure-driven mining field (the length of a crack is one third of the well spacing), the crack is prefabricated along the diagonal line of the injection and production direction through a water-soluble film, the crack is close to the production end and is perpendicular to the overlook plane of an experimental device diagram, and the length of the crack is 14cm, and the structural schematic diagram is shown in fig. 2.
2. Instrument and equipment
The main equipment is a high-temperature and high-pressure resistant rock core flow experimental device, and the equipment is matched with a double-cylinder constant-speed constant-pressure pump, a piston container, a pressure sensor, a rock core holder and a constant-temperature box; the auxiliary equipment comprises a vacuum pump, a timer, a stirrer, a metering test tube and the like, and the equipment and the flow diagram are shown in fig. 3.
3. Experimental method
1) Installing a valve at a core sampling point and a pressure measuring point and checking the air tightness of the core;
2) Connecting an electrode on the rock core to a saturation tester, and checking circuit stability;
3) Vacuumizing the rock core and saturating water, and calculating the pore volume and the porosity;
4) Injecting simulated oil from the center of the flat rock core at a pumping speed of 0.5mL/min until the four-side extraction end is anhydrous to produce, and completing the saturated oil process; standing the core for 24 hours at the experimental temperature, and calculating the oil saturation;
5) The water drive is stopped when the water content of the produced liquid is 98% at the pumping speed of 1 mL/min;
6) Forward pressure driving: closing the production end, injecting a 0.1-time pore volume displacement agent under the condition of 1MPa pressure difference, then soaking the well for 24 hours, and recovering the conventional water flooding at the injection end after the well soaking is completed until the water content of the produced liquid is 98%;
reverse pressure driving: closing an injection end, connecting an injection pump with a production end, injecting a 0.1-time pore volume displacement agent under the condition of 1MPa pressure difference, then stewing the well for 24 hours, and recovering the conventional water drive by the injection end after the well is stewed, until the water content of the produced liquid is 98%;
7) After the experiment is finished, the water content and the recovery ratio of each stage are calculated
4. Experimental results
The results of the physical simulation experiments of the different displacement schemes are shown in table 1.
Table 1: physical simulation experiment results
As can be seen from table 1, the oil increasing effect of the method is better than that of the conventional fracturing process, both in the forward pressure driving process and the reverse pressure driving process; the reason that the oil increasing effect of the forward pressure driving process and the reverse pressure driving process is different is that the experimental materials and experimental parameters of the experiment are all derived from Daqing oil fields, and the proper pressure driving processes are different due to different geological conditions, well pattern control degree, residual oil distribution characteristics and the like of different oil fields.
Example two
The embodiment provides an application of a pressure flooding method for improving recovery ratio of a low permeability reservoir in an ultra-high water content old oil field in Daqing chlamydia oil field, wherein an X1-1 well is a basic well positioned in Daqing chlamydia apricot tree sentry oil field, the well is put into production in 1996, the well is injected with sandstone 14.7m, effectively 4.4m, single-side water injection is conducted through 3 water wells before the novel pressure flooding technology provided by the invention is applied, daily production liquid of the well is 8.4t, daily production oil is 1.2t, and water content is 86.0%. The well is positioned at the side of the fault and is 153m away from the fault, the overall water drive control degree is low, the well cementation quality is good, no sleeve damage is caused, and the well selection condition of the pressure drive is met. The positive pressure driving process of the X1-1 well in application comprises the following steps:
step one, in order to reduce reserve loss, dividing 11 small layers of a whole well into 5 layer sections according to the extraction degree of an oil layer, physical properties and interlayer conditions according to the research result of fine geological data of an oil extraction factory;
step two, in order to enable the crack to effectively communicate the residual oil enrichment part, combining well pattern and well distance conditions, and passing through a crack half-length formula L f ＝dr(L f Is half-length of the split seam, and the unit is m; d is the injection well spacing and the unit m; r is the optimal ratio between the half length of the crack and the injection well spacing), the optimal half length of the crack is calculated, and the optimal ratio between the half length of the crack and the injection well spacing is preferably 1/3, namely the half length L of the crack f =d/3, the well spacing is 200-220m, thus, the optimal fracture half length is determined to be 65-70m;
step three, a relation chart of the construction displacement of the fracturing fluid and the friction of the system is established, and the construction displacement of the pressure flooding agent is determined to be 4-4.5m by combining a fracture reservoir filter stall degree calculation formula 3 /min；
Step four, building construction scale optimization plates with different pore filling coefficients according to pore permeation conditions, stratum thickness, void filling degree and residual oil distribution conditions, and determining the consumption of the pressure flooding agent to 10000-11000m by comprehensively considering factors such as reservoir reconstruction range, sand control area, effective porosity, void filling degree and the like 3 ；
Step five, in order to ensure that more fracturing agent is percolated into the stratum under the condition of controllable fracture extension, the well adopts an intermittent injection mode, namely three slugging injection is adopted, the first slug is designed to extend to 30m in fracture, the second slug injection is carried out after the pump is stopped for full fluid loss, the design is restarted to extend to 50m, the third slug injection is carried out after the pump is stopped for full fluid loss, and the fracture is designed to be re-extended to 70m;
step six, in order to make the pressure flooding agent fully contact with the crude oil of the stratum, determining the optimal well-soaking time to be 32d through a numerical simulation method;
and step seven, after the well is closed, carrying out subsequent well opening production, and monitoring the production dynamics of the oil well, wherein the result shows that the accumulated oil increase of the well is 2435t, the accumulated oil increase of surrounding oil wells is 670t, and the recovery ratio is improved by 8.6 percent.
Example III
The example provides an application of a pressure flooding method for improving recovery ratio of a low permeability reservoir in an ultra-high water content old oil field in Daqing chlamydia oil field, wherein an X1-2 well is a secondary encryption well positioned in Daqing chlamydia apricot tree sentry oil field, the well is put into production in 2007, the well is shot to open sandstone 19.9m, effective 5.4m and accumulated water injection of the well is 1.8x10 before the implementation of a reverse pressure flooding process before the application of the novel pressure flooding technology improving recovery ratio method 4 m 3 Mainly communicates with 5 oil wells, and has average daily oil yield of 6.5t, daily oil yield of 1.2t and water content of 81.5%. The well is positioned at the side of the fault and is 168m away from the fault, the overall water drive control degree is low, the well cementation quality is good, no sleeve damage is caused, and the well selection condition of the pressure drive is met. The reverse pressure driving process of the X1-2 well in application comprises the following steps:
step one, dividing 14 small layers of a whole well into 5 layer sections according to the extraction degree of an oil layer, physical properties and interlayer conditions according to the research result of fine geological data of an oil extraction factory in order to reduce reserve loss;
step two, in order to enable the crack to effectively communicate the residual oil enrichment part, combining well pattern and well distance conditions, and passing through a crack half-length formula L f ＝dr(L f Is half-length of the split seam, and the unit is m; d is the injection well spacing and the unit m; r is the optimal ratio between the half length of the crack and the injection well spacing), the optimal half length of the crack is calculated, and the optimal ratio between the half length of the crack and the injection well spacing is preferably 1/3, namely the half length L of the crack f =d/3, the well spacing is 200-220m, thus, the optimal fracture half length is determined to be 65-70m;
step three, a relation chart of the construction displacement of the fracturing fluid and the friction of the system is established, and the construction displacement of the pressure flooding agent is determined to be 4-4.5m by combining a fracture reservoir filter stall degree calculation formula 3 /min；
Step four, building construction scale optimization plates with different pore filling coefficients according to pore permeation conditions, stratum thickness, void filling degree and residual oil distribution conditions, and determining the consumption of the pressure flooding agent to 10000-11000m by comprehensively considering factors such as reservoir reconstruction range, sand control area, effective porosity, void filling degree and the like 3 ；
Step five, in order to ensure that more fracturing agent is percolated into the stratum under the condition of controllable fracture extension, the well adopts an intermittent injection mode, namely three slugging injection is adopted, the first slug is designed to extend to 30m in fracture, the second slug injection is carried out after the pump is stopped for full fluid loss, the design is restarted to extend to 50m, the third slug injection is carried out after the pump is stopped for full fluid loss, and the fracture is designed to be re-extended to 70m;
step six, in order to make the pressure flooding agent fully contact with the crude oil of the stratum, determining the optimal well-soaking time to be 36d through a numerical simulation method;
and step seven, after the well is closed, carrying out subsequent well opening production, and monitoring the production dynamics of the oil well, wherein the result shows that the accumulated oil increase of the well is 3366t, the accumulated oil increase of surrounding oil wells is 960t, and the recovery ratio is improved by 10.2 percent.
The foregoing is only a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art, who is within the scope of the present invention, should make equivalent substitutions or modifications according to the technical solution of the present invention and the inventive concept thereof, and should be covered by the scope of the present invention.
Claims (7)
1. A novel method for enhanced oil recovery from pressure flooding of medium and low permeability reservoirs, the method comprising:
step one, re-dividing the reservoir according to the research result of fine geological data of oil extraction plants and the longitudinal small layer distribution and interlayer evaluation result;
step two, optimizing crack parameters by combining well pattern well spacing conditions; wherein the fracture parameters include fracture half length;
thirdly, establishing a relation chart of the displacement of the pressure-driven construction and the friction of the system, and a relation chart of the displacement of the pressure-driven construction and the crack parameters, and determining the displacement of the pressure-driven construction by combining the geological parameters of the oil layer;
step four, building construction scale optimization plates with different pore filling coefficients according to the stratum thickness, the porosity, the permeability, the pore filling degree and the residual oil distribution condition, and comprehensively considering the reservoir transformation range, the sand control area and the effective porosity to determine the total consumption of the pressure flooding agent;
step five, selecting a pressure flooding agent injection mode;
step six, determining the optimal well-stewing time by a numerical simulation method;
step seven, aiming at the layer section re-divided in the step one, performing pressure driving construction on the target well according to the pressure driving agent injection mode selected in the step five by using the total consumption and the construction displacement of the pressure driving agent determined in the step three and the step four, wherein the joint making length is the optimal joint length calculated in the step two; closing the well after the pressure driving construction is completed, performing well logging according to the optimal well logging time determined in the step six, performing subsequent well logging production after well logging is completed, and monitoring the production dynamics of the oil well.
2. The novel method for enhanced recovery of pressure flooding of low-medium permeability reservoirs according to claim 1, wherein the pressure flooding agent is free of guanidine gum, sand and subsequent support, and is not used as a pre-fluid nor subjected to a fracturing fluid flowback stage of conventional fracturing technology.
3. The novel method for enhanced recovery of pressure flooding of a medium-low permeability reservoir according to claim 1, wherein the calculation formula of the fracture half-length is:
L f ＝d×r
wherein L is f Is half-length of the split seam, and the unit is m; d is the injection well spacing and the unit m; r is the optimal ratio between the half length of the fracture and the injection and production well spacing.
4. The novel method for enhanced oil recovery from pressure flooding of low-medium permeability reservoirs of claim 1, wherein the geological parameters of the oil layer in step three comprise reservoir physical properties, oil content, lithology.
5. The novel method for enhanced oil recovery of a low-medium permeability reservoir according to claim 1, wherein the total amount of the flooding agent in the fourth step is calculated by the formula:
Q＝π×r 2 ×H×φ×C
wherein Q is the total consumption of the pressure driving agent, and the unit is m 3 The method comprises the steps of carrying out a first treatment on the surface of the r is the transformation radius, and the unit is m; h is the thickness of sandstone, and the unit is m; phi is the porosity in units; c is the pore fullness in%.
6. The novel method for enhancing recovery ratio of pressure flooding of low-medium permeability reservoir according to claim 1, wherein the injection mode of the pressure flooding agent in the fifth step is divided into two modes of continuous injection of the pressure flooding agent after fracture fracturing and intermittent injection of the pressure flooding agent in a slug type after fracture fracturing.
7. The new method for enhanced oil recovery for pressure flooding of low-medium permeability reservoirs according to claim 1, wherein the step seven of pressure flooding construction comprises: forward and reverse pressure drives;
the forward pressure driving is to perform pressure driving construction on the injection well; and the reverse pressure driving is to perform pressure driving construction on the production well.
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