CN110318721B - Method for improving recovery ratio by foam flooding auxiliary nitrogen huff and puff of fault block oil reservoir - Google Patents
Method for improving recovery ratio by foam flooding auxiliary nitrogen huff and puff of fault block oil reservoir Download PDFInfo
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- CN110318721B CN110318721B CN201910752295.0A CN201910752295A CN110318721B CN 110318721 B CN110318721 B CN 110318721B CN 201910752295 A CN201910752295 A CN 201910752295A CN 110318721 B CN110318721 B CN 110318721B
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Abstract
A method for improving recovery ratio of a fault block oil reservoir by foam flooding auxiliary nitrogen huff and puff comprises the following steps: selecting an oil reservoir to be developed; injection well preformed foam injection; injecting nitrogen into the production well; carrying out gravity differentiation on the well-stewing oil gas; and (5) opening the production well for production. According to the invention, by utilizing the properties of large blocking, small blocking and water and oil blocking of foam, namely the properties of tendency of blocking large pore canals with higher permeability and pore canals with higher oil saturation in the stratum under common conditions, the swept volume of the foam near an injection well is enlarged, and the problem of less movable oil at the later stage of the huffing and puff of a production well is relieved to a certain extent; the invention can strengthen the vertical fluctuation of the production well when injecting nitrogen into the production well, is beneficial to expanding the longitudinal action radius of the nitrogen huff and puff, and effectively relieves the problem of difficult effect of foam flooding near the production well due to the effect of the huff and puff. The foam flooding assistance can improve the effective action period of nitrogen huff and puff, enhance the extraction degree of nitrogen huff and puff and further improve the development effect of the fault block oil reservoir.
Description
Technical Field
The invention relates to a method for improving recovery efficiency by foam flooding auxiliary nitrogen huff and puff of a fault block oil reservoir, belonging to the technical field of oil and gas field development engineering.
Background
The fault block oil reservoir refers to oil gas accumulation in traps formed by fault shielding effect, the fault blocks are often divided and not communicated with each other, the oil containing area and the reserve volume of a single fault block oil reservoir are low, and a complex injection and production well pattern cannot be established. Only one injection well and one production well are arranged in a part of fault block oil reservoirs, the development mode of 'one injection and one production' is adopted, and the characteristic of low extraction degree is shown; the edge and bottom water of part of fault block oil reservoirs grows, the water drive control degree is low, and the water content of produced liquid is high; and a stratum dip angle exists in part of the fault block oil reservoir, and residual oil is distributed at a high-structure part after water flooding is finished to form attic oil which is difficult to exploit. Aiming at the problems, research on an effective development mode of the fault block oil reservoir needs to be developed, and the recovery ratio of the fault block oil reservoir with a simple injection and production mode and complex reservoir conditions is improved.
Chinese patent CN105952425B A method for improving the recovery efficiency of a common heavy oil reservoir by throughput of CO2 assisted by a chemical agent relates to a method for improving the recovery efficiency of a common heavy oil reservoir by throughput of CO2 assisted by a chemical agent, the method combines the chemical agent with CO2 throughput, firstly injects a slug of a solution of a chemical agent of a viscosity reducing agent or a chemical agent of a foaming agent into an oil well which is subjected to throughput of an excessive period CO2, then injects a slug of high-pressure CO2 into the well, and carries out soaking after the injection is finished. During well stewing, the viscosity reducer chemical agent and common thickened oil form an oil-in-water emulsion, so that the oil-water interfacial tension can be greatly reduced, and the flow resistance of crude oil during exploitation is reduced. The addition of the foaming agent chemical agent can control the gas phase fluidity of CO2, effectively prevent CO2 from gas channeling, enable CO2 to diffuse deep in the stratum and increase the swept volume of CO2 gas. The synergistic effect of the chemicals and CO2 allows the well to maintain high oil recovery after multi-cycle throughput.
Although the above patent document can be applied to the fault block oil reservoir, the problem that the gas source is difficult to obtain exists in the application because the CO2 huff and puff is adopted, and the nitrogen preparation means used in the nitrogen huff and puff in the patent is mature, so that the cost is lower than that of CO2, and the application to the field is facilitated; on the other hand, the production mode of the invention only has throughput, although chemical agents are added for assistance, only one well is used in the production process, the oil using range is smaller, the invention is only suitable for the fault block oil reservoir with smaller oil containing area, and in the fault block oil reservoir with larger oil containing area, a one-injection one-extraction displacement system can be normally established, and at the moment, the advantages of the invention are shown, and the specific advantages are as described in the text.
Moreover, the above patent document does not adopt a one-injection-one-production-displacement mode in the working principle, and the huff-puff production mode related to the patent document is that only one well is used for injecting gas with a certain volume through the well, closing the well for a period of time and then opening the well for production; in the method, an injection-extraction displacement mode is adopted, two wells are used, one injection well is used for injection, and one production well is used for production. Both have fundamental differences in production patterns.
At present, relevant research on injection and production parameter optimization and equipment matching is carried out aiming at a foam flooding technology, but the finding effect is not ideal when the fault block oil reservoir is applied on site, and the following problems mainly exist:
(1) the foam has good generation condition on the ground, but under the harsh oil reservoir condition, the foam stability is poor, the half-life period is greatly reduced, and the continuous existence time of the foam is short.
(2) In the process of flowing of the foam under the condition of the stratum porous medium, the foam cannot enter the deep part of the stratum due to the shearing action, and the foam action distance is short.
(3) The foam has good performance in a near injection well zone, the surfactant in the foam liquid is gradually adsorbed by a stratum in the displacement process, the concentration of the surfactant is reduced after the foam is transported for a long distance, and the broken foam cannot be regenerated.
Aiming at the characteristics of the fault block oil reservoir, a method for developing by utilizing gas huff and puff is provided by a scholarly, and the commonly used method is nitrogen huff and puff or carbon dioxide huff and puff. Taking nitrogen gas throughput as an example, nitrogen gas is injected into one well of the closed fault block oil reservoir, so that the formation energy can be effectively supplemented, the nitrogen gas throughput can be realized without a perfect well pattern, and the problems that the water injection is difficult, an effective pressure system is difficult to establish and the like are solved. The problems existing when the nitrogen huff and puff is applied to the fault block oil reservoir at present mainly include the following points:
(1) with the increase of the throughput period, the nitrogen easily forms a larger continuous channel in the stratum, the gas channeling phenomenon is serious in the exploitation process, and the nitrogen cannot form effective residence in the stratum.
(2) Along with the progress of the handling, the movable oil quantity in the effective handling range is less and less, the periodic extraction degree is lower and lower, and the handling effect is not ideal any more.
(3) In the latter stage of huffing and puff, the ground pressure is greatly reduced along with the increase of the liquid volume, the formation energy is lacked, and the formation energy cannot be effectively supplemented only by a nitrogen injection energizing mode.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a method for improving the recovery ratio of a fault block oil reservoir by foam flooding auxiliary nitrogen huff and puff.
Summary of the invention:
a method for improving recovery efficiency of a fault block oil reservoir by assisting nitrogen huff and puff is characterized in that foam flooding and nitrogen huff and puff are organically combined aiming at the problems that the action distance of the foam flooding in the reservoir is short and the energy of a stratum is quickly attenuated in the later stage of the nitrogen huff and puff:
the nitrogen huff and puff at the production well end plays a role of 'priming effect', crude oil in the effective range of the production well is used, and the defect that a single foam flooding can not reach a far well zone is overcome;
the foam flooding performed at the injection well end drives crude oil at the injection well end to the production well end, and can plug the stratum, so that the gas channeling phenomenon at the later stage of nitrogen huff and puff is effectively prevented, and the stratum energy is supplemented.
The technical scheme of the invention is as follows:
a method for improving recovery efficiency of a fault block oil reservoir by foam flooding assisted nitrogen huff and puff is characterized by comprising the following steps:
(1) selecting an oil reservoir to be developed:
according to the geological characteristics and the current development situation of the oil reservoir, roughly screening the applicable oil reservoir according to the following conditions, and at least meeting the following conditions:
the oil reservoir is a closed fault block oil reservoir;
the single-layer thickness of the fault block oil reservoir is more than or equal to 10 m;
the net total thickness ratio is greater than 0.5;
oil containing area is more than 0.3km2；
The horizontal permeability is more than 1000mD, and the ratio of the vertical permeability to the horizontal permeability is more than 0.5;
the temperature of the oil layer is 30-100 ℃;
the inclination angle of the stratum is more than 10 degrees;
(2) injection well preformed foam injection: foaming on the ground, injecting a foam slug with a certain volume into the stratum through an injection well shaft, wherein the gas-liquid volume ratio of foam under the injected oil reservoir condition is 1: 1-3: 1, the foam is injected through the injection well, so that the stratum energy can be supplemented, the swept volume can be enlarged, part of crude oil is pushed to the production well direction, movable oil is provided for the follow-up nitrogen huff and puff, and the injection well is closed after the injection is finished;
(3) nitrogen injection of a production well: closing the injection well, injecting nitrogen into the stratum through a production well shaft at a constant speed, stopping the nitrogen injection when the oil reservoir pressure is increased to 0.8-1.2 times of the original oil reservoir pressure, increasing the injection resistance of the nitrogen in the horizontal direction due to the foam plugging effect at the end of the injection well, facilitating the vertical direction swept of the nitrogen, and reducing the injection amount of the nitrogen due to the fact that the injected foam supplements the stratum energy;
(4) gravity differentiation of the well soaking oil gas: after nitrogen is injected into a stratum, a production well is closed for stewing, foam at the end of the injection well is helpful for blocking a channeling channel and supplementing stratum energy, density difference exists between gas and crude oil after the foam is broken, the gas can float up and replace residual oil at the high part of the structure, the nitrogen at the end of the production well can be diffused in the vertical direction, and the residual oil at the high part of the structure can be replaced as well;
(5) and (3) well opening production of a production well: and after the well soaking is finished, opening the production well for production, and finishing the production after serious gas channeling occurs. In the recovery stage, oil gas production provides power, and the foaming agent solution after foam is broken and nitrogen in the recovery stage can be in a nitrogen foam state again under the condition of full contact, so that a high-permeability channel with less oil is blocked, and crude oil in a low-permeability channel is recovered.
According to the invention, preferably, after the foam flooding auxiliary nitrogen gas throughput of one period is finished, the steps (2) to (5) are repeated to perform foam flooding auxiliary nitrogen gas throughput of a plurality of periods.
Preferably, according to the invention, the number of cycles is 5. And the oil recovery of the production well after the multi-period foam flooding auxiliary nitrogen huff and puff is improved.
Preferably, the condition for roughly screening the suitable oil reservoirs in the step (1) further comprises: the buried depth is 1000 m-3000 m.
Preferably, the condition for roughly screening the suitable oil reservoirs in the step (1) further comprises: the oil saturation is more than 40 percent.
Preferably, the condition for roughly screening the suitable oil reservoirs in the step (1) further comprises: the porosity of the reservoir is 20-40%.
According to the invention, the volume of the foam slug injected in the step (2) is 0.05-0.2 PV, and the preferred volume of the foam slug is 0.1 PV. The preformed foam injection in the step (2) has the advantages that the quality and the strength of the injected foam are convenient to regulate and control, and the foam slug is injected from the injection well through ground pressurization equipment. Wherein the foam is nitrogen foam, the gas is nitrogen with the purity of more than 90 percent, and the mass concentration of the foaming agent is 0.5 percent. The volume of the injected foam slug is 0.05-0.2 PV, the preferred volume of the foam slug is 0.1PV, namely the volume of the pores of the reservoir is 0.1 time, and the gas-liquid volume ratio of the foam under the preferred oil reservoir condition is 2: 1.
It should be noted that: the switching state of the production well in the foam injection process in the step (2) is determined according to the reservoir pressure, and if the reservoir pressure is sufficient, the production well can be opened for production; and if the pressure of the weak oil reservoir is lower, the production well is kept closed, so that foam can be injected to supplement the formation energy.
Preferably, in step (3), the constant speed is in the range of 2000-10000 m3D, the preferred injection speed is 4000m3/d。
According to the invention, in the step (4), the soaking time is preferably 20-40 d, and the soaking time is preferably 30 d.
According to the invention, it is preferable that the gas-oil ratio in the step (5) is more than 1000m when the production gas-oil ratio is larger than3At/t, severe gas breakthrough was considered.
The technical advantages of the invention are as follows:
the oil-containing area of the selected fault block oil reservoir is large, and the movable oil area is small in the gas injection huff-puff production mode of a single well, so that the production requirement cannot be met. According to the invention, foam flooding is carried out in the injection well, and the properties of large blocking, small blocking and water and oil blocking of foam, namely the properties of tendency of blocking large pore canals with higher permeability and pore canals with higher oil saturation in the stratum under general conditions of foam are utilized, so that the swept volume of the foam near the injection well is enlarged, and meanwhile, part of crude oil is pushed to the direction of the production well, and the problem of less movable oil in the later period of production well huff and puff is relieved to a certain extent; in the nitrogen huff-and-puff process, due to the plugging effect of the foam segment plug at the end of the injection well, the vertical sweep of the production well can be strengthened when the nitrogen is injected into the production well, the longitudinal action radius of the nitrogen huff-and-puff is favorably enlarged, and meanwhile, the 'effect inducing' effect (the foam liquid is favorably induced to the direction of the production well in the blowout stage of the huff-and-puff process) effectively relieves the problem that the foam flooding is difficult to take effect near the production well; after multi-cycle huff and puff, due to the existence of foam flooding of an injection well, the formation energy is supplemented in time, and the formation of a channeling channel is reduced; the foam flooding assists in nitrogen gas throughput, flow fields in reservoirs are continuously changed due to different power directions, and a plurality of 'dead-end immobile oil zones' under a single displacement mode are effectively used.
In conclusion, the method can improve the effective action period of the nitrogen huff and puff, and the foam flooding is used for assisting to enhance the extraction degree of the nitrogen huff and puff, so that the development effect of the fault block oil reservoir is further improved.
Drawings
FIG. 1 is a schematic diagram of foam flooding assisted nitrogen huff and puff enhanced oil recovery for a fault block reservoir in accordance with the present invention;
FIG. 2 is a flow chart of the invention for foam flooding assisted nitrogen huff and puff enhanced oil recovery;
FIG. 3 is a graph comparing the foam flooding auxiliary nitrogen huff and puff with the nitrogen huff and puff multi-cycle extraction degree of a fault block reservoir;
FIG. 4 is a schematic diagram of the foam flooding auxiliary nitrogen huff and puff expansion longitudinal sweep of a fault block reservoir;
FIG. 5 is a schematic diagram of "dead-end" crude oil production during foam flooding assisted nitrogen stimulation of a fault block reservoir.
Detailed Description
The invention is described in detail below with reference to the following examples and the accompanying drawings of the specification, but is not limited thereto.
Examples of the following,
As shown in fig. 1, the principle is explained as follows:
the specific technical content of the method and the embodiment of the present invention can be known as follows:
injecting a foam slug into the injection well, adjusting a displacement profile, pushing crude oil near the injection well to the direction of the production well in a piston manner, wherein the foam displacement has poor action effect at the deep part of the stratum far away from the injection well along with the increase of the foam migration time and migration distance, but the effect of assisting the follow-up nitrogen gas huff and puff still exists, which is expressed as supplementing the stratum energy and adjusting the underground flow field; the subsequent nitrogen huffing and puff causes that crude oil cannot be used for production originally outside the action radius (near the injection well), in the recovery process, the nitrogen is fully contacted with foaming liquid, the open flow of the production well provides power conditions, and the generated foam is also beneficial to improving the yield increasing effect of the nitrogen huffing and puff.
A method for improving recovery ratio of a fault block oil reservoir by foam flooding auxiliary nitrogen huff and puff comprises the following steps:
(1) selecting an oil reservoir to be developed:
according to the geological characteristics and the current development situation of the oil reservoir, roughly screening the applicable oil reservoir according to the following conditions, and at least meeting the following conditions:
the oil reservoir is a closed fault block oil reservoir;
the single-layer thickness of the fault block oil reservoir is more than or equal to 10 m; in this embodiment, the oil layer has a thickness of 20 m;
the net total thickness ratio is greater than 0.5; in this example, the net to total thickness ratio is 0.74;
oil containing area is more than 0.3km2(ii) a In this example, the oil-containing area was 0.34km2；
The horizontal permeability is more than 1000mD, and the ratio of the vertical permeability to the horizontal permeability is more than 0.5; in this embodiment, the horizontal permeability is 1360 mD;
the temperature of the oil layer is 30-100 ℃; in this example, the oil layer temperature was 70 ℃;
the inclination angle of the stratum is more than 10 degrees; in this embodiment, the formation dip angle is 13 °;
the buried depth is 1000 m-3000 m; in this embodiment, the buried depth is 1560 m;
the oil saturation is more than 40 percent; in this example, the oil saturation is 62%;
the porosity of the reservoir is 20-40%; in this example, the average porosity was 36.5%;
(2) injection well preformed foam injection: foaming on the ground, injecting a foam slug with a certain volume into the stratum through an injection well shaft, wherein the gas-liquid volume ratio of foam under the injected oil reservoir condition is 1: 1-3: 1, the foam is injected through the injection well, so that the stratum energy can be supplemented, the swept volume can be enlarged, part of crude oil is pushed to the production well direction, movable oil is provided for the follow-up nitrogen huff and puff, and the injection well is closed after the injection is finished;
the volume of the foam slug injected in the step (2) is 0.05-0.2 PV, in the embodiment, the used gas is nitrogen with the purity of 99.9%, the foaming agent is an HY-2 type foaming agent with the mass concentration of 0.5%, the foam slug with 0.1PV is injected into the stratum through an injection well shaft, the gas-liquid volume ratio of the foam under the injected oil deposit condition is 2:1, and the production well keeps a closed state in the process;
(3) nitrogen injection of a production well: closing an injection well, injecting nitrogen into the stratum through a production well shaft at a constant speed, and stopping nitrogen injection when the oil reservoir pressure is increased to 0.8-1.2 times of the original oil reservoir pressure; in this example, nitrogen gas is supplied at 4000m3The nitrogen injection speed is increased to 1.2 times of the original oil reservoir pressure, and the nitrogen injection speed is stopped;
(4) gravity differentiation of the well soaking oil gas: after nitrogen is injected into the stratum, closing a production well for soaking, wherein according to the optimization of the method, in the step (4), the soaking time is 20-40 d, in the embodiment, the soaking time is 30 d;
(5) and (3) well opening production of a production well: after the well soaking is finished, opening the production well for production, and finishing the production after serious gas channeling occurs; when the produced gas-oil ratio is more than 1000m3At/t, severe gas breakthrough was considered.
And (5) repeating the steps (2) to (5) after the foam flooding auxiliary nitrogen throughout one period is finished, and performing foam flooding auxiliary nitrogen throughout multiple periods. The number of the periods is 5.
In this example, the block was tested for 4 wells using a foam flooding assisted nitrogen throughput production mode, with the effective rate of 4 well measures being 100%. Before the measures, only a nitrogen throughput mode of a production well is adopted, namely steps (1), (3), (4) and (5) are adopted in each period, the average daily oil production is 1.4t/d, and the effect is poor after three periods of production; after the measures, the daily oil yield of the initial stage is 2.3t/d, the daily oil yield of the peak value is 5.9t/d, the periodic oil yield is obviously increased, the effect is still better after three periods of production, and the ultimate recovery ratio is increased by 5.77%.
Examples of experiments,
By combining the technical scheme of the invention, a laboratory experiment is carried out, the process is shown in figure 2, the experiment is carried out at a constant temperature, and the actual oil reservoir environment is simulated.
In laboratory experiments, simulation explanation is performed on oil layer thickness, oil-containing area and oil reservoir burial depth:
in laboratory conditions, experimental parameters are established based on a physical simulation experiment similarity criterion and according to three methods of a traditional similarity criterion, a similarity criterion based on experimental time and a similarity criterion based on PV number, and by combining experience of a one-dimensional physical simulation experiment.
After scaling the oil layer thickness and the oil-containing area, i.e. the oil-containing volume in the corresponding experimental conditions, in combination with the similarity criteria and experimental experience, appropriate experimental parameters are formulated, such as the injection rates of nitrogen and the blowing agent in step (2), and the injection rates are adjusted under the condition that the gas-liquid ratio in the technical scheme is ensured to be 2:1 (although the technical scheme does not mention specific injection rates), so that the experimental conditions can be satisfied as well.
The oil deposit burial depth mainly determines proper temperature and pressure conditions, the pressure does not make excessive requirements in the technical scheme, the temperature requirement is clear, and therefore experiment parameters only need to ensure proper temperature.
In the experimental example, the filled core tube is utilized to meet the requirements of simulating the fault block oil reservoir, namely the horizontal permeability is more than 1000mD, and the ratio of the vertical permeability to the horizontal permeability is more than 0.5; in this experimental example, the horizontal permeability is 1700 mD;
the temperature of the oil layer is 30-100 ℃; in this experimental example, the oil layer temperature was 70 ℃;
the inclination angle of the stratum is more than 10 degrees; in this experimental example, the formation dip angle is 15 °;
the oil saturation is more than 40 percent; in this experimental example, the oil saturation was 88%;
the porosity of the reservoir is 20-40%; in this experimental example, the average porosity was 25.2%;
in fig. 2, the experimental apparatus included is mainly: the device comprises a plunger pump for providing displacement power, an intermediate container for containing HY-2 foaming agent and nitrogen, a gas flowmeter for controlling the injection speed of nitrogen, an external foam generator, a manually filled core barrel (the inclination of the core barrel is adjustable), a nitrogen cylinder (the purity of the nitrogen cylinder is 99.9%), a back pressure valve for controlling the output pressure, a hand pump for providing back pressure, a measuring cylinder for collecting the output liquid, a pressure gauge P1 (for monitoring the injection pressure), a pressure gauge P2 (for monitoring the outlet pressure), and a pressure gauge P3 (for monitoring the back pressure).
The method specifically comprises the following steps:
(1) simulating a fault block oil reservoir: filling a core tube with certain permeability by using quartz sand, weighing dry weight, vacuumizing, using 250mL of saturated water, weighing wet weight, calculating the porosity to be 25.2%, determining the water-phase permeability of the core to be 1700mD, using 220mL of saturated oil and 88% of oil saturation, adjusting the core to 70 ℃ and 5MPa of pressure, setting the back pressure to be 3.5MPa, setting the inclination angle of the core tube to be 15 degrees, and simulating a fault block oil reservoir based on the result;
(2) injection well preformed foam injection: controlling the nitrogen injection speed to be 1mL/min by a gas flowmeter, controlling the HY-2 type foaming agent injection speed to be 0.5mL/min by a plunger pump, simultaneously injecting nitrogen and the foaming agent into a foam generator to generate nitrogen foam, communicating the foam generator with an injection well, performing nitrogen foam displacement, producing crude oil at a production well, recording the oil production at a production end, and finishing the process after injecting the foam into 0.1 PV;
(3) nitrogen injection of a production well: closing an injection well, injecting nitrogen into the core tube through the production well at the speed of 1mL/min, and stopping nitrogen injection when the pressure of the core tube is increased to 6 MPa;
(4) gravity differentiation of the well soaking oil gas: after nitrogen is injected into the core tube, closing the production well for stewing for 3h, wherein the stewing time is based on a similar criterion, is simultaneously established by combining the experience of a one-dimensional physical simulation experiment, and the number of the adopted similar criteria is
(wherein λ)o: oil phase fluidity (m/s), t: time(s),
porosity (%), ρoCrude oil Density (g/cm)3),CoCrude oil compressibility, L: length (m)), derived by the similarity criterion, then:
wherein subscript M is a model parameter and subscript P is an actual parameter, for example: the actual thickness of the oil extraction layer is 10m, and the length of the core tube is 0.6m, then
The actual soaking time of the oil reservoir is 30d, then tP30d, and
therefore tMCombining the indoor soaking experiment experience, rounding the soaking time upwards, namely 3 h;
(5) and (3) well opening production of a production well: and after the well shut-in is finished, opening the production well to produce under the pressure drop gradient of 1MPa/min until the production well produces oil due to serious gas channeling.
And (5) repeating the steps (2) to (5) for 5 periods after the foam flooding auxiliary nitrogen huff and puff of one period is finished, recording the oil recovery of the production well after the foam flooding auxiliary nitrogen huff and puff of each period, and calculating the recovery degree.
Comparative example (c),
In order to compare with the method for improving the recovery ratio by using the foam flooding auxiliary nitrogen huff-and-puff of the fault block oil reservoir, a fault block oil reservoir nitrogen huff-and-puff experiment is carried out, the flow is shown in figure 2, the experiment is carried out at a constant temperature, and the actual oil reservoir environment is simulated.
The method specifically comprises the following steps:
(1) simulating a fault block oil reservoir: filling a core tube with certain permeability by using quartz sand, weighing dry weight, vacuumizing, using 255mL of saturated water, weighing wet weight, calculating the porosity to be 25.7%, measuring the water-phase permeability of the core to be 1800mD, using 225mL of saturated oil and using the oil-containing saturation to be 88%, adjusting the core to 70 ℃ and 5MPa of pressure, setting the back pressure to be 3.5MPa, setting the inclination angle of the core tube to be 15 degrees, and simulating a fault block oil reservoir based on the result;
in the comparative example, the filled core tube meets the requirements of simulating the fault block oil reservoir, namely the horizontal permeability is more than 1000mD, and the ratio of the vertical permeability to the horizontal permeability is more than 0.5; in this comparative example, the horizontal permeability is 1800 mD;
the temperature of the oil layer is 30-100 ℃; in this comparative example, the oil layer temperature was 70 ℃;
the inclination angle of the stratum is more than 10 degrees; in this comparative example, the formation dip was 15 °;
the oil saturation is more than 40 percent; in this comparative example, the oil saturation was 88%;
the porosity of the reservoir is 20-40%; in this comparative example, the average porosity was 25.7%;
(2) nitrogen injection of a production well: closing an injection well, injecting nitrogen into the core tube through the production well at the speed of 1mL/min, and stopping nitrogen injection when the pressure of the core tube is increased to 6 MPa;
(3) gravity differentiation of the well soaking oil gas: after nitrogen is injected into the core tube, closing the production well and carrying out soaking for 3 hours;
(4) and (3) well opening production of a production well: and after the well shut-in is finished, opening the production well to produce under the pressure drop gradient of 1MPa/min until the production well produces oil due to serious gas channeling.
And (4) after the nitrogen handling in one period is finished, repeating the steps (2) to (4) for 5 periods, recording the oil recovery amount of the production well after the nitrogen handling in each period, and calculating the recovery degree.
The results of comparing the multi-cycle extraction degrees of the experimental example and the comparative example are shown in FIG. 3.
Compared with pure nitrogen huff and puff, the foam flooding auxiliary nitrogen huff and puff has better recovery effect, which is shown in that the cycle recovery ratio is higher, the effective cycle is longer, the total recovery ratio is 42.15 percent after 5-cycle production, the total recovery ratio is improved by 22.73 percent compared with the nitrogen huff and puff, and the foam flooding auxiliary nitrogen huff and puff has obvious synergistic effect.
As shown in fig. 4, before nitrogen huffing and puff, a foam slug is injected into an injection well, a certain plugging effect is generated on the stratum, and nitrogen injection at a subsequent production well meets a certain resistance in the horizontal direction, so that the nitrogen injection is longitudinally expanded, crude oil which cannot be reached in the original longitudinal direction is replaced, and the yield increasing effect of the nitrogen huffing and puff is improved;
as shown in fig. 5, in the foam injection direction, there may be a "dead end" where foam displacement cannot be propagated, and the part of crude oil is not easy or cannot be produced, and similarly in the nitrogen injection direction, there may be a "dead end" where nitrogen throughput cannot be propagated, and the part of crude oil is not easy or cannot be produced. In the foam flooding auxiliary nitrogen huff-and-puff process, the two production modes are organically combined, the foam flooding 'dead end' crude oil is extracted by the nitrogen huff-and-puff mode, the nitrogen huff-and-puff 'dead end' crude oil is extracted by the foam flooding, so that the 'dead end' of the 'dead end' in the original single production mode is effectively used, and the crude oil yield increasing effect is improved.
Claims (13)
1. A method for improving recovery efficiency of a fault block oil reservoir by foam flooding assisted nitrogen huff and puff is characterized by comprising the following steps:
(1) selecting an oil reservoir to be developed:
according to the geological characteristics and the current development situation of the oil reservoir, roughly screening the applicable oil reservoir according to the following conditions, and at least meeting the following conditions:
the oil reservoir is a closed fault block oil reservoir;
the single-layer thickness of the fault block oil reservoir is more than or equal to 10 m;
the net total thickness ratio is greater than 0.5;
oil containing area is more than 0.3km2；
The horizontal permeability is more than 1000mD, and the ratio of the vertical permeability to the horizontal permeability is more than 0.5;
the temperature of the oil layer is 30-100 ℃;
the inclination angle of the stratum is more than 10 degrees;
(2) injection well preformed foam injection: foaming on the ground, and injecting a foam slug with a certain volume into the stratum through an injection well shaft, wherein the gas-liquid volume ratio of foam under the injected oil reservoir condition is 1: 1-3: 1;
(3) nitrogen injection of a production well: closing an injection well, injecting nitrogen into the stratum through a production well shaft at a constant speed, and stopping nitrogen injection when the oil reservoir pressure is increased to 0.8-1.2 times of the original oil reservoir pressure;
(4) gravity differentiation of the well soaking oil gas: after nitrogen is injected into the stratum, closing the production well for soaking;
(5) and (3) well opening production of a production well: and after the well soaking is finished, opening the production well for production, and finishing the production after serious gas channeling occurs.
2. The method for improving the recovery efficiency of the fault block oil reservoir through foam flooding auxiliary nitrogen huff and puff according to claim 1, wherein after one period of foam flooding auxiliary nitrogen huff and puff is finished, the steps (2) to (5) are repeated for a plurality of periods of foam flooding auxiliary nitrogen huff and puff.
3. The method for foam flooding assisted nitrogen throughput enhanced oil recovery for a fault block reservoir of claim 2, wherein the number of cycles is 5.
4. The method for foam flooding assisted nitrogen huff and puff enhanced oil recovery for a fault block reservoir of claim 1, wherein the step (1) of coarsely screening suitable reservoirs further comprises: the buried depth is 1000 m-3000 m.
5. The method for foam flooding assisted nitrogen huff and puff enhanced oil recovery for a fault block reservoir of claim 1, wherein the step (1) of coarsely screening suitable reservoirs further comprises: the oil saturation is more than 40 percent.
6. The method for foam flooding assisted nitrogen huff and puff enhanced oil recovery for a fault block reservoir of claim 1, wherein the step (1) of coarsely screening suitable reservoirs further comprises: the porosity of the reservoir is 20-40%.
7. The method for foam flooding assisted nitrogen huff and puff enhanced oil recovery of a fractured block reservoir of claim 1, wherein the injected foam slug volume of the step (2) is 0.05-0.2 PV.
8. The method for foam flooding assisted nitrogen throughput enhanced oil recovery for a fractured reservoir of claim 7 wherein the foam slug volume is 0.1 PV.
9. The method for foam flooding assisted nitrogen huff and puff enhanced recovery of a fractured reservoir of claim 1, wherein in the step (3), the constant velocity is in the range of 2000-10000 m3/d。
10. The method for foam flooding assisted nitrogen huff and puff enhanced recovery of a fractured reservoir of claim 9 wherein the injection rate is 4000m3/d。
11. The method for improving the recovery efficiency of a fault block oil reservoir by using foam flooding assisted nitrogen huff and puff as claimed in claim 1, wherein in the step (4), the soaking time is 20-40 d.
12. The method of foam flooding assisted nitrogen huff and puff enhanced recovery for a fractured reservoir of claim 11 wherein the soak time is 30 days.
13. The method for foam flooding assisted nitrogen huff and puff enhanced oil recovery of a fractured reservoir of claim 1, wherein the step (5) is performed when the produced gas-oil ratio is more than 1000m3At/t, severe gas breakthrough was considered.
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| CN111456692A (en) * | 2020-03-23 | 2020-07-28 | 中国石油大学(北京) | Gas-drive oil production method and device |
| CN111720116B (en) * | 2020-05-14 | 2021-09-14 | 中国石油化工股份有限公司 | Fracture-cavity type oil reservoir unit nitrogen gas flooding gas channeling judgment method and injection-production channeling prevention method |
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| CN113216917B (en) * | 2021-06-17 | 2022-11-18 | 中国石油大学(华东) | Method for controlling nitrogen channeling in oil reservoir nitrogen injection huff-puff exploitation process |
| CN113653475A (en) * | 2021-09-18 | 2021-11-16 | 中国石油大学(华东) | Treatment and utilization method of foam gas-displacement channel |
| CN115898347B (en) * | 2022-12-05 | 2024-04-19 | 西南石油大学 | Method for improving shale oil reservoir recovery ratio by air foam assisted air throughput |
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