Development method of deep low-permeability heavy oil reservoir

Abstract

The invention relates to a method for developing a deep low-permeability heavy oil reservoir, which comprises the following steps of: deploying a gas drive, gas huff and puff and multi-element slug type combination drive horizontal well three-dimensional development well pattern which comprises a plurality of basic development units, each unit comprises an injection horizontal well which is arranged at the top of the oil reservoir and is provided with a fishbone type branch well, a production horizontal well with two-wing fracturing cracks is arranged at the bottom of an oil reservoir, and auxiliary production horizontal wells with two-wing fracturing cracks are arranged on the two sides of the production horizontal well; first gas injection is conducted through the injection horizontal well, meanwhile, gas huff and puff exploitation is conducted on the production horizontal well and the auxiliary production horizontal well, and second gas injection is conducted; and after multiple rounds of gas huff and puff, when the gas cavities at the top and the bottom of the oil reservoir are communicated, injecting into the horizontal well for first oil emulsion gas drive, and performing second oil emulsion gas drive on the production horizontal well to assist the production horizontal well in oil extraction. According to the development method, oil is produced effectively and efficiently under the dual action of top gas drive and bottom emulsification water drive, and economic benefits can be improved.

Description

Technical Field

[0001] The present invention relates to the field of oilfield development, and in particular to a method for developing a deep low-permeability heavy oil reservoir. Background Art

[0002] At present, the burial depth of deep ultra-low permeability heavy oil reservoirs is greater than 1000m, and the average permeability is less than 50mD. This reservoir is characterized by deep burial, poor physical properties, and strong heterogeneity. There is basically no natural production capacity, and there is currently a lack of effective means to mobilize it.

[0003] Due to the poor seepage conditions in deep, low-permeability reservoirs, it's difficult to establish an effective injection-production pressure differential in injection-production wells. Development methods primarily include fracturing, supercritical boiler steam injection, and chemical huff-and-puff. Test results show that while these methods achieve a certain initial yield, the subsequent stable production period is short, failing to alleviate long-term development challenges. Production characteristics include low daily liquid production, a short effective production period, difficulty removing sand from the formation, uneven horizontal and vertical reserve utilization, and generally no more than 15% recovery. Overall, this type of reservoir currently lacks effective development methods.

[0004] At present, most of the exploration of effective development methods is in the experimental research stage. In order to improve the development effect of deep heavy oil, Gaosheng Oilfield has carried out a development method of fracturing + anti-expansion steam injection, that is, first fracturing and conventional pressure release for production, followed by high-pressure anti-expansion steam injection to maximize production efficiency. However, it is greatly affected by reservoir physical properties, resulting in poor development results.

[0005] For example, CN108442908A discloses a method for improving the single-well productivity of an ultra-deep low-permeability heavy oil reservoir, comprising the following steps: selecting a suitable reservoir, which is an ultra-deep low-permeability heavy oil reservoir; injecting 200t-1000t of a 1.5wt% aqueous solution of a foam oil promoter into the ultra-deep low-permeability heavy oil reservoir; and then injecting 150,000m3 of a foam oil promoter under standard conditions. 3 -500,000 m 3 The invention also provides a step of deploying a long horizontal well in the oil layer of the above-mentioned oil reservoir, and performing at least three-stage fracturing on the long horizontal well to form multiple fractures, wherein the fractures extend radially outward from the long horizontal well to the oil layer, and the fractures change radial flow into linear flow and pseudo-radial flow, thereby improving the oil and gas seepage conditions in the near-wellbore area.

[0006] For example, CN114033342A discloses a viscosity reduction and flooding method for effectively mobilizing low-permeability heavy oil in deep formations. The method includes: selecting a viscosity reducer system; determining the well spacing of the reservoir well pattern; conducting a viscosity reducer huff-and-puff flooding simulation on production wells, optimizing the flooding cycle and viscosity reducer injection rate, and determining the optimal viscosity reduction huff-and-puff flooding solution; and optimizing the displacement method and viscosity reducer concentration to determine the optimal viscosity reduction and flooding solution.

[0007] CN116220634A discloses a method for chemical thermodynamic viscosity reduction and flooding in an ultra-deep low-permeability heavy oil reservoir. The method comprises the following steps: 1, injecting an aqueous solution of a high-energy chemical agent A into the ultra-deep low-permeability heavy oil reservoir; 2, injecting a small amount of an aqueous solution of a high-energy chemical agent B into the reservoir, followed by post-injection of clean water; 3, starting to soak the well. After soaking the well for a period of time, the AB two-component system reacts rapidly in the diffusion contact zone; 4, detecting the production pressure and bottom hole temperature of the oil well; and 5, judging the timing of opening the well for oil production based on pressure changes in the casing and tubing.

[0008] In summary, during the low-permeability heavy oil displacement recovery stage, only small-scale throughput tests have been carried out. The displacement process is easily affected by water and gas channeling, and the final recovery rate is still low. It is urgent to develop a new technology and development method to improve the recovery rate of this type of oil reservoir. Summary of the Invention

[0009] In view of the problems existing in the prior art, the purpose of the present invention is to provide a method for developing deep low-permeability heavy oil reservoirs, which solves the problem of low recovery rate in deep low-permeability heavy oil exploitation.

[0010] To achieve this object, the present invention adopts the following technical solutions:

[0011] The present invention provides a method for developing a deep low-permeability heavy oil reservoir, the method comprising:

[0012] S1. Deploy a three-dimensional development well pattern of gas drive + gas huff-and-puff + multi-element slug composite drive horizontal wells, including at least one basic development unit; the basic development unit includes an injection horizontal well with a fishbone branch well at the top of the reservoir, a production horizontal well with two-wing hydraulic fractures at the bottom of the reservoir, and a first auxiliary production horizontal well and a second auxiliary production horizontal well with two-wing hydraulic fractures on both sides of the production horizontal well;

[0013] S2, injecting the first gas into the injection horizontal well at the top of the oil reservoir, and simultaneously performing gas huff and puff, injecting the second gas into the production horizontal well, the first auxiliary production horizontal well, and the second auxiliary production well at the bottom of the oil reservoir, and then shutting down the well to produce oil;

[0014] S3. After step S2 is repeated 2-3 times, when the gas cavities at the top and bottom of the reservoir are connected, the drive is switched to multi-segment composite drive, the injection horizontal well performs the first oil-emulsion-gas drive, the production horizontal well performs the second oil-emulsion-gas drive, and the first auxiliary production horizontal well and the second auxiliary production horizontal well both produce oil.

[0015] The development method provided by the present invention is to arrange an injection horizontal well with a branch well structure at the top of the oil layer, arrange three production horizontal wells at the bottom of the oil reservoir, perform fracturing operations at the bottom of the oil reservoir, and form a top gas cap after gas is injected from the top. The top gas cap drive can be quickly formed through the branch wells to expand the scope of the gas. The three bottom production horizontal wells are simultaneously produced by gas throughput. When the top gas interface drops to the vicinity of the bottom production well, the bottom production well is converted into a water injection well, and water and emulsifier are injected to achieve an oil-water emulsion, forming an emulsified water drive. The injection system of the top and bottom horizontal wells alternates the injection of gas, water and emulsifier at fixed intervals to achieve a better emulsifier displacement effect. Under the dual effects of the top gas cap and the bottom emulsified water drive, this technical solution effectively reduces water and gas channeling, effectively and efficiently produces oil, and is conducive to improving economic benefits.

[0016] As a preferred technical solution of the present invention, the injection horizontal well is designed as a fishbone branch well structure, and the angle between the branch well and the horizontal well is 45-60°; the two-wing hydraulic fractures and the production horizontal well are in a vertical position relationship, the fractures between the horizontal wells are staggered, and the length of the hydraulic fractures is controlled at 35-50m.

[0017] As a preferred technical solution of the present invention, in step S1, the ratio of the number of injection horizontal wells at the top of the reservoir, the number of production horizontal wells at the bottom of the reservoir, and the number of auxiliary production horizontal wells at the bottom of the oil layer is 1:1:2.

[0018] As a preferred technical solution of the present invention, the following steps are specifically included:

[0019] S201, injecting a first gas into the horizontal injection well at the top of the oil reservoir, wherein the injected first gas includes one or a combination of at least two of nitrogen, carbon dioxide, or methane;

[0020] S202, performing gas huff and puff on the production horizontal well at the bottom of the oil reservoir, the first auxiliary production horizontal well, and the second auxiliary production horizontal well, injecting a sufficient amount of second gas required for the gas huff and puff, then shutting down the wells and then producing, wherein the second gas injected during the gas huff and puff includes nitrogen and / or carbon dioxide;

[0021] S203. When the gas cavities at the top and bottom of the oil reservoir are connected, the injection horizontal well performs a first oil-emulsion-gas drive, and the production horizontal well performs a second oil-emulsion-gas drive. The first oil-emulsion-gas drive performed by the injection horizontal well and the second oil-emulsion-gas drive performed by the production horizontal well are performed alternately at fixed cycles, and the first auxiliary production horizontal well and the second auxiliary production horizontal well both produce oil.

[0022] As a preferred technical solution of the present invention, the injection endpoint of the first gas is a gas cavity at the top of the reservoir with a volume of 35-45% of the initial gas cavity volume at the top of the reservoir.

[0023] As a preferred technical solution of the present invention, the injection medium of the first oil-emulsion gas flooding and the second oil-emulsion gas flooding includes a combination of a gas medium and a liquid medium or a gas medium.

[0024] As a preferred technical solution of the present invention, the injection rate of the first gas injected into the horizontal well in step S201 is obtained by formula (I):

[0025] Q g =0.05πabH(I)

[0026] Where Q g is the total gas injection volume of a single horizontal injection well, in m 3 ; π is 3.14, dimensionless; a and b are the major and minor axis processing radii of the ellipsoid centered on the horizontal section trajectory of the horizontal well, in meters; H represents the oil layer thickness, in meters.

[0027] As a preferred technical solution of the present invention, the injection speed of the second gas in the gas throughput in step S202 is obtained by formula (II):

[0028]

[0029] Where, ν g is the gas injection rate of a single horizontal well, in m 3 / day; π is 3.14, dimensionless; α is the empirical coefficient, dimensionless; P is the formation pressure, unit is MPa; a and b are the major and minor axis treatment radii of the ellipsoid centered on the horizontal section trajectory of the horizontal well, unit is m; H is the oil layer thickness, unit is m; ρ g is the density of injected gas, in g / L; T is the formation temperature, in °C; n is the number of gas huff-and-puff cycles, dimensionless; t c It is the gas throughput cycle, in day.

[0030] As a preferred technical solution of the present invention, the gas medium includes nitrogen and / or carbon dioxide.

[0031] Preferably, the injection speed of the gas medium is 20000-50000m 3 / d.

[0032] Preferably, the liquid medium comprises water and an emulsion.

[0033] Preferably, the injection rate of water in the liquid medium is 200-250 t / d.

[0034] Preferably, the injection rate of the emulsion in the liquid medium is 50-60 t / d.

[0035] Preferably, the mass ratio of the emulsion to water is 1:(9-9.5).

[0036] Preferably, the emulsion comprises, by weight percentage, 50-60 wt % of a Span emulsifier, 5-15 wt % of an ammonium salt anti-swelling agent, and 25-45 wt % of carbonamide.

[0037] As a preferred technical solution of the present invention, the well spacing between the production horizontal well and the first auxiliary production horizontal well is 70-100m.

[0038] Preferably, the well spacing between the production horizontal well and the second auxiliary production horizontal well is 70-100m.

[0039] Preferably, the horizontal section length of the production horizontal well is 200-300m.

[0040] Compared with the existing technical solutions, the present invention has the following beneficial effects:

[0041] (1) The present invention provides a horizontal well stereoscopic well network mining method, in which one horizontal injection well is arranged at the top of the oil reservoir, one production well is located at the bottom of the oil reservoir, and two auxiliary production horizontal wells are located on both sides of the production well. Gas is injected horizontally at the top of the oil layer through a branch well to form a certain volume of air cavity. After that, a large amount of gas is injected, and a top gas cap is quickly formed, thereby expanding the gravity oil drainage effect and the affected volume. Due to the existence of the horizontal well stereoscopic well network, gas injection and energy replenishment can be achieved within a short distance, reducing the wellhead pressure of the injected gas and improving the safety of the entire production. N2 is easy to obtain and is not corrosive to equipment. CO2 and CH4 can further reduce the viscosity of crude oil.

[0042] (2) After multiple rounds of gas injection and huff-and-puff in the top and bottom production wells, the displacement phase begins. The top horizontal well injects gas to form gravity drive, while the bottom production well switches to alternate slug injection of gas, water, and emulsifier to create an oil-in-water emulsion, forming an emulsified water drive. Under the dual effects of top gas cap drive and bottom emulsified water drive, efficient oil production is achieved in the auxiliary production wells on both sides of the production well.

[0043] (3) The present invention provides a horizontal well technology with branch wells at the top of the oil reservoir, which expands the swept volume of gas and displacement agent and facilitates the recovery of residual oil between wells. The bottom horizontal well adopts fracturing technology, with two wing seams arranged in a staggered manner, which improves the fluidity of low-permeability reservoirs and increases the single-well production of heavy oil production wells in such deep low-permeability reservoirs. The design of the top branch horizontal well and the bottom segmented fracturing horizontal well improves oil displacement efficiency and ultimate recovery.

[0044] (4) The present invention provides an emulsifier formulation that has the effects of emulsification and viscosity enhancement, improving oil displacement efficiency, and improving water sensitivity. Injected water and emulsifiers will contact underground oil to form a water-in-oil emulsion, increasing the viscosity of the crude oil and forming an emulsified oil belt to prevent water and gas channeling. The amine salt anti-swelling agent in the formulation has the dual effects of preventing swelling and promoting emulsification, has strong physical and chemical adsorption capacity, and its adsorption performance is not affected by pH value. This composite formulation can achieve the stability of the water-in-oil emulsion under high water content conditions.

[0045] (5) The mining method provided by the present invention can significantly improve the recovery rate and development effect of deep low-permeability heavy oil reservoirs. The deep heavy oil reservoir development plan and gas injection plan have been systematically optimized. The throughput recovery rate of deep heavy oil at home and abroad is usually less than 15%. The patented gas injection energy enhancement and anti-channeling technology of this invention can achieve continuous oil production throughout the entire stage, and the recovery rate of the final gas displacement + emulsified oil displacement stage can reach 30-35%. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 Schematic diagram of the distribution of basic development units of a three-dimensional well pattern of horizontal wells in an embodiment of the present invention;

[0047] Figure 2 is a cross-sectional schematic diagram of the gas cavity formed by gas intake and discharge in an embodiment of the present invention;

[0048] Figure 3 1. It is a cross-sectional diagram of the mechanism of injecting gas medium and liquid medium into a production horizontal well and injecting gas medium into an injection horizontal well in an embodiment of the present invention;

[0049] Figure 4 This is a cross-sectional diagram of the mechanism of injecting gas medium into a production horizontal well and injecting gas medium and liquid medium into an injection horizontal well in an embodiment of the present invention;

[0050] Figure 5 Schematic diagram of vertical cross-section distribution of a three-dimensional well pattern of multiple horizontal wells in an embodiment of the present invention;

[0051] In the figure: 1-production horizontal well, 2-injection horizontal well, 3.1-first auxiliary production horizontal well, 3.2-second auxiliary production horizontal well, 4-branch well, 5-two wing slots;

[0052] 1.1-first production horizontal well, 1.2-second production horizontal well, 2.1-first injection horizontal well, 2.2-second injection horizontal well, 3.3-third auxiliary production horizontal well.

[0053] The present invention is further described in detail below. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims. DETAILED DESCRIPTION

[0054] To better illustrate the present invention and facilitate understanding of the technical solutions of the present invention, typical but non-limiting embodiments of the present invention are as follows:

[0055] This embodiment provides a method for developing a deep low-permeability heavy oil reservoir, the method comprising:

[0056] S1. Deploy a three-dimensional development well pattern of gas drive + gas huff and puff + multi-element slug composite drive horizontal wells, such as Figure 1 As shown, it includes at least one basic development unit; the basic development unit includes an injection horizontal well 2 with a fishbone-shaped branch well 4 set at the top of the reservoir, a production horizontal well 1 with two-wing hydraulic fractures set at the bottom of the reservoir, and a first auxiliary production horizontal well 3.1 and a second auxiliary production horizontal well 3.2 set on both sides of the production horizontal well 1 and also with two-wing hydraulic fractures;

[0057] S2, the injection horizontal well 2 at the top of the oil reservoir injects the first gas, and the production horizontal well 1, the first auxiliary production horizontal well 3.1, and the second auxiliary production horizontal well 3.2 at the bottom of the oil reservoir simultaneously perform gas huff and puff, inject the second gas, and then shut down the wells for oil production;

[0058] S3. After step S2 is repeated 2-3 times, when the gas cavities at the top and bottom of the reservoir are connected, the drive is switched to multi-segment composite drive. The injection horizontal well 2 performs the first oil-emulsion-gas drive, the production horizontal well 1 performs the second oil-emulsion-gas drive, and the first auxiliary production horizontal well 3.1 and the second auxiliary production horizontal well 3.2 both produce oil.

[0059] In the present invention, deep low-permeability heavy oil refers to a deep low-permeability heavy oil reservoir with a burial depth greater than 1000m, an average permeability lower than 50mD, and basically no natural production capacity underground, and currently lacks effective means of mobilization.

[0060] In the present invention, the production horizontal well 1 is located directly below the injection horizontal well 2.

[0061] In the present invention, the production horizontal well 1, the first auxiliary production horizontal well 3.1 and the second auxiliary production horizontal well 3.2 can be optionally located in the same horizontal plane, or can be at a certain vertical distance, i.e., based on the horizontal plane, the distances are different, but the difference is less than 1m.

[0062] Among them, the injection horizontal well 2 is designed as a fishbone-type branch well 4 structure, and the angle between the branch well 4 and the horizontal well is 45-60°; the two-wing hydraulic fractures and the production horizontal well 1 are in a vertical position relationship, the fractures between the horizontal wells are staggered, and the length of the hydraulic fractures is controlled at 35-50m.

[0063] Specifically, the injection horizontal well 2 is designed as a branch well 4 structure, and the angle between the branch well 4 and the horizontal well is 45-60°, for example, it can be 45°, 46°, 48°, 50°, 52°, 54°, 56°, 58° or 60°, etc., but is not limited to the listed values, and other unlisted values ​​within this range also meet the requirements.

[0064] In the present invention, the angle direction is the angle between the branch well 4 and the flow direction of the material entering the horizontal well.

[0065] Among them, the horizontal section length of the injection horizontal well 2 is 300-500m, for example, it can be 300m, 320m, 340m, 360m, 380m, 400m, 420m, 440m, 460m, 480m or 500m, but is not limited to the listed values. Other unlisted values ​​within this range also meet the requirements.

[0066] Among them, the length of the branch well 4 in the injection horizontal well 2 is 80-100m, for example, it can be 80m, 82m, 84m, 86m, 88m, 90m, 92m, 94m, 96m, 98m or 100m, etc., but is not limited to the listed values. Other unlisted values ​​within this range meet the requirements.

[0067] Among them, the vertical distance between adjacent branch wells 4 is 40-60m, for example, it can be 40m, 42m, 44m, 46m, 48m, 50m, 52m, 54m, 56m, 58m or 60m, etc., but is not limited to the listed values. Other unlisted values ​​within this range meet the requirements.

[0068] Specifically, the well spacing between the production horizontal well 1 and the first auxiliary production horizontal well 3.1 is 70-100m, for example, it can be 70mm, 75mm, 80mm, 85mm, 90mm, 95mm or 100mm, etc., but is not limited to the listed values. Other unlisted values ​​within this range meet the requirements.

[0069] Specifically, the well spacing between the production horizontal well 1 and the second auxiliary production horizontal well 3.2 is 70-100m, for example, it can be 70mm, 75mm, 80mm, 85mm, 90mm, 95mm or 100mm, etc., but is not limited to the listed values. Other unlisted values ​​within this range meet the requirements.

[0070] In the present invention, the production horizontal well 1, the first auxiliary production horizontal well 3.1 and the second auxiliary production horizontal well 3.2 all adopt fracturing operation, the cracks are two wing cracks 5, the cracks are staggered, and the fracturing crack length is controlled within 35-50m, for example, it can be 35m, 36m, 38m, 40m, 42m, 44m, 46m, 48m or 50m, etc., but is not limited to the listed values. Other values ​​not listed within this range meet the requirements.

[0071] In the present invention, the horizontal section length of the production horizontal well 1 is 200-300m, for example, it can be 200m, 210m, 220m, 230m, 240m, 250m, 260m, 270m, 280m, 290m or 300m, but is not limited to the listed values. Other unlisted values ​​within this range meet the requirements.

[0072] In the present invention, the horizontal section length of the first auxiliary production horizontal well 3.1 is 200-300m, for example, it can be 200m, 210m, 220m, 230m, 240m, 250m, 260m, 270m, 280m, 290m or 300m, etc., but is not limited to the listed values. Other unlisted values ​​within this range meet the requirements.

[0073] In the present invention, the horizontal section length of the second auxiliary production horizontal well 3.2 is 200-300m, for example, it can be 200m, 210m, 220m, 230m, 240m, 250m, 260m, 270m, 280m, 290m or 300m, etc., but is not limited to the listed values. Other unlisted values ​​within this range meet the requirements.

[0074] Specifically, in step S1 , the ratio of the number of injection horizontal wells 2 at the top of the reservoir, the number of production horizontal wells 1 at the bottom of the reservoir, and the number of auxiliary production horizontal wells at the bottom of the oil layer is 1:1:2.

[0075] Furthermore, the method specifically includes the following steps:

[0076] S201, injecting a first gas into the injection horizontal well 2 at the top of the oil reservoir, wherein the injected first gas includes one or a combination of at least two of nitrogen, carbon dioxide, or methane;

[0077] S202: Perform gas huff and puff in the production horizontal well 1, the first auxiliary production horizontal well 3.1, and the second auxiliary production horizontal well 3.2 at the bottom of the oil reservoir. After injecting a sufficient amount of second gas required for the gas huff and puff, the wells are shut down and then produced. The second gas injected during the gas huff and puff includes nitrogen and / or carbon dioxide.

[0078] S203. When the gas cavities at the top and bottom of the reservoir are connected, the injection horizontal well 2 performs the first oil-emulsion-gas drive, and the production horizontal well 1 performs the second oil-emulsion-gas drive. The first oil-emulsion-gas drive by the injection horizontal well 2 and the second oil-emulsion-gas drive by the production horizontal well 1 are performed alternately in a fixed cycle, and the first auxiliary production horizontal well 3.1 and the second auxiliary production horizontal well 3.2 both produce oil.

[0079] In the present invention, the first gas injection of the injection horizontal well 2 and the gas huff and puff production of the production horizontal well 1, the first auxiliary production horizontal well 3.1 and the second auxiliary production horizontal well 3.2 are started and stopped simultaneously.

[0080] Specifically, the endpoint of the first gas injection is that the volume of the air cavity at the top of the oil reservoir is 35-45% of the initial air cavity volume at the top of the oil reservoir, for example, it can be 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44% or 45%, etc., but is not limited to the listed values, and other unlisted values ​​within this range meet the requirements.

[0081] Specifically, the injection rate of the first gas injected into the horizontal well 2 in step S201 is obtained by formula (I):

[0082] Q g =0.05πabH(I)

[0083] Where Q g is the total gas injection volume of the single horizontal injection well 2, in m 3 ; π is 3.14, dimensionless; a and b are the major and minor axis processing radii of the ellipsoid centered on the horizontal section trajectory of the horizontal well, in meters; H represents the oil layer thickness, in meters.

[0084] Specifically, the injection rate of the second gas in the gas throughput in step S202 is obtained by formula (II):

[0085]

[0086] Where, ν g is the gas injection rate of a single horizontal well, in m 3 / day; π is 3.14, dimensionless; α is the empirical coefficient, dimensionless; P is the formation pressure, unit is MPa; a and b are the major and minor axis treatment radii of the ellipsoid centered on the horizontal section trajectory of the horizontal well, unit is m; H is the oil layer thickness, unit is m; ρ g is the density of injected gas, in g / L; T is the formation temperature, in °C; n is the number of gas huff-and-puff cycles, dimensionless; t c It is the gas throughput cycle, in day.

[0087] In the present invention, α is an empirical coefficient, dimensionless, and can be exemplarily selected as 0.1-0.5.

[0088] Specifically, the second gas injected in the gas huff-and-puff production includes nitrogen and / or carbon dioxide.

[0089] In the present invention, when the daily production of a single well is too low during gas huff and puff production, the process can be repeated. For example, when the daily production of a single well drops below 3t / d, the next round of gas huff and puff is started. The cross-sectional diagram of the gas cavity formed during gas huff and puff is shown in FIG. Figure 2 As shown in the figure, it can be seen that there are three steam cavities and oil leakage areas formed by steam stimulation of the horizontal production wells and auxiliary production wells below the oil layer.

[0090] Furthermore, after gas huffing and puffing, the well is shut down and then mined. The number of days for shutting down the well is designed based on actual conditions. For example, in the present invention, it can be selected as 3-5 days.

[0091] Specifically, the injection medium in the first oil-emulsion gas flooding includes a combination of a gas medium and a liquid medium or a gas medium.

[0092] Specifically, the injection medium in the second oil-emulsion gas flooding includes a combination of a gas medium and a liquid medium or a gas medium.

[0093] Among them, when the injection medium of the first oil-emulsion-gas drive is a gas medium, the injection medium of the second oil-emulsion-gas drive is a combination of a gas medium and a liquid medium; when the injection medium of the first oil-emulsion-gas drive is a combination of a gas medium and a liquid medium, the injection medium of the second oil-emulsion-gas drive is a gas medium, and they are performed alternately.

[0094] Among them, the interval of alternating injection is adaptively selected according to the actual production situation. For example, the alternating injection interval is 25-40 days. For example, after 30 days of injecting gas medium in the first oil-emulsion gas drive, the injection medium is changed to a combination of gas medium and liquid medium. The gas medium is injected first and then the liquid medium is injected. The gas medium injection time is maintained for 4-6 days and then the liquid medium is injected. This cycle is repeated until the injection interval is reached. Other days are selected by analogy. The corresponding action mechanism profile is as follows: Figure 3 and 4 shown.

[0095] When the injected medium is a combination of a gas medium and a liquid medium, the gas medium is injected first and then the liquid medium is injected.

[0096] An exemplary alternating injection interval process is as follows: taking an interval of 30 days as an example, the first oil-emulsion gas drive starts with the injection of gas medium, and the second oil-emulsion gas drive is a combination of gas medium and liquid medium; then the first oil-emulsion gas drive directly injects gas medium for 30 days, while the second oil-emulsion gas drive injection process is to inject gas medium for 5 days and then liquid medium for 5 days, then change to injecting gas medium for 5 days and then injecting liquid medium for 5 days, then injecting gas medium for 5 days and then injecting liquid medium for 5 days, that is, 30 days; then alternating is performed, and the first oil-emulsion gas drive is changed to injecting a combination of gas medium and liquid medium, and the second oil-emulsion gas drive is to inject gas medium; now, the second oil-emulsion gas drive is to inject gas medium for 30 days, while the first oil-emulsion gas drive injection process is to inject gas medium for 5 days and then liquid medium for 5 days, then change to injecting gas medium for 5 days and then injecting liquid medium for 5 days, then injecting gas medium for 5 days and then liquid medium for 5 days, that is, 30 days; then alternating is performed, and this cycle is repeated. The injection rate is kept constant during the alternating process, that is, after the injection rule is determined, the injection volume remains unchanged during the periodic alternating injection until the end of production.

[0097] Wherein, the gas medium includes nitrogen and / or carbon dioxide.

[0098] The injection speed of the gas medium is 20000-50000m 3 / d, for example, it can be 20000m 3 / d, 25000m 3 / d, 30000m 3 / d, 35000m 3 / d, 40000m 3 / d, 45000m 3 / d or 50000m 3 / d, etc., but not limited to the listed values. Other values ​​not listed within this range meet the requirements.

[0099] Wherein, the liquid medium includes water and emulsion.

[0100] The injection rate of water in the liquid medium is 200-250t / d, for example, it can be 200t / d, 210t / d, 220t / d, 230t / d, 240t / d or 250t / d, but is not limited to the listed values. Other values ​​not listed within this range meet the requirements.

[0101] The injection rate of the emulsion in the liquid medium is 50-60 t / d, for example, it can be 50 t / d, 52 t / d, 54 t / d, 56 t / d, 58 t / d or 60 t / d, but is not limited to the listed values. Other values ​​not listed within this range meet the requirements.

[0102] The mass ratio of the emulsion to water is 1:(9-9.5), for example, 1:9, 1:9.1, 1:9.2, 1:9.3, 1:9.4 or 1:9.5, etc., but is not limited to the listed values. Other values ​​not listed within this range meet the requirements.

[0103] The emulsion comprises, by weight percentage, 50-60% of a Span emulsifier, 5-15% of an ammonium salt anti-swelling agent, and 25-45% of carbonamide.

[0104] In the present invention, the mass percentage of the Span emulsifier in the emulsion is 50-60%, for example, it can be 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59% or 90%, etc., but is not limited to the listed values. Other values ​​not listed within this range meet the requirements.

[0105] In the present invention, the ammonium salt anti-swelling agent in the emulsion is 5-15% by mass, for example, it can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%, etc., but is not limited to the listed values. Other values ​​not listed within this range meet the requirements.

[0106] In the present invention, the mass percentage of carbonamide in the emulsion is 25-45%, for example, it can be 25%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44% or 45%, etc., but is not limited to the listed values. Other values ​​not listed within this range meet the requirements.

[0107] In the present invention, the total mass percentage of the Span emulsifier, the ammonium salt anti-swelling agent and the carbonic acid amide in the emulsion is 100%.

[0108] The Span emulsifier includes one of Span 20, Span 40, Span 60 or Span 80, or a combination of at least two of them.

[0109] The ammonium salt anti-swelling agent includes one or a combination of at least two of trimethylalkylammonium salt, polyquaternium salt, ethanolamine, diethanolamine, triethanolamine or acrylamide.

[0110] Furthermore, the present invention provides a schematic cross-sectional diagram of a well pattern when multiple production horizontal wells exist, such as Figure 5As shown, the system comprises a first injection horizontal well 2.1 and a second injection horizontal well 2.2 with fishbone-shaped branch wells at the top of the reservoir, a first production horizontal well 1.1 and a second production horizontal well 1.2 with two-wing hydraulic fractures at the bottom of the reservoir, and a first auxiliary production horizontal well 3.1, a second auxiliary production horizontal well 3.2 and a third auxiliary production horizontal well 3.3 with two-wing hydraulic fractures on both sides of the production horizontal wells.

[0111] Furthermore, in order to illustrate the efficient mining effect of the mining method provided by the present invention, a specific embodiment is used for illustration, as follows:

[0112] Example 1

[0113] In this embodiment, a well pattern design and a production system design were carried out based on the conditions of a deep low-permeability heavy oil reservoir in Xinjiang using the mining method provided by the present invention.

[0114] Reservoir parameters: Reservoir depth is 2000m, crude oil degassing viscosity is 650mPa·s at reservoir temperature, and density is 0.92kg / cm 3 The porosity is 0.22, the permeability is 45md, the oil saturation is 0.62, the formation pressure is 29MPa, the natural gas is mainly methane, the bubble point pressure is 12MPa, the crude oil volume coefficient is 1.0536, and the oil layer thickness is 17m.

[0115] 1. Deployment of horizontal well pattern

[0116] A three-dimensional horizontal well pattern was deployed within the production area of ​​the heavy oil reservoir. The top of the pattern was an injection well with laterals. The horizontal section of the injection well was 300 meters long. The laterals were arranged symmetrically on either side of the horizontal well in a fishbone pattern, forming a 60-degree angle with the horizontal section of the injection well. Each lateral was 80 meters long, with a 50-meter spacing between adjacent laterals. A production well was deployed at the bottom of the reservoir, with two auxiliary production wells located on the same horizontal plane, one on each side. The three horizontal wells at the bottom were spaced 80 meters apart. During the fracturing operation, the fractures were 30 meters long, with two laterals arranged in a staggered pattern.

[0117] 2. Gas huff and puff mining stage

[0118] The horizontal well at the top of the oil layer injects N2 for 30 days. The N2 injection rate is calculated to be 20,000 m3 according to the injection rate formula of the first gas. 3 / d. The production horizontal wells and auxiliary production horizontal wells at the bottom of the oil layer are simultaneously produced by huff-and-puff production. The gas injection rate of the production horizontal wells and auxiliary horizontal wells during the injection phase is calculated as 23000m according to the injection rate formula of the second gas. 3 / d for 3 weeks, then the well is shut down for 3 days. When the daily output of a single well drops to 3t / d during the mining phase, production is terminated and the next round of gas huff and puff is started until the top and bottom air cavities are connected.

[0119] 3. Emulsifier + gas displacement mining stage

[0120] When the top gas interface drops to the vicinity of the bottom production well so that the top and bottom gas cavities are connected, the bottom production horizontal well is injected with a plug-type combination of N2, water and emulsifier (the mass ratio of emulsion to water is 1:9, and the emulsion contains, by mass percentage, 50% of Span 40, 15% of ethanolamine, and 45% of carbonamide) for 5 days, respectively, at an injection rate of 25,000 m 3 / d, 200t / d and 50t / d. The injection rate of N2 in the horizontal well is 30000m 3 The production and injection horizontal wells alternated for one month, with auxiliary production horizontal wells on both sides producing oil. The peak production rate for a single well was 17 tons per day. Production was terminated when the well group's daily production dropped to 4 tons per day.

[0121] Table 1

[0122]

[0123]

[0124] As shown in Table 1, the effective production period using the three-dimensional well pattern + emulsifier flooding + gas flooding technology is 21 years, with an ultimate recovery of 36%, significantly improving oil production rate. The mining method of the present invention extends the economically effective production period by approximately 8.5 years while simultaneously increasing oil production rate and ultimate recovery rate.

[0125] Example 2

[0126] In this embodiment, a well pattern design and a production system design were carried out based on the conditions of a deep low-permeability heavy oil reservoir in Xinjiang using the mining method provided by the present invention.

[0127] Reservoir parameters: Reservoir depth is 1500m, crude oil degassing viscosity is 600mPa·s at reservoir temperature, and density is 0.92kg / cm 3 The porosity is 0.19, the permeability is 40md, the oil saturation is 0.63, the formation pressure is 22MPa, the natural gas is mainly methane, the bubble point pressure is 11.8MPa, the crude oil volume coefficient is 1.0542, and the oil layer thickness h is 21m.

[0128] 1. Horizontal well pattern

[0129] A three-dimensional horizontal well pattern was deployed within the production area of ​​the heavy oil reservoir. The top of the pattern was an injection well with laterals. The horizontal section of the injection well was 500 meters long. The laterals were arranged symmetrically on either side of the horizontal well in a fishbone pattern, forming a 60° angle with the horizontal section of the injection well. Each lateral was 100 meters long, with a 50-meter spacing between adjacent laterals. A production well was deployed at the bottom of the reservoir, with two auxiliary production wells located on the same horizontal plane, one on each side. The three horizontal wells at the bottom were spaced 100 meters apart. During the fracturing operation, the fractures were 35 meters long, with two laterals arranged in a staggered pattern.

[0130] 2. Gas huff and puff mining stage

[0131] The injection well at the top of the oil layer injects CO2 for 30 days. The injection rate of CO2 is calculated as 40,000 m according to the injection rate formula of the first gas. 3 / d. The production horizontal wells and auxiliary production horizontal wells at the bottom of the oil layer are simultaneously produced by huff-and-puff production. The gas injection rate of the production horizontal wells and auxiliary horizontal wells during the injection phase is calculated as 25,000 m / s according to the injection rate formula of the second gas. 3 / d for 3 weeks, then the well is shut down for 3 days. When the daily output of a single well drops to 3t / d during the mining phase, production is terminated and the next round of gas huff and puff is started until the top and bottom air cavities are connected.

[0132] 3. Emulsifier + gas displacement mining stage

[0133] When the top gas interface drops to the vicinity of the bottom production well, so that the top and bottom gas cavities are connected, a combination of CO2, water and emulsifier (the mass ratio of emulsion to water is 1:9.5, and the mass percentage of emulsion includes: Span 60 is 60%, acrylamide is 5%, and carbonamide is 35%) is injected into the bottom production horizontal well in a slug-like manner for 5 days at an injection rate of 20,000 m 3 / d, 240t / d and 60t / d. The injection rate of CO2 in the horizontal well is 50000m 3 The production and injection horizontal wells alternated for two months, with auxiliary production horizontal wells on both sides producing oil. Peak production per well reached 15 t / d. Production ceased when the well group's daily production dropped to 4 t / d.

[0134] Table 2

[0135] Technology Comparison Time (year) Recovery rate (%) Single well peak oil production rate (t / d) Gas throughput 15 17 10 Mining method of the present invention 25 38.6 15

[0136] As shown in Table 2, based on production data, the effective production time using the measures of the present invention is 25 years, and the ultimate recovery rate is 38.6%. The mining method of the present invention extends the economically effective production time by approximately 10 years, while also increasing the oil production rate and ultimate recovery rate.

[0137] In summary, the mining method provided by the present invention uses a mining method in which gas, water and emulsifiers are injected in an alternating plug-like manner at the top and bottom of the oil. This method uses horizontal wells with branch wells and fracturing technology to maintain formation energy, expand the volume of gas and emulsifier swept, and improve oil recovery efficiency. At the same time, the injection type and injection speed of gas in each stage are optimized to achieve the best development effect and extend the mining period by 10-15 years. At the same time, the compounded emulsifier in the present invention can efficiently form an emulsified oil belt to prevent gas and water channeling, which is beneficial to improving the displacement efficiency. Compared with traditional emulsifiers, the water content range of the emulsified oil produced stably is large. When the water content is as high as 60%, the emulsification effect remains unchanged, which has the advantages of low cost and good effect. Furthermore, the present invention adopts a three-dimensional well pattern development method of jointly injecting gas and emulsifier. The injection of gas replenishes the formation energy and forms a top gravity drive; the injection of emulsifier at the bottom improves the gas displacement efficiency and prevents gas channeling; the two auxiliary production wells are located on both sides of the production well, which is conducive to the production of residual oil at the edge, and the peak oil production rate of a single well is increased by 50%, and the final recovery rate is increased by more than 20%.

[0138] It should be noted that the present invention uses the above-described embodiments to illustrate the detailed structural features of the present invention. However, the present invention is not limited to these detailed structural features, and this does not mean that the present invention must rely on these detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent replacements for selected components, additions of auxiliary components, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present invention.

[0139] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

[0140] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0141] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for developing a deep low-permeability heavy oil reservoir, characterized in that: The development method includes: S1. Deploy a three-dimensional development well pattern of gas drive + gas huff-and-puff + multi-element slug composite drive horizontal wells, including at least one basic development unit; the basic development unit includes an injection horizontal well with a fishbone branch well at the top of the reservoir, a production horizontal well with two-wing hydraulic fractures at the bottom of the reservoir, and a first auxiliary production horizontal well and a second auxiliary production horizontal well with two-wing hydraulic fractures on both sides of the production horizontal well; S2, injecting the first gas into the injection horizontal well at the top of the oil reservoir, and simultaneously performing gas huff and puff, injecting the second gas into the production horizontal well, the first auxiliary production horizontal well, and the second auxiliary production well at the bottom of the oil reservoir, and then shutting down the well to produce oil; S3. After step S2 is repeated 2-3 times, when the gas cavities at the top and bottom of the reservoir are connected, the drive is switched to multi-segment composite drive, the injection horizontal well performs the first oil-emulsion-gas drive, the production horizontal well performs the second oil-emulsion-gas drive, and the first auxiliary production horizontal well and the second auxiliary production horizontal well both produce oil.

2. The method for developing a deep low-permeability heavy oil reservoir according to claim 1, characterized in that: The injection horizontal well is designed as a fishbone branch well structure, with the angle between the branch well and the horizontal well being 45-60°; the two-wing hydraulic fractures and the production horizontal well are in a vertical position relationship, the fractures between the horizontal wells are staggered, and the length of the hydraulic fractures is controlled at 35-50m.

3. The method for developing a deep low-permeability heavy oil reservoir according to claim 1 or 2, characterized in that: In step S1, the ratio of the number of injection horizontal wells at the top of the reservoir, the number of production horizontal wells at the bottom of the reservoir, and the number of auxiliary production horizontal wells at the bottom of the oil layer is 1:1:

2.

4. The method for developing a deep low-permeability heavy oil reservoir according to any one of claims 1 to 3, characterized in that: The specific steps include: S201, injecting a first gas into the horizontal injection well at the top of the oil reservoir, wherein the injected first gas includes one or a combination of at least two of nitrogen, carbon dioxide, or methane; S202, performing gas huff and puff in the production horizontal well, the first auxiliary production horizontal well, and the second auxiliary production horizontal well at the bottom of the oil reservoir, injecting a sufficient amount of second gas required for the gas huff and puff, then shutting down the wells, and then producing, wherein the second gas injected during the gas huff and puff comprises nitrogen and / or carbon dioxide; S203. When the gas cavities at the top and bottom of the oil reservoir are connected, the injection horizontal well performs a first oil-emulsion-gas drive, and the production horizontal well performs a second oil-emulsion-gas drive. The first oil-emulsion-gas drive performed by the injection horizontal well and the second oil-emulsion-gas drive performed by the production horizontal well are performed alternately at fixed cycles, and the first auxiliary production horizontal well and the second auxiliary production horizontal well both produce oil.

5. The method for developing a deep low-permeability heavy oil reservoir according to claim 4, characterized in that: The injection endpoint of the first gas is when the volume of the gas cavity at the top of the oil reservoir is 35-45% of the initial volume of the gas cavity at the top of the oil reservoir.

6. The method for developing a deep low-permeability heavy oil reservoir according to claim 4 or 5, characterized in that: The injection medium of the first oil-emulsion gas flooding and the second oil-emulsion gas flooding includes a combination of a gas medium and a liquid medium or a gas medium.

7. The method for developing a deep low-permeability heavy oil reservoir according to any one of claims 4 to 6, characterized in that: The injection rate of the first gas injected into the horizontal well in step S201 is obtained by formula (I): Q g =0.05πabH(I) Where Q g is the total gas injection volume of a single horizontal injection well, in m 3 ;π is 3.14, dimensionless; a and b are the major and minor axis treatment radii of the ellipsoid centered on the horizontal section trajectory of the horizontal well, in m; H represents the thickness of the oil layer, in m.

8. The development method according to any one of claims 1 to 7, characterized in that: The injection rate of the second gas in the gas throughput in step S202 is obtained by formula (II): Where, ν g is the gas injection rate of a single horizontal well, in m 3 / day; π is 3.14, dimensionless; α is the empirical coefficient, dimensionless; P is the formation pressure, unit is MPa; a and b are the major and minor axis treatment radii of the ellipsoid centered on the horizontal section trajectory of the horizontal well, unit is m; H represents the thickness of the oil layer, in m; ρ g is the density of injected gas, in g / L; T is the formation temperature, in °C; n is the number of gas huff-and-puff cycles, dimensionless; t c It is the gas throughput cycle, in day.

9. The method for developing a deep low-permeability heavy oil reservoir according to any one of claims 4 to 8, characterized in that: The gaseous medium includes nitrogen and / or carbon dioxide; Preferably, the injection speed of the gas medium is 20000-50000m 3 / d; Preferably, the liquid medium comprises water and an emulsion; Preferably, the injection rate of water in the liquid medium is 200-250t / d; Preferably, the injection rate of the emulsion in the liquid medium is 50-60 t / d; Preferably, the mass ratio of the emulsion to water is 1:(9-9.5); Preferably, the emulsion comprises, by weight percentage, 50-60 wt % of a Span emulsifier, 5-15 wt % of an ammonium salt anti-swelling agent, and 25-45 wt % of carbonamide.

10. The method for developing a deep low-permeability heavy oil reservoir according to any one of claims 4 to 9, characterized in that: The well spacing between the production horizontal well and the first auxiliary production horizontal well is 70-100m; Preferably, the well spacing between the production horizontal well and the second auxiliary production horizontal well is 70-100m; Preferably, the horizontal section length of the production horizontal well is 200-300m.

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