Chemical flooding development method for strong heterogeneous medium-low permeability oil reservoir

Abstract

This disclosure relates to a chemical flooding development method for highly heterogeneous, low-to-medium permeability reservoirs. The method involves preferentially injecting a first substance into the thin, poor-permeability layer of the reservoir, followed by the simultaneous injection of a second, third, and fourth substance into both the thin, poor-permeability layer and the good-permeability layer. The second substance blocks the dominant flow channels in the target layer; the third substance adjusts the liquid absorption profile of the target layer, expands the swept volume, and improves the oil displacement efficiency; and the fourth substance prevents the third substance from advancing along the dominant flow channels. Ultimately, the remaining oil in the thin, poor-permeability layer is effectively displaced, and the dominant flow channels in the good-permeability layer are blocked, forming a balanced, continuous, and effective displacement method suitable for highly heterogeneous, low-to-medium permeability reservoirs. Therefore, the chemical flooding development method provided by this invention can effectively improve the recovery rate of low-to-medium permeability reservoirs.

Description

Technical Field

[0001] This invention relates to the fields of reservoir engineering and tertiary oil recovery technology, and in particular to a chemical flooding development method for highly heterogeneous, low-permeability reservoirs. Background Technology

[0002] The statements in this section provide only background information in connection with this disclosure and do not constitute prior art.

[0003] In domestic and international sandstone and conglomerate oilfields, water injection development can achieve an average recovery rate of around 35%. To further improve oil recovery, chemical flooding is typically employed after waterflooding to extract remaining oil. High-permeability reservoirs, benefiting from their large reservoir thickness, high permeability, and low heterogeneity, benefit from effective displacement of remaining oil after chemical flooding, potentially increasing recovery by 15-20 percentage points compared to waterflooding. As oilfield development progresses into the mid-to-late stages, the target of chemical flooding gradually deteriorates, shifting from high-permeability reservoirs to medium-to-low-permeability reservoirs.

[0004] In existing technologies, chemical flooding in low-to-medium permeability reservoirs uses the same methods as in high-permeability reservoirs. However, due to factors such as thin reservoir thickness, low permeability, and strong interlayer heterogeneity, this method cannot effectively tap the remaining oil in thin and poor layers of low-to-medium permeability reservoirs, resulting in a limited increase in recovery rate of only 5-10 percentage points.

[0005] Therefore, it is necessary to explore an efficient chemical flooding development method for medium- and low-permeability reservoirs, so as to fully exploit the remaining oil in both good and poor layers of medium- and low-permeability reservoirs, thereby further improving the development effect.

[0006] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art. Summary of the Invention

[0007] In view of this, the present invention provides a chemical flooding development method suitable for highly heterogeneous medium-low permeability reservoirs, which solves the problem that using the same method for chemical flooding in medium-low permeability reservoirs as in high permeability reservoirs cannot effectively tap the remaining oil in thin and poor layers, resulting in limited improvement in oil recovery.

[0008] To solve the above-mentioned technical problems, the present invention provides a method for chemical flooding development of highly heterogeneous, low-to-medium permeability reservoirs. The technical concept of this method is as follows:

[0009] By prioritizing the injection of the first substance into the thin, poor-quality layer of the reservoir, and then simultaneously injecting the second, third, and fourth substances into both the thin, poor-quality layer and the good-quality layer in sequence, the aim is to effectively displace the remaining oil in the thin, poor-quality layer and effectively block the dominant seepage channels in the good-quality layer, thereby ultimately improving the development effect.

[0010] To achieve the above-mentioned objective, the chemical flooding development method for highly heterogeneous, low-to-medium permeability reservoirs comprises the following steps:

[0011] Injecting a first substance into a thin, concave layer of the target reservoir to expand the swept volume and effectively displace the remaining oil in the thin, concave layer;

[0012] A second substance is simultaneously injected into both the good and poor layers of the target reservoir to block the dominant seepage channels of the target layer.

[0013] A third substance is simultaneously injected into the thin poor layer and the good layer to adjust the liquid absorption profile of the target layer, expand the swept volume and improve the oil displacement efficiency.

[0014] A fourth substance is simultaneously injected into both the thin, poor layer and the good layer to prevent the third substance from advancing along the dominant seepage channel.

[0015] In this disclosure and possible embodiments, water is injected into the thin layer of the target reservoir before simultaneously injecting the second substance into the good layer and the thin layer of the target reservoir until the water cut of the produced fluid reaches 98%.

[0016] In this disclosure and possible embodiments, after simultaneously injecting a fourth substance into the thin poor layer and the good layer, water is simultaneously injected into the good layer and the thin poor layer of the target reservoir until the water content of the produced fluid reaches 98%.

[0017] In this disclosure and possible embodiments, the injection amount of the first substance is 0.05-0.6 PV; the injection amount of the second substance is 0.05-0.3 PV; the injection amount of the third substance is 0.2-0.8 PV; the injection amount of the fourth substance is 0.1-0.5 PV; where PV is the pore volume of the target reservoir.

[0018] In this disclosure and possible embodiments, the first substance is selected from at least one of water, a first polymer, and a first surfactant;

[0019] The second substance is a second polymer;

[0020] The third substance is selected from at least one of the first polymer, binary composite system, and ternary composite system;

[0021] The fourth substance is the first polymer.

[0022] In this disclosure and possible embodiments, the water is clean water from the oilfield and / or wastewater from the oilfield.

[0023] The first polymer is partially hydrolyzed polyacrylamide;

[0024] The first surfactant is selected from at least one of petroleum sulfonate, alkylbenzene sulfonate, steric hindrance surfactant, and fatty alcohol polyoxypropylene ether sulfate;

[0025] The second polymer is a partially hydrolyzed polyacrylamide with a molecular weight and viscosity greater than that of the first polymer;

[0026] The binary composite system, by weight percentage, comprises: 0.1-0.5% of a first surfactant, 0.05-0.3% of a first polymer, and the remainder being wastewater from the oilfield.

[0027] The ternary composite system, by weight percentage, comprises: 0.1-0.4% of a first surfactant, 0.05-0.3% of a first polymer, 0.05-1.8% of an additive, and the balance being wastewater from the oilfield; the additive is selected from at least one of sodium hydroxide, sodium bicarbonate, sodium carbonate, and sodium chloride.

[0028] In this disclosure and possible embodiments, the injection method of the first substance includes:

[0029] (3) Inject the water, the first polymer, or the first surfactant separately;

[0030] (4) The first polymer and the first surfactant are injected sequentially.

[0031] In this disclosure and possible embodiments, the injection method of the first substance includes:

[0032] (1) Inject 0.05-0.6 PV of the water, the first polymer, or the first surfactant separately;

[0033] (2) Sequentially inject 0.05-0.3 PV of the first polymer and 0.05-0.3 PV of the first surfactant.

[0034] In this disclosure and possible embodiments, the injection method of the third substance includes:

[0035] (1) Inject the first polymer, the binary composite system, or the ternary composite system separately;

[0036] (2) The first polymer and the binary composite system are injected sequentially;

[0037] (3) The first polymer and the ternary composite system are injected sequentially.

[0038] In this disclosure and possible embodiments, the injection method of the third substance includes:

[0039] (1) The first polymer, the binary composite system, or the ternary composite system are injected separately at a concentration of 0.2-0.8 PV;

[0040] (2) Sequentially inject 0.05-0.2 PV of the first polymer and 0.15-0.6 PV of the binary composite system;

[0041] (3) Sequentially inject 0.05-0.2 PV of the first polymer and 0.15-0.6 PV of the ternary composite system.

[0042] In this disclosure and possible embodiments, the partially hydrolyzed polyacrylamide is one of the following: salt-resistant partially hydrolyzed polyacrylamide with added salt-resistant functional monomers, hydrophobic partially hydrolyzed polyacrylamide with added hydrophobic functional monomers, modified partially hydrolyzed polyacrylamide with added salt-resistant and hydrophobic functional monomers, thermally tackifying partially hydrolyzed polyacrylamide with added thermally tackifying functional monomers, and salt-tackifying partially hydrolyzed polyacrylamide with added salt-tackifying functional monomers.

[0043] In this disclosure and possible embodiments, based on reservoir logging interpretation, waterflood interpretation, fine description, profile test data, and core well data, the depth range of oil layers with small effective thickness, low permeability, and low water washing degree in the target reservoir is determined as the aforementioned thin and poor layers, and the remaining layers are the good layers.

[0044] The present invention has the following beneficial effects:

[0045] The chemical flooding development method for highly heterogeneous, low-to-medium permeability reservoirs of the present invention involves preferentially injecting a first substance into the thin, poor-permeability layer of the reservoir, and then simultaneously injecting a second, third, and fourth substance into the thin, poor-permeability layer and the good-permeability layer in sequence. This effectively displaces the remaining oil in the thin, poor-permeability layer and blocks the dominant seepage channels in the good-permeability layer, forming a balanced, continuous, and effective displacement method adapted to highly heterogeneous, low-to-medium permeability reservoirs. The chemical flooding development method provided by the present invention can effectively improve the recovery rate of low-to-medium permeability reservoirs. Attached Figure Description

[0046] The above and other objects, features and advantages of the present invention will become clearer from the following description of embodiments of the invention with reference to the accompanying drawings, in which:

[0047] Figure 1 This is a schematic diagram of a highly heterogeneous, low-permeability core model in Embodiment 1 of the present invention;

[0048] Figure 2 This is a schematic diagram of the thin, poor layer and the good layer in Embodiment 2 of the present invention;

[0049] Figure 3 These are the chemical flooding development effect curves of the thin, poor layer and the good layer in Embodiment 2 of the present invention. Detailed Implementation

[0050] The present invention will now be described based on embodiments, but it is worth noting that the present invention is not limited to these embodiments. In the following detailed description of the invention, certain specific details are described in detail. However, those skilled in the art will fully understand the invention for the parts not described in detail.

[0051] Furthermore, unless the context explicitly requires it, the words "comprising," "including," and similar terms throughout the specification and claims should be interpreted as including rather than exclusive or exhaustive; that is, meaning "including but not limited to."

[0052] The chemical flooding development method for highly heterogeneous, low-to-medium permeability reservoirs described in various embodiments of the present invention includes the following steps:

[0053] 1. Based on reservoir logging interpretation, water flooding interpretation, detailed description, profile test data, and core well data, determine the depth range of oil layers with small effective thickness, low permeability, and low water washing degree in the target reservoir. These are the thin and poor layers, and the remaining layers are the good layers.

[0054] 2. Inject the first substance into the thin, poor-quality layer of the target reservoir determined in step 1 to expand the swept volume and improve the oil displacement efficiency;

[0055] In one specific embodiment, the first substance is selected from at least one of water, a first polymer, and a first surfactant; wherein, the first polymer is partially hydrolyzed polyacrylamide, and the partially hydrolyzed polyacrylamide may be one of the following: salt-resistant partially hydrolyzed polyacrylamide with added salt-resistant functional monomers, hydrophobic partially hydrolyzed polyacrylamide with added hydrophobic functional monomers, modified partially hydrolyzed polyacrylamide with added salt-resistant and hydrophobic functional monomers, thermally tackifying partially hydrolyzed polyacrylamide with added thermally tackifying functional monomers, and salt-tackifying partially hydrolyzed polyacrylamide with added salt-tackifying functional monomers; the first surfactant is selected from one of petroleum sulfonate, alkylbenzene sulfonate, steric hindrance surfactant, and fatty alcohol polyoxypropylene ether sulfate.

[0056] In one specific embodiment, the injection of the first substance may be carried out in the following manner:

[0057] (1) Inject 0.05-0.6 PV of the water separately;

[0058] (2) Injecting 0.05-0.6 PV of the first polymer separately;

[0059] (3) Injecting 0.05-0.6 PV of the first surfactant separately;

[0060] (4) Sequentially inject 0.05-0.3 PV of the first polymer and 0.05-0.3 PV of the first surfactant.

[0061] 3. Inject water into the thin, poor-quality layer of the target reservoir until the water cut of the produced fluid reaches 98%;

[0062] 4. Simultaneously inject a second substance into both the good and poor layers of the target reservoir to block the dominant seepage channels of the target layer;

[0063] The superior seepage channel refers to a seepage channel with a larger pore size in the target reservoir. During liquid seepage, this seepage channel has an advantage over other channels in terms of flow rate and / or flow velocity.

[0064] In one specific embodiment, the second substance is a second polymer, which is a partially hydrolyzed polyacrylamide with a molecular weight and viscosity greater than that of the first polymer.

[0065] 5. Simultaneously inject a third substance into the good and poor layers of the target reservoir to adjust the liquid absorption profile of the target layer, expand the swept volume, and improve the oil displacement efficiency.

[0066] The liquid absorption profile refers to the distribution ratio of the injected liquid in each layer at the injection end, with a high liquid absorption ratio in the high permeability layer and a low liquid absorption ratio in the low permeability layer.

[0067] In one specific embodiment, the third substance is selected from at least one of the first polymer, a binary composite system, and a ternary composite system; the binary composite system, by weight percentage, comprises: 0.1-0.5% of the first surfactant, 0.05-0.3% of the first polymer, and the balance being wastewater from the oilfield; the ternary composite system, by weight percentage, comprises: 0.1-0.4% of the first surfactant, 0.05-0.3% of the first polymer, 0.05-1.8% of the additive, and the balance being wastewater from the oilfield; the additive is selected from at least one of sodium hydroxide, sodium bicarbonate, sodium carbonate, and sodium chloride.

[0068] In one specific embodiment, the injection method of the third substance includes:

[0069] (1) Injecting 0.2-0.8 PV of the first polymer separately;

[0070] (2) The binary composite system is injected separately at a concentration of 0.2-0.8 PV;

[0071] (3) The ternary composite system is injected separately at a concentration of 0.2-0.8 PV;

[0072] (4) Sequentially inject 0.05-0.2 PV of the first polymer and 0.15-0.6 PV of the binary composite system;

[0073] (5) Sequentially inject 0.05-0.2 PV of the first polymer and 0.15-0.6 PV of the ternary composite system.

[0074] 6. Simultaneously inject a fourth substance into the good and poor layers of the target reservoir to prevent the third substance from advancing along the dominant seepage channels;

[0075] In one specific embodiment, the fourth substance is the first polymer.

[0076] 7. Simultaneously inject water into the good and poor layers of the target reservoir until the water cut of the produced fluid reaches 98%.

[0077] In one specific embodiment, the injection amount of the first substance is 0.05-0.6 PV; the injection amount of the second substance is 0.05-0.3 PV; the injection amount of the third substance is 0.2-0.8 PV; and the injection amount of the fourth substance is 0.1-0.5 PV; wherein PV is the pore volume of the target reservoir.

[0078] The following are preferred embodiments of this disclosure.

[0079] Example 1

[0080] In Example 1, chemical flooding was performed on a simulated oil reservoir with strong heterogeneity and low permeability according to the method of the present invention, and the experimental results of the chemical flooding method were evaluated. The simulated oil reservoir was a three-layer heterogeneous planar core model, from top to bottom, namely layer 1, layer 2, and layer 3, with effective permeabilities of 30, 60, and 120 mD, heights of 1.25, 1.25, and 2.5 cm, and lengths and widths of 50 and 50 cm, respectively. Before chemical flooding of the simulated strong heterogeneous low permeability oil reservoir, the simulated oil reservoir needed to be pretreated. The pretreatment method was to water flood the simulated oil reservoir to a water cut of 98% at 45°C.

[0081] The specific chemical flooding method steps in Example 1 are as follows:

[0082] (1) Based on the permeability and thickness characteristics of simulated strong heterogeneous low-permeability reservoirs, layer 1 and layer 2 were determined to be thin and poor layers, while layer 3 was a good layer.

[0083] (2) The first material was injected into the thin layers (layers 1 and 2) at a rate of 0.2 PV:

[0084] In this embodiment 1, the first material injected into the thin differential layers (layers 1 and 2) adopted the following sixteen schemes:

[0085] Options a1-a4: Water;

[0086] Schemes a5-a8: First surfactant A1;

[0087] Schemes a9-a12: First polymer B1;

[0088] Schemes a13-a16: First polymer C1;

[0089] The first surfactant, A1, is 0.3% petroleum sulfonate, prepared from wastewater injected into the Daqing Oilfield.

[0090] The first polymer B1 is a modified partially hydrolyzed polyacrylamide of 0.15% (degree of hydrolysis 21%, molecular weight 8 million) with thickening, injection and emulsifying properties. It was prepared from injected wastewater from Daqing Oilfield and the system viscosity is 20 mPa·s.

[0091] The first polymer C1 comprises the following components by weight percentage: 0.15% partially hydrolyzed polyacrylamide, with water as the balance. The partially hydrolyzed polyacrylamide has a degree of hydrolysis of 23% and a molecular weight of 8 million; the water is wastewater injected from Daqing Oilfield; the system viscosity is 20 mPa·s.

[0092] (3) Inject water into the thin differential layers (layers 1 and 2) until the water content of the produced liquid reaches 98%.

[0093] (4) The second substance is injected into the thin poor layer and the good layer (layer 1, 2, 3) at the same time, and the injection amount is 0.1PV.

[0094] In this Example 1, a second polymer was simultaneously injected into the thin poor layer and the good layer (layers 1, 2, 3). The composition of the polymer, by weight percentage, is as follows: 0.2% partially hydrolyzed polyacrylamide, with water as the balance; the degree of hydrolysis of the partially hydrolyzed polyacrylamide is 22%, and the molecular weight is 12 million; the water is wastewater injected from Daqing Oilfield; the viscosity of the system is 42 mPa·s.

[0095] (5) A third substance was simultaneously injected into the thin, poor-quality layer and the good-quality layer (layers 1, 2, and 3), with an injection volume of 0.6 PV:

[0096] In this embodiment 1, the third substance simultaneously injected into the thin poor layer and the good layers (layers 1, 2, and 3) includes the following sixteen schemes:

[0097] Option a1: First polymer B2;

[0098] Option a2: First polymer C2;

[0099] Option a3: Binary composite system;

[0100] Option a4: Ternary composite system;

[0101] Option a5: First polymer B2;

[0102] Scheme a6: First polymer C2;

[0103] Option a7: Binary composite system;

[0104] Option A8: Ternary composite system;

[0105] Option a9: First polymer B2;

[0106] Scheme a10: First polymer C2;

[0107] Scheme a11: Binary composite system;

[0108] Option a12: Ternary composite system;

[0109] Option a13: First polymer B2;

[0110] Scheme a14: First polymer C2;

[0111] Scheme A15: Binary composite system;

[0112] Option a16: Ternary composite system;

[0113] The first polymer B2 is 0.20% modified partially hydrolyzed polyacrylamide (degree of hydrolysis 21%, molecular weight 8 million) with thickening, injection and emulsifying properties, prepared from sewage injected from Daqing Oilfield, with a system viscosity of 30 mPa·s.

[0114] The first polymer C2, by weight percentage, comprises: 0.20% partially hydrolyzed polyacrylamide and the balance water. The partially hydrolyzed polyacrylamide has a degree of hydrolysis of 23% and a molecular weight of 8 million; the water is wastewater injected from Daqing Oilfield; the system viscosity is 31 mPa·s.

[0115] The binary composite system comprises, by weight percentage: 0.3% first surfactant, 0.28% first polymer, and the balance being water; wherein the first surfactant is petroleum sulfonate; the first polymer is partially hydrolyzed polyacrylamide with a degree of hydrolysis of 23% and a molecular weight of 8 million; and the water is wastewater injected from Daqing Oilfield. The interfacial tension of the binary composite system is 8.5 × 10⁻⁶. -3 mN / m, viscosity is 31mPa·s.

[0116] The ternary composite system comprises, by weight percentage: 0.3% first surfactant, 0.26% first polymer, 1.2% additives, and the balance being water; wherein the first surfactant is petroleum sulfonate; the first polymer is partially hydrolyzed polyacrylamide with a degree of hydrolysis of 23% and a molecular weight of 8 million; the additive is sodium carbonate; and the water is wastewater injected from Daqing Oilfield. The interfacial tension of the ternary composite system is 5.5 × 10⁻⁶.-3 mN / m, viscosity is 32mPa·s.

[0117] (6) A fourth substance was simultaneously injected into the thin poor layer and the good layer (layers 1, 2, 3), with an injection amount of 0.2 PV.

[0118] In this Example 1, the fourth substance injected is the first polymer C2.

[0119] (7) Simultaneously inject water into the thin, poor layer and the good layer (layers 1, 2, 3) until the water content of the produced liquid reaches 98%.

[0120] The results of the chemical flooding experiment in Example 1 are shown in Table 1:

[0121] Table 1. Experimental results of chemical flooding in a simulated highly heterogeneous low-to-medium permeability reservoir in Example 1.

[0122]

[0123]

[0124] As shown in Table 1, the total recovery rate can be increased by 17.2% to 29.0%.

[0125] Comparative Example 1

[0126] For ease of comparison, chemical flooding experiments were conducted using the simulated highly heterogeneous low-permeability reservoir and existing chemical flooding methods suitable for high-permeability reservoirs. The steps of the chemical flooding method suitable for high-permeability reservoirs are as follows:

[0127] (1) The first substance was injected into the thin poor layer and the good layer (layer 1, 2, 3) at a rate of 0.2 PV.

[0128] (2) The second substance is injected into the thin poor layer and the good layer (layer 1, 2, 3) at the same time, and the injection amount is 0.1PV.

[0129] (3) A third substance was simultaneously injected into the thin poor layer and the good layer (layers 1, 2, 3), with an injection amount of 0.6 PV.

[0130] (4) A fourth substance was simultaneously injected into the thin poor layer and the good layer (layers 1, 2, 3), with an injection amount of 0.2 PV.

[0131] (5) Simultaneously inject water into the thin, poor layer and the good layer (layers 1, 2, and 3) until the water content reaches 98%.

[0132] The first, second, third, and fourth substances are completely identical to those in Example 1. Chemical flooding experiments were conducted using existing methods suitable for high-permeability reservoirs, and the results are shown in Table 2.

[0133] Table 2 shows the experimental results of chemical flooding in a simulated highly heterogeneous low-permeability reservoir, as described in Comparative Example 1.

[0134]

[0135] As shown in Table 2, the simultaneous injection of the first, second, third, and fourth substances and water into the thin, poor, and good layers of the simulated reservoir can increase the total oil recovery by 14.2% to 23.3%.

[0136] As can be seen from the comparison of Tables 1 and 2, under the same simulated highly heterogeneous low-permeability reservoir conditions, the method of this invention improves the total oil recovery rate by 3.0-5.7% compared with the existing chemical flooding methods suitable for high-permeability reservoirs, showing a significant improvement in performance.

[0137] Example 2

[0138] The method of this invention is further illustrated through a field chemical flooding test in the Beierdong Gaotaizi oil reservoir of the Sabei Development Zone in the Daqing Changyuan Oilfield. The Beierdong Gaotaizi oil reservoir is a highly heterogeneous, low-to-medium permeability reservoir with uneven reservoir thickness and remaining oil distribution, and large permeability variations (permeability variation = maximum permeability value in the reservoir / minimum permeability value in the reservoir; excessively large permeability variations will affect the effectiveness of chemical flooding). The specific method steps are as follows:

[0139] 1. Based on reservoir logging interpretation, water flooding interpretation, detailed description, profile testing data, and core data, the oil layers in the GⅠ-GⅡ section of the chemical flooding test area of ​​the Beierdong Gaotaizi oil reservoir with an effective thickness of no more than 0.5m and a permeability of no more than 50mD were identified as thin and poor layers, with an average depth range of 1065-1165m. Furthermore, the oil layers in the GⅠ10-GⅡ14 section of the test area with an effective thickness of more than 0.5m and a permeability of more than 50mD were identified as good layers, with an average depth range of 1083-1136m.

[0140] 2. Inject the first substance into the thin, poor-quality layer of the chemical flooding test area of ​​the Beierdong Gaotaizi oil reservoir determined in step 1. The injection method is as follows:

[0141] (1) The first material injected into the thin layer is the first polymer A1, and the injection amount is 0.1 PV;

[0142] (2) The first material injected into the thin layer is the first polymer A2, and the injection amount is 0.3 PV;

[0143] (3) The first material injected into the thin layer is the first polymer A3, and the injection amount is 0.2 PV;

[0144] The first polymer A1 is 0.14% partially hydrolyzed polyacrylamide (degree of hydrolysis 23%, molecular weight 4 million), formulated from wastewater injected from Daqing Oilfield, with a system viscosity of 15 mPa·s.

[0145] The first polymer A2 is 0.2% partially hydrolyzed polyacrylamide (degree of hydrolysis 23%, molecular weight 8 million), formulated from wastewater injected from Daqing Oilfield, with a system viscosity of 30 mPa·s.

[0146] The first polymer A3 is 0.16% partially hydrolyzed polyacrylamide (degree of hydrolysis 23%, molecular weight 6 million), formulated from wastewater injected from Daqing Oilfield, with a system viscosity of 20 mPa·s.

[0147] 3. Inject water into the thin layer until the produced liquid has a water content of 98%.

[0148] 4. Simultaneously inject a second substance into both the poor and good layers, with an injection volume of 0.1 PV.

[0149] The second substance is the first polymer A4, which is 0.28% partially hydrolyzed polyacrylamide (degree of hydrolysis 23%, molecular weight 8 million). The first polymer was prepared from wastewater injected into Daqing Oilfield, and the system viscosity is 40 mPa·s.

[0150] 5. Simultaneously inject a third substance into both the good layer and the poor layer. The specific injection method is as follows:

[0151] (1) The third substance injected into both the good layer and the poor layer is the first polymer A2, and the injection amount is 0.1 PV;

[0152] (2) The third material injected into both the good layer and the poor layer is a ternary composite system B1, and the injection amount is 0.35PV.

[0153] (3) The third material injected into both the good layer and the poor layer is a ternary composite system B2, and the injection amount is 0.25 PV.

[0154] The ternary composite system B1, by weight percentage, comprises: 0.3% first surfactant, 0.26% first polymer, 1.2% additives, and the balance being water; wherein the first surfactant is petroleum sulfonate; the first polymer is partially hydrolyzed polyacrylamide with a degree of hydrolysis of 23% and a molecular weight of 8 million; the additive is sodium carbonate; and the water is wastewater injected from Daqing Oilfield. The interfacial tension of the ternary composite system B1 is 4.5 × 10⁻⁶. -3 mN / m, viscosity is 32mPa·s.

[0155] The ternary composite system B2, by weight percentage, comprises: 0.2% first surfactant, 0.26% first polymer, 1.0% additive, and the balance being water; wherein the first surfactant is petroleum sulfonate; the first polymer is partially hydrolyzed polyacrylamide with a degree of hydrolysis of 23% and a molecular weight of 10 million; the additive is sodium carbonate; and the water is wastewater injected from Daqing Oilfield. The interfacial tension of the ternary composite system B2 is 8.5 × 10⁻⁶. -3 mN / m, viscosity is 40mPa·s.

[0156] 6. The fourth substance, the first polymer A5, is simultaneously injected into the good layer and the thin poor layer, with an injection amount of 0.2 PV.

[0157] The first polymer A5 is 0.20% partially hydrolyzed polyacrylamide (degree of hydrolysis 23%, molecular weight 10 million), formulated from wastewater injected into Daqing Oilfield, with a system viscosity of 40 mPa·s.

[0158] 7. Simultaneously inject water into both the good layer and the poor layer until the water content of the produced liquid reaches 98%.

[0159] The results of chemical flooding in Example 2 are shown in Table 3:

[0160] Table 3 Results of chemical flooding in Example 2

[0161]

[0162] Table 3 shows that developing thin, poor-permeability reservoirs first using chemical flooding alone, followed by simultaneous chemical flooding of both thin, poor-permeability, and good-permeability reservoirs, can improve oil recovery by 14.5% throughout the process. Simulations using a mathematical model of the Beierdong Gaotaizi oil reservoir block show that existing chemical flooding methods suitable for high-permeability reservoirs can improve oil recovery by 9.5% throughout the process.

[0163] As can be seen from the above embodiments and comparative examples, the method of the present invention can effectively tap the remaining oil in thin and poor layers of reservoirs, achieve balanced and continuous effect on good layers and thin and poor layers, increase the recovery rate by 5% compared with existing methods, and achieve a significant oil increase effect.

[0164] This chemical flooding method offers flexible injection options that can be adjusted to suit different site conditions and requirements. All the substances used have strong salt tolerance, do not pollute the environment, do not damage the formation, and do not contain prohibited chemicals.

[0165] The above description is merely for the purpose of enabling those skilled in the art to understand the technical solutions of the present invention, and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for chemical flooding development of highly heterogeneous, low-to-medium permeability reservoirs, characterized in that, The steps are as follows: Injecting a first substance into a thin, concave layer of the target reservoir to expand the swept volume and effectively displace the remaining oil in the thin, concave layer; A second substance is simultaneously injected into both the good and poor layers of the target reservoir to block the dominant seepage channels of the target layer. A third substance is simultaneously injected into the thin poor layer and the good layer to adjust the liquid absorption profile of the target layer, expand the swept volume and improve the oil displacement efficiency. A fourth substance is simultaneously injected into both the thin, poor layer and the good layer to prevent the third substance from advancing along the dominant seepage channel.

2. The chemical flooding development method for highly heterogeneous, low-to-medium permeability reservoirs according to claim 1, characterized in that: Before simultaneously injecting the second substance into both the good layer and the poor layer of the target reservoir, the poor layer of the target reservoir is injected until the water cut of the produced fluid reaches 98%.

3. The chemical flooding development method for highly heterogeneous, low-to-medium permeability reservoirs according to claim 2, characterized in that: After simultaneously injecting the fourth substance into the thin, poor layer and the good layer, water is simultaneously injected into the good layer and the thin, poor layer of the target reservoir until the water cut of the produced fluid reaches 98%.

4. The chemical flooding development method for highly heterogeneous, low-to-medium permeability reservoirs according to any one of claims 1-3, characterized in that: The injection volume of the first substance is 0.05-0.6 PV; the injection volume of the second substance is 0.05-0.3 PV; the injection volume of the third substance is 0.2-0.8 PV; the injection volume of the fourth substance is 0.1-0.5 PV; where PV is the pore volume of the target reservoir.

5. The chemical flooding development method for highly heterogeneous, low-to-medium permeability reservoirs according to claim 4, characterized in that: The first substance is selected from at least one of water, the first polymer, and the first surfactant; The second substance is a second polymer; The third substance is selected from at least one of the first polymer, binary composite system, and ternary composite system; The fourth substance is the first polymer.

6. The chemical flooding development method for highly heterogeneous, low-to-medium permeability reservoirs according to claim 5, characterized in that: The water is either clean water or wastewater from the oilfield. The first polymer is partially hydrolyzed polyacrylamide; The first surfactant is selected from one of petroleum sulfonate, alkylbenzene sulfonate, steric hindrance surfactant, and fatty alcohol polyoxypropylene ether sulfate; The second polymer is a partially hydrolyzed polyacrylamide with a molecular weight and viscosity greater than that of the first polymer; The binary composite system, by weight percentage, comprises: 0.1-0.5% of a first surfactant, 0.05-0.3% of a first polymer, and the remainder being wastewater from the oilfield. The ternary composite system, by weight percentage, comprises: 0.1-0.4% of a first surfactant, 0.05-0.3% of a first polymer, 0.05-1.8% of an additive, and the balance being wastewater from the oilfield; the additive is selected from at least one of sodium hydroxide, sodium bicarbonate, sodium carbonate, and sodium chloride.

7. The chemical flooding development method for highly heterogeneous, low-to-medium permeability reservoirs according to claim 5 or 6, characterized in that, The injection method of the first substance includes: (1) Inject the water, the first polymer, or the first surfactant separately; (2) The first polymer and the first surfactant are injected sequentially.

8. The chemical flooding development method for highly heterogeneous, low-to-medium permeability reservoirs according to claim 7, characterized in that: (1) Inject 0.05-0.6 PV of the water, the first polymer, or the first surfactant separately; (2) Sequentially inject 0.05-0.3 PV of the first polymer and 0.05-0.3 PV of the first surfactant.

9. The method for chemical flooding development of highly heterogeneous, low-to-medium permeability reservoirs according to any one of claims 5-8, characterized in that, The method of injecting the third substance includes: (1) Inject the first polymer, the binary composite system, or the ternary composite system separately; (2) The first polymer and the binary composite system are injected sequentially; (3) The first polymer and the ternary composite system are injected sequentially.

10. The chemical flooding development method for highly heterogeneous, low-to-medium permeability reservoirs according to claim 9, characterized in that: (1) The first polymer, the binary composite system, or the ternary composite system are injected separately at a concentration of 0.2-0.8 PV; (2) Sequentially inject 0.05-0.2 PV of the first polymer and 0.15-0.6 PV of the binary composite system; (3) Sequentially inject 0.05-0.2 PV of the first polymer and 0.15-0.6 PV of the ternary composite system.

11. The chemical flooding development method for highly heterogeneous, low-to-medium permeability reservoirs according to claim 6, characterized in that: The partially hydrolyzed polyacrylamide is one of the following: salt-resistant partially hydrolyzed polyacrylamide with added salt-resistant functional monomers, hydrophobic partially hydrolyzed polyacrylamide with added hydrophobic functional monomers, modified partially hydrolyzed polyacrylamide with added salt-resistant and hydrophobic functional monomers, thermally tackifying partially hydrolyzed polyacrylamide with added thermally tackifying functional monomers, and salt-tackifying partially hydrolyzed polyacrylamide with added salt-tackifying functional monomers.

12. The chemical flooding development method for highly heterogeneous, low-to-medium permeability reservoirs according to claim 1, characterized in that: Based on reservoir logging interpretation, water flooding interpretation, detailed description, profile test data, and core well data, the depth range of oil layers with small effective thickness, low permeability, and low water washing degree in the target reservoir is determined as the above-mentioned thin and poor layers, and the remaining layers are the good layers.

Images