A CO2 channeling control system and a method for regulating gas channeling

Abstract

The application relates to the technical field of oil and gas field development, in particular to a CO2 flooding channeling sealing system and a method for regulating gas channeling. The CO2 flooding channeling sealing system comprises an oil-soluble surfactant and supercritical CO2, and the volume ratio of the oil-soluble surfactant to the supercritical CO2 is 1:1000-50:1000 under the conditions of a temperature of 60-80 DEG C and a pressure of 30-35 MPa. The system has the advantages of convenient injection, reduced water sensitivity damage and corrosion and good oil displacement effect.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field development technology, specifically to a CO2 flooding and containment system and a method for regulating gas channeling. Background Technology

[0002] As oil exploration and development continue to deepen, water-injected oilfields are gradually entering a "dual-high" production stage characterized by "high water cut and high recovery rate".

[0003] Water injection development in low-permeability reservoirs not only presents challenges in injection but also carries the risk of damaging water-sensitive reservoirs. For low-permeability tight reservoirs where waterflooding is ineffective, CO2 flooding can achieve better results. However, due to reservoir heterogeneity and the low viscosity of CO2, the unfavorable mobility ratio between CO2 and crude oil easily leads to cross-flow, severely impacting development efficiency. Therefore, controlling the ineffective flow of CO2 fluid in high-permeability channels can increase sweep efficiency, improve CO2 flooding efficiency, and ultimately enhance oil recovery.

[0004] Chinese patent CN107365576B discloses a flow control system for CO2 flooding in low-permeability or ultra-low-permeability reservoirs. The flow control system is a CO2 smart sensitive material that forms a gel-like sealing substance after contacting CO2, thereby blocking CO2 gas migration.

[0005] Chinese patent application CN103628846A discloses a method for improving the CO2 flooding efficiency of low-permeability reservoirs. This method involves reacting the injected CO2 with the previously injected sodium silicate aqueous solution to generate an inorganic gel, which inhibits the flow of CO2 along high-permeability areas, thereby achieving the purpose of sealing and regulating the flooding.

[0006] Chinese patent application CN107435532A discloses a method for controlling CO2 gas channeling using a CO2-responsive surfactant. The method involves first mixing the CO2-responsive surfactant with water at room temperature and pressure and injecting the mixture into the reservoir, and then injecting CO2 to form foam that blocks high-permeability channels, thereby increasing the sweep efficiency of subsequent gas injection. The CO2-responsive surfactant is selected from amidine compounds, guanidine compounds, and amidine / guanidine mixtures.

[0007] Chinese patent application CN105255473A discloses a silicon-containing CO2 aerosol foaming agent. The foaming agent is a non-aqueous medium anti-channeling system. Studies have shown that the CO2 aerosol foaming agent can effectively foam in supercritical CO2 under low water conditions (water content <5%). The CO2 aerosol foaming agent can not only be used in oilfield CO2 gas drive to effectively prevent gas channeling during the gas drive process, but also solve the corrosion problem of equipment.

[0008] Current mainstream channeling control technologies include water-gas alternation technology, foam plugging technology, polymer gel plugging technology, and aerosol foam channeling control technology. However, since these technologies use water-soluble plugging materials, they still cannot solve the problems of difficult injection into highly water-sensitive low-permeability reservoirs, water-sensitive damage, and corrosion of the tubing by carbonated water formed during CO2 injection. These problems severely restrict the efficient development of CO2 injection into highly water-sensitive low-permeability reservoirs.

[0009] Therefore, it is essential to develop a CO2 channeling and containment system that can solve the above-mentioned technical problems and a method for regulating gas channeling. Summary of the Invention

[0010] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a CO2 flooding and sealing system and a method for controlling gas channeling, mainly solving three major technical problems: ① Solving the problem of high injection pressure and difficulty in injecting the sealing agent into water-sensitive, low-permeability reservoirs. ② Solving the problem of damage to highly water-sensitive reservoirs by the sealing agent. ③ Avoiding the corrosion of the downhole tubing caused by the formation of carbonated water from injected CO2 and aqueous solution.

[0011] This invention is achieved through the following technical solutions:

[0012] A CO2 flooding and blocking system includes an oil-soluble surfactant and supercritical CO2, with a volume ratio of 1:1000-50:1000 at a temperature of 60-80℃ and a pressure of 30-35MPa.

[0013] The lipophilic groups of oil-soluble surfactants can effectively interact with formation crude oil and form a foam oil system with CO2.

[0014] Preferably, the oil-soluble surfactant is a nonionic surfactant.

[0015] More preferably, the nonionic surfactant includes at least one of fluorinated acrylic copolymers, perfluorinated alkyl esters, and sucrose ester surfactants.

[0016] This invention also relates to a method for controlling gas channeling using the above-mentioned CO2 channeling control system, comprising the following steps:

[0017] (1) Inject oil-soluble surfactants into the formation after mixing them with supercritical CO2;

[0018] (2) Inject pure CO2 to obtain foam oil, which forms a seal.

[0019] Preferably, the slub content of the oil-soluble surfactant is 0.1-0.4 PV.

[0020] Preferably, the slug injected with pure CO2 in step (2) has a slug strength of 1.0-3.0 PV.

[0021] Preferably, the linear velocity of the injected pure CO2 in step (2) is 0.1-10 m / d to ensure the foaming effect and prevent excessive linear velocity from causing the CO2 to escape.

[0022] Preferably, the pressure difference between the two ends of the displacement is 0.1-0.75 MPa.

[0023] More preferably, when the pressure difference between the two displacing ends changes, an oil-soluble surfactant (0.1-0.4 PV) is injected into the slug to ensure that the pressure difference between the two displacing ends is 0.1-0.75 MPa, thereby achieving a dynamic balance between defoaming and foam generation and ensuring the stability of the plugging control.

[0024] For highly water-sensitive, low-permeability, heterogeneous reservoirs, after injecting pure CO2 into the formation, the pure CO2 first surges along high-permeability channels (see details). Figure 2 (Schematic diagram), when encountering foamy oil (schematic diagram of foamy oil as shown) Figure 1 (As shown) After that, the front end reacts with the foam oil, resulting in the simultaneous generation and collapse of the foam oil. Subsequently, pure CO2 is forced to redirect to lower permeability areas (see details). Figure 3 (Illustrative diagram) This expands the sweep efficiency of pure CO2 injection, improving oil recovery. When the gas proportion in foamed oil increases to a certain level, the strength of the foamed oil weakens, and the defoaming rate exceeds the foam formation rate (see details). Figure 4 (Schematic diagram) Due to a certain tendency for gas channeling, in order to prevent the subsequent injection of pure CO2 from breaking through the high-permeability temporary plugging area, a next round of anti-channeling and control measures are needed. In the form of a slug, supercritical CO2 is used as a carrier to inject oil-soluble surfactants into the formation, forming a dynamic balance between foam defoaming and foam generation in the foam oil, maintaining the foam oil within a certain strength range, and ensuring the effect of sealing and controlling channeling and regulating the injected CO2 oil displacement.

[0025] This invention first mixes an oil-soluble surfactant with supercritical CO2 for later use. A supercritical CO2 slug containing the oil-soluble surfactant is then injected, followed by the injection of pure CO2 to create foam oil, temporarily blocking the high-permeability layer. Subsequent injections of pure CO2 then flow around into the low-permeability zone to displace the oil. As the injection volume increases, the strength of the foam oil decreases, and the displacement pressure differential reduces, requiring further anti-channeling control measures. The overall process is as follows: Figure 5 As shown.

[0026] More preferably, the method further includes repeating steps (1) and (2) to ensure the effect of controlling gas flow.

[0027] More preferably, the method includes the following steps:

[0028] First, an oil-soluble surfactant is mixed with supercritical CO2 and injected into the formation. Then, pure CO2 is injected at a linear velocity of 0.1 m / d-10 m / d (foaming occurs under low-velocity conditions, resulting in strong foam oil formation). This generates foam oil with an oil-soluble surfactant concentration of 0.1-5%, which blocks millimeter-level high-permeability channels and establishes a megapascal-level pressure differential (0.1-0.75 MPa). The effect of foam in controlling high-permeability channels is judged by the pressure change at the wellhead (injection end). Based on the pressure change at the injection end, surfactant (0.1-0.4 PV) is injected into the formation slug to ensure that the foam oil formation rate and collapse rate remain in dynamic equilibrium. This forces the subsequently injected pure CO2 to continuously shift towards oil displacement and enter the low-permeability area, thereby improving the oil displacement efficiency of highly water-sensitive formations.

[0029] The beneficial effects of this invention are:

[0030] This invention utilizes an oil-soluble surfactant as a foaming agent and supercritical CO2 as a carrier. The oil-soluble surfactant is injected into the formation, and upon contact with the formation crude oil, it generates foam oil in situ to block high-permeability gas channeling pathways. This forces subsequently injected pure CO2 into the low-permeability matrix, increasing sweep efficiency. This method can delay or control CO2 gas channeling during CO2 flooding, and the resulting high-viscosity foam oil promotes piston-like displacement, effectively improving CO2 flooding efficiency.

[0031] The oil-soluble surfactant of this invention can prevent water-based materials from reacting with injected CO2 to form carbonated water, which can corrode the wellbore and cause water-sensitive damage to highly water-sensitive reservoirs.

[0032] The method of this invention can change the direction of CO2 gas displacement and expand the gas sweep volume, thereby improving the efficiency of CO2 oil displacement; it can reduce the gas-liquid mobility ratio during CO2 displacement in low-permeability reservoirs, solving the problem of low displacement efficiency caused by the sudden advance of CO2 gas along high-permeability parts in low-permeability reservoirs; and it can avoid wellbore corrosion caused by injected aqueous solution and water-sensitive damage to highly water-sensitive reservoirs. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the structure of foam oil.

[0034] Figure 2 A schematic diagram illustrating the inrush of CO2 gas along a high-permeability layer during the CO2 injection process in a highly water-sensitive, low-permeability, heterogeneous reservoir.

[0035] Figure 3 This diagram illustrates how supercritical CO2 carrying oil-soluble surfactants into the formation can be used to inject CO2 to seal high-permeability channels, thereby forcing subsequent CO2 injections to redirect into low-permeability areas for oil displacement.

[0036] Figure 4This diagram illustrates how, as the amount of injected CO2 increases, the strength of the foam oil at the CO2 injection front decreases, and the defoaming rate is stronger than the foam generation rate.

[0037] Figure 5 The flowchart illustrates the process of regulating gas channeling using the CO2 channeling and sealing system of this invention. Detailed Implementation

[0038] The present invention will be further described below with reference to specific embodiments, and the advantages and features of the present invention will become clearer as a result. However, these embodiments are merely exemplary and do not constitute any limitation on the scope of the present invention. Those skilled in the art should understand that modifications or substitutions can be made to the details and form of the technical solutions of the present invention without departing from the spirit and scope of the present invention, but all such modifications and substitutions fall within the protection scope of the present invention.

[0039] Example 1: A CO2 flooding and channeling control system and regulation method for highly water-sensitive, low-permeability oil reservoirs.

[0040] Supercritical CO2 carrying an oil-soluble surfactant (sucrose ester surfactant C-1805, Mitsubishi-Kagaku Food Corporation) was injected into a highly water-sensitive, low-permeability reservoir with a water sensitivity index of 0.73–0.80 and a matrix permeability of 4.5 mD. The slugging effect was tested under different supercritical CO2 carrying oil-soluble surfactant slugging conditions (0.1–0.4 PV) and subsequent injection of the same pure CO2 conditions (2 PV).

[0041] Example 2: A CO2 flooding and channeling control system and regulation method for a highly water-sensitive, low-permeability oil reservoir

[0042] Supercritical CO2 carrying an oil-soluble surfactant (sucrose ester surfactant C-1805, Mitsubishi-Kagaku Food Corporation) was injected into a highly water-sensitive, low-permeability reservoir with a water sensitivity index of 0.73–0.80 and a matrix permeability of 4.5 mD. Subsequently, CO2 was injected at different injection rates (0.1 m / d–10 m / d) to study the sealing and channeling effect under the same pure CO2 injection conditions (2 PV), as shown in Table 2.

[0043] Example 3: A CO2 flooding and channeling control system and regulation method for highly water-sensitive, low-permeability oil reservoirs.

[0044] Supercritical CO2 carrying an oil-soluble surfactant (sucrose ester surfactant C-1805, Mitsubishi-Kagaku Food Corporation) was injected into a highly water-sensitive, low-permeability reservoir with a water sensitivity index of 0.73–0.80 and a matrix permeability of 4.5 mD. After injecting the same oil-soluble surfactant (0.2 PV) into the slug, the sealing and channeling effects under different injection amounts of pure CO2 (1–3 PV) were compared, as shown in Table 3.

[0045] Example 4: A CO2 flooding and channeling control system and regulation method for highly water-sensitive, low-permeability oil reservoirs.

[0046] A slug injection method was used to inject supercritical CO2 carrying an oil-soluble surfactant (fluorinated acrylic copolymer FS-22, DuPont), followed by continuous injection of pure CO2 for displacement. The effects of this oil-soluble surfactant injected into the formation on the sealing and regulation of subsequent pure CO2 injection were studied. The results showed that the effect was similar to that of sucrose ester surfactants.

[0047] Example 5: A CO2 flooding and channeling system and control method for highly water-sensitive, low-permeability oil reservoirs.

[0048] Without oil-soluble surfactants, different amounts of pure CO2 (1-3 PV) were injected to compare the effects of adding oil-soluble surfactants on sealing and regulating high and low permeability channels in foamed oil. Without oil-soluble surfactants, it was difficult to form foam and there was no effect on controlling the flow of foam.

[0049] Example 6: A CO2 flooding and channeling control system and regulation method for highly water-sensitive, low-permeability oil reservoirs.

[0050] Supercritical CO2 was injected via slug injection, followed by the injection of a non-oil-soluble surfactant (dimethyltetradecyl) via slug injection, and then pure CO2 was continuously injected for displacement. The study investigated the effect of the non-oil-soluble surfactant injected into the formation on the sealing and regulation of subsequent pure CO2 injection. It was found that no foam could be effectively formed and no channeling control effect was achieved.

[0051] Example 7: A CO2 flooding and channeling control system and regulation method for highly water-sensitive, low-permeability oil reservoirs.

[0052] Supercritical CO2 was injected via slug injection, followed by the injection of a non-oil-soluble surfactant (sodium dodecyl sulfate) via slug injection, and then pure CO2 was continuously injected for displacement. The study investigated the effect of the non-oil-soluble surfactant injected into the formation on the sealing and regulation of subsequent pure CO2 injection. No significant pressure difference was established between the injection end and the outlet end, and there was no channeling control effect.

[0053] Specific application examples

[0054] Experimental conditions: Simulated reservoir temperature (65℃) and reservoir pressure (31MPa), using CO2 with a purity of 99.99%, and using core samples taken from the formation in the field.

[0055] 1. Anti-channeling and control without using the CO2 drive-and-block system of this invention.

[0056] Formation core samples (38mm in diameter, 90mm in length) were saturated with formation crude oil (using a core saturation device to saturate the crude oil until the core weight no longer changed). Using a core displacement device, and with controlled confining and back pressure, pure CO2 (2PV) was continuously injected at a certain rate (0.1mL / min, equivalent to a linear velocity of 0.1m / d). The pressure difference between the injection port and outlet of the core holder was tested. The test showed no significant pressure difference between the inlet and outlet (a small pressure difference of 0.005-0.01MPa existed, possibly due to the injected CO2 surging along the high-permeability channel).

[0057] 2. Using the CO2 drive-and-block system of the present invention for anti-channeling control.

[0058] ① First, add different amounts (0.1 mL, equivalent to a volume concentration of 0.02%; 0.5 mL, equivalent to a volume concentration of 0.1%; 1 mL, equivalent to a volume concentration of 0.2%; 2 mL, equivalent to a volume concentration of 0.4%; 5 mL, equivalent to a volume concentration of 1%; 25 mL, equivalent to a volume concentration of 5%) of sucrose ester surfactant C-1805 to an intermediate container with a volume of 500 mL. Then, fill the intermediate container with CO2 under the same temperature and pressure conditions, and adjust the pressure and temperature in the intermediate container (65℃, 35 MPa) to adjust the CO2 in the intermediate container to a supercritical state. Formation core samples (38mm in diameter, 90mm in length) were saturated with formation crude oil (using a core saturation device to saturate the crude oil until the core weight no longer changed). Using a core displacement device, the confining pressure and back pressure were controlled. Supercritical CO2 was used to carry and inject slugs containing different concentrations of oil-soluble surfactants. Pure CO2 (2PV) was continuously injected at a certain rate (0.1mL / min, equivalent to a linear velocity of 0.1m / d). The pressure difference between the injection port and outlet of the core holder was tested.

[0059] ② Add a certain amount (0.5 mL, equivalent to a volume concentration of 0.1%) of sucrose ester surfactant C-1805 to an intermediate container with a volume of 500 mL. Then, fill the intermediate container with CO2 under the same temperature and pressure conditions, and adjust the pressure and temperature in the intermediate container (65℃, 35MPa) to adjust the CO2 in the intermediate container to a supercritical state. Formation core samples (38 mm in diameter, 90 mm in length) were saturated with formation crude oil (using a core saturation device to saturate the crude oil until the core weight no longer changed). Using a core displacement device, the confining pressure and back pressure were controlled. Supercritical CO2 was used to carry and inject oil-soluble surfactant slugs of the above concentration (0.1% by volume) at different injection rates (0.1 mL / min, equivalent to a linear velocity of 0.1 m / d; 0.5 mL / min, equivalent to a linear velocity of 0.5 m / d; 1.0 mL / min, equivalent to a linear velocity of 1.0 m / d; 5.0 mL / min, equivalent to a linear velocity of 5 m / d; 10 mL / min, equivalent to a linear velocity of 10 m / d) to continuously inject pure CO2 (2 PV). The pressure difference between the injection port and outlet of the core holder was tested.

[0060] ③ Add a certain amount (0.5 mL, equivalent to a volume concentration of 0.1%) of sucrose ester surfactant C-1805 to a 500 mL intermediate container. Then, fill the intermediate container with CO2 under the same temperature and pressure conditions, and adjust the pressure and temperature in the intermediate container (65℃, 35 MPa) to adjust the CO2 in the intermediate container to a supercritical state. Saturate the formation core (38 mm in diameter, 90 mm in length) with formation crude oil (using a core saturation device to saturate the crude oil until the core weight no longer changes). Using a core displacement device, control the confining pressure and back pressure, and use supercritical CO2 to carry the oil-soluble surfactant slugs of the above concentration (0.1% volume concentration) continuously injected at a certain rate (0.1 mL / min, equivalent to a linear velocity of 0.1 m / d) at different volumes of pure CO2 (1 PV, 2 PV, 3 PV). Test the pressure difference between the injection port and outlet of the core holder.

[0061] The pressure difference between the inlet and outlet of the clamp used in the experiment was compared under different concentrations of oil-soluble surfactants, different injection rates, and different amounts of pure CO2 injected continuously. The experimental results are shown in Tables 1, 2, and 3, respectively.

[0062] Table 1. Inlet and outlet displacement pressure difference under different concentrations of oil-soluble surfactants.

[0063]

[0064] Table 2. Inlet and outlet displacement pressure difference under different injection rates

[0065]

[0066] Table 3. Inlet and outlet displacement pressure difference under different injected pure CO2 quantities.

[0067]

[0068] Table 1 shows that the addition of oil-soluble surfactants can establish a significant pressure difference between the inlet and outlet of the displacement reservoir, and the concentration of surfactants has a significant impact on the pressure difference change. Meanwhile, the injection rate (Table 2) and the volume of injected CO2 (Table 3) have a significant impact on the sealing and regulation effects. This fully demonstrates that the foam oil system designed in this invention can effectively seal and regulate oil flow, and is of great significance for improving the recovery rate of highly water-sensitive, low-permeability reservoirs, overcoming the limitations of previous water-based foam applications.

[0069] The above detailed description is a specific description of one of the feasible embodiments of the present invention. This embodiment is not intended to limit the patent scope of the present invention. All equivalent implementations or modifications that do not depart from the present invention should be included within the scope of the technical solution of the present invention.

Claims

1. A CO2 flooding and containment system for highly water-sensitive, low-permeability oil reservoirs, characterized in that, It includes oil-soluble surfactants and supercritical CO2, with a volume ratio of 1:1000-50:1000 at a temperature of 60-80℃ and a pressure of 30-35MPa. The oil-soluble surfactant is sucrose ester surfactant C-1805.

2. A method for controlling gas channeling using the CO2 channeling control system described in claim 1, characterized in that, Includes the following steps: (1) Inject oil-soluble surfactants into the formation after mixing them with supercritical CO2; (2) Inject pure CO2 to obtain foam oil, which forms a seal.

3. The method according to claim 2, characterized in that, The slub content of oil-soluble surfactants is 0.1-0.4 PV.

4. The method according to claim 2, characterized in that, In step (2), the slug injected with pure CO2 has a slug capacity of 1.0-3.0 PV.

5. The method according to claim 2, characterized in that, In step (2), the linear velocity of the injected pure CO2 is 0.1-10 m / d.

6. The method according to claim 2, characterized in that, The pressure difference between the two ends of the displacement is 0.1-0.75 MPa.

7. The method according to claim 6, characterized in that, In step (2), when the pressure difference between the two displacing ends changes, an oil-soluble surfactant is injected into the slug to ensure that the pressure difference between the two displacing ends is 0.1-0.75 MPa.

8. The method according to claim 7, characterized in that, It also includes repeating steps (1) and (2) to ensure the effect of regulating gas flow.

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