Method for using remaining oil for equal-density driving of fracture-vug type oil reservoir

Abstract

The invention relates to a method for using remaining oil for equal-density driving of a fracture-vug type oil reservoir. The method comprises the following steps that crude oil density data of the fracture-vug type oil reservoir are detected and calculated; preparing a liquid phase equal density system which can tolerate 120 DEG C and has salt tolerance of 220000 ppm, wherein the liquid phase equal density system comprises the following components: a foaming agent, a foam stabilizer and water; foaming the liquid phase equal-density system, nitrogen and a nanoparticle additive for adjusting the density together to generate a foam equal-density system with the density equal to that of the crude oil; alternately injecting the foam isodensity system and nitrogen into the fracture-vug type oil reservoir to generate a Jamin effect; and after the foam equal-density system displaces corner oil and streaming oil of the fractured-vuggy oil reservoir, crude oil of the fractured-vuggy oil reservoir is collected. According to the method, an equal-density system with the same density as crude oil is used for seepage in a fracture-cavity unit, the influence caused by gravitational differentiation is weakened from the aspect of fluid physical property difference, gas channeling and water channeling are prevented and controlled, more remaining oil in the lower middle portion of a fracture-cavity is used, and therefore the recovery rate of the fracture-cavity type oil reservoir is increased.

Description

Technical Field

[0001] The invention relates to the field of residual oil exploitation, in particular to a residual oil exploitation method for isodensity driving of fracture-cavity oil reservoirs. Background Art

[0002] Carbonate fracture-cave oil reservoirs have great resource potential. For example, the tertiary oil reserves in the Tarim Basin have reached more than 3 billion tons. The oil reservoirs are buried deep (5,000-7,000 meters), with temperatures as high as 160°C and a mineralization of more than 200,000 mg / L. The karst patterns can be divided into surface weathering crust karst, fault-controlled karst, and ancient underground river karst. The storage space is mainly large caves, large fractures, and dissolution pores. The scales vary greatly, from micrometers to meters, with strong heterogeneity and generally low recovery rates. At present, the main methods to improve the recovery rate of fracture-cave carbonate reservoirs in Tahe are water injection, gas injection and supporting efficiency-enhancing technologies. Since the proportion of cave reservoirs in the total reservoir types is about 60%-70%, the collapse and filling degrees are high, the flow characteristics in the fracture development zone vary greatly, and the injected medium is easy to penetrate along the high-conductivity channel. As a result, during the water and gas injection process, the phenomenon of "gas goes to the upper gas channel and water goes to the lower water channel" caused by gravity differentiation is serious, resulting in the dynamic response of water drive and gas drive in the well group is not obvious, the efficiency is not high, and the effect is very different. Because both gas drive and water drive have the problem of low efficiency of water drive, and nitrogen injection drive has a high risk of gas channeling, it is necessary to find more effective methods and theoretical guidance to improve the recovery rate of fracture-cave carbonate reservoirs.

[0003] At present, in response to the above practical problems and characteristics of fracture-cavity reservoirs, oil fields have adopted technical measures such as gas-water synergy, foam drive assisted throughput, and profile adjustment and water plugging, which can alleviate the gas and water channeling caused by gas-water gravity differentiation in fracture-cavity reservoirs under high temperature and high salinity conditions to a certain extent and expand the sweep efficiency.

[0004] However, the fluid pressure field redistributed quickly due to the gas-water synergy measures, and the initial effect was obvious, but the subsequent effect of improving oil recovery needs to be stabilized; the foam drive-assisted throughput is concentrated, and there are still certain challenges in utilizing a large amount of residual oil between wells; the gel foam system used in profile control and water plugging needs to be optimized for adaptability in ultra-high salinity reservoirs, and the gel foam system developed in the early stage involves a variety of agents in the formation process. The system is relatively complex, resulting in increased use costs; in addition, the existing mine construction process for gas-water gravity separation technology is cumbersome and needs to be optimized. Summary of the invention

[0005] The present invention solves the problems that crossflow exists in both current gas drive and water drive, the water drive efficiency is low, and there is a high risk of gas channeling in nitrogen injection drive, which affects the recovery rate of carbonate fracture-vug reservoirs. There is a need for new methods and theoretical guidance for improving the recovery rate to further increase the recovery rate of carbonate fracture-vug reservoirs. The present invention provides a method for remaining oil in an isodensity drive of a fracture-vug reservoir to solve this technical problem. By using an isodensity system with the same density as the crude oil to percolate in the fracture-vug unit, the influence brought by gravity differentiation is weakened from the differences in fluid physical properties, gas and water channeling are prevented, the resistance coefficient of the displacement system between wells is increased, the oil displacement power is increased, and more remaining oil in the lower part of the fractures and vugs is mobilized, thereby improving the recovery rate of the fracture-vug reservoir.

[0006] To solve the above technical problems, the technical solution of the present invention is as follows:

[0007] A method for remaining oil in an isodensity drive of a fracture-vug reservoir, comprising the following steps:

[0008] S1. Detect and calculate the crude oil density data of the fracture-vug reservoir;

[0009] S2. Prepare a liquid isodensity system that can withstand 120°C and has a salt tolerance performance of up to 220,000 ppm. The components of the liquid isodensity system include a foaming agent, a foam stabilizer, and water;

[0010] S3. Input the liquid isodensity system into a ground foaming device, and input nitrogen and a nanoparticle additive for density adjustment into the ground foaming device to generate a foam isodensity system with the same density as the crude oil;

[0011] S4. Alternately inject the foam isodensity system and nitrogen into the fracture-vug reservoir to produce the Jamin effect and weaken the gas-liquid differentiation in the fracture-vug reservoir;

[0012] S5. After the foam isodensity system displaces the corner oil and bypassed oil in the fracture-vug reservoir, recover the crude oil in the fracture-vug reservoir.

[0013] Preferably, in the foam isodensity system, the content of the foaming agent is 0.1% to 0.2%, the content of the foam stabilizer is 0.3% to 0.4%, the ratio of nitrogen to the liquid isodensity system is between 1:1 and 1:4, and the content of the nanoparticle additive is calculated and added according to the crude oil density to be displaced.

[0014] Preferably, a stabilizer for improving the stability of the foam isodensity system is also added to the foam isodensity system.

[0015] Preferably, the stabilizer is xanthan gum.

[0016] Preferably, the nanoparticle additive includes nano-SiO 2Particles and / or polyimide nanoparticles.

[0017] Preferably, in step S2, the step of preparing the liquid equal-density system includes:

[0018] S2-1. First, add water accounting for 60%-80% of the total volume of the stirring device to the stirring device;

[0019] S2-2. Start stirring and add the remaining components of the liquid equal-density system into the stirring device;

[0020] S2-3. Stir the components of the liquid equal-density system evenly.

[0021] Advantageous technical effects of the technical solution of the present invention:

[0022] (1) By injecting an equal-density system with the formation crude oil, on the premise of ensuring long-term stable existence under reservoir conditions, the density of the displacement phase is adjusted to inhibit the gravity segregation effect of the injected gas or injected water. The foam equal-density system with the same density as the crude oil is used to flow in the fracture-cavity unit, and the influence brought by gravity segregation is weakened from the difference in fluid physical properties, preventing gas channeling and water channeling, increasing the resistance coefficient of the displacement system between wells, increasing the oil displacement power, mobilizing more remaining oil in the middle and lower parts, and thus improving the recovery rate of the fracture-cavity reservoir. Description of the Drawings

[0023] Figure 1 Shows a schematic diagram of the remaining oil distribution pattern in the fracture-cavity reservoir after the failure of water flooding and gas flooding in the background technology of the present invention;

[0024] Figure 2 Shows a schematic diagram of the remaining oil distribution pattern in the reservoir after the remaining oil is driven by the foam equal-density in the embodiment of the present invention. Detailed Embodiments

[0025] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the following further details a method for remaining oil in a fractured-vuggy reservoir with isopycnic drive proposed by the present invention in combination with the accompanying drawings and specific embodiments. According to the following description, the advantages and features of the present invention will be clearer. It should be noted that the accompanying drawings are in a very simplified form and all use non-precise scales, only for conveniently and clearly assisting in explaining the objectives of the embodiments of the present invention. In order to make the objectives, features and advantages of the present invention more obvious and understandable, please refer to the accompanying drawings. It should be noted that the structures, scales, sizes, etc. shown in the drawings of this specification are only used to cooperate with the content disclosed in the specification for those skilled in this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention. Therefore, they do not have technical essence. Any modification of the structure, change of the proportional relationship or adjustment of the size, without affecting the effects that the present invention can produce and the objectives that can be achieved, should still fall within the scope covered by the technical content disclosed by the present invention.

[0026] Embodiment

[0027] The following will Figure 1 and 2 specific embodiments are used to elaborate in detail the technical solution of a method for remaining oil in a fractured-vuggy reservoir with isopycnic drive of the present invention.

[0028] As Figure 1 shown in Figure 2 a method for remaining oil in a fractured-vuggy reservoir with isopycnic drive of this embodiment includes the following steps:

[0029] S1. Detect and calculate the crude oil density data of the fractured-vuggy reservoir;

[0030] S2. Prepare a liquid isopycnic system that can withstand 120 °C and has a salt tolerance performance of up to 220,000 ppm. The components of the liquid isopycnic system include a foaming agent, a foam stabilizer, and water. The specific preparation process includes:

[0031] S2-1. First, add water accounting for 60%-80% of the total volume of the stirring device to the stirring device;

[0032] S2-2. Start stirring and add the remaining components of the liquid isopycnic system into the stirring device;

[0033] S2-3. Stir the components of the liquid isopycnic system evenly;

[0034] S3. Input the liquid isopycnic system into a ground foaming device, and input nitrogen and a nano-particle additive for density adjustment into the ground foaming device to generate a foam isopycnic system with the same density as the crude oil;

[0035] S4. Alternately inject the foam equal-density system and nitrogen into the fracture-vug reservoir to generate the Jamin effect and weaken the gas-water differentiation in the fracture-vug reservoir;

[0036] S5. After the foam equal-density system displaces the corner oil and bypassed oil in the fracture-vug reservoir, recover the crude oil in the fracture-vug reservoir.

[0037] When the foam equal-density system percolates in the fracture-vug unit, its apparent viscosity (apparent viscosity or effective viscosity) is much higher than that of active water and gas. At the same flow rate, it can reach hundreds of times the waterflooding pressure and increases with the increase of the medium porosity (or permeability). When the foam equal-density system and nitrogen are alternately injected into the formation, the residence time of nitrogen in the formation can be increased, and the breakthrough time of gas can be delayed. If the injected gas is air, the oxygen content of the injected air can also be reduced. At the same time, the viscosity of the equal-density system decreases with the increase of shear stress. This characteristic is beneficial to increasing the displacement pressure and expanding the swept volume, and is very suitable for improving the recovery rate of weathered crust formations.

[0038] The method for remaining oil by equal-density drive in the fracture-vug reservoir of the present invention is prepared through a system formula on-site. The obtained foam equal-density system is also the foam equal-density drive for injecting into the formation to displace crude oil. The foam equal-density system is not only similar to the crude oil in the reservoir in physical properties, but also requires sufficient long-term stability under formation conditions. Injecting the foam equal-density system into the formation can significantly inhibit the gas-water gravity differentiation phenomenon in the fracture-vug reservoir, increase the resistance coefficient of the inter-well displacement system, and improve the oil displacement power, so that more remaining oil in the lower part of the fracture can be produced.

[0039] In the fracture-vug reservoir, the prepared foam equal-density drive in this solution first enters the high-permeability zone to improve the mobility ratio between the displacement fluid and the crude oil. With the alternate injection of the equal-density system and the subsequent gas, the Jamin effect is generated, and the flow resistance in the high-permeability layer gradually increases. Subsequently, the foam equal-density system can successively enter the low-permeability zone that cannot be entered by the displacement medium in the waterflooding and gas flooding stages, inhibit viscous fingering, adjust the interlayer relationship, improve the injection profile, and thus increase the vertical swept volume. Subsequently, the foam equal-density system blocks the channel of the high-permeability zone for crossflow. The continuously injected foam equal-density system subsequently must flow in other directions with poor sweeping conditions. Through fluid diversion, the areal sweep efficiency can be expanded. Especially at the connected parts under different sedimentary conditions, the remaining oil such as "corner oil" in these unproduced and difficult-to-exploit parts can be swept out to increase the reservoir swept volume. After the foam equal-density system is injected, relying on the same density as the crude oil in the formation and a relatively high viscosity, it can enter the low-permeability layers that cannot be entered by waterflooding and the channels shielded due to the too high mobility of gas flooding. And additives can also be used in the system to further increase the stability of the system and ensure the influence of the foam equal-density drive on the flow resistance under formation conditions.

[0040] After the injection of the foam equal-density system, since the density of the foam equal-density system is equal to that of the crude oil, it can change the flow path, enter the fractures or pores with poor connectivity, displace the "corner oil" therein, increase the degree of formation crude oil utilization, improve the sweep efficiency, and expand the swept area. In addition, due to the high apparent viscosity and Jamin effect of the foam equal-density drive in this solution, it can effectively inhibit gas override, increase the gas migration resistance, prevent gas channeling, and the increase in injection pressure can overcome the increased migration resistance of the system in the unit body, so that the lateral driving force between wells is supplemented, and the remaining oil between wells after the failure of gas drive is further utilized, thereby improving the recovery factor.

[0041] During the gas drive process, obvious mobility differences lead to the formation of channeling channels, and the strong shielding of the dominant channels causes the lack of driving force in the middle and lower parts and the edge parts of the oil reservoir. At this time, injecting the foam equal-density system into the formation can improve the flow heterogeneity, inhibit the tendency to accumulate at the top, and more parts in the middle and lower layers obtain the driving force for oil displacement. The "bypass oil" formed by bypass flow and the "corner oil" at the edge are also utilized.

[0042] After the previous water drive and gas drive are completed, the injected water is mainly distributed in the lower dominant channels, while the injected gas occupies the top of the unit body, and there is a certain recovery effect on the "attic oil". However, as the distance from the injection end increases, the gas-water segregation phenomenon gradually becomes more serious, with "gas flowing through the upper airway and water flowing through the lower waterway", the oil displacement driving force weakens, and a large amount of remaining oil is distributed between wells. The method for remaining oil in fractured-vuggy reservoirs using equal-density drive provided by the present invention utilizes the foam equal-density system with a density equal to that of the formation oil and a relatively high viscosity to change the flow path, and can enter fractures, pores with poor connectivity, low-permeability layers that cannot be entered by water drive, and channels shielded due to too high gas drive mobility, displace the "corner oil" therein, improve the sweep efficiency, significantly inhibit the gravity segregation phenomenon, increase the resistance coefficient of the displacement system between wells, increase the oil displacement driving force, and more remaining oil in the middle and lower parts is utilized, and it can be applied to further displace the oil reservoir after the failure of water drive and gas drive.

[0043] After water drive and gas drive, using the foam equal-density drive in this solution can specifically supplement the lateral driving force between wells in fractured-vuggy reservoirs. The water drive and gas drive processes are mature, the injection difficulty at the wellhead is small, and the economic cost is lower. Therefore, the equal-density drive in this solution can be used after the failure of water drive and gas drive. Of course, it should be understood that the foam equal-density drive can also be directly injected in the early stage.

[0044] After injecting the equal-density system, the remaining oil in the middle part of the fractured-vuggy unit is significantly utilized, the outlet channels in the structural unit no longer have a unified interface, the gas-water segregation effect is significantly weakened, and more remaining oil including "bypass oil" and "corner oil" is displaced from the parts shielded due to mobility differences before the entry of the equal-density system, and the recovery factor is improved.

[0045] Furthermore, in foam equal-density systems, the content of the foaming agent is 0.1% to 0.2%, the content of the foam stabilizer is 0.3% to 0.4%, and the ratio of nitrogen to the liquid equal-density system is between 1:1 and 1:4. The ratio required for special reservoirs may reach 1:1, and 1:4 may also be used to reduce the cost of agents. During actual preparation, the dosages of each component should be calculated in advance, and at the same time, a suitable ratio should be selected for nitrogen and the liquid equal-density system according to needs. Commonly used foaming agents include sodium alkyl sulfonate, sodium alkyl benzene sulfonate, polyoxyethylene alkyl alcohol ether, etc.; the foam stabilizer can be selected from polyacrylamide, polyvinyl alcohol, protein, polypeptide, starch, and cellulose.

[0046] The content of the nanoparticle additive is calculated and added according to the density of the crude oil to be displaced, so that the final foam equal-density system can achieve the same density as the crude oil. The nanoparticle additive can be selected from nano-SiO 2 particles and / or polyimide nanoparticles. Specifically, which nanoparticle additive to choose should be determined by experimental methods according to the characteristics of the reservoir fluid properties to select whether a single system or a composite system of the two is more suitable.

[0047] A stabilizer for improving the stability of the foam equal-density system is also added to the foam equal-density system. The stabilizer is xanthan gum, and it can be added when using a ground foaming device to stir the nitrogen and the liquid equal-density system to form a foam equal-density system.

[0048] In addition, it should be noted that when using the liquid equal-density system and nitrogen to form a foam equal-density system by foaming and when alternately injecting the foam equal-density system and nitrogen into the formation, generally nitrogen is selected as the gas. However, in combination with the reservoir requirements, carbon dioxide or air can also be used to replace nitrogen.

[0049] In this embodiment, nitrogen is injected into the formation. Nitrogen has stable properties and will not affect the properties of petroleum processing products. Moreover, the mixture of nitrogen and crude oil can be easily separated and measured at the wellhead of the production well. The liquid equal-density system is mainly water with nanoparticles added and is immiscible with crude oil.

[0050] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered to be within the scope described in this specification.

[0051] The above-described embodiments merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all fall within the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A method for remaining oil in a fracture-cavity reservoir under isodensity drive, characterized in that, it includes the following steps: S1. Detect and calculate the crude oil density data of the fracture-cavity reservoir; S2. Prepare a liquid-phase isodensity system that can withstand 120 °C and has a salt tolerance performance of up to 220,000 ppm. The components of the liquid-phase isodensity system include a foaming agent, a foam stabilizer, and water; S3. Input the liquid-phase isodensity system into a ground foaming device, and input nitrogen and a nano-particle additive for density adjustment into the ground foaming device to generate a foam isodensity system with the same density as the crude oil by foaming; S4. Inject the foam isodensity system and nitrogen into the fracture-cavity reservoir alternately to produce the Jamin effect and weaken the gas-water differentiation in the fracture-cavity reservoir; S5. After the foam isodensity system displaces the corner oil and bypass oil in the fracture-cavity reservoir, recover the crude oil in the fracture-cavity reservoir.

2. A method for remaining oil in a fracture-cavity reservoir under isodensity drive as described in claim 1, characterized in that, in the foam isodensity system, the content of the foaming agent is 0.1% to 0.2%, the content of the foam stabilizer is 0.3% to 0.4%, the ratio of the nitrogen to the liquid-phase isodensity system is between 1:1 and 1:4, and the content of the nano-particle additive is calculated and added according to the crude oil density to be displaced.

3. A method for remaining oil in a fracture-cavity reservoir under isodensity drive as described in claim 1, characterized in that, a stabilizer for improving the stability of the foam isodensity system is further added to the foam isodensity system.

4. A method for remaining oil in a fracture-cavity reservoir under isodensity drive as described in claim 3, characterized in that, the stabilizer is xanthan gum.

5. A method for remaining oil in a fracture-cavity reservoir under isodensity drive as described in claim 1, characterized in that, The nano-particle additive includes nano-SiO 2 particles and / or polyimide nano-particles.

6. A method for remaining oil in a fracture-cavity reservoir under isodensity drive as described in claim 1, characterized in that, in step S2, the steps for preparing the liquid-phase isodensity system include: S2-1. First, add water accounting for 60%-80% of the total volume of the stirring device to the stirring device; S2-2. Start stirring and add the remaining components of the liquid-phase isodensity system into the stirring device; S2-3. Stir the components of the liquid-phase isodensity system evenly.

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