A heterogeneous viscosity-reducing composite equilibrium displacement system and its injection method

Abstract

The present application relates to the technical field of oilfield exploration and development, and particularly relates to a heterogeneous viscosity-reducing composite balanced displacement system and an injection method thereof. The system comprises a heterogeneity regulator, a viscosity reducer and a mobility control agent. The heterogeneity regulator is composed of a dispersed gel system and / or gel particles. The viscosity reducer is a solution of an anionic-nonionic amphoteric surfactant. The mobility control agent is a polymer solution. By injecting the heterogeneity regulator first, the heterogeneous viscosity-reducing composite balanced displacement system can block the dominant seepage channel and achieve wave spreading in the near-wellbore zone. By injecting the viscosity reducer and the mobility control agent later, the system can achieve integrated efficient balanced displacement and substantially improve the recovery rate in the deep far-wellbore zone.

Description

Technical Field

[0001] This invention relates to the field of oilfield exploration and development technology, specifically to a heterogeneous viscosity-reducing composite equilibrium displacement system and its injection method. Background Technology

[0002] Ordinary heavy oil is an important alternative to unconventional resources, and the efficient development of heavy oil is of great significance to ensuring national energy security.

[0003] CN111091476B discloses a numerical simulation method for oil reservoirs in highly heterogeneous formations. The method includes the following steps: Step 1, identifying regions with strong discontinuities and dividing them into networks; Step 2, calculating the gradient intensity factor and obtaining local analytical solutions; Step 3, applying the local analytical solutions to calculate the equivalent permeability between grids; Step 4, constructing a formula for calculating cross-interface phase flow; Step 5, solving the algebraic equations for the variables to be determined; Step 6, verifying the algorithm's efficiency and grid independence. This numerical simulation method helps to gain a deeper understanding of the oil displacement mechanism in highly heterogeneous oil reservoir formations, improves the efficiency and accuracy of reservoir numerical simulation, and guides the adjustment and optimization of reservoir development methods.

[0004] CN111022013B discloses a steam huff and puff method for heterogeneous heavy oil reservoirs. The method includes: injecting nitrogen foam slugs into the oil layer; injecting viscosity-reducing slugs into the oil layer; injecting nitrogen slugs into the oil layer again; injecting steam into the oil layer; and then performing well shut-in and recovery. First, nitrogen foam is injected. The Jamin effect of nitrogen foam can effectively regulate and plug high-permeability, high-production zones, prompting subsequent slugs to enter low-permeability, low-production zones with high oil saturation, thereby expanding the steam sweep effect. The viscosity-reducing slugs effectively reduce crude oil viscosity. Nitrogen slugs not only help push the viscosity-reducing slugs deeper into the oil layer, expanding their effective radius, but also improve crude oil flowback during production. The synergistic effect of each slug increases the cycle production and recovery rate of a single well in heterogeneous heavy oil reservoirs.

[0005] CN113153209A discloses a multi-medium composite huff and puff development method for heavy oil reservoirs. This method includes: injecting a high-temperature plugging agent into the formation; after the high-temperature plugging agent condenses, injecting a viscosity reducer, a foaming agent, and a non-condensable gas, or injecting a viscosity reducer, a foaming agent, and urea; and finally injecting steam into the formation. This invention, by sequentially injecting a multi-medium mixture of high-temperature plugging agent, viscosity reducer, foaming agent, and non-condensable gas (or urea) into the bottom layer before steam injection, achieves the goals of increasing reservoir profile utilization, reducing crude oil viscosity, replenishing formation energy, thereby increasing cycle oil production, oil-gas ratio, reservoir recovery, and economic benefits.

[0006] Traditional waterflooding for the development of ordinary heavy oil suffers from a high water-to-oil mobility ratio and low waterflood sweep efficiency and recovery. To improve the waterflood sweep efficiency and recovery of ordinary heavy oil, polymers and viscosity reducers are added to increase the viscosity of the aqueous phase and decrease the viscosity of the oil phase. However, in highly heterogeneous reservoirs, traditional single-phase chemical flooding systems are prone to channeling in the sluice gate, failing to achieve balanced displacement. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a heterogeneous viscosity-reducing composite equilibrium displacement system and its injection method. The system described in this invention can achieve viscosity reduction, oil displacement, wave propagation, and integrated, efficient, and equilibrium displacement in deep wells, significantly improving oil recovery.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] This invention provides a heterogeneous viscosity-reducing composite equilibrium displacement system, the system comprising a heterogeneous regulator, a viscosity reducer, and a flowability control agent;

[0010] The heterogeneous regulator is composed of a dispersion gel system and / or gel particles; the viscosity reducer is an anionic nonamphoteric surfactant solution; and the flow control agent is a polymer solution.

[0011] Furthermore, the dispersion gel system is cross-linked from a polymer and a phenolic resin cross-linking agent; the gel particles include pre-cross-linked gel particles.

[0012] Furthermore, the viscosity reducer is an anionic nonamphoteric sulfonate surfactant solution with the following molecular structural formula:

[0013]

[0014] Where x, y, m, and n are all positive integers.

[0015] Furthermore, x takes the value of a positive integer ≤ 5, y is an integer between 2 and 7, and m and n are both integers between 2 and 4.

[0016] The preparation method of the anionic non-ampholyte sulfonate surfactant is a conventional existing technology and will not be described in detail here.

[0017] Furthermore, the mass concentration of the viscosity reducer is 0.3%-0.5%.

[0018] Furthermore, the flow control agent is a partially hydrolyzed polyacrylamide solution, wherein the partially hydrolyzed polyacrylamide has a molecular weight of 30-35 million and a mass concentration of 0.1%-0.3%.

[0019] The present invention also provides an injection method for the heterogeneous viscosity-reducing composite equilibrium displacement system described above, wherein the method comprises injecting a heterogeneous regulator, a viscosity reducer and a flow control agent in a segmented plug.

[0020] Furthermore, a heterogeneous regulator slug is first injected, followed by a combination slug of viscosity reducer and flow control agent.

[0021] Furthermore, the injection volume of the heterogeneous regulator slug combined with the viscosity reducer and flow control agent slug is 1-5:1-5.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] The heterogeneous viscosity-reducing composite equilibrium displacement system described in this invention can block dominant seepage channels and achieve near-wellbore diffusion by first injecting a heterogeneous regulator; then injecting a viscosity reducer and a flow rate control agent to achieve integrated, efficient, and balanced displacement of viscosity reduction, oil displacement, and diffusion in deep wells and significantly improve oil recovery. Detailed Implementation

[0024] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0025] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. Furthermore, it should be understood that when the terms "comprising" or "including" are used in this specification, they indicate the presence of features, steps, operations, and combinations thereof.

[0026] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0027] Example 1

[0028] A heterogeneous viscosity-reducing composite equilibrium displacement system, the system comprising a heterogeneous regulator, a viscosity reducer, and a flow control agent:

[0029] The heterogeneity regulator is a phenolic resin dispersion gel prepared by a conventional crosslinking reaction of a low-concentration polymer and a crosslinking agent. The polymer is partially hydrolyzed polyacrylamide with a molecular weight of 20 million and a polymer mass concentration of 0.2%. The crosslinking agent is a phenolic resin prepolymer with a crosslinking agent concentration of 0.4%.

[0030] The viscosity reducer is an anionic nonamphoteric sulfonate surfactant solution, with the following molecular structural formula:

[0031]

[0032] Where x = 2, y = 5, m = 3, and n = 3. The mass concentration of the viscosity reducer is 0.3%.

[0033] The flow control agent is an ultra-high molecular weight partially hydrolyzed polyacrylamide solution, wherein the partially hydrolyzed polyacrylamide has a molecular weight of 35 million and a degree of hydrolysis of 20%; the mass concentration of the partially hydrolyzed polyacrylamide is 0.15%.

[0034] The injection method of the heterogeneous viscosity-reducing composite equilibrium displacement system is to inject the heterogeneous regulator, viscosity reducer, and flow control agent in stages via a plug:

[0035] First, inject a heterogeneous regulator slug, then inject a combination slug of viscosity reducer and flow control agent; the injection volume of the slug is 0.4 PV, and the injection ratio of the heterogeneous regulator slug to the combination slug of viscosity reducer and flow control agent is 1:1.

[0036] Example 2

[0037] A heterogeneous viscosity-reducing composite equilibrium displacement system, the system comprising a heterogeneous regulator, a viscosity reducer, and a flow control agent:

[0038] The heterogeneous regulator is a pre-crosslinked gel particle with a particle size of 500–1000 μm.

[0039] The viscosity reducer is an anionic nonamphoteric sulfonate surfactant solution, with the following molecular structural formula:

[0040]

[0041] Where x = 5, y = 2, m = 2, n = 2. The mass concentration of the viscosity reducer is 0.4%.

[0042] The flow control agent is an ultra-high molecular weight partially hydrolyzed polyacrylamide solution, wherein the partially hydrolyzed polyacrylamide has a molecular weight of 30 million and a degree of hydrolysis of 20%; the mass concentration of the partially hydrolyzed polyacrylamide is 0.3%.

[0043] The injection method of the heterogeneous viscosity-reducing composite equilibrium displacement system is to inject the heterogeneous regulator, viscosity reducer, and flow control agent in stages via a plug:

[0044] First, inject a heterogeneous regulator slug, then inject a combination slug of viscosity reducer and flow control agent; the injection volume of the slug is 0.4 PV, and the injection ratio of the heterogeneous regulator slug to the combination slug of viscosity reducer and flow control agent is 5:1.

[0045] Example 3

[0046] A heterogeneous viscosity-reducing composite equilibrium displacement system, the system comprising a heterogeneous regulator, a viscosity reducer, and a flow control agent:

[0047] The heterogeneity regulator is composed of a phenolic resin dispersion gel made by a conventional crosslinking reaction of low concentration polymer and crosslinking agent, and pre-crosslinked gel particles.

[0048] The polymer is partially hydrolyzed polyacrylamide with a molecular weight of 20 million and a polymer mass concentration of 0.2%. The crosslinking agent is a phenolic resin prepolymer with a crosslinking agent concentration of 0.4%.

[0049] The pre-crosslinked gel particles have a particle size of 500–1000 μm.

[0050] The viscosity reducer is an anionic nonamphoteric sulfonate surfactant solution, with the following molecular structural formula:

[0051]

[0052] Where x = 3, y = 7, m = 4, and n = 4. The mass concentration of the viscosity reducer is 0.5%.

[0053] The flow control agent is an ultra-high molecular weight partially hydrolyzed polyacrylamide solution, wherein the partially hydrolyzed polyacrylamide has a molecular weight of 35 million and a degree of hydrolysis of 20%; the mass concentration of the partially hydrolyzed polyacrylamide is 0.1%.

[0054] The method of using the heterogeneous viscosity-reducing composite equilibrium displacement system is to inject the heterogeneous regulator, viscosity reducer, and flow control agent in stages:

[0055] First, inject a heterogeneous regulator slug, then inject a combination slug of viscosity reducer and flow control agent; the injection volume of the slug is 0.4 PV, and the injection ratio of the heterogeneous regulator slug to the combination slug of viscosity reducer and flow control agent is 1:5.

[0056] Parallel sand-filled pipe model With a permeability ratio of 3:1, the study investigated the enhanced oil recovery capability of the heterogeneous viscosity-reducing composite equilibrium displacement described in each embodiment.

[0057] Table 1. Value-added benefits of different chemical agent systems for improving oil recovery

[0058]

[0059] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A heterogeneous viscosity-reducing combined conformance flooding system, characterized in that, The system comprises a heterogeneity regulator, a viscosity reducer and a flow control agent; The heterogeneity regulator is composed of a dispersed gel system and / or gel particles; the dispersed gel system is crosslinked by a polymer and a phenolic resin crosslinking agent; the gel particles include pre-crosslinked gel particles; The viscosity reducer is a solution of an anionic-zwitterionic surfactant; the viscosity reducer is a solution of an anionic-zwitterionic sulfonate surfactant, and the molecular structure is as follows: ； x is a positive integer ≤5, y is an integer between 2 and 7, and m and n are integers between 2 and 4; the mass concentration of the viscosity reducer is 0.3%-0.5%; The flow control agent is a polymer solution, and the flow control agent is a solution of partially hydrolyzed polyacrylamide with a molecular weight of 3000-35 million and a mass concentration of 0.1%-0.3%.

2. The method of injecting the heterogeneous viscosity-reducing combined displacement system of claim 1, characterized in that, The heterogeneity regulator, the viscosity reducer and the flow control agent are injected in separate slugs.

3. The method of claim 2, wherein, The heterogeneity regulator slug is injected first, followed by the combined slug of the viscosity reducer and the flow control agent.

4. The method of claim 2, wherein, The injection amount of the heterogeneity regulator slug to the combined slug of the viscosity reducer and the flow control agent is 1-5:1-5.

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