Method for reducing bottom water coning interface of heavy oil reservoir

Abstract

The invention belongs to the technical field of heavy oil reservoir water plugging, and discloses a method for reducing a heavy oil reservoir bottom water coning interface, which comprises the following steps of: 1, determining a water outlet oil layer caused by bottom water coning, 2, injecting a nitrogen foam pressurized water cone to protect the oil layer, and 3, injecting high-temperature-resistant gel to meet the requirement of subsequent steam injection for steam huff and puff development. And 4, injecting a high-strength sealing agent, and establishing an artificial partition plate. According to the method, the water cone form is researched, the position of a water outlet oil layer is more accurately calculated, a composite water plugging formula of a nitrogen foam pressurized water cone protection oil layer, high-temperature-resistant gel and a high-strength sealing agent is selected, the problem that production of a heavy oil reservoir with sufficient bottom water energy is affected by bottom water coning is solved, and the overall development effect of the heavy oil reservoir is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of water plugging in heavy oil reservoirs, and in particular relates to a method for reducing a bottom water cone interface in a heavy oil reservoir. Background Art

[0002] Bottom water coning is a very common phenomenon in oil and gas well production. The main reason is that the pressure drop around the wellbore occurs during oil well production. As the oil well produces at a certain rate, the oil-water interface near the bottom of the well will rise in a cone shape. The higher the oil well production, the stronger the bottom water coning force, and the earlier the oil well will see water. After the bottom water coning phenomenon occurs, the water saturation near the bottom of the well increases, which reduces the permeability of the oil phase and causes water plugging. The premature water breakthrough of the oil well not only increases the load of the well pump and reduces the oil production, but also corrodes the downhole and surface equipment, increases the workload and energy consumption of the dewatering pump station, and increases the cost of oil production. Compared with ordinary bottom water reservoirs, heavy oil reservoirs with sufficient bottom water energy are more affected by bottom water coning. The main reason is that the viscosity of heavy oil is greater than that of conventional crude oil, and the flow capacity of the water phase far exceeds the flow capacity of the heavy oil phase. The water out of the oil layer caused by bottom water coning is more prominent. If the problem of edge and bottom water invasion cannot be effectively solved, it will seriously affect the overall development effect of the heavy oil reservoir.

[0003] Water plugging technology can be divided into two categories: mechanical water plugging and chemical water plugging. Chemical water plugging includes non-selective water plugging and selective water plugging. Mechanical water plugging is to use packers and downhole supporting tools to seal the water-producing layer in the oil well, but it can only achieve the purpose of "sealing but not plugging", and the problem of water production in the oil layer has not been fundamentally solved. Non-selective water plugging mostly relies on precipitated particles to block the formation pores. This water plugging method blocks the oil-producing pores while blocking the water-producing pores, and eventually the water-producing oil layer is "blocked", and the oil layer can no longer produce oil. Selective water plugging is to squeeze high molecular polymers or inorganic substances that precipitate and solidify when encountering water into the formation. The hydrophilic groups in the high molecular polymers have affinity and adsorption for water when encountering water, and expand. They shrink when encountering oil and have no adsorption effect. Inorganic substances that precipitate and solidify when encountering water can block the water-producing pores of the formation, and will not precipitate or solidify when encountering oil, achieving the purpose of "blocking but not killing". Before adopting the selective water plugging process for water plugging, the bottom water that has entered a certain height should usually be pressed. The commonly used method of pressing the cone is to shut in the well and press the cone. The operation of shutting in the well and pressing the cone is simple, but the effect after the implementation of the pressing cone is generally not ideal. Not only will the oil production of the oil well be affected during the shut-in period, but the water content of the oil well will quickly rise to the level before the shut-in and pressing the cone after the well is opened. In addition, the pressing power of the shut-in and pressing cone is the gravity difference between oil and water in the formation. Affected by factors such as mineralization and long-term contact of bottom water with heavy oil, the density of bottom water will tend to increase in the direction of heavy oil density, resulting in a smaller oil-water density difference, a reduced pressing power, and a longer pressing time and shut-in time, which ultimately affects the production and the application effect is not ideal.

[0004] In the field of bottom water cone in heavy oil reservoirs, advanced, practical and concise methods and technologies are urgently needed. Nitrogen is a non-condensable gas with high compression coefficient and strong expansion property. After entering the formation, it can replenish formation energy and increase formation pressure in time. Nitrogen foam fluid has high stability in the formation and its flow resistance is greatly improved compared with water. It can be used to plug water channeling channels. Nitrogen foam fluid water cone technology has high research and promotion value. Summary of the invention

[0005] In order to overcome the shortcomings of the prior art, the main purpose of the present invention is to provide a method for reducing the bottom water cone interface of heavy oil reservoirs, injecting nitrogen foam to compress the water cone downward, using high-temperature resistant gel to adjust the profile and plug water, and then injecting a high-strength sealing agent to achieve the purpose of partition plugging. The method is simple to construct and has a high success rate. It provides a new and effective method for solving the problem of high water content in oil wells after bottom water cone advancement in heavy oil reservoirs, and has a high research and promotion value.

[0006] The above purpose is achieved through the following technical solutions:

[0007] A method for reducing the bottom water cone interface of a heavy oil reservoir comprises the following steps:

[0008] The first step is to determine the water-producing oil layer caused by the bottom water cone. When the oil well is a vertical well, the water cone is often in the shape of a curved cone. The water cone height, water cone bottom radius, and water cone volume when the water cone breaks through the bottom of the wellbore perforation section are derived according to the empirical formula as a reference for the amount of nitrogen foam injected when compressing the water cone.

[0009] The second step is to inject nitrogen foam to compress the water cone to protect the oil layer. According to the principle of minimizing seepage resistance, nitrogen and foaming agent are injected first into the production deficit and the low-pressure layer near the wellbore to fill the deficit and protect the oil layer. When the continuous injection reaches a certain pressure, a pressure balance is generated between various parts of the oil layer to reach the starting pressure of the water layer. The subsequently injected nitrogen foam begins to enter the water invasion channel, compressing the water cone to move downward to prevent the bottom water from diluting the subsequent plugging agent.

[0010] The third step is to inject high-temperature resistant gel to meet the needs of subsequent steam injection for steam huff-and-puff development. Under the starting pressure of the water layer, a mixed solution of polyacrylamide, enhancer, cross-linker and initiator is injected into the well. The mixed solution is mixed with the injected nitrogen in the porous medium. Before gelation, it has a strong retention capacity and plays a "supporting" role, forcing the subsequent plugging agent to diffuse around to avoid crossflow or bypass flow. After construction, gel foam is formed at the formation temperature to expand the plugging radius.

[0011] The fourth step is to inject high-strength sealing agent to build an artificial baffle. Under the high squeezing pressure formed by the pre-plugging agent, a mixed plugging agent of permeability regulator and thickener is injected into the bottom water intrusion channel. After the plugging agent is retained and solidified, its strength is high, close to that of oil well cement, and it can withstand temperatures above 300°C. Its structure is close to that of the formation matrix rock, forming a spatial network-like artificial baffle, producing permanent plugging, preventing bottom water from rising, and restoring normal production of the oil well.

[0012] The beneficial effects of the present invention compared with the prior art are:

[0013] (1) By studying the water cone morphology, the location of the oil layer with water outlet can be calculated more accurately.

[0014] (2) The composite water plugging formula of nitrogen foam water cone to protect the oil layer + high temperature resistant gel + high strength sealing agent was selected to solve the problem that the production of heavy oil reservoirs with sufficient bottom water energy was affected by the bottom water cone advance, thereby improving the overall development effect of the heavy oil reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0016] Figure 1 is a flow chart of the method of the present invention;

[0017] Figure 2 It is a schematic diagram of a curved water cone;

[0018] Figure 3 It is a schematic diagram of the theoretical model of numerical simulation;

[0019] Figure 4 This is a comparison chart of the optimization of nitrogen foam dosage in numerical simulation;

[0020] Figure 5 The comparison photos of the plugging agent for oil and water wells before and after gelling are shown in Figure 1. (a) is before the plugging agent for oil and water wells is gelled, and (b) is after the plugging agent for oil and water wells is gelled.

[0021] Figure 6 This is a comparison chart of the optimization of the dosage of high temperature resistant gel in numerical simulation;

[0022] Figure 7 This is a comparison chart of optimization of plugging agent dosage in numerical simulation of oil and water wells;

[0023] Figure 8 This is a schematic diagram of the stratum conditions behind the bottom water pressure cone. DETAILED DESCRIPTION

[0024] In order to describe the features of the present invention in more detail and accurately, the following reference embodiments are given for detailed description with reference to the relevant drawings, which are intended to be used to explain the present invention but cannot be interpreted as limiting the present invention.

[0025] Example 1

[0026] The present invention is achieved in that:

[0027] 1. When the oil well is a vertical well, the water cone is often in the shape of a curved cone. The water cone height, water cone bottom radius, and water cone volume are derived based on empirical formulas when the water cone breaks through the bottom of the wellbore perforation section.

[0028] 2. The gas pre-injected for cone compression must meet certain thermal insulation, expansion and compressibility, and the gas source should be widely available. The cost and construction safety should also be taken into consideration. Based on the above considerations, nitrogen is selected for injection in the implementation mode of the present invention. The injection amount should be combined with the theoretical research results of reservoir numerical simulation, and at the same time, it should meet the needs of subsequent steam injection for steam huff and puff development.

[0029] 3. After the water cone at the bottom of the well is pressed down, the temperature-resistant gel is injected. In this embodiment, the effect evaluation method of different numerical simulation calculation schemes is to inject a mixed solution into the well, and prepare 400m 3 , injection displacement 0.5m 3 / min; the pressure reaches above 8MPa, which can ensure a good plugging effect.

[0030] 4. Inject a mixed plugging agent of permeability regulator and thickener, wherein the mass of permeability regulator is 25g per 100mL water, and the mass of thickener is 4-5g per 100mL water.

[0031] 5. Oil and water well plugging agent, 200m3 of liquid 3 , displacement 0.2m 3 / min, the construction pressure reaches 8-10MPa. During the implementation process, the concentration and dosage of the plugging agent are adjusted on site according to the pressure changes. Displace clean water, the replacement amount is determined according to the volume of the pipe column, and after waiting for 24 hours, deepen the pipe column to the bottom of the artificial well. Circulate and wash the well for 2 weeks, pull out the pipe column, and perform other processes.

[0032] When the oil well is a vertical well, the water cone is often in the shape of a curved cone. Figure 2 The water cone height is derived from the following equations ① and ②. The height h of a point A on the water cone surface from the oil-water interface is A The relationship between the radial distance r between this point and the oil well is as follows:

[0033]

[0034] Among them, h A——The height of point A from the oil-water interface, m;

[0035] h——oil layer thickness, m;

[0036] μ o ——Underground crude oil viscosity, mPa﹒s;

[0037] Q o ——Surface oil well production, m 3 / d;

[0038] B o ——Volume coefficient of crude oil;

[0039] K——average formation permeability, μm 2 ;

[0040] Δρ wo ——Difference in density between water and oil, g / cm 3 ;

[0041] r——the radial distance between point A and the oil well, m;

[0042] r c ——Radius of the bottom of water cone, m.

[0043] When r is equal to the wellbore radius r W When A is the water cone height, that is:

[0044]

[0045] From this formula ②, the radius of the bottom of the water cone can be derived as follows:

[0046]

[0047] Since the volume of the water cone is the volume of a solid of revolution, the volume V of the water cone can be approximately expressed by the following integral formula ④:

[0048]

[0049] Positive nitrogen injection 150000m 3 , treatment radius 25m;

[0050] The foaming agent is a high temperature resistant sulfonate foaming agent. The sweep radius of the foam fluid around the oil well is calculated as 3m, the foaming agent concentration under formation conditions is calculated as 0.6%, and the foaming agent dosage is 3 tons. The foaming agent dosage is calculated by formula ⑤:

[0051] Q=2πr 2 hφn ⑤

[0052] Where: Q——foaming agent dosage, t;

[0053] r——wave radius, m;

[0054] h——oil layer thickness, m;

[0055] φ——porosity, decimal;

[0056] n——foaming agent solution concentration;

[0057] The high temperature resistant gel is a gel system formed by copolymerization of 0.4%-0.5% polyacrylamide by mass, 0.3% reinforcing agent by mass, 0.3% cross-linking agent such as N, N-methylenebisacrylamide, dibenzoyl peroxide, etc., and 0.3% initiator such as azobisisoheptanenitrile, persulfate (such as potassium persulfate), etc. The reinforcing agent is prepared by compounding hard glucan and modified starch in a mass ratio of 1:1.

[0058] The effect evaluation method is to inject the mixed solution into the well and prepare 400m 3 .

[0059] A mixed plugging agent of permeability regulator and thickener is injected, wherein the mass of permeability regulator is 25g per 100mL water, and the mass of thickener is 4-5g per 100mL water. The plugging agent is a new type of inorganic polymer material formed under certain catalytic conditions after high-temperature calcination activation with a variety of natural minerals as the main raw materials. The main component is magnesium silicate / lithium aluminum salt, which does not contain sulfur and is composed of [SiO4] and [AlO4] tetrahedrons. The structural characteristics are crystal and semi-crystal, and the complete reaction body structure reaches nanometer level. The molecular formula is M X -[-(Si-O2) Z -Al-O-] N -wH2O.

[0060] The plugging agent is being injected into the oil and water wells. The injection position is shown in the attached Figure 8 , 200m 3 During the implementation process, the concentration and dosage of the plugging agent are adjusted on site according to the pressure changes.

[0061] The above-described embodiments are only preferred embodiments of the present invention, but not all feasible embodiments of the present invention. For those skilled in the art, any obvious changes made thereto without departing from the principles and spirit of the present invention should be considered to be included in the scope of protection of the claims of the present invention.

Claims

1. A method for reducing the bottom water cone interface of a heavy oil reservoir, characterized in that: The following steps are involved: The first step is to determine the water-producing oil layer caused by the bottom water cone. When the oil well is a vertical well, the water cone is often in the shape of a curved cone. The water cone height, water cone bottom radius, and water cone volume when the water cone breaks through the bottom of the wellbore perforation section are derived according to the empirical formula as a reference for the amount of nitrogen foam injected when the water cone is compressed. The second step is to inject nitrogen foam to compress the water cone to protect the oil layer. According to the principle of minimizing seepage resistance, nitrogen foam and foaming agent are injected, and they are preferentially injected into the production deficit and the low-pressure layer near the wellbore to fill the deficit and protect the oil layer. When the injection reaches a certain pressure, the pressure balance is generated between the various parts of the oil layer, reaching the starting pressure of the water layer. The subsequently injected nitrogen foam begins to enter the water invasion channel, compressing the water cone to move downward, and preventing the bottom water from diluting the subsequent plugging agent; The third step is to inject high temperature resistant gel to meet the needs of subsequent steam injection for steam huff and puff development, that is, inject a mixed solution of polyacrylamide, enhancer, cross-linker and initiator into the well under the starting pressure of the water layer; The fourth step is to inject high-strength sealing agent to build an artificial baffle, and under the higher squeezing pressure formed by the pre-plugging agent, inject a mixed plugging agent of permeability regulator and thickening agent into the bottom water intrusion channel.

2. The method for reducing the water cone interface at the bottom of a heavy oil reservoir as claimed in claim 1, characterized in that the empirical formula in the first step is: the height h of a point A on the water cone surface from the oil-water interface A The relationship between the radial distance r between this point and the oil well is as follows: in, h A ——The height of point A from the oil-water interface, m; h——oil layer thickness, m; μ o ——Underground crude oil viscosity, mPa﹒s; Q o ——Surface oil well production, m 3 / d; B o ——Volume coefficient of crude oil; K——average formation permeability, μm 2 ; Δρ wo ——Difference in density between water and oil, g / cm 3 ; r——the radial distance between point A and the oil well, m; r c ——radius of the bottom of the water cone, m; When r is equal to the wellbore radius r W When A is the water cone height, that is: From this formula ②, the radius of the bottom of the water cone can be derived as follows: Since the volume of the water cone is the volume of a solid of revolution, the volume V of the water cone can be approximately expressed by the following integral formula ④:

3. The method for reducing the bottom water cone interface of heavy oil reservoir according to claim 1, characterized in that: The nitrogen foam injection volume in the second step is 150000m 3 , processing radius 25m.

4. The method for reducing the bottom water cone interface of heavy oil reservoir according to claim 1, characterized in that: The foaming agent in the second step is a high temperature resistant sulfonate foaming agent.

5. The method for reducing the bottom water cone interface of heavy oil reservoir according to claim 1, characterized in that: In the second step, the foaming agent has a radius of 3 m and a mass concentration of 0.6%.

6. The method for reducing the bottom water cone interface of heavy oil reservoir according to claim 1, characterized in that: The composition of the high temperature resistant gel in the third step is: 0.4%-0.5% by weight of polyacrylamide, 0.3% by weight of reinforcing agent, 0.3% by weight of cross-linking agent, and 0.3% by weight of initiator.

7. The method for reducing the bottom water cone interface of a heavy oil reservoir as claimed in claim 6, characterized in that: The reinforcing agent is prepared by compounding hard glucan and modified starch in a mass ratio of 1:

1.

8. The method for reducing the bottom water cone interface of heavy oil reservoir according to claim 6, characterized in that: The cross-linking agent is N,N-methylenebisacrylamide or dibenzoyl peroxide.

9. The method for reducing the bottom water cone interface of a heavy oil reservoir as claimed in claim 6, characterized in that: The initiator is azobisisoheptanenitrile or persulfate.

10. The method for reducing the bottom water cone interface of heavy oil reservoir according to claim 1, characterized in that: The molecular formula of the high-strength sealant in the fourth step is: M X -[-(Si-O2) Z -Al-O-] N -wH2O.

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