CN110863808A - Thickened oil exploitation method for enhancing water drive efficiency through electric heating - Google Patents

Abstract

A heavy oil recovery method with electric heating to enhance water flooding efficiency. First, an electric heating tube or an electric heating cable is fixed to the outside of an insulating tube with grooves in a ring manner, and is lowered to a target oil reservoir through a production string to expand and isolate the The tube makes the heating tube close to the production casing to heat the formation near the wellbore; after the heating distance reaches the preset value, the heating will continue to be maintained, and the heating power will be adjusted to continuously reduce the viscosity of the heavy oil in the vicinity of the production well. Flow resistance and mobility ratio; start the ordinary heavy oil water flooding process, inject displacement fluid into the injection well, and displace the crude oil in the formation to move towards the production well; the crude oil, water and gas flowing to the production well are lifted through the production well The device is lifted to the ground. The invention combines thermal recovery and cold recovery, reduces the flow resistance and displacement fingering in the near-well area of the production well, accelerates the production effective period of water flooding and the recovery efficiency of heavy oil, and improves the ultimate recovery rate.

Description

A heavy oil recovery method with electric heating to enhance water flooding efficiency

technical field

The invention relates to a heavy oil recovery method, which belongs to the technical field of oilfield oil recovery.

Background technique

Heavy oil contains a relatively high proportion of asphalt and colloid components, and its underground viscosity is much higher than that of conventional crude oil (generally greater than 50 mPa·s), resulting in poor fluidity of heavy oil and high mining difficulty. However, the viscosity of heavy oil is highly sensitive to temperature. Usually, the original viscosity can be reduced by half for every 10°C increase in temperature. Therefore, thermal recovery methods are often used in the recovery of heavy oil, such as steam flooding, steam huff and puff, combustion of oil layer, electric heating, etc., especially for super and extra heavy oil with high viscosity (viscosity greater than 10000mPa·s). For ordinary heavy oil (viscosity less than 10000mPa·s), due to its certain fluidity, it can be directly exploited by high-pressure fluid displacement, such as water flooding. Compared with the thermal recovery method, the water flooding heavy oil recovery technology has low cost and relatively simple construction. The recovery process does not involve heat transfer problems such as heat diffusion efficiency and heat loss, and there is no need to arrange boilers on site for heating water or generating steam. equipment, the initial investment is small, so water flooding is widely used in ordinary heavy oil production.

However, there are still some problems in the actual production of water flooding heavy oil technology: First, the production is slow and the initial output is low. The main reason is that the fluid changes from the overall flow in the oil layer to the radial flow to the production well near the production well. The wellbore area of the production well is much smaller than the vertical cross-sectional area of the formation, so the formation flow resistance in the near-wellbore area is large, resulting in low oil production. ; Second, in the process of water flooding heavy oil, due to the high mobility ratio between the displacing fluid (water) and the displaced fluid (heavy oil), it is easy to produce viscous fingering under the displacement pressure gradient. For the process of water flooding heavy oil, the mobility ratio is much greater than 1, and the pressure gradient in the production well area is large, and the actual reservoir is heterogeneous, during the process of water flooding heavy oil, the viscosity finger near the production well is The phenomenon will be more serious. Once the fingering front is connected to the production well, it will easily lead to a premature displacement breakthrough, and the oil displacement efficiency will be greatly reduced, which will eventually lead to uneven production of the oil layer, which will seriously affect the sweep efficiency and ultimate recovery factor.

For the problem of low recovery rate of ordinary heavy oil by water flooding, Chinese patents (application numbers 201010622259.1 and 201410407879.1) propose a method of plugging with artificial foam or gel to improve the sweep efficiency during water flooding. In response to the problem of slow production of heavy oil production, the Chinese patent (Application No. 201611187914.9) proposes to use electric heating rods to heat the oil reservoir in the injection well and production well during the start-up stage in the process of steam-assisted gravity drainage in the combination of dual horizontal wells. The method is to speed up the communication between the injection well and the production well, and switch to the steam-assisted gravity drainage (SAGD) stage in advance to achieve the effect of accelerating production. The Chinese patent (Application No. 201510794640.9) proposes a method of exploiting heavy oil by using electric energy: a dipole antenna is arranged in a vertical well, the formation water is heated by electricity, the viscosity of the heavy oil in the reservoir is reduced, and the crude oil flows to the horizontal well at the bottom under the action of gravity and output, in order to achieve the effect of reducing energy consumption, water consumption and environmental pollution. The Chinese patent (Application No. 201821146620.6) proposes a gravity drainage device assisted by electric heating, which generates high-temperature steam by means of in-situ electric heating, drives the gravity drainage process of heavy oil, and improves the production efficiency of SAGD in horizontal wells at the same time. uniform problem. However, the above-mentioned patented technologies only involve a single thermal recovery or cold recovery method for heavy oil, and cannot simultaneously solve the problems of slow recovery, severe fingering and low sweep coefficient in the process of ordinary heavy oil cold recovery.

SUMMARY OF THE INVENTION

In order to solve the above problems, combined with the applicant's knowledge of the principle of water-flooding heavy oil technology and field operation experience, the present invention proposes a heavy oil recovery method with bottom-hole electric heating of production wells to enhance water-flooding efficiency. Electric heating is applied inside to increase the temperature of the oil layer near the production well, reduce the flow resistance and displacement fingering in the near-wellbore area, speed up the production effective period of water flooding and the recovery efficiency of heavy oil, and improve the ultimate recovery factor.

To achieve the above object, the present invention adopts the following technical solutions:

A heavy oil recovery method with electric heating enhancing water flooding efficiency, comprising the following steps:

Step 1. Fix the electric heating pipe or electric heating cable outside the insulating pipe with grooves in a ring-shaped arrangement, lower it to the target oil reservoir through the production string, and expand the insulating pipe to tighten the heating pipe and the production casing. The heat spreads evenly around the production casing to heat the formation near the wellbore. The heating power and time need to be adjusted according to the pre-measured thermal diffusivity of the reservoir to reduce the viscosity and flow of heavy oil in the vicinity of the production well. The ratio of resistance and fluidity; the isolation pipe mainly plays the role of insulation, heat insulation and leakage prevention; when expanding, the hydraulic expander is used for local expansion;

Step 2: After the heating distance reaches the preset value, continue to keep heating, and adjust the heating power to continuously reduce the viscosity, flow resistance and mobility ratio of the heavy oil in the vicinity of the production well, thereby reducing the influence of the displacement viscous fingering phenomenon ; Adjust the heating power according to the flow rate of the produced liquid, and the specific setting can be carried out according to the following formula:

P=Q _v C _v (T _f -T _res )+Q _r

where P is the heating power, Q _v is the volume flow of the produced fluid, C _v is the specific heat capacity of the produced fluid, _Tres is the reservoir temperature, T _f is the temperature of the produced fluid, Q _r is the heating power to the reservoir, oil After the temperature of the reservoir heating zone is stable, this part of the heat is mainly used to make up for the heat loss of the upper and lower caprocks of the reservoir.

Step 3, starting the ordinary heavy oil water flooding production process, injecting displacement fluid into the injection well, the displacement fluid is propelled to the production well under the pressure difference between the injection pressure and the formation pressure, and the crude oil in the displacement formation moves toward the production well; The crude oil, water and gas flowing to the production well are lifted to the surface through the lifting device in the production well. Due to the preheating and continuous heating of the near-wellbore area, the flow resistance in the near-wellbore area can always be kept at a low level. The increase of heavy oil production is accelerated, and the formation heavy oil is continuously produced through the production well under the displacement of the displacement fluid.

Further, the electric heating method is heat conduction type resistance heating or induction type electromagnetic and microwave, and the heating power source can be single-phase or three-phase power supply.

Further, in step 1, the heating power and time are determined according to the following formula:

According to the unsteady heat transfer process of the fixed-point heat source, the time t required to raise the temperature from the heat source position L to the temperature T can be calculated as follows:

为预先测量的油层平均热扩散系数，以表征不同孔隙度和含水率的油层热扩散能 力，T_res为油藏温度，T_s为电加热装置的表面温度。in

is the pre-measured average thermal diffusivity of the oil layer to characterize the thermal diffusivity of the oil layer with different porosity and water content, _Tres is the reservoir temperature, and T _s is the surface temperature of the electric heating device.

Further, the displacement fluid injected in the injection well is one or a combination of water, gas, and polymer.

Further, the preset value is the electric heating distance, which is controlled within a range of 0.5 to 5 meters around the production well. The flow resistance in the heated area is low, and the low resistance flow area is proportional to the heating distance. The larger the heating range, the smaller the displacement resistance. This value needs to be calculated according to the viscosity of the heavy oil on site to determine the amount to be reduced. resistance ratio. According to the viscosity of ordinary heavy oil, heating in the range of 0.5 to 5 meters can reduce the original displacement resistance by 5% to 20%.

Further, the heating method adopts continuous heating or intermittent heating according to production needs.

Most of the heavy oil exploited by the above-mentioned water flooding method is ordinary heavy oil (defined in the technical background), which has a certain flow capacity at the initial temperature of the formation, and the production well does not need to maintain a too high temperature, and can be adjusted according to needs. Generally maintained between 50-150 ℃.

The above method can be applied to the well group combination of different types of injection wells and production wells, which can be vertical injection wells and vertical production wells, vertical injection wells and horizontal production wells, horizontal injection wells and horizontal production wells, etc., indicating that the scope of application of the present invention is wider.

The present invention has the following advantages due to taking the above technical solutions:

The innovation of the present invention lies in the combination of thermal recovery technology and cold recovery technology, taking into account the advantages of low recovery cost of common heavy oil cold recovery (such as water flooding, etc.), and at the same time utilizing thermal energy to the production well with the highest efficiency to increase oil well production and displacement efficiency.

1. Use the heat energy where the heat is most needed, and heat the oil layer near the production well before and during the displacement process, which reduces the viscosity of crude oil and the flow resistance of crude oil, and relieves the rapid reduction of the flow cross section near the production well. The problems of high flow resistance and difficulty in production have accelerated the effective period of production wells and increased crude oil production; 2. Due to the increased mobility of heavy oil near production wells, the mobility ratio has been reduced, and the displacement front has been greatly improved. The stability of the area close to the production well slows down the phenomenon of viscous fingering, and improves the sweep efficiency and ultimate recovery of reservoir displacement; 3. It overcomes the pure downhole electric heating production method, which mainly relies on the natural energy of the formation (strata). 4. For ordinary heavy oil reservoirs, the heating temperature is not high, generally between 50-150 °C, and only 0.5 ℃ around the production well is heated The area within ~5 meters, and the installation and operation of heating equipment is relatively simple, so the increase in investment cost is small. As the oil well production and ultimate recovery factor are improved, the purpose of improving the overall economic benefit of ordinary heavy oil production is achieved.

Description of drawings

Figure 1 is a schematic side view of the combination of the electric heating device and the production casing.

Figure 2 is a schematic top view of the combination of the electric heating device and the production casing.

Figure 3 is a schematic side view of a typical vertical injection well-vertical production well water flooding heavy oil recovery process.

Figure 4 is a schematic top view of a typical vertical injection well-vertical production well water flooding heavy oil recovery process.

Figure 5 is a schematic side view of the application of electric heating enhanced water flooding to the heavy oil recovery process of vertical injection wells-vertical production wells.

FIG. 6 is a schematic top view of the application of electric heating enhanced water flooding to the heavy oil recovery process of vertical injection wells and vertical production wells.

Figure 7 is a schematic top view of a typical vertical injection well-horizontal production well water flooding heavy oil recovery process.

The codes in the accompanying drawings are respectively: 1 is a flexible electric heating pipe or heating belt, 2 is a production well casing, 21 is a flexible insulating pipe with grooves, 22 is a thermal insulation asbestos layer, 31 is a heavy oil layer, 32 is an oil layer Bottom, 33 is the top of the oil layer, 34 is the vertical injection well, 35 is the interface in the early stage of displacement, 36 is the main advancing direction of the displacement interface, 37 is the interface in the later stage of displacement, 38 is the viscous fingering breakthrough, 39 is the vertical production well, and 310 is the Production fluid, 311 is the downhole lifting device, 312 is the production tubing, 51 is the electric heating device, 52 is the power line of the electric heating device, 53 is the heat generated by the electric heating device, 54 is the electric heating heat conduction interface, 71 is the horizontal production well.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

In order to spread the electric heating heat evenly to the formation near the production well, a plurality of flexible electric heating pipes 1 are annularly attached to the production well casing 2, as shown in Figure 1. In the present invention, this effect is achieved by adding a flexible insulating tube 21 with grooves, as shown in FIG. 2 . First of all, the outer surface of the flexible insulating pipe 21 with grooves is provided with a layer of insulating asbestos layer 22, and the flexible insulating pipe 21 with grooves is hollow so as to facilitate the passage of equipment such as production oil pipes and lifting devices. During installation, the flexible electric heating pipe 1 is fixed to the non-groove on the outer surface of the insulating pipe by means of a clamp, and after the fixing is completed, it is lowered to the target position in the casing 2 of the production well. Then, the pipe expansion device is passed through the isolation pipe, so that the flexible electric heating pipe 1 is closely attached to the production sleeve 2. Before the pipe expansion, the distance between the flexible electric heating pipe 1 and the inner wall of the production sleeve 2 is generally less than 1 cm. The thickness of the groove on the outer surface of the flexible insulating tube 21 with grooves is half of the thickness of the flexible electric heating tube 1. The function of this groove is that when the heating device needs to be taken out, it is only necessary to rotate the expanded flexible insulating pipe 21 with grooves by 5-30°, and the gap between the production sleeve 2 and the flexible electric heating pipe 1 is Under the action of friction, the flexible electric heating pipe 1 is stationary relative to the production casing 2, and only the flexible insulating pipe 21 with grooves rotates, so that the flexible electric heating pipe 1 is located at the groove position of the flexible insulating pipe 21 with grooves. The flexible insulating tube 21 with grooves can be taken out, and the flexible electric heating tube 1 can also be taken out. When installing again, just repeat the installation steps. Figures 1 and 2 show the key points of the arrangement, installation and removal of the electric heating device in the present invention.

Figure 3 shows a typical water-flooding common heavy oil recovery process. Generally speaking, water is injected into the heavy oil layer 31 through the vertical injection well 34, and under the action of the pressure difference between the injection pressure and the formation pressure, the heavy oil is displaced, and the early displacement interface 35 is gradually formed, and the output of the production well Liquid 310 is mainly heavy oil. Produced fluids are lifted to the surface by downhole lifts 311 and production tubing 312. As the displacement mining process progresses, the pre-displacement interface 35 advances along the main advancing direction 36 of the displacement interface. Due to the heterogeneity of the oil layer and the displacement mobility ratio greater than 1, the interface 37 is prone to viscous fingering in the later stage of displacement. When the viscous finger communicates with the production well, the viscous finger breakthrough 38 is formed, and at this time, the production fluid 310 in the vertical production well 39 is composed of an oil-water mixture. The top view of a typical water flooding heavy oil recovery process is shown in Figure 4. The occurrence of viscous fingering breakthrough 38 will lead to low oil production efficiency and affect ultimate recovery.

Embodiment 1: As shown in FIG. 5, the present invention is applied to the exploitation of heavy oil, and is carried out according to the following method: the electric heating device 51 is put into the oil jacket annulus of the vertical production well 39 according to the installation process of the aforementioned electric heating device, The power supply line 52 of the electric heating device is connected to the power supply equipment; the heat 53 generated by the electric heating device diffuses around the vertical production well 39, so that the temperature of the formation within 3 meters nearby rises to above 100°C. According to the unsteady heat transfer process of the fixed-point heat source, the time t required to raise the temperature from the heat source position L to the temperature T can be calculated as follows:

为预先测量的油层平均热扩散系数，以表征不同孔隙度和含水率的油层热扩散能 力，T_res为油藏温度，T_s为电加热装置的表面温度。根据上述公式，可估算或调控预热时间。 以直径为4.5英寸(114.3mm)的管径为例，垂直生产井39附近的低阻力流动截面在加热前 后之比为114.3²:3000²＝1:689，因此，水驱过程在垂直生产井39附近的压力损失可大幅度降 低。in

is the pre-measured average thermal diffusivity of the oil layer to characterize the thermal diffusivity of the oil layer with different porosity and water content, _Tres is the reservoir temperature, and T _s is the surface temperature of the electric heating device. According to the above formula, the warm-up time can be estimated or adjusted. Taking a pipe diameter of 4.5 inches (114.3 mm) as an example, the ratio of the low resistance flow section near the vertical production well 39 before and after heating is 114.3 ² : 3000 ² = 1:689. Therefore, the water flooding process in the vertical production well The pressure loss near 39 can be greatly reduced.

After the heating distance reaches the preset value, the heating is continued, and at the same time, water is injected into one end of the vertical injection well 34 to drive the formation crude oil to be lifted to the surface through the downhole lifting device 311 in the vertical production well 39 to realize continuous production of heavy oil. At this time, the produced fluid 310 in the vertical production well 39 is mainly heavy oil. Under the heating of the electric heating device 51, the flow resistance in the vicinity is reduced. Therefore, compared with the traditional water flooding heavy oil process without electric heating, the initial output after the application of the present invention can be doubled. With the progress of the water flooding heavy oil recovery process, the pre-displacement interface 35 advances along the main advancing direction 36 of the displacement interface. In the middle and late stage of water flooding, under the heating of the electric heating device 51, the oil displacement mobility ratio near the vertical production well 39 decreases, so that the displacement interface can advance to the production well in a more uniform and stable manner, effectively reducing the displacement index. into the phenomenon. The schematic top view of the present invention applied to the heavy oil recovery process is shown in Figure 6. During the whole process of water flooding heavy oil, the output of the production wells was relatively stable. It should be noted that during the production process, with the displacement and production of heavy oil, the heat near the production well will be taken away. When the temperature of the heating zone near the production well is stable and the heat loss to the surrounding formation is ignored, the electric heating The heating power of the device 51 needs to be adjusted according to the flow rate of the produced liquid, and the specific setting can be carried out according to the following formula:

P=Q _v C _v (T _f -T _res )+Q _r

where P is the heating power, Q _v is the volume flow of the produced fluid, C _v is the specific heat capacity of the produced fluid, _Tres is the reservoir temperature, T _f is the temperature of the produced fluid, and Q _r is the heating power to the reservoir.

Compared with the traditional water-flooding heavy oil, the technical effect obtained in this embodiment is that the initial production is larger, the overall production is also higher and more stable, the viscous fingering phenomenon during the displacement process can be significantly reduced, and the production efficiency and final recovery are improved. yield.

Example 2: The present invention can also be applied to the heavy oil production in the vertical injection well-horizontal production well group combination, as shown in Figure 7. The process of the present embodiment is similar to that of embodiment 1, and the technical effect obtained is the same as that obtained in embodiment 1, which can also improve the initial water flooding heavy oil production and reduce the viscous fingering phenomenon in the later stage of the displacement.

To sum up, the heavy oil recovery method with electric heating to enhance water flooding efficiency according to the present invention combines the mechanisms and advantages of thermal recovery and cold injection fluid displacement. By applying electric heating in a specific range near the production well, the effective period of the water flooding heavy oil production process is shortened and the production efficiency is improved; the thermal diffusion of electric heating makes the displacement front near the production well more stable, and the viscous fingering The phenomenon is reduced and the swept volume is increased, thereby effectively improving the efficiency and ultimate recovery of heavy oil by water flooding.

Claims (6)

1. a heavy oil exploitation method of electric heating enhancing water drive efficiency, is characterized in that, comprises the following steps: Step 1. Fix the electric heating pipe or electric heating cable outside the insulating pipe with grooves in a ring-shaped arrangement, lower it to the target oil reservoir through the production string, and expand the insulating pipe to tighten the heating pipe and the production casing. The heat spreads evenly around the production casing to heat the formation near the wellbore; Step 2: After the heating distance reaches the preset value, continue to keep heating, and adjust the heating power to continuously reduce the viscosity, flow resistance and mobility ratio of the heavy oil in the vicinity of the production well, thereby reducing the influence of the displacement viscous fingering phenomenon ; Adjust the heating power according to the flow rate of the produced liquid, and the specific setting can be carried out according to the following formula: P=Q _v C _v (T _f -T _res )+Q _r where P is the heating power, Q _v is the volume flow of the produced fluid, C _v is the specific heat capacity of the produced fluid; _Tres is the reservoir temperature, and T _f is the temperature of the produced fluid. Q _r is the heating power to the reservoir. Step 3, starting the ordinary heavy oil water flooding production process, injecting displacement fluid into the injection well, the displacement fluid is propelled to the production well under the pressure difference between the injection pressure and the formation pressure, and the crude oil in the displacement formation moves toward the production well; The crude oil, water and gas flowing to the production well are lifted to the surface through the lifting device in the production well. Due to the preheating and continuous heating of the near-wellbore area, the flow resistance in the near-wellbore area can always be kept at a low level. The increase of heavy oil production is accelerated, and the formation heavy oil is continuously produced through the production well under the displacement of the displacement fluid. 2. the heavy oil recovery method of a kind of electric heating enhancing water flooding efficiency as claimed in claim 1, is characterized in that, described electric heating mode is the resistance heating of heat conduction type or induction type electromagnetic, microwave, and the heating power source can adopt Single-phase or three-phase power supply. 3. the heavy oil exploitation method of a kind of electric heating enhancement water drive efficiency as claimed in claim 1, is characterized in that, in step 1, heating power and time are determined by following formula: According to the unsteady heat transfer process of the fixed-point heat source, the time t required to raise the temperature from the heat source position L to the temperature T is calculated as follows:

in

is the pre-measured average thermal diffusivity of the oil layer to characterize the thermal diffusivity of the oil layer with different porosity and water content, _Tres is the reservoir temperature, and T _s is the surface temperature of the electric heating device. 4 . The heavy oil recovery method with electric heating enhancing water flooding efficiency according to claim 1 , wherein the displacement fluid injected into the injection well is one of water, gas, and polymer or a combination thereof. 5 . 5 . The heavy oil recovery method with electric heating enhancing water flooding efficiency according to claim 1 , wherein the preset value is the electric heating distance, which is controlled within a range of 0.5 to 5 meters around the production well. 6 . . 6 . The heavy oil recovery method with electric heating enhancing water flooding efficiency according to claim 1 , wherein the heating method adopts continuous heating or intermittent heating according to production needs. 7 .

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