CN114790878B

CN114790878B - Underground electric preheating method and system for steam-assisted gravity drainage of fractured reservoir

Info

Publication number: CN114790878B
Application number: CN202110103178.9A
Authority: CN
Inventors: 吴永彬; 桑林翔; 杨智; 蒋有伟; 杨果; 周晓义
Original assignee: Petrochina Co Ltd
Current assignee: Petrochina Co Ltd
Priority date: 2021-01-26
Filing date: 2021-01-26
Publication date: 2023-08-22
Anticipated expiration: 2041-01-26
Also published as: CN114790878A

Abstract

The invention provides a method and a system for downhole electric preheating of a fractured reservoir by steam assisted gravity drainage, wherein the method comprises the following steps: arranging a sleeve in a downhole horizontal section, wherein the sleeve comprises a plurality of pipelines which are sequentially connected, the pipelines are blind pipes or sieve tubes, and the lengths and positions of the blind pipes and the sieve tubes are determined according to the mud leakage rate of the downhole horizontal section; plugging treatment is carried out on stratum cracks of the blind pipe sections; the invention can realize uniform preheating, avoid preferential heat communication during conventional steam circulation heat, and promote the uniform preheating start of SAGD and the uniform development of a steam cavity transferred into the SAGD production stage along a horizontal section by using lower cost.

Description

Underground electric preheating method and system for steam-assisted gravity drainage of fractured reservoir

Technical Field

The invention relates to the technical field of geophysical exploration, in particular to a method and a system for downhole electric preheating of a fractured reservoir by steam assisted gravity drainage.

Background

Steam Assisted Gravity Drainage (SAGD) is invented by Bulter in Canada in 1978, and is successfully applied to heavy oil reservoirs in Canada oil sand mining areas, liaohe oil fields in China, xinjiang oil fields and the like, the principle is that a horizontal well pair which is overlapped up and down is deployed in the same oil reservoir, high-dryness steam is injected into an upper injection well, the steam is upwards overlapped in the stratum to form a steam cavity because the density is far less than that of crude oil, and the steam cavity is continuously upwards and laterally expanded along with continuous injection of the steam, so that heat exchange is carried out with the crude oil in the oil reservoir. The heated crude oil has reduced viscosity and flows downwards with condensed water under the action of gravity, and is extracted from the horizontal production well at the lower part of the oil layer. Up to now, SAGD technology has achieved scale development in heavy oil reservoirs in the domestic Liaohe, xinjiang, etc.

The method is characterized in that under the high-temperature and high-pressure effect of conventional cyclic preheating steam, the cracks are opened, injected steam flows along the cracks, so that the steam quantity returned from the oil pipe of a shaft section in the preheating stage is only 30% -50% of the injected steam quantity, a large amount of steam enters the oil layer, and the situation that the crack section is heated preferentially but not the crack section is difficult to heat occurs.

SAGD cycle preheating start-up optimization study of double horizontal wells indicates (Mat Changfeng, ma Desheng, et al; university of southwest Petroleum report (Nature science edition), 2010, 32 (4)), SAGD production is divided into two stages: a SAGD start-up phase and a SAGD production phase. In the SAGD start-up phase, there are two methods of throughput preheating start-up and steam injection circulation preheating start-up at present, wherein the throughput preheating start-up has high injection pressure and high temperature, and is easy to damage the well structure of the well completion. Steam injection circulation preheating, starting and heating are even, starting is stable, and the method generally comprises three steps: (1) Steam circulates in the two wells, and the reservoir mainly transfers heat by heat conduction; (2) Forming a pressure difference between the two wells, wherein the pressure of an injection well is higher than that of a production well, so that crude oil between the wells flows to the production well, and preparation is made for transferring to complete SAGD production; (3) The upper steam injection well annulus stops draining, the lower production well stops injecting steam, and the process goes into a complete SAGD production stage.

Before SAGD production can take place, the well must be started up for a thermal cycle. The phase from steam injection into the production well and injection well to the beginning of the transition to SAGD production is referred to as the start-up phase, or the preheat phase. The aim of the preheating stage is to realize uniform heating of an oil layer in the shortest time, so that an injection well and a production well are uniformly heated and communicated, and a drainage channel is established between the injection well and the production well.

Because the heavy oil reservoir deposition environments of Liaohe, xinjiang and the like all belong to river phase deposition, the reservoir is strong in heterogeneity and large in leakage reservoir development, in the conventional steam injection circulation preheating process of the reservoir, under the condition of high-speed steam injection, certain pressure difference exists between an injection well and a production well horizontal section, steam easily enters an intermediate reservoir between the injection well and the production well along a high-permeability channel of the horizontal section under the action of the pressure difference, and enters a production shaft, so that preferential thermal communication is caused, and the communication rate of the SAGD horizontal section preheated by the steam circulation is less than 70 percent according to statistics. The preferential thermal communication section has great influence on uniform steam injection transferred into the SAGD production stage, and can lead to preferential development of a steam cavity of the section, thereby leading to the incapability of uniform utilization of the horizontal section and influencing the yield and recovery ratio. It is counted that with dual horizontal well SAGD preheated by conventional injection steam cycle, less than 50% of the horizontal segments develop steam cavities.

The Chinese patent application with application number 201611187914.9 discloses a method and a device for starting steam assisted gravity drainage of a horizontal well. The method comprises the following steps: respectively placing two groups of steam-assisted gravity drainage starting devices of the horizontal wells in an injection well and a production well; the length of an electric heating rod in the horizontal well steam auxiliary gravity oil drainage starting device is the same as the length of the horizontal section of the injection well or the length of the horizontal section of the production well; an electric heating rod in the horizontal well steam auxiliary gravity oil drainage starting device performs heating operation; and monitoring the temperature between the injection well and the production well, and stopping the electric heating rod from executing the heating operation when the temperature between the injection well and the production well reaches a preset first temperature. SAGD fast warm-up start-up can be achieved. However, the simple electric heating rod is very easy to corrode in the environment of water vapor, CO2 and H2S generated at high temperature in a shaft, so that the insulation of the heater is invalid; meanwhile, the welding spots of the electric heating rod are easy to deform under the condition of continuous high-temperature heating, stress damage cracks are generated, and the heater is also invalid; in addition, the surface heating power of the electric heater needs to be regulated by means of underground temperature monitoring, but an underground temperature measuring probe is extremely fragile, so that the power of the heater is difficult to be effectively regulated, and the risk that the surface heating temperature of the heater is higher than the highest temperature resistance and insulation failure occurs is extremely easy to occur; the fourth risk is that the current commercial three-core heating cable usually used at present has the heating length of more than 400 meters, the diameter of only 1.5inch, and when the power is more than 1000W/m, the voltage of the heating inlet end is more than 2000V, and the risk that the high-voltage electricity breaks through the insulating filler to burst the heater is very easy to occur at the inlet end of the three-core cable, so that the small-diameter three-core heating cable breaking through the voltage is not available at home at present, and is difficult to enter the field application.

The Chinese patent application No. 2014105868578. X discloses a method for accelerating preheating communication by solvent auxiliary steam, which comprises the following specific steps: (1) high-power electric heating of an injection well and a production well; (2) Simultaneously injecting solvent into the long oil pipe and the short oil pipe of the injection well and the production well; (3) Simultaneously injecting a solvent and steam mixed fluid into the long oil pipe and the short oil pipe of the injection well, and injecting a solvent and steam mixed fluid into the long oil pipe of the production well, thereby draining the liquid in the short oil pipe of the production well; (4) And closing electric heating, and simultaneously injecting pure steam into the long oil pipe and the short oil pipe of the injection well, and simultaneously draining the liquid of the long oil pipe and the short oil pipe of the production well. However, the solvent is expensive, the solvent needs to be separated at a high temperature after being produced on the ground, so that high cost is brought, and the solvent assists in starting steam, so that the risk of preferential communication of the lost section in the strong heterogeneous horizontal section is difficult to avoid.

International patent publication WO2014000096A1 discloses a method of operation of SAGD of a fractured reservoir, using recovery rate to determine the severity of the leak and thereby reduce or increase the operating pressure in the horizontal zone downhole, which is simply a general method of reducing the leak by depressurization, but without pretreatment of the leak zone, and after entering the reservoir, the steam still tends to develop preferentially along the horizontal zone where the fracture develops, thereby making the horizontal zone difficult to equalize.

International patent publication No. WO2016028464A1 discloses a method for plugging a leakage SAGD oil layer by steam foam, which comprises injecting a mixed fluid of a foaming surfactant and steam in a certain proportion into a shaft through an injection well, forming high-temperature foam after entering the oil layer, plugging a leakage section, and promoting the development of a steam cavity of a non-leakage section. However, the steam foam is only suitable for a high-permeability channel with small leakage, and is difficult to be applied to a horizontal segment with serious leakage and massive development of cracks.

For a fractured reservoir, in the steam cycle preheating stage, injected steam enters an oil layer along a fracture, so that the huge risk of preferential communication of high-permeability horizontal sections is caused, and conventional steam cycle preheating is difficult to be applied. Therefore, the dual-horizontal well SAGD preheating starting method suitable for the fractured reservoir is a key for realizing uniform preheating communication of horizontal sections and ensuring high yield in the SAGD production stage.

Disclosure of Invention

The invention aims to provide a steam assisted gravity drainage downhole electric preheating method for a fractured reservoir, which can realize uniform preheating, avoid preferential heat communication during conventional steam circulation heat, and promote uniform preheating start of SAGD and uniform development of a steam cavity transferred into a SAGD production stage along a horizontal section by using lower cost. The invention further aims to provide a steam assisted gravity drainage downhole electric preheating system for the fractured reservoir.

In order to achieve the above purpose, the invention discloses a method for downhole electric preheating of a fractured reservoir by steam assisted gravity drainage, which comprises the following steps:

arranging a sleeve in a downhole horizontal section, wherein the sleeve comprises a plurality of pipelines which are sequentially connected, the pipelines are blind pipes or sieve tubes, and the lengths and positions of the blind pipes and the sieve tubes are determined according to the mud leakage rate of the downhole horizontal section;

plugging treatment is carried out on stratum cracks of the blind pipe sections;

and arranging a first oil pipe in the sleeve, arranging a heating cable in the first oil pipe, injecting water, and heating and preheating through the heating cable.

Preferably, the method further comprises:

determining the leakage rate of each position of the underground horizontal section in the drilling process;

determining a horizontal segment with the leakage rate larger than a preset threshold value as a leakage segment;

and determining the length and the position of the blind pipes according to the leakage sections, and connecting the blind pipes of each section through a screen pipe to form a sleeve.

Preferably, perforations are formed in the blind pipe.

Preferably, the plugging treatment for the stratum fracture of the blind pipe section specifically includes:

the two ends of each blind pipe of the sleeve are respectively provided with a packer;

arranging the end part of the second oil pipe between two packers corresponding to the blind pipe sections;

And injecting a slug solution into the stratum corresponding to the blind pipe through the second oil pipe.

Preferably, the injecting the slug solution into the stratum corresponding to the blind pipe through the second oil pipe specifically includes:

injecting a first high-concentration polymer solution and modified expanded graphite into the first oil pipe to form a pre-slug;

injecting a second high-concentration polymer solution through a second oil pipe to replace the pre-slug;

and (5) lifting out the second oil pipe and the packer.

Preferably, the water injection and the heating and preheating by the heating cable specifically include:

injecting a first hot water slug, and heating and preheating for a preset time through a heating cable;

injecting a solvent slug;

injecting a second hot water slug to a preset pressure.

Preferably, the heating preheating by the heating cable includes:

heating the heating cable through a heating device;

detecting the surface temperature of the heating cable through a detection device arranged on the surface of the heating cable;

the heating device adjusts the heating power of the heating cable through the surface temperature.

Preferably, the method further comprises:

performing numerical simulation on the stratum oil reservoir attribute distribution;

and if the temperature of the stratum oil reservoir layer and the viscosity of the crude oil reach preset conditions, finishing preheating.

The invention also discloses a steam assisted gravity drainage underground electric preheating system for the fractured reservoir, which comprises a sleeve arranged in the underground horizontal section, wherein the sleeve comprises a plurality of pipelines which are sequentially connected, the pipelines are blind pipes or sieve tubes, and the lengths and the positions of the blind pipes and the sieve tubes are determined according to the mud leakage rate of the underground horizontal section, a first oil pipe arranged in the sleeve and a heating cable arranged in the first oil pipe.

Preferably, perforations are formed in the blind pipe.

Preferably, the system further comprises a plurality of packers and a second oil pipe for plugging the stratum fracture of the blind pipe section;

the plurality of packers are respectively arranged at two ends of each blind pipe of the casing, and the end parts of the second oil pipes are sequentially arranged between the two packers corresponding to the blind pipe sections and are used for injecting slug solution into the stratum corresponding to the blind pipe.

Preferably, the device further comprises a heating device and a detection device arranged on the surface of the heating cable;

the heating device is used for heating the heating cable and adjusting the heating power of the heating cable according to the surface temperature of the heating cable detected by the detection device.

Preferably, the system further comprises a numerical simulation module for performing numerical simulation on the attribute distribution of the stratum oil reservoir, and if the temperature of the stratum oil reservoir and the viscosity of crude oil reach preset conditions, preheating is completed.

The invention adopts the blind pipe or the screen pipe to connect to form the sleeve, carries out horizontal section well completion by the way of connecting the blind pipe and the screen pipe in series and completing the well, and enters the blind pipe into the leakage section and enters the slotted screen pipe into the non-leakage section according to the leakage rate, thereby effectively preventing and controlling the leakage of a large amount of fluid injected into the shaft during the cyclic preheating of the leakage section and ensuring the equal flow of the fluid entering the oil layer from the different sections. Furthermore, the stratum cracks of the blind pipe sections are subjected to plugging treatment, so that deep leakage of an oil layer of a leakage section can be prevented. And finally, arranging the first oil pipe in the underground horizontal section, arranging a heating cable in the first oil pipe, and then injecting water to heat and preheat. The invention adopts unconventional well completion and plugging mode to preheat, has the multiple advantages of small fluid leakage of a shaft, uniform electric heating and solvent acceleration and viscosity reduction between wells, can reach the preheating requirement in a shorter time, has uniform preheating rate of more than 90% in a horizontal section, and has obvious economic benefit.

Drawings

In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a schematic diagram of a production well structure of a method for downhole electric preheating of a fractured reservoir steam assisted gravity drainage well according to the present invention.

FIG. 2 is a schematic diagram of a production well injection fluid slug of the inventive fractured reservoir steam assisted gravity drainage downhole electrical preheating method.

FIG. 3 is a schematic diagram of an injection well structure of the method for downhole electric preheating of a fractured reservoir steam assisted gravity drainage well of the present invention.

Reference numerals:

1. a sleeve; 21. an oil pump; 22. an oil pumping pipe; 31. a blind pipe; 32. a screen pipe; 41. a first high concentration polymer solution and modified bulk expanded graphite; 42. a second high concentration polymer solution; 51. a conductive segment; 52. a heating section; 53. a temperature thermocouple; 54. a second oil pipe; 61. a first hot water slug; 62. a solvent slug; 63. and a second hot water slug.

Detailed Description

The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

According to one aspect of the invention, the embodiment discloses a steam-assisted gravity drainage downhole electric preheating method for a fractured reservoir. As shown in fig. 1, the method includes:

s100: the casing 1 is arranged in a downhole horizontal section, the casing 1 comprises a plurality of pipelines which are sequentially connected, the pipelines are blind pipes 31 or sieve pipes 32, and the lengths and positions of the blind pipes 31 and the sieve pipes 32 are determined according to the mud loss rate of the downhole horizontal section.

S200: and plugging the stratum cracks of the blind pipe 31 section.

S300: a first oil pipe is arranged in the sleeve 1, a heating cable is arranged in the first oil pipe, and water injection is carried out to heat and preheat.

According to the invention, the blind pipe 31 or the screen pipe 32 is connected to form the casing 1, the horizontal section well completion is carried out by connecting the blind pipe 31 and the screen pipe 32 in series, the blind pipe 31 is arranged in the leakage section according to the leakage rate, the slotted screen pipe 32 is arranged in the non-leakage section, a large amount of leakage of fluid injected into a shaft in the period of cyclic preheating of the leakage section can be effectively prevented, and the equal flow of fluid entering an oil layer from different sections is ensured. Further, the stratum cracks of the blind pipe 31 section are subjected to plugging treatment, so that deep leakage of an oil layer of the leakage section can be prevented. And finally, arranging the first oil pipe in the underground horizontal section, arranging a heating cable in the first oil pipe, and then injecting water to heat and preheat. The invention adopts unconventional well completion and plugging mode to preheat, has the multiple advantages of small fluid leakage of a shaft, uniform electric heating and solvent acceleration and viscosity reduction between wells, can reach the preheating requirement in a shorter time, has uniform preheating rate of more than 90% in a horizontal section, and has obvious economic benefit.

In a preferred embodiment, the method further comprises:

s010: determining the leakage rate of each position of the underground horizontal section in the drilling process;

s020: determining a horizontal segment with the leakage rate larger than a preset threshold value as a leakage segment;

s030: the length and position of the blind pipes 31 are determined according to the lost circulation sections, and the blind pipes 31 of each section are connected through the sieve tube 32 to form the sleeve 1.

It will be appreciated that suitable SAGD well groups may be screened according to the drilling process. And in the drilling stage, the oil layer corresponding to the well group with the mud loss rate larger than the preset threshold value is a fractured oil layer, and the oil layer is selected as a target well group. Preferably, the leakage rate of the preset threshold value can be 20% -50%.

In the drilling process of the well, the instantaneous leakage rate of the slurry drilled to different horizontal sections is recorded, and the horizontal sections are divided into leakage sections and non-leakage sections according to the different leakage rates of the different horizontal sections, wherein the length of the single leakage section or the non-leakage section is preferably greater than 50 meters. Then, a series connection well completion mode is adopted to complete a horizontal section, specifically, a blind pipe 31 is put into a leakage section, a slotted screen pipe 32 is put into a non-leakage section, and the blind pipe 31 and the screen pipe 32 are connected through threads.

In a preferred embodiment, perforations are formed in the blind pipe 31. It will be appreciated that perforations are formed in the blind pipe 31 to allow exchange of liquid gas in the pipe with formation crude oil. The common screen pipe wall is in a grid shape, so that liquid gas in the casing pipe can be conveniently exchanged with stratum crude oil, and crude oil extraction is realized.

In one specific example, blind pipe 31 may be perforated and perforation density is designed according to the following equation based on the total leak-off rate of the segment.

Wherein D is _f The perforation density is zero-dimensional; q is the flow rate of fluid injected from the wellhead, m ³ /d; psi is the total leakage rate of the horizontal segment, and is dimensionless; v is the flow velocity in the perforation, m/d; h is the length of the horizontal segment, m; d is the diameter of perforation and m.

In a preferred embodiment, the step S200 of plugging the formation fracture of the blind pipe 31 specifically includes:

s210: a packer is set at each end of each blind pipe 31 of the casing 1.

S220: the end of the second tubing 54 is positioned intermediate the two corresponding packers of the blind pipe 31 section.

S230: a slug solution is injected into the formation corresponding to the blind pipe 31 through the second tubing 54.

It can be understood that the horizontal section packer can be utilized to perform the section-by-section upward return type plugging treatment on the lost circulation section, so that the stratum cracks can be plugged, and the uneven preheating caused by the existence of the cracks during preheating can be prevented.

In a preferred embodiment, the injecting the slug solution into the formation corresponding to the blind pipe 31 through the second oil pipe 54 in S230 specifically includes:

s231: the first high concentration polymer solution and the modified expanded graphite 41 are injected through the second tubing 54 to form a pre-slug.

S232: the second high concentration polymer solution 42 is injected through the second tubing 54 to displace the pre-slug.

S233: the second tubing 54 and packer are set up.

In one specific example, a pre-slug of high concentration polymer solution (first high concentration polymer solution) and modified expanded graphite is first injected into both SAGD well pairs, and then a mid-high concentration polymer solution (second high concentration polymer solution 42) is injected to displace the pre-slug to 10-30 m deep in the reservoir. And after the treatment is finished, the packer is started.

Preferably, the concentration of the high concentration polymer solution is 1% to 5%, but needs to be lower than the critical micelle concentration; the graphite particles are high-temperature expanded graphite, the initial expansion temperature is 200-300 ℃, the volume expansion multiple is 100-300 times, and the size of the graphite particles is 200-500 meshes.

In a preferred embodiment, the injecting water into the S300 and heating and preheating by the heating cable specifically includes:

s311: the first hot water slug 61 is injected and heated by the heating cable for a preset time.

S312: a solvent slug 62 is injected.

S313: the second hot water slug 63 is injected to a preset pressure.

Specifically, as shown in FIG. 2, in an alternative embodiment, the first hot water slug 61 may be injected to preheat the reservoir, heated for 5-10 days, then the solvent slug 62 is injected, followed by the second hot water slug 63 to a preset pressure, preferably 1-2 MPa below the alternative cap rupture pressure.

Preferably, the first hot water slug 61 is 80-300 t in quantity and the hot water temperature is 50-100 ℃; the solvent slug 62 is one or a plurality of compositions of light alkane solvent with 1-10 carbon atoms, light aromatic hydrocarbon solvent with 6-15 carbon atoms and oil-soluble viscosity reducer; the solvent slug 62 is 10-150 t; the amount of the second hot water slug 63 is 40-300 t, and the hot water temperature is 50-100 ℃.

In a preferred embodiment, the heating and preheating of S300 by the heating cable specifically includes:

s321: the heating cable is heated by the heating device.

S322: the surface temperature of the heating cable is detected by a detection device arranged on the surface of the heating cable.

S323: the heating device adjusts the heating power of the heating cable through the surface temperature.

It will be appreciated that a resistive heating cable may be run into the first tubing within the wellbore, wherein the heating cable may include a heating section 52 and a conductive section 51, wherein the heating section 52 is preferably from heel to toe (end to end) of the horizontal section, with the remaining sections being conductive sections 51. The surface of the heating cable is measured by a detection device, for example, the surface of the heating cable can be measured by a thermocouple 53, the heating cable and the thermocouple 53 can be preset to a continuous oil pipe in parallel, and the heating cable is put into the toe of the horizontal section, and the distance between the heating cable and the thermocouple 53 is 40-60 m from the toe. The ground can be provided with an electricity control box serving as a heating device, and the electricity control box can automatically control heating power according to the surface temperature measurement of the heating cable. Specifically, the electric control box can increase the heating power of the heating cable when the surface temperature of the heating cable is higher than a preset temperature, and decrease the heating power of the heating cable when the surface temperature of the heating cable is lower than the preset temperature. Preferably, the preset temperature is 10-30 ℃ below the coking temperature of the crude oil in the oil layer, namely the highest temperature of the surface of the heating cable is controlled to be 10-30 ℃ below the coking temperature of the crude oil in the oil layer, and the heating power range of the heating cable by the electric control box is 300-1500W/m.

Preferably, the heating cable is a stainless steel armoured mineral insulated cable, and the internal insulating filler of the cable heating section is magnesium oxide; the inner insulating filler of the cable conductive section 51 is magnesium oxide or polytetrafluoroethylene; the highest withstand voltage of the cable is 10-20 MPa, the highest temperature resistance of the heating section is 450 ℃, the highest temperature resistance of the conductive section 51 is 230-450 ℃, and the highest power of the heating section is 1500W/m.

In a preferred embodiment, the method further comprises:

s410: and carrying out numerical simulation on the stratum oil reservoir attribute distribution.

S420: and if the temperature of the stratum oil reservoir layer and the viscosity of the crude oil reach preset conditions, finishing preheating.

It is understood that the attribute distribution of the formation reservoir in the preheating process can be simulated by numerical simulation software, and the attribute of the formation reservoir can be analyzed. The property of the oil reservoir can be the temperature of the oil reservoir, the viscosity of crude oil and other property parameters. Preferably, the preset condition is that the viscosity of the crude oil reaches 100mPa.s, and when the viscosity of the crude oil is reduced to 100mPa.s through numerical simulation, the SAGD circulation preheating is completed. Further, after the preheating of the SAGD circulation is finished, water vapor can be continuously injected from the upper injection well, the lower production well is continuously produced, the operation pressure difference between the injection well and the production well in the horizontal section is kept at 0.3-1.0 MPa, and the SAGD circulation is transferred to the SAGD production stage. Wherein, an oil pumping pipe 22 can be arranged in production, and an oil pump 21 is arranged in the oil pumping pipe 22, and crude oil exchanged from the stratum is extracted by the oil pump 21, wherein, the injection well section is shown in figure 3.

It should be noted that the numerical simulation may be performed using commercially available well-established reservoir numerical simulation software. More preferably, the reservoir numerical simulation software includes CMG-STAR from CMG, canada and/or ECLIPSE from Schlembese, USA.

The invention is further illustrated by the following specific examples.

Example 1

The embodiment provides a downhole electric preheating starting method of a fractured super heavy oil reservoir developed by double horizontal well SAGD, which comprises the following specific steps:

(1) Screening for appropriate SAGD well groups. And in the drilling stage, the oil layer corresponding to the well group with the mud loss rate of more than 20% is a fractured oil layer, and 1 SAGD well group is selected as a target well group.

(2) Special completions. In the drilling process, the instantaneous leakage rate of the slurry which is drilled to different horizontal sections is recorded, and the horizontal sections are divided into leakage sections and non-leakage sections according to the different leakage rates of the different horizontal sections, wherein the lengths of the leakage sections and the non-leakage sections are 200 meters respectively.

The horizontal well completion is carried out by adopting a serial well completion mode, specifically, a blind pipe 31 is put into a leakage section, a slotted screen pipe 32 is put into a non-leakage section, and the blind pipe 31 and the screen pipe 32 are connected through threads.

The blind pipe 31 is perforated, and the perforation density is designed according to the following formula according to the total leak rate of the section.

Wherein Q is the flow rate of fluid injected from a wellhead, 200m ³ /d; psi is the total leakage rate of the horizontal segment, which is 0.5; v is the flow velocity in the holes, 0.002m/d; h is the length of the horizontal segment, 400m; d is the diameter of perforation holes and is 0.012m; calculated D _f The perforation density per meter is 26 holes/m;

(3) A resistive heating cable is run into the wellbore, with the heating section 52 being from the heel to the toe of the horizontal section and the remaining sections being conductive sections 51. The surface of the heating cable adopts a thermocouple 53 to measure the temperature, the heating cable and the thermocouple 53 are parallelly preset to the continuous oil pipe, and the horizontal section toe is lowered, and the distance between the heating cable and the thermocouple 53 is 40m; the ground is provided with an electric control box, and the power is automatically controlled according to the surface temperature measurement of the heating cable.

The heating cable is a stainless steel armoured mineral insulated cable, and the internal insulating filler of the cable heating section is magnesium oxide; the inner insulating filler of the cable conductor section 51 is polytetrafluoroethylene; the highest withstand voltage of the cable is 10MPa, the highest temperature resistance of the heating section is 450 ℃, the highest temperature resistance of the conducting section 51 is 230 ℃, and the highest power of the heating section is 1500W/m.

(4) And (5) preprocessing the oil layer of the leakage section. The method comprises the steps of performing section-by-section upward return type plugging treatment on a lost circulation section by utilizing a horizontal section packer, specifically, firstly injecting a pre-slug consisting of high-concentration polymer solution and modified expanded graphite into two wells of an SAGD well pair, and then injecting a medium-high-concentration polymer solution to replace the pre-slug to the deep part of an oil layer by 10m; and after the treatment is finished, the packer is started.

The concentration of the high-concentration polymer solution is 1 percent and is lower than the critical micelle concentration; the graphite particles are high-temperature expanded graphite, the initial expansion temperature is 200 ℃, the volume expansion multiple is 100 times, and the size of the graphite particles is 200 meshes.

(5) The heating cable starts to heat the shaft, the highest temperature of the surface of the heating cable is 10 ℃ below the coking temperature of the crude oil in the oil layer, and the heating power is 300W/m.

(6) The first hot water slug 61 was injected to preheat the reservoir, heated for 10 days, then the solvent slug 62 was injected, followed by the second hot water slug 63 to 1MPa below the cap-fracturing pressure.

The first hot water slug 61 is 80t in quantity and the hot water temperature is 50 ℃; the solvent slug 62 is a light alkane solvent of 6 carbon atoms; the solvent slug 62 is 10t; the second hot water slug 63 is 40t in quantity and the hot water temperature is 50 c.

(7) And determining the temperature of an oil layer and the viscosity of crude oil between SAGD well pairs by utilizing tracking numerical simulation, and after the viscosity of the crude oil of the oil layer is reduced to 100mPa.s, finishing SAGD cyclic preheating, continuously injecting water vapor into an upper injection well, continuously producing a lower production well, and switching into an SAGD production stage by using the operation pressure difference between the injection well and the production well in a horizontal section of 0.3 MPa.

The numerical model is performed using commercially mature reservoir numerical simulation software. More preferably, the reservoir numerical simulation software includes CMG-STAR from CMG, canada and/or ECLIPSE from Schlembese, USA.

Steam cavity monitoring after SAGD production shows that by adopting the SAGD preheating starting method of the embodiment, the uniform development of the steam cavity of the whole horizontal section of the fractured reservoir is realized, compared with the adjacent SAGD well pair of the conventional circulating preheating method, the steam leakage rate is reduced from 30% to below 5%, the development scale of the steam cavity along the horizontal section reaches 98% (the adjacent conventional SAGD preheating starting well pair: 41%), and the oil production speed reaches 40 tons/day (the adjacent conventional SAGD preheating starting well pair: 22 tons/day).

Example 2

(1) Screening for appropriate SAGD well groups. And in the drilling stage, the oil layer corresponding to the well group with the mud leakage rate of more than 30% is a fractured oil layer, and 1 SAGD well group is selected as a target well group.

(2) Special completions. In the drilling process, the instantaneous leakage rate of the slurry which is drilled to different horizontal sections is recorded, and the horizontal sections are divided into leakage sections and non-leakage sections according to the different leakage rates of the different horizontal sections, wherein the lengths of the leakage sections and the non-leakage sections are 300 meters respectively.

Wherein Q is the flow rate of fluid injected from a wellhead, 200m ³ /d; psi is the total leakage rate of the horizontal segment, which is 0.5; v is the flow velocity in the holes, which is 0.003m/d; h is the length of the horizontal segment, 400m; d is the diameter of perforation holes and is 0.012m; calculated D _f The perforation density per meter is 13 holes/m;

(3) A resistive heating cable is run into the wellbore, with the heating section 52 being from the heel to the toe of the horizontal section and the remaining sections being conductive sections 51. The surface of the heating cable adopts a thermocouple 53 to measure the temperature, the heating cable and the thermocouple 53 are parallelly preset to the continuous oil pipe, and the horizontal section toe is lowered to be 50m away from the toe; the ground is provided with an electric control box, and the power is automatically controlled according to the surface temperature measurement of the heating cable.

The heating cable is a stainless steel armoured mineral insulated cable, and the internal insulating filler of the cable heating section is magnesium oxide; the inner insulating filler of the cable conductor section 51 is magnesium oxide; the highest withstand voltage of the cable is 15MPa, the highest temperature resistance of the heating section is 450 ℃, the highest temperature resistance of the conductive section 51 is 450 ℃, and the highest power of the heating section is 1500W/m.

(4) And (5) preprocessing the oil layer of the leakage section. The method comprises the steps of performing section-by-section upward return type plugging treatment on a lost circulation section by utilizing a horizontal section packer, specifically, firstly injecting a pre-slug consisting of high-concentration polymer solution and modified expanded graphite into two wells of an SAGD well pair, and then injecting a medium-high-concentration polymer solution to replace the pre-slug to the deep part of an oil layer by 20m; and after the treatment is finished, the packer is started.

The concentration of the high-concentration polymer solution is 3 percent and is lower than the critical micelle concentration; the graphite particles are high-temperature expanded graphite, the initial expansion temperature is 250 ℃, the volume expansion multiple is 200 times, and the size of the graphite particles is 300 meshes.

(5) The heating cable starts to heat the shaft, the highest temperature of the surface of the heating cable is 20 ℃ below the coking temperature of the crude oil in the oil layer, and the heating power is 1000W/m.

(6) The first hot water slug 61 was injected to preheat the reservoir, heated for 70 days and then the solvent slug 62 was injected immediately followed by the second hot water slug 63 to 1.5MPa below the cap fracture pressure.

The first hot water slug 61 is 200t in quantity and the hot water temperature is 75 ℃; the solvent slug 62 is a light aromatic hydrocarbon solvent with 6 carbon atoms; the solvent slug 62 is 100t; the second hot water slug 63 is in an amount of 100t and the hot water temperature is 75 ℃.

(7) And determining the temperature of an oil layer and the viscosity of crude oil between SAGD well pairs by utilizing tracking numerical simulation, and after the viscosity of the crude oil of the oil layer is reduced to 100mPa.s, finishing SAGD cyclic preheating, continuously injecting water vapor into an upper injection well, continuously producing a lower production well, and switching into an SAGD production stage by using the operation pressure difference between the injection well and the production well in a horizontal section of 0.5 MPa.

Steam cavity monitoring after SAGD production shows that by adopting the SAGD preheating starting method of the embodiment, the uniform development of the steam cavity of the whole horizontal section of the fractured reservoir is realized, compared with the adjacent SAGD well pair of the conventional circulating preheating method, the steam leakage rate is reduced from 40% to below 5%, the development scale of the steam cavity along the horizontal section reaches 98% (the adjacent conventional SAGD preheating starting well pair: 45%), and the oil production speed reaches 50 tons/day (the adjacent conventional SAGD preheating starting well pair: 26 tons/day).

Example 3

(1) Screening for appropriate SAGD well groups. And in the drilling stage, the oil layer corresponding to the well group with the mud loss rate of more than 50% is a fractured oil layer, and 1 SAGD well group is selected as a target well group.

(2) Special completions. In the drilling process, the instantaneous leakage rate of the slurry which is drilled to different horizontal sections is recorded, and the horizontal sections are divided into leakage sections and non-leakage sections according to the different leakage rates of the different horizontal sections, wherein the lengths of the leakage sections and the non-leakage sections are 400 meters respectively.

Wherein Q is the flow rate of fluid injected from a wellhead, 200m ³ /d; psi is the total leakage rate of the horizontal segment, which is 0.5; v is the flow velocity in the holes, 0.004m/d; h is the length of the horizontal segment, 400m; d is the diameter of perforation holes and is 0.012m; calculated D _f The perforation density per meter is 9 holes/m;

(3) A resistive heating cable is run into the wellbore, with the heating section 52 being from the heel to the toe of the horizontal section and the remaining sections being conductive sections 51. The surface of the heating cable adopts a thermocouple 53 to measure the temperature, the heating cable and the thermocouple 53 are parallelly preset to the continuous oil pipe, and the horizontal section toe is lowered, and the distance between the heating cable and the thermocouple 53 is 60m; the ground is provided with an electric control box, and the power is automatically controlled according to the surface temperature measurement of the heating cable.

The heating cable is a stainless steel armoured mineral insulated cable, and the internal insulating filler of the cable heating section is magnesium oxide; the inner insulating filler of the cable conductor section 51 is magnesium oxide; the highest withstand voltage of the cable is 20MPa, the highest temperature resistance of the heating section is 450 ℃, the highest temperature resistance of the conductive section 51 is 450 ℃, and the highest power of the heating section is 1500W/m.

(4) And (5) preprocessing the oil layer of the leakage section. The method comprises the steps of performing section-by-section upward return type plugging treatment on a lost circulation section by utilizing a horizontal section packer, specifically, firstly injecting a pre-slug consisting of high-concentration polymer solution and modified expanded graphite into two wells of an SAGD well pair, and then injecting a medium-high-concentration polymer solution to replace the pre-slug to the deep part of an oil layer by 30m; and after the treatment is finished, the packer is started.

The concentration of the high-concentration polymer solution is 5 percent and is lower than the critical micelle concentration; the graphite particles are high-temperature expanded graphite, the initial expansion temperature is 300 ℃, the volume expansion multiple is 300 times, and the size of the graphite particles is 500 meshes.

(5) The heating cable starts to heat the shaft, the highest temperature of the surface of the heating cable is 30 ℃ below the coking temperature of the crude oil in the oil layer, and the heating power is 1500W/m.

(6) The first hot water slug 61 was injected to preheat the reservoir, heated for 5 days, then the solvent slug 62 was injected, followed by the second hot water slug 63 to 2MPa below the cap-fracturing pressure.

The first hot water slug 61 is 300t in quantity and the hot water temperature is 100 ℃; the solvent slug 62 is a light alkane solvent with the carbon number of 10 and a light aromatic hydrocarbon solvent with the carbon number of 15 according to the mass ratio of 1:1, a composition of matter of formula 1; the solvent slug 62 is in an amount of 150t; the second hot water slug 63 is 300t in quantity and the hot water temperature is 100 ℃.

(7) And determining the temperature of an oil layer and the viscosity of crude oil between SAGD well pairs by utilizing tracking numerical simulation, and after the viscosity of the crude oil of the oil layer is reduced to 100mPa.s, finishing SAGD cyclic preheating, continuously injecting water vapor into an upper injection well, continuously producing a lower production well, and switching into an SAGD production stage by using the operation pressure difference between the injection well and the production well in a horizontal section of 1.0 MPa.

Steam cavity monitoring after SAGD production shows that by adopting the SAGD preheating starting method of the embodiment, the uniform development of the steam cavity of the whole horizontal section of the fractured reservoir is realized, compared with the adjacent SAGD well pair of the conventional circulating preheating method, the steam leakage rate is reduced from 60% to below 5%, the development scale of the steam cavity along the horizontal section reaches 98% (the adjacent conventional SAGD preheating starting well pair: 39%), and the oil production speed reaches 80 tons/day (the adjacent conventional SAGD preheating starting well pair: 39 tons/day).

In summary, the method for starting the underground electric preheating of the double-horizontal well SAGD of the fractured heavy oil reservoir has the following technical effects:

(1) Compared with the conventional well completion mode of the conventional screen pipe 32 of the SAGD horizontal section, the well completion method of the SAGD horizontal section is adopted to complete the horizontal section, the blind pipe 31 is arranged in the leakage section, the slotted screen pipe 32 is arranged in the non-leakage section, and the blind pipe 31 is subjected to flow-limiting perforation, so that a large amount of leakage of fluid injected into a shaft in the period of cyclic preheating of the leakage section can be effectively prevented, and the equal flow of the fluid entering an oil layer from different sections is ensured;

(2) The invention uses the horizontal section packer to perform the section-by-section upward return type plugging treatment on the leakage section, thereby preventing the deep leakage of the oil layer of the leakage section. The invention adopts a front slug composed of high-concentration polymer solution and modified expanded graphite, and can rapidly expand and plug an oil layer when Gao Wenqi channeling occurs in the high-temperature expanded graphite in view of the initial expansion temperature of 200-300 ℃, so as to prevent steam channeling; the medium-low temperature fluid is not expanded when passing through, and is not blocked, so that the selective blocking effect can be achieved. In addition, the volume expansion multiple is 100-300 times, so that the high-temperature steam channel can be completely blocked, and the high-temperature steam channel has an important effect on high-temperature selective blocking in the SAGD preheating stage and the production stage.

(3) The wellbore fluid is saturated with a multistage plug and the reservoir is pressurized. After the first hot water slug 61 is injected into the well bore, the temperature is raised and becomes high temperature steam under the action of the electric heating cable, the oil layer in the near well zone is heated, and the solvent is injected on the basis, because the oil layer is preheated, the viscosity of crude oil in the near well zone is obviously reduced, the injected solvent enters the oil layer under lower flow resistance, and the solvent is displaced into the oil layer between the injection and production wells under the action of the subsequent second slug, thereby playing a role of deep viscosity reduction, and greatly shortening the time for the simple electric heating to reach the requirement of transferring SAGD production.

(4) The invention adopts the unconventional well completion, plugging and solvent displacement mode for preheating, has the multiple advantages of small fluid leakage of a shaft, uniform electric heating and solvent acceleration and viscosity reduction between wells, can reach the preheating requirement in a shorter time, has the uniform preheating rate of a horizontal section of more than 90 percent, and has obvious economic benefit.

Based on the same principle, the embodiment also discloses a steam assisted gravity drainage underground electric preheating system for the fractured reservoir. The system comprises a casing 1 arranged in a horizontal section of a well, wherein the casing 1 comprises a plurality of pipelines which are sequentially connected, the pipelines are blind pipes 31 or sieve pipes 32, and the lengths and positions of the blind pipes 31 and the sieve pipes 32 are determined according to the mud leakage rate of the horizontal section of the well, a first oil pipe arranged in the casing 1 and a heating cable arranged in the first oil pipe.

In a preferred embodiment, perforations are formed in the blind pipe 31.

In a preferred embodiment, further comprising a plurality of packers and a second tubing 54 for plugging formation fractures of the blind pipe 31 section;

the plurality of packers are respectively arranged at two ends of each blind pipe 31 of the casing 1, and the end parts of the second oil pipes 54 are sequentially arranged between the two packers corresponding to the segments of the blind pipes 31 and are used for injecting slug solution into the stratum corresponding to the blind pipes 31.

In a preferred embodiment, the heating device further comprises a heating device and a detection device arranged on the surface of the heating cable;

In a preferred embodiment, the system further comprises a numerical simulation module for performing numerical simulation on the attribute distribution of the formation oil reservoir, and if the temperature of the formation oil reservoir and the viscosity of crude oil reach preset conditions, preheating is completed.

Since the principle of solving the problem of the system is similar to that of the above method, the implementation of the system can be referred to the implementation of the method, and will not be repeated here.

In this specification, each embodiment is described in a progressive manner, and identical and similar parts of each embodiment are all referred to each other, and each embodiment mainly describes differences from other embodiments. In particular, for system embodiments, since they are substantially similar to method embodiments, the description is relatively simple, as relevant to see a section of the description of method embodiments.

The foregoing is merely exemplary of the present application and is not intended to limit the present application. Various modifications and variations of the present application will be apparent to those skilled in the art. Any modification, equivalent replacement, improvement, etc. which come within the spirit and principles of the application are to be included in the scope of the claims of the present application.

Claims

1. The utility model provides a crack nature oil reservoir steam assisted gravity drainage underground electricity preheats method which characterized in that includes:

plugging treatment is carried out on stratum cracks of the blind pipe sections;

arranging a first oil pipe in the sleeve, arranging a heating cable in the first oil pipe, injecting water, and heating and preheating through the heating cable;

the plugging treatment for the stratum cracks of the blind pipe sections specifically comprises the following steps:

injecting a slug solution into the stratum corresponding to the blind pipe through the second oil pipe;

the step of injecting the slug solution into the stratum corresponding to the blind pipe through the second oil pipe specifically comprises the following steps:

lifting out the second oil pipe and the packer;

The water injection and the heating and preheating through the heating cable specifically comprise the following steps:

injecting a solvent slug;

injecting a second hot water slug to a preset pressure.

2. The fractured reservoir steam assisted gravity drainage downhole electrical preheating method of claim 1, further comprising:

3. The method of claim 1, wherein perforations are formed in the blind pipe.

4. The method of claim 1, wherein the preheating by heating the heating cable comprises:

heating the heating cable through a heating device;

5. The fractured reservoir steam assisted gravity drainage downhole electrical preheating method of claim 1, further comprising:

6. A fractured reservoir steam assisted gravity drainage downhole electrical preheating system for performing the method of claim 1, comprising a casing disposed in a downhole horizontal section, the casing comprising a plurality of tubes connected in sequence, the tubes being blind pipes or screens, the lengths and positions of the blind pipes and screens being determined according to mud loss rates of the downhole horizontal section, the system further comprising a first tubing disposed in the casing and a heating cable disposed in the first tubing.

7. The fractured reservoir steam assisted gravity drainage downhole electrical preheating system of claim 6 wherein perforations are formed in the blind pipe.

8. The fractured reservoir steam assisted gravity drainage downhole electric preheating system of claim 6, further comprising a heating device and a detection device disposed on a surface of the heating cable;

9. The system of claim 6, further comprising a numerical simulation module for performing numerical simulation on the formation reservoir property distribution, wherein the preheating is completed if the temperature of the formation reservoir layer and the viscosity of the crude oil reach preset conditions.