CA3012371C - Method for communication of dual horizontal wells - Google Patents

Abstract

The invention discloses a method for communication of dual horizontal wells, and relates to the oil and gas development field. The method comprises said steps of: testing steam-injection horizontal wells and production horizontal wells; injecting solvents into the steam-injection horizontal wells and the production horizontal wells respectively; injecting water into the steam-injection horizontal wells via wellbores of the steam-injection horizontal wells, injecting water into the production horizontal wells via wellbores of the production horizontal wells; continuously injecting water into the steam-injection wells and the production horizontal wells respectively, and improving water-injection pressure of the steam-injection horizontal wells, water-injection pressure of the production horizontal wells; after closing the steam-injection horizontal wells and the production horizontal wells meets a first preset condition, injecting gas into the steam-injection horizontal wells and the production horizontal wells respectively, so that underground water flows back to ground; and after the underground water flows back to the ground, injecting isobaric steam into the steam-injection horizontal wells and the production horizontal wells meets a second preset condition. The present application can effectively enhance a degree of uniformity of communication between dual horizontal wells, shorten communication time between the dual horizontal wells, and significantly reduce consumption of solvents.

Description

METHOD FOR COMMUNICATION OF DUAL HORIZONTAL WELLS
Technical Field The present invention relates to the oil and gas development field, particularly to a method for communication of dual horizontal wells.
Background of the Invention Exploitation of super heavy oil in shallow reservoirs adopting Steam Assisted Gravity Drainage (SAGD) with dual horizontal wells is successful in Canada, and is commercially available, and therefore such an exploitation approach has also been gradually appreciated in our country accordingly. In the SAGD startup stage, an oil reservoir has a low initial temperature, crude oil has a high viscosity, an effective communication is difficultly established between dual horizontal wells with traditional 5 meters well spacing, thus the heavy oil having a flowing capacity cannot .. flow downwards after peripheries of the steam-injection wells are heated, a vapor chamber also cannot be expanded, and therefore it seems quite significant to establish an effective fluid communication. In addition, an inter-well thermal communication is also of vital importance, thermal losses occur in the heavy oil heated at the top in the process of slow seepage to the production wells at the bottom, so that the temperature drops and the viscosity increases, thereby making it difficult to flow crude oil between wells, and impossible to complete the drainage process successfully.
Summary of the Invention In order to overcome the above-mentioned drawbacks of the prior art, the technical problem to be solved by the embodiments of the present invention is to provide a method for communication of dual horizontal wells, which can effectively enhance a degree of uniformity of communication between dual horizontal wells, shorten communication time between the dual horizontal wells.
The concrete technical solutions of the embodiments of the present invention are provided as follows:
A method for communication of dual horizontal wells comprising steam-injection horizontal wells and production horizontal wells, the method comprising the following steps:
testing the steam-injection horizontal wells and the production horizontal wells to obtain a minimum principal stress of the steam-injection horizontal wells, a fracture-initiation pressure of the steam-injection horizontal wells, a minimum principal stress of the production horizontal wells and a fracture-initiation pressure of the production horizontal wells;
injecting solvents into the steam-injection horizontal wells and the production horizontal wells respectively;
injecting water into the steam-injection horizontal wells via wellbores of the steam-injection horizontal wells, injecting water into the production horizontal wells via wellbores of the production horizontal wells, so that the solvents in the wellbores of the steam-injection horizontal wells and the production horizontal wells are displaced in oil reservoirs;
continuously injecting water into the steam-injection wells and the production horizontal wells respectively, improving water-injection pressure of the steam-injection horizontal wells to between the minimum principal stress of the steam-injection horizontal wells and the fracture-initiation pressure of the steam-injection horizontal wells, and improving the water-injection pressure of the production horizontal wells to between the minimum principal stress of the production horizontal wells and the fracture-initiation pressure of the production horizontal wells;
after a high water-cut region is formed in the respective solvent area of the steam-injection horizontal wells and the production horizontal wells; after closing the steam-injection horizontal wells and the production horizontal wells meets a first preset condition, injecting gas into the steam-injection horizontal wells and the production horizontal wells respectively, so that underground water flows back to ground, and after the underground water flows back to the ground, injecting isobaric steam into the steam-injection horizontal wells and the production horizontal wells to meet a second preset condition.
In a preferred embodiment, continuously injecting the water into the steam-injection wells and the production horizontal wells respectively, improving the water-injection pressure of the steam-injection horizontal wells to between the minimum principal stress of the steam-injection horizontal wells and the fracture-initiation pressure of the steam-injection horizontal wells, and improving the water-injection pressure of the production horizontal wells to between the minimum principal stress of the production horizontal wells and the fracture-initiation pressure of the production horizontal wells, so that one high water-cut region centered on wellbores is formed in the solvent area of the steam-injection horizontal wells and the production horizontal wells respectively, and the high water-cut region of the steam-injection horizontal wells is not in communication with the high water-cut region of the production horizontal wells.
In a preferred embodiment, the method for communication of dual horizontal wells further comprises the following steps injecting water with pressure into the steam-injection horizontal wells and the production horizontal wells respectively, in order to determine development of underground fractures.
In a preferred embodiment, the method for communication of dual horizontal wells further comprises the following steps:
Cyclically injecting water into the steam-injection horizontal wells and the production horizontal wells respectively, in order to clean up wellbore walls.

2 In a preferred embodiment, the method for communication of dual horizontal wells further comprises the following steps:
before said step of injecting water into the steam-injection horizontal wells via the wellbores of the steam-injection horizontal wells, injecting water into the production horizontal wells via the wellbores of the production horizontal wells, so that the solvents in the wellbores of the steam-injection horizontal wells and the production horizontal wells are displaced in oil reservoirs, injecting a soluble gum of slugs into a wellbore annulus of the steam-injection horizontal wells and the production horizontal wells respectively.
In a preferred embodiment, providing a first pipe string and a second pipe string longer than the first pipe string in the steam-injection horizontal wells, providing a third pipe string and a fourth pipe string longer than the third pipe string in the production horizontal wells, in said step of after closing the steam-injection horizontal wells and the production horizontal wells meets a first preset condition, injecting gas into the steam-injection horizontal wells and the production horizontal wells respectively, so that underground water flows back to ground, injecting gas into a well annulus of the steam-injection horizontal wells and the production horizontal wells respectively, so that the underground water of the steam-injection horizontal wells flows back from the first or second pipe string to the ground, the underground water of the production horizontal wells flows back from the third or fourth pipe string to the ground.
In a preferred embodiment, in said step of injecting gas into the well annulus of the steam-injection horizontal wells and the production horizontal wells, so that the underground water of the steam-injection horizontal wells flows back from the first or second pipe string to the ground, the underground water of the production horizontal wells flows back from the third or fourth pipe string to the ground, gradually reducing down-hole pressure, so as to promote the underground water to flow back to the ground.
In a preferred embodiment, the first preset condition is that closing time of the steam-injection horizontal wells and the production horizontal wells is greater than or equal to 24 hours.
In a preferred embodiment, the second preset condition is that the time of injection of the isobaric steam into the steam-injection horizontal wells and the production horizontal wells is greater than or equal to 2 months.
In a preferred embodiment, in said step of injecting the solvents into the steam-injection horizontal wells and the production horizontal wells respectively, so that the wellbores of the steam-injection horizontal wells and the wellbores of the production horizontal wells are filled up with the solvents, adjusting flow rate and pressure of the solvents injected by injection pressure, when the wellbores of the

3 steam-injection horizontal wells and the wellbores of the production horizontal wells are filled up with the solvents.
In a preferred embodiment, the steam-injection horizontal wells and the production horizontal wells meet the following conditions: there exists no inter-well interlayer between the steam-injection horizontal wells and the production horizontal wells; the oil reservoir where the steam-injection horizontal wells and the production horizontal wells are located belongs to a Group III of oil reservoir; there exists no natural fracture in an oil reservoir region where the steam-injection horizontal wells and the production horizontal wells are located; and there exists no edge-bottom water in the oil reservoir region where the steam-injection horizontal wells and the production horizontal wells are located.
In a preferred embodithent, the solvents and heavy oil can be miscible with each other, and asphaltene is not precipitated out.
In a preferred embodiment, the viscosity of the solvents at room temperature ranges between 1mPa.S and 100mPa.S, and the density ranges between 0.7g/cm3 and 1 .2 giem3.
In a preferred embodiment, the solvents have viscosity-reduction properties at the oil reservoir temperature, and viscosity of mixtures containing the solvents of which mass fraction is 20% and crude oil should be less than 5,000mPaS.
In a preferred embodiment, the solvents include at least one of benzene, toluene, =
xylene, kerosene, diesel oil, petroleum ether and light crude oil.
In a preferred embodiment, in said step of after closing the steam-injection horizontal wells and the production horizontal wells meets a first preset condition, injecting gas into the steam-injection horizontal wells and the production horizontal wells respectively, so that underground water flows back to ground, the gas is nitrogen.
In a preferred embodiment, injecting the solvents into the steam-injection horizontal wells and the production horizontal wells respectively, so that the wellbores of the steam-injection horizontal wells and the wellbores of the production horizontal wells are filled up with the solvents.
The technical solutions of the present invention have the following remarkable advantageous effects:
the method for communication of dual horizontal wells in this application comprises said steps of: injecting solvents into dual horizontal wells, next, injecting water to displace the mixture formed of solvents and heavy oil, thus gradually forming a high water-cut region centered on wellbores, and then injecting steam into the dual horizontal wells for circulation. Since the high water-cut region enlarges a radius of a

4 linear heat source, heat transfer distances between the dual horizontal wells are declined to a great extent, so that a rate of rise in temperature is substantially increased between the dual horizontal wells, as a result, this method can significantly shorten communication time between the dual horizontal wells, so as to save a large amount of steam; in addition, a degree of uniformity of communication can also be enhanced dramatically between the dual horizontal wells.
Brief description of the drawings The drawings described herein are for illustration purposes only and are not intent to limit the scope of the present disclosure in any way. In addition, shapes and proportional dimensions of components in the drawings are only schematic to facilitate an understanding of the present invention, and are not intent to concretely define the shapes and proportional dimensions of components of the present invention.
Under the teachings of the present invention, those skilled in the. art can select various possible shapes and proportional dimensions to implement the present invention in dependence on the specific circumstances.
FIG. I is a sectional view along the direction of horizontal wells under routine SAGD
productions;
FIG. 2 is a schematic diagram illustrating a temperature field under unsteady-state heat transfer of double heat sources with 5 meters well spacing under routine SAGD
productions;
FIG. 3 is a schematic diagram illustrating unsteady-state heat conduction by conventional steam injection circulation in thermal communication with the double heat sources;
FIG. 4 is a schematic diagram illustrating steps of the method for communication of dual horizontal wells in the embodiments of the present application;
FIG. 5 is an effect graph illustrating fingering formed by injecting water after solvents are injected in the embodiments of the present application; and _ FIG. 6 is a relationship graph illustrating a midpoint temperature of dual horizontal wells where steam is circulated changes over time under conditions of different heating radius in the embodiments of the present application.
The reference numerals of the figures mentioned above:

1. steam-injection horizontal wells; 11. first pipe string; 12. second pipe string; 2.
production horizontal wells; 21. third pipe string; 22. fourth pipe string; 3.
central line of dual horizontal wells.
Detailed description of the Invention Details of the invention will become more apparent in the light of the description of the accompanying drawings and the embodiments of the present invention.
However, the embodiments of invention described herein are provided only for the purpose of illustration and are not to be construed as limiting the scope of the invention in any .. way. Under the teachings of the present invention, any possible deformation can be devised by those skilled in the art based on the present invention and these should be contemplated as being within the scope of the invention. It will be understood that when an element is referred to as being "disposed on" another element, it can be directly on another element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to another element or intervening elements may also be present. The terms "mounted", "interconnected" and "connected" are to be understood broadly, e.g., either electrical or mechanical connections, or interior communications of two elements, or direct connections, or indirect connections through intermediaries, the specific meanings of those terms can be understood by those skilled in the art depending on the specific circumstances. The terms "perpendicular", "horizontal", "upper", "lower", "left", "right" and the like as used herein are for illustrative purposes only, and not intent to represent the only embodiment.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs. The terminology used in the Description of the present application herein is only used for purposes of describing specific embodiments, and is not intent to limit the present application. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
FIG. 1 is a sectional view along the direction of horizontal wells under routine SAGD
productions. As shown in FIG 1, the current mainstream operating technique is arranging a dual tubing pipe string structure at steam-injection wells at the top and production wells at the bottom, performing an isobaric steam-injection circulation preheating for the steam-injection wells and the production wells simultaneously, to form a stable high-temperature region in the vicinity of wellbores, then transferring heat to depth of a reservoir in a form of heat conduction in dependence on temperature difference, so as to slowly heat the oil reservoirs between injection-production wells. FIG 2 is a schematic diagram illustrating a temperature field under unsteady-state heat transfer of double heat sources with 5 meters well spacing under routine SAGD productions; FIG. 3 is a schematic diagram illustrating unsteady-state heat conduction by conventional steam-injection circulation in thermal communication with the double heat sources. As shown in FIGS. 2 and 3, it is analyzed from the perspective of heat transfer theory that the above-mentioned method has the following intrinsic drawbacks: 1. there exists a low-temperature bottleneck zone in a portion of the region between the steam-injection horizontal wells 1 and the production horizontal wells 2, and the low-temperature bottleneck zone easily leads to nonuniformity of communication between the steam-injection horizontal wells 1 and the production horizontal wells 2 in a later period; 2.
an invalid heating zone can be formed due to the heat conduction below the production wells, where heat utilization efficiency is not high; 3. the fixed double heat sources have a slow heat-transfer rate, and a high energy consumption; and 4. well killing for cooling is desired when switching to SAGD and repairing pumps, thus a large amount of heat-energy losses can be caused within the wells.
For the horizontal wells buried about 350 meters deep, steam-injection temperature is about 260 degrees Celsius, pressure is 4.5MPa, and length of the horizontal wells is 400 meters or so with an openhole diameter of 9.186 inch or so, and steam-injection flowrate is about 70M3/d. At present, main heat sources are steam boilers using natural gas, and it is calculated based on such a flow rate that the natural gas cost of a single well group is namely more than 10,000 CNY in a single day. In general, the circulating and preheating process at least needs to last about 4 months to ensure effective communications between the wells, so that normal SAGD production phases can be switched to. However, impacts of a plurality of unfavorable factors, such as high water saturation of oil reservoirs, poor thermo-physical properties, poor control of drilling tracks, deep burying, thin oil layer, low quality of injection steam, unequal underground heating, arise during inter-well communications, the above-mentioned factors may result in poor effects on circulating and pre-heating, and time-consuming, the duration of circulating and pre-heating may take nearly 1 year or so if serious, thus the overall oil-gas ratio, economic efficiency of SAGD exploitations will be significantly affected. In addition, in the SAGD startup stage, if the previous circulating and pre-heating effect is poor, it often leads to a low producing degree of the horizontal wells after switching to SAGD, the oil production rate does not reach the expected rate designed by solutions, then even if measurements are taken subsequently to improve the producing degree of the horizontal wells, the effects after the producing degree is improved are also extremely limited, thus the communication effects between the wells in the initial startup stage are in a poorer state, which will -- significantly affect the development effects of SAGD.
In order to effectively enhance communication effects between dual horizontal wells, shorten communication time between the dual horizontal wells, the present application proposes a method for communication of dual horizontal wells, where the dual horizontal wells comprise: steam-injection horizontal wells 1 and production horizontal wells 2, the steam-injection horizontal wells 1 can be provided with a first pipe string 11 and a second pipe string 12 longer than the first pipe string 11, the production horizontal wells 2 can be provided with a third pipe string 21 and a fourth pipe string 22 longer than the third pipe string 21, a central line 3 of dual horizontal wells is provided between the steam-injection horizontal wells 1 and the production horizontal wells 2, at the same time, the steam-injection horizontal wells 1 and the production horizontal wells 2 meet the following conditions: there exists no inter-well interlayer between the steam-injection horizontal wells 1 and the production horizontal wells 2; the oil reservoir where the steam-injection horizontal wells 1 and the production horizontal wells 2 are located belongs to a Group III of oil reservoir;
there exists no natural fracture in an oil reservoir region where the steam-injection horizontal wells 1 and the production horizontal wells 2 are located; and there exists no edge-bottom water in the oil reservoir region where the steam-injection horizontal wells 1 and the production horizontal wells 2 are located. Certainly, when the method in the present application is applied to the steam-injection horizontal wells 1 and the production horizontal wells 2, test data of ground stress of the wells adjacent to the block where the steam-injection horizontal wells 1 and the production horizontal wells 2 are located and other related data, e.g., physical property parameters of reservoirs and crude oil, such as porosity, permeability, formation water salinity, oil saturation, crude oil viscosity, etc., should be obtained in advance, so as to implement the corresponding data support provided in this method. FIG. 4 is a schematic diagram illustrating steps of the method for communication of dual horizontal wells in the embodiments of the present application, and the method for communication of dual horizontal wells comprises the following steps:
S101: injecting water with pressure into the steam-injection horizontal wells 1 and the production horizontal wells 2 respectively, in order to determine development of underground fractures. In this step, the water with pressure can be injected into the steam-injection horizontal wells 1 and the production horizontal wells 2 respectively, so as to determine whether there exist underground natural fractures and development states of underground fractures. If information on the underground natural fractures and development states of underground fractures of the steam-injection horizontal wells 1 and the production horizontal wells 2 mentioned above has already been known, this step can be omitted.
S102: cyclically injecting water into the steam-injection horizontal wells 1 and the production horizontal wells 2 respectively, in order to clean up wellbore walls. In this step, water can be injected into wellbores of the steam injection wells 1 or the first pipe string 11 or the second pipe string 12, so as to clean the mud on the wall of the wellbores of the steam-injection horizontal wells 1, the waste water after cleaning can flow back to ground from the corresponding wellbore or the first pipe string 11 or the second pipe string 12. For example, water is injected into the wellbores of the steam-injection horizontal wells 1, then the waste water after cleaning can flow back to the ground from the first pipe string 11 or the second pipe string 12.
Likewise, water can be injected into the wellbores of the production horizontal wells 2 or the third pipe string 21 or the fourth pipe string 22, so as to clean the mud on the wall of the wellbores of the production horizontal wells 2, the waste water after cleaning can flow back to the ground from the corresponding wellbore or the third pipe string 21 or the fourth pipe string 22. If the wellbore walls of the steam-injection horizontal wells 1 and the production horizontal wells 2 meet the requirements, this step cannot be implemented.
S103: testing the steam-injection horizontal wells 1 and the production horizontal wells 2 to obtain a minimum principal stress of the steam-injection horizontal wells 1, a fracture-initiation pressure of the steam-injection horizontal wells 1, a minimum principal stress of the production horizontal wells 2 and a fracture-initiation pressure of the production horizontal wells 2. In general, that test can be a microfracture test.
S104: injecting solvents into the steam-injection horizontal wells 1 and the production horizontal wells 2 respectively, so as to inject the solvents into the wellbores of the steam-injection horizontal wells 1 and the wellbores of the production horizontal wells 2. In this step, when injecting the solvents into the wellbores of the steam-injection horizontal wells 1 and the wellbores of the production horizontal wells 2, adjusting flow rate and down-hole pressure of the solvents injected by injection pressure. When the down-hole pressure increases to the minimum principal stress, the flow rate of the injected solvents is reduced, that is, decreasing the injection pressure; and when the down-hole pressure decreases continuously, the flow rate of the injected solvents can be properly increased, that is, improving the injection pressure. Meanwhile, the down-hole gas can be first emptied, then the wellbores of the steam-injection horizontal wells 1 and the wellbores of the production horizontal wells 2 are filled up completely as quickly as possible.
When the solvents are injected into the steam-injection horizontal wells and the production horizontal wells respectively, the solvent injection pressure is consistently less than the minimum principal stress. The step S104 is pressurizing and squeezing the solvents, and solvent fingering can form a low viscous solvent fingering area, and the subsequent water injection displaces the solvent fingering area, thereby forming .. high water-cut regions that are centered on wellbores of the injection and production horizontal wells respectively; both of the high water-cut regions require tight control over size, so as not to allow for its local priority communication.
The injected solvents have no effects of fracture and dilatation, and no pore space communicated between wells is created by fracture and dilatation. Also, after the solvents reduce viscosity of crude oil in near bore zones, the pore space that the crude oil leaves and stays is carried.
In this embodiment, types of the solvents can be diversified, e.g., the solvents can be made of either a single component, or a mixture, as long as it meets the following conditions: the solvents and heavy oil can be miscible with each other, and asphaltene is not precipitated out; the viscosity of the solvents at room temperature ranges between 1mPa.S and 100mPa.S, and the density ranges between 0.7g/cm3 and 1.2g/cm3; the solvents have viscosity-reduction properties at the oil reservoir temperature, and the viscosity of mixtures containing the solvents of which mass fraction is 20% and crude oil should be less than 5,000mPaS. When steam is subsequently injected into the steam-injection horizontal wells 1 and the production horizontal wells 2, the solvents can be in either liquid phase or gas phase under the .. influence of high temperature steam. For example, the solvents can at least include one of benzene, toluene, xylene, kerosene, diesel oil, petroleum ether and light crude oil.
The injection rate at which the solvents are injected into the steam-injection horizontal .. wells 1 and the production horizontal wells 2 varies with types of the solvents.
Generally, for a solvent chamber having a radius of 1 meter formed with centre at the wellbores at an injection rate of 400 meters or so as a target horizontal well, an optimal injection rate ranges between 78 cubic meters and 144 cubic meters.
.. After the wellbores of the steam-injection horizontal wells 1 and the wellbores of the production horizontal wells 2 are filled up with the solvents, the solvents carrying the heavy oil viscosity-reduced partially in the wells go deep into the reservoir along radial directions of the wells, so that one columnar solvent area centered on wellbores can be formed.
S105: injecting a soluble gum of slugs into a wellbore annulus of the steam-injection horizontal wells 1 and the production horizontal wells 2 respectively. To enable injection of water into the steam-injection horizontal wells 1 and the production horizontal wells 2 in the later stage and separation of water from the solvents .. previously injected, forming a displacement process, since organic solvents have a lower density than water, the soluble gum of slugs can be injected into wellbore annulus at this moment, thus subsequently, the solvents in the wellbores can be pressed into the formation as much as possible. Such a soluble gum can be dissolved at high temperature, and therefore when steam is injected into the steam-injection horizontal wells 1 and the production horizontal wells 2 in the later stage, the soluble gum can be dissolved under the influence of steam heating, so as to avoid it from influencing fluid communications and thermal communications between the steam-injection horizontal wells 1 and the production horizontal wells 2.
S106: injecting water into the steam-injection horizontal wells 1 via the wellbores of the steam-injection horizontal wells 1, injecting water into the production horizontal wells 2 via the wellbores of the production horizontal wells 2, so that the solvents in the wellbores of the steam-injection horizontal wells 1 and the production horizontal wells 2 are displaced in oil reservoirs. In this step, injecting water into the steam-injection horizontal wells 1 and the production horizontal wells 2 via the wellbores, the injected water displaces the original solvents of horizontal and vertical sections of the steam-injection horizontal wells 1 and the production horizontal wells 2 in oil reservoirs.
lo S107: continuously injecting water into the steam injection wells 1 and the production horizontal wells 2 respectively, improving water-injection pressure of the steam-injection horizontal wells 1 to between the minimum principal stress of the steam-injection horizontal wells 1 and the fracture-initiation pressure of the steam-injection horizontal wells 1, and improving the water-injection pressure of production horizontal wells 2 to between the minimum principal stress of the production horizontal wells 2 and the fracture-initiation pressure of the production horizontal wells 2.
In this step, continuously injecting water into the steam-injection wells 1 and the production horizontal wells 2, improving water-injection pressure, and improving the water-injection pressure of the steam-injection horizontal wells 1 to between the minimum principal stress of the steam-injection horizontal wells 1 and the fracture-initiation pressure of the steam-injection horizontal wells 1, so that mobile oil in the solvent area of the steam-injection horizontal wells 1 is displaced by water to the deeper inside of the oil reservoirs, in this way, a high water-cut region centered on wellbores is formed inside and in the vicinity of the solvent area of the steam-injection horizontal wells 1. Similarly, improving the water-injection pressure of the production horizontal wells 2 to between the minimum principal stress of the production horizontal wells 2 and the fracture-initiation pressure of the production horizontal wells 2, so that mobile oil in the solvent area of the production horizontal wells 2 is displaced by water to the deeper inside of the oil reservoirs, in this way, a high water-cut region centered on wellbores is formed inside and in the vicinity of the solvent area of the production horizontal wells 2. Meanwhile, the high water-cut region of the steam-injection horizontal wells 1 is not in communication with the high water-cut region of the production horizontal wells 2. FIG. 5 is an effect graph illustrating fingering formed by injecting water after solvents are injected in the embodiments of the present application. As shown in FIG 5, two black circles indicate the steam-injection horizontal wells 1 and the production horizontal wells 2 respectively; it indicates in turn outward from the start of the black circles, the wellbores (the black circles), the high water-cut area centered on wellbores, the solvent-affected area, and the original oil reservoirs. A part of the crude oil can reduce viscosity in near bore zones by this step, and the crude oil is displaced by water into stratum depths, a high water-cut saturation area is formed in the near bore zones after the crude oil is displaced by water, the following objectives can be realized using the high water-cut saturation area: 1. a heat transfer by convection mode with high heat transfer efficiency is mainly adopted in the high water-cut saturation area, corresponding to increasing a diameter of a horizontal hole, shortening a distance between wells where heat is transferred inefficiently, so as to shorten steam circulation time and accelerate communication process, and also save consumption of steam. 2. Since the high water-cut saturation areas respectively centered on the steam-injection horizontal wells 1 and the production horizontal wells 2 are not in full communication, which avoids a local priority communication during subsequent steam circulation, as a result, the section temperature at a part of the horizontal section is significantly increased, and the part of the horizontal section cannot be effectively heated, i.e., the problem of non-uniform communication of the dual horizontal wells.
S108: closing the steam-injection horizontal wells 1 and the production horizontal wells 2 meets a first preset condition, injecting gas into the steam-injection horizontal wells 1 and the production horizontal wells 2 respectively, so that underground water flows back to ground, after the high water-cut region is formed in the respective solvent area of the steam-injection horizontal wells and the production horizontal wells. In this step, first closing the first steam-injection horizontal wells 1 and the production horizontal wells 2 meets the first preset condition, where the first preset condition is a length of time, under which, a more stable high water-cut region is formed inside and in the vicinity of the solvent area of the steam-injection horizontal wells 1 and the production horizontal wells 2. In general, the first preset condition is that closing time of the steam-injection horizontal wells 1 and the production horizontal wells 2 is greater than or equal to 24 hours. Then injecting gas into the steam-injection horizontal wells 1 and the production horizontal wells 2 respectively, so that the underground water flows back to the ground, the gas can be a safe gas insoluble in water that can be flushed into underground, for example, nitrogen. In a feasible embodiment, injecting gas into a well annulus of the steam-injection horizontal wells 1 and the production horizontal wells 2 respectively, so that the underground water of the steam-injection horizontal wells 1 flows back from the first pipe string 11 or the second pipe string 12 to the ground, the underground water of the production horizontal wells 2 flows back from the third pipe string 21 or the fourth pipe string 22 to the ground. In the above process, down-hole pressure can be gradually reduced to promote underground water to flow back to the ground, so as to reduce the contents of underground fluid having a high specific heat capacity to water, for the sake of quickly raising the temperature in the near bore zones and using latent heat of steam more effectively in next step.
S109: after the underground water flows back to the ground, injecting isobaric steam into the steam-injection horizontal wells 1 and the production horizontal wells 2 meets a second preset condition. In this step, steam can be injected into the second pipe string 12 of the steam-injection horizontal wells 1, the liquid returns via the first pipe string 11 of the steam-injection horizontal wells 1 for circulation;
similarly, steam can be injected into the fourth pipe string 22 of the production horizontal wells 2, the liquid returns via the third pipe string 21 of the production horizontal wells 2 for circulation. Since a high water-cut region is formed inside and in the vicinity of the steam-injection horizontal wells 1 and the production horizontal wells 2, the temperature of this high water-cut region is raised quickly due to convection heat transfer of mobile water. In the steam-injection phase, its temperature can rise up close to a saturated-steam temperature, accordingly, with respect to the effective heating radius being originally equal to the radius length of a horizontal well wellbore, in this case, the effective heating radius is enlarged. That is, the radius of the original linear heat source is a radius length of a horizontal well wellbore, the radius of the present linear heat source is slightly less than a radius length of the high water-cut region, and thus the radius of the linear heat source is effectively enlarged.
When injecting the isobaric steam into the steam-injection horizontal wells 1 and the production horizontal wells 2 for heating between the wells, because the increase in radius of the linear heat source of the steam-injection horizontal wells 1 and the production horizontal wells 2 results in a decrease in heat transfer distances between the steam-injection horizontal wells 1 and the production horizontal wells 2, therefore, the rate at which the temperature between the wells rises in the heating process can be substantially increased, so on the premise that an inter-well distance is unchanged, effective communications can be achieved between two wells, and time of communication is significantly shortened between two wells; typically, the second preset condition is that the time of injection of isobaric steam into the steam-injection horizontal wells 1 and the production horizontal wells 2 can be shortened to 2 months or more. Shortening the time of communication between two wells can save substantial amounts of injected steam, and substantially reduce the communication cost. This method can achieve an effective communication between the two wells, and therefore the track requirements can be reduced for well-drilling wellholes, the even producing degree of the horizontal section is improved when oil reservoirs are exploited, which gives full play to advantages of gravity drainage in horizontal wells.
In this embodiment, heat transfer occurs only in a manner of convection of heat in a high water-cut band (equivalent to an effect of enlarging a radius of a wellbore), and the final communication between wells still relies on steam-injection circulation, in other words, it is completed by heat conduction, wherein characteristics of the heat conduction are that uniformity is preferable. FIG. 6 is a relationship graph illustrating a midpoint temperature of dual horizontal wells where steam is circulated changes over time under conditions of different heating radius in the embodiments of the present application. As shown in FIG. 6, in one embodiment, steam-injection temperature is 250 degrees Celsius, steam-injection flowrate is 75 cubic meters/day, a relation of a midpoint temperature of dual horizontal wells against steam circulation preheating time when effective radii of wellbores are calculated as 0.11 meter and 1.11 meters respectively is obtained according to an unsteady-state heat transfer model when dual linear heat sources have an infinite radius, where 0.11m can be a radius of the horizontal hole, and 1.1Im can be a radius of the high water-cut area formed after solvents is injected, followed by water; in the steam circulation process, equivalent to that the radius of the wellbore is enlarged to 1.11m. It can be appreciated from the relation of the midpoint temperature calculated based on different heating radii (radii of linear heat source) with time that after the radius is increased to 1.11m, it is only necessary to increase the inter-well midpoint temperature (i.e., 2.5m when a drilling trajectory is idealized) up to more than 100 C in 30 days. And the heating radius (the radius of linear heat source) in a conventional method is only 0.11m, it needs to take more than 100 days of steam circulation time for increase in inter-well midpoint temperature up to 100 C. Thus it can be appreciated by contrast that after the heating radius (the radius of linear heat source) is enlarged, the rate at which the interwell temperature rises is substantially increased, and the steam-injection time required by crude oil that possesses flowing capacity is also significantly shortened, from the viewpoint of this embodiment, the steam-injection time is about 1/3 of that of the conventional solution. Since the steam-injection time is significantly shortened, substantial amounts of steam cost can be saved, while the water processing cost can also be greatly decreased, so the solution has a preferable economic benefit.
The following is an example that the method for communication of dual horizontal wells in the present application is applied in some specific oil reservoir.
The oil reservoir is a heavy oil reservoir buried at 440m depth, where a degassed crude oil has a viscosity of 106,000mPa.S at 50 C, the oil reservoir has a porosity of 30%, and a permeability of 1,400md, an oil saturation of 85%, a reservoir thickness of 25m. The minimum principal stress obtained by field testing is 6.3MPa, and the fracture-initiation pressure is 8.5MPa. A length of the horizontal section of the dual horizontal wells in the oil reservoir is provided at 400 meters, with wellhole diameter of 8.5in, 5 meters well spacing of the dual horizontal wells, and production horizontal wells are located 1 meter above the basement rock at the bottom. 80 cubic meters of xylene is injected into the dual horizontal wells respectively, and subsequently, 117 cubic meters of water is injected into each of the dual horizontal wells in 5 days in total, then nitrogen is injected from the respective well annulus of the dual horizontal wells, the water is drained from the pipe strings in wells, the well annulus pressure is progressively reduced, and finally, steam is injected from the respective long pipe string of the dual horizontal wells, the returned liquid is circulated in the short pipe strings, where the steam-injection pressure is 4MPa, underground steam flow rate is 75 cubic meter/day, steam quality is 95% at wellhead, and it determines after the circulation in 2 months that good communications occur between the dual horizontal wells, the effective production rate of the horizontal section of the dual horizontal wells reaches 90%, normal SAGD productions are switched after switching to half SAGD transition. Relative to other neighboring well groups using a conventional method, the circulation preheating time is shortened by nearly 10 months.
The method for communication of dual horizontal wells in the present application is injecting solvents into dual horizontal wells, next, injecting water to displace the mixture formed of solvents and heavy oil, thus gradually forming a high water-cut region centered on wellbores, and then injecting steam into the dual horizontal wells for circulation. Since the high water-cut region enlarges a radius of a linear heat source, heat transfer distances between the dual horizontal wells are declined to a great extent, so that a rate of rise in temperature is substantially increased between the dual horizontal wells, as a result, the method in the application can significantly shorten communication time between the dual horizontal wells, so as to save a large amount of steam, in addition, a degree of uniformity of communication can also be enhanced dramatically between the dual horizontal wells.

At the same time, the method for communication of dual horizontal wells in this embodiment avoids a risk of a local priority communication of horizontal wells by strictly controlling the down-hole pressure to be less than the minimum principal stress, inter-well non-differential pressure operations, pressurized soaking of the solvents, sizes of the solvent fingering area and high water-cut regions, so as to enhance a degree of uniformity of communication.
In addition, finally, the method for communication of dual horizontal wells provided in this embodiment also implements the steam circulation preheating for a predetermined time period (e.g., 3 months or so), which thus helps development of steam cavity and reservations of heat after switching to SAGD. Since the solvents injected in the early stage form a solvent fingering, the temperature rises due to conduction of heat in the later stage, both the solvents and the heat reduce the viscosity of crude oil above the steam-injection well in a collaborative manner, which facilitates development of a steam chamber after switching to SAGD and improvement of production rate.
All disclosed articles and references, including patent applications and publications, are hereby incorporated by reference for all purposes. The term "consisting essentially of' to describe a combination shall include the element, ingredient, component or step that is being determined and other elements, ingredients, components or steps that do not essentially affect basic novel characteristics of the combination. Use of the term "comprising" or "including" to describe a combination of elements, ingredients, components or steps herein also contemplates embodiments that are substantially composed of those elements, ingredients, components or steps. Any property described to demonstrate that a term "may" includes is selectable by use of the term "may" herein. A plurality of elements, ingredients, components or steps can be provided by a single integrated element, ingredient, component or step.
Alternatively, the single integrated element, ingredient, component, or step may be divided into a plurality of separated elements, ingredients, components, or steps. The disclosure of "a" or "an" to describe an element, an ingredient, a component, or a step is not intended to exclude other elements, ingredients, components, or steps.
The embodiments in the Description are described in a progressive manner, and the embodiments highlight the differences from another embodiment, referring to the identical or similar part between the embodiments mutually. The above embodiments are merely intent to illustrate the technical concept and characteristics of the present invention, and aim to allow for those skilled in the art to understand the disclosure contained in the present invention and implement the present invention based thereon, and it is not intent to limit the protection scope of the present invention.
Any equivalent change or modification in accordance with the spirit of the invention is intent to be covered by the protection scope of the present invention.

Claims (18)

What is claimed is:

1. A method for communication of dual horizontal wells comprising steam-injection horizontal wells and production horizontal wells, wherein, the method comprising the following steps:
testing the steam-injection horizontal wells and the production horizontal wells to obtain a minimum principal stress of the steam-injection horizontal wells, a fracture-initiation pressure of the steam-injection horizontal wells, a minimum principal stress of the production horizontal wells and a fracture-initiation pressure of the production horizontal wells;
injecting solvents into the steam-injection horizontal wells and the production horizontal wells respectively;
injecting water into the steam-injection horizontal wells via wellbores of the steam-injection horizontal wells, injecting water into the production horizontal wells via wellbores of the production horizontal wells, so that the solvents in the wellbores of the steam-injection horizontal wells and the production horizontal wells are displaced in oil reservoirs;
continuously injecting water into the steam-injection wells and the production horizontal wells respectively, improving water-injection pressure of the steam-injection horizontal wells to between the minimum principal stress of the steam-injection horizontal wells and the fracture-initiation pressure of the steam-injection horizontal wells, and improving the water-injection pressure of the production horizontal wells to between the minimum principal stress of the production horizontal wells and the fracture-initiation pressure of the production horizontal wells;
after a high water-cut region is formed in the respective solvent area of the steam-injection horizontal wells and the production horizontal wells; after closing the steam-injection horizontal wells and the production horizontal wells meets a first preset condition, injecting gas into the steam-injection horizontal wells and the production horizontal wells respectively, so that underground water flows back to ground, and after the underground water flows back to the ground, injecting isobaric steam into the steam-injection horizontal wells and the production horizontal wells to meet a second preset condition.

2. The method for communication of dual horizontal wells according to claim 1, wherein, continuously injecting the water into the steam-injection wells and the production horizontal wells respectively, improving the water-injection pressure of the steam-injection horizontal wells to between the minimum principal stress of the steam-injection horizontal wells and the fracture-initiation pressure of the steam-injection horizontal wells, and improving the water-injection pressure of the production horizontal wells to between the minimum principal stress of the production horizontal wells and the fracture-initiation pressure of the production horizontal wells, so that one high water-cut region centered on wellbores is formed in the solvent area of the steam-injection horizontal wells and the production horizontal wells respectively, and the high water-cut region of the steam-injection horizontal wells is not in communication with the high water-cut region of the production horizontal wells.

3. The method for communication of dual horizontal wells according to claim 1, wherein, the method for communication of dual horizontal wells further comprises the following steps injecting water with pressure into the steam-injection horizontal wells and the production horizontal wells respectively, in order to determine development of underground fractures.

4. The method for communication of dual horizontal wells according to claim 1, wherein, the method for communication of dual horizontal wells further comprises the following steps:
cyclically injecting water into the steam-injection horizontal wells and the production horizontal wells respectively, in order to clean up wellbore walls.

5. The method for communication of dual horizontal wells according to claim 1, wherein, the method for communication of dual horizontal wells further comprises the following steps:
before said step of injecting water into the steam-injection horizontal wells via the wellbores of the steam-injection horizontal wells, injecting water into the production horizontal wells via the wellbores of the production horizontal wells, so that the solvents in the wellbores of the steam-injection horizontal wells and the production horizontal wells are displaced in oil reservoirs, injecting a soluble gum of slugs into a wellbore annulus of the steam-injection horizontal wells and the production horizontal wells respectively.

6. The method for communication of dual horizontal wells according to claim 1, wherein, providing a first pipe string and a second pipe string longer than the first pipe string in the steam-injection horizontal wells, providing a third pipe string and a fourth pipe string longer than the third pipe string in the production horizontal wells, in said step of after closing the steam-injection horizontal wells and the production horizontal wells meets a first preset condition, injecting gas into the steam-injection horizontal wells and the production horizontal wells respectively; so that underground water flows back to ground, injecting gas into a well annulus of the steam-injection horizontal wells and the production horizontal wells respectively, so that the underground water of the steam-injection horizontal wells flows back from the first or second pipe string to the ground, the underground water of the production horizontal wells flows back from the third or fourth pipe string to the ground.

7. The method for communication of dual horizontal wells according to claim 6, wherein, in said step of injecting gas into the well annulus of the steam-injection horizontal wells and the production horizontal wells, so that the underground water of the steam-injection horizontal wells flows back from the first or second pipe string to the ground, the underground water of the production horizontal wells flows back from the third or fourth pipe string to the ground, gradually reducing down-hole pressure, so as to promote the underground water to flow back to the ground.

8. The method for communication of dual horizontal wells according to claim 1, wherein, the first preset condition is that closing time of the steam-injection horizontal wells and the production horizontal wells is greater than or equal to 24 hours.

9. The method for communication of dual horizontal wells according to claim 1, wherein, the second preset condition is that the time of injection of the isobaric steam into the steam-injection horizontal wells and the production horizontal wells is greater than or equal to 2 months.

10. The method for communication of dual horizontal wells according to claim 1, wherein, in said step of injecting the solvents into the steam-injection horizontal wells and the production horizontal wells respectively, so that the wellbores of the steam-injection horizontal wells and the wellbores of the production horizontal wells are filled up with the solvents, adjusting flow rate and pressure of the solvents injected by injection pressure, when the wellbores of the steam-injection horizontal wells and the wellbores of the production horizontal wells are filled up with the solvents.

11. The method for communication of dual horizontal wells according to claim 1, wherein, the steam-injection horizontal wells and the production horizontal wells meet the following conditions: there exists no inter-well interlayer between the steam-injection horizontal wells and the production horizontal wells; there exists no natural fracture in an oil reservoir region where the steam-injection horizontal wells and the production horizontal wells are located; and there exists no edge-bottom water in the oil reservoir region where the steam-injection horizontal wells and the production horizontal wells are located.

12. The method for communication of dual horizontal wells according to claim 1, wherein, the solvents and heavy oil miscible with each other, and asphaltene is not precipitated out.

13. The method for communication of dual horizontal wells according to claim 1, wherein, the viscosity of the solvents at room temperature ranges between 1mPa.S
and 100mPa.S, and the density ranges between 0.7g/cm3 and 1.2g/cm3.

14. The method for communication of dual horizontal wells according to claim 1, wherein, the solvents have viscosity-reduction properties at the oil reservoir temperature, and viscosity of mixtures containing the solvents of which mass fraction is 20% and crude oil should be less than 5,000mPaS.

15. The method for communication of dual horizontal wells according to claim l , wherein, the solvents include at least one of benzene, toluene, xylene, kerosene, diesel oil, petroleum ether and light crude oil.

16. The method for communication of dual horizontal wells according to claim 1, wherein, in said step of after closing the steam-injection horizontal wells and the production horizontal wells meets a first preset condition, injecting gas into the steam-injection horizontal wells and the production horizontal wells respectively, so that underground water flows back to ground, the gas is nitrogen.

17. The method for communication of dual horizontal wells according to claim 1, wherein, injecting the solvents into the steam-injection horizontal wells and the production horizontal wells respectively, so that the wellbores of the steam-injection horizontal wells and the wellbores of the production horizontal wells are filled up with the solvents.

18. The method for communication of dual horizontal wells according to claim 1, wherein, when the solvents are injected into the steam-injection horizontal wells and the production horizontal wells respectively, the injection pressure of the solvents is consistently less than the minimum principal stress.