CN113047821A - Water vapor-gas combined circulating displacement method - Google Patents

Abstract

A water vapor-gas combined cycle displacement method is disclosed. The method can comprise the following steps: step 1: dividing a plurality of well groups according to the well pattern structure, and determining a steam injection well of each well group; step 2: injecting steam-gas into the steam injection well; and step 3: injecting nitrogen into the steam injection well; and 4, step 4: injecting carbon dioxide into the steam injection well; and 5: and (5) repeating the steps 2-4 until the oil-gas ratio is lower than a set threshold value. The invention forms multi-section multiphase multi-component seepage in the oil reservoir by coupling multiple displacement mechanisms of heating viscosity reduction, gas energization, interface tension reduction, multiphase flow resistance reduction, steam channeling prevention and the like of water vapor and other gases and changing the steam-gas displacement combination and slug design, thereby improving the formation capability and the displacement pressure difference, improving the displacement efficiency and the sweep coefficient and making up the defects of steam swallowing and other existing methods.

Description

Water vapor-gas combined circulating displacement method

Technical Field

The invention relates to the field of oil and gas field development, in particular to a water vapor-gas combined circulating displacement method.

Background

The global heavy oil resource is very rich, and the residual geological reserves of the heavy oil, the oil sand and the asphalt are about 8000 hundred million tons and account for about 70 percent of the global total petroleum resource. The thick oil thermal recovery is a process of extracting thick oil from a geological reservoir by reducing the viscosity of crude oil in rock pores of an underground reservoir in a heating mode and enhancing the flowing capability. The thermal recovery technology mainly comprises the following steps: steam huff and puff, steam assisted gravity drainage, steam flooding, in-situ combustion and bottom hole electrical heating. Methods that can be used to heat the formation are steam, hot water or underground combustion, electrical heating, electromagnetic heating, and the like. The use of water vapor is the most common method of heating. The heavy oil steam injection thermal recovery has various types, for example, according to a driving mode, the heavy oil steam injection recovery can be divided into two stages of steam huff and puff and steam flooding, which is a common practice abroad. Steam flooding is often performed after several cycles of steam throughput.

Steam stimulation (Huff and Puff) is a single well operation, with each well being both a steam injection well and a production well. It is sometimes called well Stimulation, Cyclic Steam Injection, Steam soaking, etc. Each cycle of the steam stimulation process technology comprises three steps: steam injection stage (swallowing stage), well shut-in stage (stewing) and oil extraction stage (spitting). Steam flooding refers to the process of continuing steam injection from a steam injection well while continuing oil production from an adjacent production well. The steam flooding process involves at least one injection well and one production well. The steam huff-and-puff method is simple, the economic risk is small, each well can be huff-and-puff operated for more than 5-8 cycles, the oil extraction speed is high, but the crude oil recovery rate is low and is only 10% -20%, and a large amount of recoverable reserves are lost. The steam stimulation is effective to heat the formation to a radius of less than 30m, so that a large amount of residual oil remains in the formation after the multiple cycle stimulation.

Steam flooding oil recovery is a thermal recovery method adopted for further improving the recovery efficiency after heavy oil reservoirs are subjected to steam huff-and-puff oil recovery, because the steam huff-and-puff oil recovery can only recover crude oil in oil reservoirs near each oil well, a large amount of dead oil zones are left between the oil wells. Steam flooding oil extraction is that high-dryness steam is continuously injected into an oil layer from an injection well, and the steam continuously heats the oil layer, so that the viscosity of crude oil in the stratum is greatly reduced. The injected steam becomes a hot fluid in the formation, driving the crude oil around the production wells and being produced to the surface. The steam flooding generally adopts an area well pattern form, steam is continuously injected from an injection well, and crude oil is continuously produced from a production well. In the steam flooding process, there are several mechanisms that act to different degrees, including viscosity reduction, steam distillation, thermal expansion, oil miscible flooding, dissolved gas flooding, and emulsion flooding. Among the dominant ones are viscosity reduction, distillation of steam, thermal expansion and oil miscible flooding. Steam Flooding (steam Flooding) can make up the deficiency of steam throughput in principle, can realize that whole oil reservoir effectively uses, but technical requirement is high, the input is big, the energy consumption is high, whether can obtain higher recovery efficiency and economic benefits, then depends on oil reservoir geological conditions and the advance and the adaptability of technology. Factors influencing steam huff and puff and steam flooding effect are many, and the geology mainly comprises reservoir thickness, depth, lithology, fluid property, heterogeneity and the like; the engineering mainly comprises a well pattern form, a well type, a pipe column, a steam injection mode and the like, and the ground process comprises parameters of a boiler, a ground manifold flow and the like.

Almost all formations are more or less heterogeneous to some extent, which can be manifested as inhomogenities at the reservoir plane, i.e. intrastratal inhomogenities; and can also be expressed as longitudinal heterogeneity, i.e. interlaminar heterogeneity; but also on a variety of scales, such as on the microscopic pore scale. Due to the presence of heterogeneity, the displacement medium injected into the subsurface will preferentially follow channels that are easy to flow, forming so-called hypertonic channels. Due to the existence of the high-permeability channel, steam penetration (steam channeling) is easily formed in the heavy oil thermal recovery process, so that the oil well is prematurely high in water content and even flooded with water. Both throughput and steam blow-by are one of the major factors leading to failure. Engineers adopt various physical and chemical methods to prevent and treat steam channeling, and various water plugging and controlling materials and processes are researched and applied, but most of the water plugging and controlling materials have the defects of poor effectiveness, short validity period, higher cost and the like. In addition, most of the existing plugging and adjusting materials need to be gelatinized at a certain part in a stratum to form plugging, but the controllability of gelatinizing time is always a difficult problem.

In the aspect of displacement efficiency, some researchers try to add some chemical agents or gases on the basis of water vapor to improve the effect of steam injection, but the technical methods are not always effective, and have the defects of weak pertinence, insufficient popularization, high cost and the like, and especially have unobvious effect on ultra-heavy oil reservoirs with small oil layer thickness and strong heterogeneity. In addition, the prior art has more applications in single well stimulation and less applications in the whole oil reservoir, so that the sweep efficiency is lower, a large amount of residual oil between wells is retained in the stratum and cannot be exploited. Therefore, it is necessary to develop a water vapor-gas combined cycle displacement method.

The information disclosed in this background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

Disclosure of Invention

The invention provides a steam-gas combined circulating displacement method, which can form multi-section multi-phase multi-component seepage in an oil reservoir by coupling multiple displacement mechanisms of heating viscosity reduction, gas energization, interface tension reduction, multiphase flow resistance reduction, steam channeling prevention and the like of steam and other gases and changing a steam-gas displacement combination and a slug design, thereby improving the formation capability and the displacement pressure difference, improving the displacement efficiency and the sweep efficiency, and making up the defects of steam swallowing and other existing methods.

The method may include: step 1: dividing a plurality of well groups according to the well pattern structure, and determining a steam injection well of each well group; step 2: injecting steam-gas into the steam injection well; and step 3: injecting nitrogen into the steam injection well; and 4, step 4: injecting carbon dioxide into the steam injection well; and 5: and (5) repeating the steps 2-4 until the oil-gas ratio is lower than a set threshold value.

Preferably, each well group further comprises at least one production well.

Preferably, the production well performs oil recovery production during the steam injection of the steam injection well.

Preferably, the number of steam injection wells per well group is at least one.

Preferably, the well group is of a five-point structure, and the steam injection well is the center of the five-point structure.

Preferably, the well group is of a nine-point structure, and the steam injection well is the center of the nine-point structure.

Preferably, the well group is in a row structure, and the steam injection wells and the production wells are alternately arranged in a linear mode.

Preferably, the gas is a mixed gas of nitrogen and carbon dioxide.

Preferably, the injection amount of the water vapor-gas is 10-20% of the total underground pore volume, wherein the volume percentage of the water vapor is 80%, and the volume percentage of the gas is 20%.

Preferably, the ratio of carbon dioxide to nitrogen in the gas is from 3:1 to 1: 1.

Preferably, the steam injection amount of thestep 3 is 1/3 of thestep 2, and the steam injection amount of thestep 4 is 1/3-1/2 of thestep 2.

Preferably, thestep 3 further comprises: the blowing agent is injected simultaneously with the nitrogen injection.

Preferably, the injection-production ratio of the steam injection well to the production well is 1:1-1: 2.

The method of the present invention has other features and advantages which will be apparent from or are set forth in detail in the accompanying drawings and the following detailed description, which are incorporated herein, and which together serve to explain certain principles of the invention.

Drawings

The above and other objects, features and advantages of the present invention will become more apparent by describing in more detail exemplary embodiments thereof with reference to the attached drawings, in which like reference numerals generally represent like parts.

Fig. 1 shows a flow chart of the steps of a combined water vapor-gas cycle displacement method according to the invention.

Detailed Description

The invention will be described in more detail below with reference to the accompanying drawings. While the preferred embodiments of the present invention are shown in the drawings, it should be understood that the present invention may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

Fig. 1 shows a flow chart of the steps of a combined water vapor-gas cycle displacement method according to the invention.

In this embodiment, the water vapor-gas combined cycle displacement method according to the present invention may include: step 1: dividing a plurality of well groups according to the well pattern structure, and determining a steam injection well of each well group; step 2: injecting steam-gas into the steam injection well; and step 3: injecting nitrogen into the steam injection well; and 4, step 4: injecting carbon dioxide into the steam injection well; and 5: and (5) repeating the steps 2-4 until the oil-gas ratio is lower than a set threshold value.

In one example, each well group further includes at least one production well.

In one example, the production well produces oil during the steam injection of the steam injection well.

In one example, the number of steam injection wells per well group is at least one.

In one example, the well group is a five-point configuration and the steam injection well is the center of the five-point configuration.

In one example, the well group is a nine-point configuration and the steam injection well is the center of the nine-point configuration.

In one example, the well groups are arranged in a row, and the steam injection wells and the production wells are arranged alternately in a linear manner.

In one example, the water vapor-gas injection is 10% to 20% of the total subsurface pore volume, with 80% water vapor by volume and 20% gas by volume.

In one example, the ratio of carbon dioxide to nitrogen in the gas is 3:1 to 1: 1.

In one example, the steam injection amount ofstep 3 is 1/3 ofstep 2, and the steam injection amount ofstep 4 is 1/3-1/2 ofstep 2.

In one example, the gas is a mixture of nitrogen and carbon dioxide.

In one example,step 3 further comprises: the blowing agent is injected simultaneously with the nitrogen injection.

In one example, the injection-production ratio of the steam injection well to the production well is 1:1 to 1: 2.

Specifically, most of the thick oil belongs to non-Newtonian fluid under the original stratum condition, a transformation temperature exists, the thick oil can be transformed into Newtonian fluid above the transformation temperature, the flow of the thick oil conforms to the flow law of the Newtonian fluid, a certain yield value exists in most of the thick oil, and the thick oil can flow above the driving force. Thus, two basic conditions are required for the thick oil to flow in the formation: reduce the viscosity of the thick oil and provide a certain displacement pressure. Most heavy oil reservoirs belong to high-permeability oil reservoirs, the radius of pore throats of the reservoirs is large, and enough space can be provided for seepage of multiphase fluid, so that the main contradiction of fluid flow in the development process of the heavy oil reservoirs is not caused by space limitation but by a flow channeling phenomenon caused by overhigh fluidity. The steam flooding is a process of continuously injecting steam from a steam injection well and continuously producing oil from an adjacent production well by using high-temperature steam as a heat-carrying fluid and a driving medium and improving the oil displacement efficiency by using the injected heat and quality.

The steam with certain dryness is injected into the stratum through the pipe column, the fluid and the rock in the stratum can be heated, wherein the viscosity of the crude oil is obviously reduced along with the temperature increase, the fluidity is increased, and the crude oil is converted into the Newtonian fluid. Meanwhile, the water vapor can generate condensation due to the loss of heat, and the water vapor is converted from a vapor state into a liquid state. During the steam flow from the injection well to the production well, several zones of different temperatures are formed: steam zone and partial condensed water zone, hot oil zone and original oil zone. In different temperature zones, the viscosity and rheological property of thick oil, water vapor and formation water can change obviously due to temperature change, so that complex multiphase seepage characteristics are presented.

The viscosity ratio (fluidity ratio) is a main factor influencing the flowing capacity of the multi-phase fluid in the porous medium, in a high-temperature steam area, steam exists in a steam phase, the viscosity of the steam is far lower than that of crude oil, and therefore, the steam phase fluidity is far higher than that of an oil phase, so that steam channeling is easily caused; in the condensation zone, the water vapor begins to be converted into hot water, a three-phase seepage zone of a vapor phase, a water phase and an oil phase appears at the moment, and the viscosity of the water phase is greater than that of the water vapor; the hot water region mainly shows oil-water two-phase flow, and the viscosity of the crude oil begins to rise again at the moment. The hot oil zone is mainly represented by the single-phase flow of low-viscosity crude oil under water-bound conditions. The cold oil band exhibits single phase flow of high viscosity oil under water-bound conditions.

Based on the basic principle and the physical and chemical process in the heavy oil thermal recovery process, the relative permeability is adjusted by designing the injection mode, the injection time and the injection amount of the water vapor and the gas, the oil phase permeability is improved, the gas channeling and the water channeling are controlled, and the development effect is improved.

The water vapor-gas combined cycle displacement method according to the present invention may include:

step 1: and dividing a plurality of well groups according to the well pattern structure, and determining the steam injection wells and the production wells of each well group, wherein the number of the steam injection wells and the production wells of each well group is at least one.

The well group can be a five-point structure, the steam injection well is the center of the five-point structure, and the rest are production wells; the well group can be a nine-point structure, the steam injection well is the center of the nine-point structure, and the rest are production wells; the well group can be in a row structure, the steam injection wells and the production wells are in linear alternate arrangement, and the well group can be divided by a person skilled in the art according to the well pattern structure.

Step 2: and injecting steam-gas into the steam injection well, wherein the gas is a mixed gas of nitrogen and carbon dioxide, the gas can be flue gas, a mixed gas prepared in proportion, or a mixed gas generated by other gas generators, and the injection proportion of the steam, the nitrogen and the carbon dioxide is adjusted according to the properties of the thick oil, the development stage and the state of underground residual oil. The timing and amount of the water vapor-gas injection was determined by laboratory experiments or numerical simulations.

The main effect of this slug is that make stratum intensification, viscous crude viscosity reduction, and wherein carbon dioxide plays the viscosity reduction effect through dissolving the diffusion effect and preferentially getting into the viscous crude under the high temperature effect, because gravity differentiates the different effect, partly nitrogen gas can be toward oil reservoir upper portion migration, and the thermal-insulated effect of performance, partly nitrogen gas is detained with the bubble form and is played in the hole and transfer stifled effect, and partly in addition can form bubble oil with crude oil, reduces oil phase viscosity. The main points of the slug injection are that the injection pressure is lower than the rupture pressure, the steam dryness at the bottom of the well is kept to be more than 40 percent, and the steam, the nitrogen and the carbon dioxide are mixed and injected to avoid the formation of a continuous phase by the nitrogen and the carbon dioxide.

And step 3: and (3) injecting nitrogen into the steam injection well, wherein the steam injection amount is 1/3 of thestep 2. The purpose of the slug injection is to continue to exert a displacement effect after thestep 2, expand longitudinal sweep by using the overlying effect of nitrogen, form bubble oil with crude oil, and reduce the viscosity of an oil phase. The foaming agent can be injected at the same time of injecting nitrogen, and foam is generated after the foaming agent is injected into the stratum, so that the seepage resistance is further improved.

And 4, step 4: and (3) injecting carbon dioxide into the steam injection well, wherein the steam injection amount is 1/3-1/2 in thestep 2. The slug has the function of leading the injected carbon dioxide to fully generate diffusion and dissolution with the residual oil in the oil reservoir by utilizing the separation function of thestep 2 and thestep 3 so as to generate continuous seepage.

And 5: and in the steam injection process of the steam injection well, the production well carries out oil extraction production, the liquid recovery amount of the production well is calculated according to the total liquid amount of the oil field, the injection-production ratio of the steam injection well to the production well is 1:1-1:2, and the step 2-4 is repeated until the oil-steam ratio is lower than a set threshold value.

The method forms multi-section multiphase multi-component seepage in the oil reservoir by coupling multiple displacement mechanisms of heating viscosity reduction, gas energization, interface tension reduction, multiphase flow resistance reduction, steam channeling prevention and the like of steam and other gases and changing a steam-gas displacement combination and a slug design, improves the formation capacity and the displacement pressure difference, improves the displacement efficiency and the sweep coefficient, and makes up for the defects of steam swallowing and other existing methods.

Application example

To facilitate understanding of the solution of the embodiments of the present invention and the effects thereof, a specific application example is given below. It will be understood by those skilled in the art that this example is merely for the purpose of facilitating an understanding of the present invention and that any specific details thereof are not intended to limit the invention in any way.

The P oil field belongs to an extra-heavy oil reservoir, the viscosity of crude oil is 8000mPa.s-35000mPa.s, the heterogeneity is strong, the plunging coefficient is more than 3, the steam huffing and puff development is adopted in the early stage, but the problems of steam channeling, high water content and the like cause the cycle yield to be reduced quickly, the single-well yield and the oil-steam ratio are reduced obviously, and the economic benefit is reduced. In addition, the oil reservoir stratum capacity is reduced quickly, the liquid supply capacity is insufficient, the steam injection heat loss is large, and the heat efficiency is low.

Step 1: dividing a plurality of five-point type structure well groups according to the well pattern structure of the P oil field, and determining a steam injection well and a production well of each well group, wherein each well group comprises 1 steam injection well and 4 production wells.

Step 2: and injecting steam-gas into the steam injection well, wherein the gas is a mixed gas of nitrogen and carbon dioxide, the injection amount of the steam-gas is 10% -20% of the total underground pore volume, the volume of the steam is 80%, the proportion of the mixed gas of the carbon dioxide and the nitrogen is about 20%, the proportion of the carbon dioxide and the nitrogen is 3:1, and the dryness of the steam at the bottom of the well is more than 40%.

And step 3: and (3) injecting nitrogen into the steam injection well, wherein the steam injection amount is 1/3 of thestep 2.

And 4, step 4: and (3) injecting carbon dioxide into the steam injection well, wherein the steam injection amount is 1/3-1/2 in thestep 2.

And 5: and in the steam injection process of the steam injection well, the production well performs oil extraction production, the injection-production ratio of the steam injection well to the production well is 1:1-1:2, and the step 2-4 is repeated until the oil-steam ratio is lower than a set threshold value.

In conclusion, the invention forms multi-section multiphase multi-component seepage in the oil reservoir by coupling multiple displacement mechanisms of heating viscosity reduction, gas energization, interface tension reduction, multiphase flow resistance reduction, steam channeling prevention and the like of steam and other gases and changing the steam-gas displacement combination and slug design, thereby improving the formation capability and the displacement pressure difference, improving the displacement efficiency and the sweep coefficient and making up the defects of steam swallowing and other existing methods.

It will be appreciated by persons skilled in the art that the above description of embodiments of the invention is intended only to illustrate the benefits of embodiments of the invention and is not intended to limit embodiments of the invention to any examples given.

Having described embodiments of the present invention, the foregoing description is intended to be exemplary, not exhaustive, and not limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments.

Claims (10)

1. A water vapor-gas combined cycle displacement method, comprising:

step 1: dividing a plurality of well groups according to the well pattern structure, and determining a steam injection well of each well group;

step 2: injecting steam-gas into the steam injection well;

and step 3: injecting nitrogen into the steam injection well;

and 4, step 4: injecting carbon dioxide into the steam injection well;

and 5: and (5) repeating the steps 2-4 until the oil-gas ratio is lower than a set threshold value.

2. The water vapor-gas combined cycle displacement method of claim 1, wherein each well group further comprises at least one production well.

3. A combined steam-gas cycle displacement method according to claim 2, wherein the production well is producing oil during the steam injection of the steam injection well.

4. A water vapor-gas combined cycle displacement method according to claim 1, wherein the number of steam injection wells per well group is at least one.

5. The water vapor-gas combined cycle displacement method of claim 1, wherein the gas is a mixed gas of nitrogen and carbon dioxide.

6. The water vapor-gas combined cycle displacement method of claim 5, wherein the water vapor-gas is injected in an amount of 10-20% of the total subsurface pore volume, wherein the water vapor is 80% by volume and the gas is 20% by volume.

7. A water vapour-gas combined cycle displacement method according to claim 6, wherein the ratio of carbon dioxide to nitrogen in the gas is from 3:1 to 1: 1.

8. The water vapor-gas combined cycle displacement method of claim 1, wherein the steam injection amount of step 3 is 1/3 of step 2, and the steam injection amount of step 4 is 1/3-1/2 of step 2.

9. The water vapor-gas combined cycle displacement method of claim 1, wherein step 3 further comprises:

the blowing agent is injected simultaneously with the nitrogen injection.

10. A water vapour-gas combined cycle displacement method according to claim 2, wherein the injection-production ratio of the steam injection well to the production well is 1:1-1: 2.

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