Gas-steam hybrid oil recovery method

Abstract

This invention discloses a gas-steam fusion oil recovery method, which can improve the recovery rate of heavy oil reservoirs, increase the economically recoverable reserves of heavy oil reservoirs at marginal conditions, and achieve good development results and high economic benefits. The method includes the following steps: Based on reservoir crude oil oxidation kinetics experiments, the oxidation activity and ignition delay of the heavy oil are obtained; based on the oxidation activity and ignition delay of the heavy oil, it is determined whether the heavy oil possesses the oxidation activity to overcome the "valley of death," where the "valley of death" is the stage where the heavy oil cannot achieve high-temperature oxidation due to ignition delay; if the heavy oil possesses the oxidation activity to overcome the "valley of death," an optimal combustion temperature experiment is conducted to obtain the optimal combustion temperature of the heavy oil; if not, the activity of the heavy oil is improved until it possesses the oxidation activity to overcome the "valley of death"; the injection wells for injecting air and steam are ignited, and the combustion temperature is controlled to the optimal combustion temperature, with production wells around the injection wells producing oil, thus achieving oil recovery.

Description

Technical Field

[0001] This invention relates to the field of heavy oil or extra-heavy oil extraction technology, specifically a gas-vapor fusion oil recovery method. Background Technology

[0002] Based on the current development status of heavy oil, one-third of the heavy oil reserves cannot be effectively developed using existing main development technologies to achieve profitable production. Currently, steam huff and puff technology is commonly used for developing heavy oil reservoirs, but this technology has low recovery rates, leaving a significant amount of residual oil. For example, current reservoir development results show that after multiple rounds of steam huff and puff development, inter-well interference and crossflow are severe, the cycle oil-steam ratio has dropped to a low level, water cut is high, huff and puff efficiency is no longer effective, recovery rates are poor, and a large amount of crude oil remains in the reservoir.

[0003] Therefore, based on the current selection criteria for main technologies in heavy oil development, there are no suitable extraction technologies available for these reservoirs. They are unsuitable for continued steam injection or conversion to steam drive development, and they also lack the conditions for SAGD (Super Aquaculture Diversion). How to further improve the recovery rate of these reservoirs is one of the current challenges for relevant professionals. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a gas-vapor fusion oil recovery method that can improve the recovery rate of heavy oil reservoirs, increase the economically recoverable reserves of heavy oil reservoirs under marginal conditions, and achieve good development results and high economic benefits.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A gas-vapor fusion oil recovery method includes the following steps:

[0007] Based on reservoir crude oil oxidation kinetics experiments, the oxidation activity and ignition delay of heavy oil were obtained;

[0008] Based on the oxidative activity and ignition delay of heavy oil, it is determined whether the heavy oil has the oxidative activity to cross the "valley of death," where the "valley of death" is the stage in which the heavy oil cannot achieve high-temperature oxidation due to the ignition delay phenomenon.

[0009] If the heavy oil has the oxidative activity to cross the valley of death, conduct an optimal combustion temperature experiment to obtain the optimal combustion temperature of the heavy oil. If it does not have this activity, improve the activity of the heavy oil until it has the oxidative activity to cross the valley of death.

[0010] The injection well, which injects air and steam, is ignited, and the combustion temperature is controlled to the optimal combustion temperature. Oil is produced in the production wells around the injection well, thus achieving oil recovery.

[0011] Furthermore, before the injection well for igniting air and steam, the oil production and development area is divided into several well rows, with each well row producing and injecting simultaneously.

[0012] Furthermore, before igniting the injection well for injecting air and steam, a preheating treatment is also included, with the following steps:

[0013] Steam is injected into the injection well for preheating and puffing operations until the average temperature between wells reaches the temperature corresponding to the second inflection point of the crude oil viscosity-temperature relationship curve, at which point the preheating treatment is completed.

[0014] Furthermore, during the preheating and injection operation, the steam dryness at the bottom of the injection well is not less than 50%.

[0015] Furthermore, during the preheating and injection operation, the steam simmering time of the injection well is 2.5 to 3.5 days, and the production-injection ratio of the injection well is 0.8 to 1.3.

[0016] Furthermore, the method for controlling the combustion temperature to the optimal combustion temperature includes analyzing the heat retention rate of the burned zone, with the following steps:

[0017] Based on the gas-vapor fusion oil production situation of the reservoir, control the gas injection rate of the injection well and / or intermittently inject air and / or rotate the ignition wells until the combustion temperature is the optimal combustion temperature.

[0018] Furthermore, when rotating the ignition wells, the ignition wells to be rotated are selected along the deposition direction and / or parallel to the contour lines.

[0019] Furthermore, the timing for rotating the ignition well is as follows: following the sequence of air injection ignition, surrounding well production, rapid rise in oil well temperature and pressure, well shut-in, gas injection well shut-off, well opening and production up to the single well's maximum production, the timing for rotating the ignition well is when the temperature and pressure of the oil wells surrounding the ignition well rise rapidly.

[0020] Furthermore, after several rotations of the rotating ignition wells, several oil wells located in the same structural high position and with the same physical properties are injected with gas and ignited, and then displacement is carried out in a linear well row mode until the oil wells are shut in.

[0021] Preferably, the injection-production well pattern adopts a square-shaped well pattern.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] This invention provides a gas-vapor fusion oil recovery method. The design concept is based on the mesophilic oxidation mechanism, providing a reasonable explanation for problems such as "pore blockage" and "ignition delay" that hinder gas-vapor fusion oil recovery. Based on this, an optimized oil recovery method is proposed. Specifically, before gas-vapor fusion oil recovery, "good oil" is first screened. This involves using reservoir crude oil oxidation kinetics experiments within a temperature range below 1000K to determine whether the heavy oil possesses the oxidation activity to overcome the "valley of death." "Good oil" exhibits high oxidation activity and a short ignition delay, allowing for controlled combustion temperature. By controlling the combustion temperature within the optimal combustion temperature range, stable advancement of the combustion front can be ensured, enabling the heavy oil to successfully transition from the mesophilic oxidation zone to the high-temperature oxidation zone, thus overcoming the "valley of death" and avoiding "pore blockage" and "ignition delay." This phenomenon successfully drives oil through fire, while reducing fuel consumption. Furthermore, it facilitates gas-steam fusion oil recovery by igniting injection wells containing air and steam, promoting chemical reactions in the crude oil. Using the well bottom where air is injected as the origin, high-temperature oxidation occurs near the injection well, while low-temperature oxidation or no oxidation occurs near the production well. This places the entire reservoir in a low-temperature to medium-temperature oxidation process. The generated gas mixes with the injected fluid, carrying heat into the deeper reservoir. The heated, viscosity-reduced crude oil is displaced to the bottom of the production well and subsequently extracted, thereby increasing the economically recoverable reserves of heavy oil reservoirs at the margin of development through steam injection.

[0024] Preferably, steam preheating is performed before gas-steam fusion oil production. Correspondingly, during fire flooding, injection wells that combine air and steam injection are ignited. Compared to no preheating, steam preheating not only consumes less fuel and produces more net oil, which helps to achieve full reservoir displacement, but also meets the requirement that the near-well saturation after steam preheating is higher than 25%, maintaining combustion and stable advancement of the combustion zone.

[0025] Preferably, during steam preheating, the development unit is divided into several well rows, and injection and production are carried out in alternating rows. This can create a production pressure difference between well rows, which promotes the overall migration of high-temperature fluid from the high-pressure area to the low-pressure area, providing a reservoir environment for subsequent development.

[0026] Preferably, during preheating and injection, the bottom hole steam dryness is not less than 50%, the steam injection simmering time is 2.5-3.5 days, and the production-injection ratio is 0.8-1.3, preferably 1.0, in order to provide a suitable injection-production strategy, in order to achieve inter-well displacement and produce the steam injection effect that cannot be achieved by elastic energy alone. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the crude oil oxidation process based on the intermediate-temperature oxidation of crude oil in this invention;

[0028] Figure 2 This is a well location diagram from Embodiment 1 of the present invention;

[0029] Figure 3 This is a well location diagram from Embodiment 2 of the present invention;

[0030] Figure 4 This is a flowchart of the gas-vapor fusion oil recovery method of the present invention. Detailed Implementation

[0031] The principles and features of the present invention will be further described in detail below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention. It should be noted that the accompanying drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clearly illustrate the purpose of the embodiments of the present invention.

[0032] It should be noted that when a component is said to be "fixed to" another component, it can be directly on the other component or it can be in a centered component. When a component is said to be "connected to" another component, it can be directly connected to the other component or it may also be in a centered component. When a component is said to be "set to" another component, it can be directly set on the other component or it may also be in a centered component.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0034] This invention provides a gas-vapor fusion oil recovery method, such as... Figure 4 As shown, it includes the following steps:

[0035] Based on reservoir crude oil oxidation kinetics experiments, the oxidation activity and ignition delay of heavy oil were obtained;

[0036] Based on the oxidative activity and ignition delay of heavy oil, it is determined whether the heavy oil has the oxidative activity to cross the "valley of death," where the "valley of death" is the stage in which the heavy oil cannot achieve high-temperature oxidation due to the ignition delay phenomenon.

[0037] If the heavy oil has the oxidative activity to cross the valley of death, conduct an optimal combustion temperature experiment to obtain the optimal combustion temperature of the heavy oil. If it does not have this activity, improve the activity of the heavy oil until it has the oxidative activity to cross the valley of death.

[0038] The injection well, which injects air and steam, is ignited, and the combustion temperature is controlled to the optimal combustion temperature. Oil is produced in the production wells around the injection well, thus achieving oil recovery.

[0039] This invention designs a gas-vapor fusion oil recovery method. The design concept is based on the intermediate-temperature oxidation mechanism, which considers the crude oil oxidation process to include intermediate-temperature oxidation. This intermediate-temperature oxidation is between low-temperature oxidation and high-temperature oxidation, and is the critical inflection point between the two. "Ignition delay" affects the occurrence time and range of high-temperature oxidation. Within the intermediate-temperature oxidation range, the reaction rate decreases as the temperature increases. If the duration of the intermediate-temperature oxidation range is too long, i.e. the "ignition delay" phenomenon is obvious, the oxidation process will fall into the "valley of death," resulting in the inability to occur high-temperature oxidation and the failure of fire flooding. This invention reasonably explains the problems of "pore blockage" and "ignition delay" that restrict gas-vapor fusion oil recovery. Based on this, an optimized oil recovery method is proposed. Before gas-gas fusion oil recovery, the first step is to screen for "good oil." This involves conducting reservoir crude oil oxidation kinetic experiments within a temperature range below 1000K to determine if the heavy oil possesses the oxidation activity to overcome the "valley of death." "Good oil" exhibits high oxidation activity and a short ignition delay time, allowing for controlled combustion temperature. By controlling the combustion temperature within the optimal range, stable advancement of the combustion front can be ensured, enabling the heavy oil to successfully transition from the intermediate-temperature oxidation zone to the high-temperature oxidation zone, thus overcoming the "valley of death" and avoiding phenomena such as "pore blockage" and "delayed ignition." Successful fire-driven oil recovery reduces fuel consumption. Furthermore, based on this, gas-steam fusion oil recovery is implemented, igniting injection wells that inject air and steam to induce chemical reactions in the crude oil. Using the bottom of the well ignited by air injection as the origin, high-temperature oxidation occurs primarily near the injection well, while low-temperature oxidation or no oxidation occurs near the production well. This places the entire reservoir within the controlled area in a low-temperature to medium-temperature oxidation process. The generated gas mixes with the injected fluid, carrying heat into the deeper reservoir. The heated, viscosity-reduced crude oil is displaced to the bottom of the production well and subsequently extracted, thereby increasing the economically recoverable reserves of heavy oil reservoirs at the margin of steam injection development.

[0040] Because the recovery rate of heavy oil reservoirs using steam huff and puff is low, with a large amount of oil remaining, taking a reservoir in Xinjiang Oilfield as an example, its burial depth is 250m, crude oil viscosity is 40000mPa·s, oil layer thickness is 10.5m, net total thickness ratio is 0.3-0.4, and permeability is 550mD. After 13 rounds of steam huff and puff development, inter-well interference and crossflow are severe, the cycle oil-steam ratio has dropped to 0.07, the water cut is 95%, and there is no longer any huff and puff benefit. The recovery rate is 17.1%, and a large amount of crude oil remains in the reservoir. Therefore, this invention provides a gas-steam fusion oil recovery method for heavy and extra-heavy oil, specifically including the following steps:

[0041] Step 1: Conduct oxidation kinetics experiments on reservoir crude oil. Based on the oxidation activity and ignition delay, determine whether the heavy oil has the oxidation activity to cross the "valley of death" and screen out the "easy-to-burn" heavy oil.

[0042] This invention is based on the intermediate-temperature oxidation characteristics of crude oil, assuming that the crude oil oxidation process includes intermediate-temperature oxidation, which lies between low-temperature and high-temperature oxidation, representing a critical inflection point between the two. "Ignition delay" affects the occurrence time and range of high-temperature oxidation. Within the intermediate-temperature oxidation range, the reaction rate decreases with increasing temperature. If the intermediate-temperature oxidation range lasts too long, i.e., the "ignition delay" phenomenon is significant, the oxidation process will fall into a "valley of death," preventing high-temperature oxidation and resulting in fire-driven failure. Figure 1 As shown.

[0043] Indoor studies have shown that under reasonable combustion conditions, the combustion chamber temperature of "easy-to-burn" heavy oil remains relatively reasonable and stable. Therefore, "easy-to-burn" heavy oil has the conditions to control its combustion temperature. In other words, by controlling the combustion front temperature of the heavy oil to be higher than the ignition temperature, and ensuring the stable advancement of the combustion front, it is possible to ensure that the heavy oil crosses the "valley of death" and enters high-temperature oxidation. This achieves both a wide range of high-temperature oxidation and sufficient mixed gas production between injection and production wells, while also avoiding severe pore blockage and ignition delay.

[0044] Step 2: If the ignition delay of heavy oil is less than 100ms in a temperature range below 1000K, then the heavy oil has the oxidation activity to cross the "valley of death". Conduct experimental research on the optimal combustion temperature to determine the optimal combustion temperature of "good burning" heavy oil (i.e. "good oil") under reservoir conditions. The optimal combustion temperature can ensure the stable advancement of the combustion front and is the optimal fuel consumption.

[0045] Appropriately increasing the temperature helps crude oil boil over and ensures combustion propulsion speed; however, excessively high temperatures result in fuel loss. Numerical simulations show that the combustion temperature of heavy oil is 250–400℃, with a generally accepted effective combustion temperature of 343℃. To ensure stable propulsion of the combustion front and optimal fuel consumption, the average peak combustion temperature is 538℃.

[0046] Because different heavy oils have different oxidation kinetics, viscosity, composition and other properties, their optimal combustion temperatures also differ.

[0047] Based on this, and taking into account the crude oil fluidity under reservoir conditions, and ensuring that the crude oil can be displaced by the mixed gas, gas-vapor fusion oil recovery is carried out. The combustion temperature is controlled to the optimal combustion temperature to achieve the best mode of economical and efficient combustion and make full use of the heat generated by combustion.

[0048] Step 3: Analyze the viscosity-temperature relationship curve of the reservoir crude oil. With the aim of meeting the minimum fluidity requirements under reservoir conditions, design group steam injection before and during the gas-vapor fusion oil production stage to preheat the average temperature between gas-vapor fusion oil production wells to the temperature corresponding to the second inflection point of the viscosity-temperature relationship curve.

[0049] Preferably, steam preheating is performed before gas-steam fusion oil production. Correspondingly, during fire flooding, the injection well is ignited by a combination of air and steam injection. Compared to no preheating, steam preheating not only consumes less fuel and produces more net oil, which helps to achieve full reservoir displacement, but also meets the requirement that the near-well saturation after steam preheating is higher than 25%, maintaining combustion and stable advancement of the combustion zone.

[0050] Preferably, during steam preheating, the development unit is divided into several well rows, and injection and production are carried out in alternating rows. This can create a production pressure difference between well rows, which promotes the overall migration of high-temperature fluid from the high-pressure area to the low-pressure area, providing a reservoir environment for subsequent development.

[0051] Preferably, during preheating and injection, the bottom hole steam dryness is not less than 50%, the steam injection simmering time is 2.5-3.5 days, and the production-injection ratio is 0.8-1.3, preferably 1.0, in order to provide a suitable injection-production strategy, so as to achieve inter-well displacement and produce the steam injection effect that cannot be achieved by elastic energy alone.

[0052] Step 4: Ignite the injection well that combines air and steam injection, i.e., ignite the injection well that injects air after steam preheating, and control the combustion temperature to the optimal combustion temperature, while the surrounding production wells produce.

[0053] Taking the bottom of the well, which is ignited by a combination of air and steam injection, as the origin, high-temperature oxidation mainly occurs near the injection well, while low-temperature oxidation or no oxidation occurs near the production well. The entire reservoir is placed in a low-temperature oxidation-medium-temperature oxidation process. The generated gas mixes with the injected fluid, carrying heat into the deep reservoir. The crude oil, which is heated and has reduced viscosity, is driven to the bottom of the production well and then extracted, thereby increasing the economically recoverable reserves of suitable reservoirs.

[0054] Step four also includes analyzing the heat retention rate of the burned zone, and based on the gas-vapor fusion oil recovery status of the reservoir, controlling the combustion front temperature to the optimal combustion temperature by adjusting the gas injection rate and / or intermittent air injection and / or rotating ignition wells, thereby promoting deep heat exchange and improving the utilization rate of heat generated by reservoir combustion.

[0055] Controlling the ventilation intensity and injection rate to maintain optimal combustion temperature in gas-vapor fusion oil recovery is crucial. Alternatively, analyzing the heat retention rate of the burned zone and adjusting the combustion temperature through intermittent air injection or rotating ignition wells based on the reservoir's gas-vapor fusion oil recovery utilization is a more practical and effective approach. Maintaining the combustion temperature within the optimal range through intermittent air injection and / or rotating ignition wells promotes deep heat exchange and improves the utilization rate of reservoir combustion heat. During intermittent air injection, the area to be ignited is preheated. During well rotation, air injection is stopped, and steam preheating is performed on the well to be ignited. Therefore, well rotation includes intermittent air injection, and also includes steam and air injection during well switching.

[0056] Among them, it is preferable to adopt the alternate ignition well gas-steam integrated oil production, which is easy to operate ignition, can realize intermittent air injection, and compared with fire flooding, the mixed gas and heat utilization of the alternate ignition well gas-steam integrated oil production are sufficient, there will be no serious pore plugging and ignition delay, and the net oil production is basically the same. When rotating the ignition wells, in order to form a uniform displacement front during the gas-steam integrated oil production stage, comparing well selection along the deposition direction and perpendicular to the deposition direction and random well selection, the development effect of rotating wells along the deposition direction is good; comparing the selection of ignition wells parallel and perpendicular to the contour line, the development effect of rotating wells parallel to the contour line is good. The rotation timing is designed in the order of air injection ignition - production of surrounding wells - rapid increase of well temperature and pressure - shut-in well - soaking of injection wells - opening the well for production until the single well limit production. Changing wells when the temperature and pressure of surrounding oil wells rise rapidly, compared with changing wells at a fixed rotation time, the method of the present invention fully considers the influence of reservoir and displacement heterogeneity on the effectiveness of each well, and ensures the balanced effectiveness of gas-steam integrated oil production in the whole well area. After rotating the ignition wells several times, it is preferable to inject gas and ignite several oil wells that are in the high position of the structure and have basically the same physical properties, and then displace them in a linear well pattern until the oil wells are shut in, with good development effect and high economic benefits (the specific number of rotation times and the number of oil wells selected for gas injection ignition are determined according to the actual working conditions).

[0057] Preferably, a "return" - shaped well pattern or a "square" - shaped well pattern is adopted to efficiently utilize the mixed gas generated by the oxidation reaction of crude oil and achieve a high efficient movable oil capture rate.

[0058] Example

[0059] Example 1

[0060] This example is a heavy oil reservoir in Xinjiang. The burial depth of the reservoir is 250m. The reservoir thickness is 13.7m. The viscosity of the degassed oil under reservoir conditions is 8500mPa·s, and the reservoir permeability is 385mD. There are 20 wells in this well area (as Figure 2 shown) put into production in 2006. By September 2019, the recovery factor is 30.2%, the oil-steam ratio is 0.147, the injection-production ratio is 1.15, and the water cut is 87.2%.

[0061] Since the reservoir is a typical medium porosity and medium permeability sandy conglomerate reservoir, with medium to strong water sensitivity and velocity sensitivity. According to calculations, this reservoir is not suitable for continued steam stimulation or conversion to steam flooding development, nor does it have the reservoir conditions for carrying out SAGD.

[0062] Carry out reservoir oxidation kinetics experiments. The experiments and reservoir engineering research show that the heavy oil in a certain oil reservoir in Xinjiang has ignition delay. In the temperature range of 743 - 868KK, the ignition delay is less than 100ms, with good oxidation activity and short ignition delay time, having the oxidation activity to cross the "valley of death". The heavy oil in Example 1 has the conditions to control the combustion temperature and is suitable for carrying out gas-steam integrated oil production;

[0063] Experimental studies on optimal combustion temperature (Table 1) show that the optimal combustion temperature of the heavy oil in Example 1 should be controlled between 450-500℃ and not higher than 550℃.

[0064] Table 1. Optimal combustion temperature data for heavy oil in Example 1

[0065]

[0066] Table 2 shows the predicted effects of gas-vapor fusion oil recovery and the results of the optimization of start-up and displacement methods in Example 1. In Example 1, the crude oil viscosity in the reservoir was high, resulting in high fuel consumption and low net oil production without preheating. Only the narrow streamline region between injection and production wells could be utilized, making it difficult to achieve full reservoir displacement. Combustion tube experiments confirmed that an oil saturation of 25% could maintain combustion and stable combustion zone advancement. After steam preheating, the near-well saturation was higher than 25%, meeting the requirements. After thermochemical preheating, the near-well saturation was lower, failing to meet the subsequent requirements for gas-vapor fusion oil recovery.

[0067] High-temperature fire-driven oil recovery yields a higher oil production, but the air-to-oil ratio is high and the output temperature is high. Continuous gas-vapor fusion oil recovery yields a lower oil production, a lower air-to-oil ratio, and higher mixed gas and heat utilization, but oxygen production may exceed 5%. Intermittent gas-vapor fusion oil recovery solves safety risks and increases oil production, but continuous ignition at the same well point is difficult. Gas-vapor fusion oil recovery with alternating ignition wells yields less oil than fire-driven oil recovery, but the net oil production is basically the same, making it technically feasible.

[0068] Table 2. Example 1: Prediction of Gas-Vacuum Fusion Oil Recovery Effect and Optimization of Start-up and Displacement Methods

[0069]

[0070] Example 1: It is difficult to form a regular area well network in the well area. Further densification of the well network increases oil production, but the input-output ratio is high; fully utilizing existing wells... The well pattern can fully capture movable oil in the area affected by the mixed gas, and the gas-vapor fusion oil recovery effect is good (Table 3).

[0071] Table 3 Example 1: Optimization of Well Spacing in Gas-Vapor Fusion Oil Production Network

[0072]

[0073] In Example 1, the main oil layers in the well area lack interlayers, and the mixed gas in gas-vapor fusion oil production has strong overburden. To achieve a high vertical sweep volume in the oil layers, special design is required. Selectively perforating the lower oil layers and sealing the original perforated sections will force the mixed gas into the less mobile area, lengthen the displacement flow lines, and reduce crossflow (Tables 4 and 5).

[0074] Table 4 Optimization of Perforation Methods for Gas-Vacuum Fusion Oil Production Wells

[0075] Ignition well perforation method Oil-to-gas ratio (f) Air-to-fuel ratio (f) Recovery rate (%) Shoot open the upper half 0.467 662 20.6 Shoot the lower 1 / 3 0.612 505 27.1 Shoot the lower 1 / 2 0.576 535 25.6 Full Shot 0.497 623 21.9

[0076] Table 5 Optimization of Perforation Methods in Gas-Vapor Fusion Oil Production Wells

[0077] Oil well perforation methods Oil-to-gas ratio (f) Air-to-fuel ratio (f) Recovery rate (%) Shoot open the upper half 0.483 638 21.4 Shoot the lower 1 / 3 0.560 551 24.8 Shoot the lower 1 / 2 0.612 505 27.1 Full Shot 0.552 560 24.3

[0078] Steam preheating design includes research on preheating huff and puff methods and preheating injection-production strategies. There are two main preheating methods: simultaneous injection and production, and alternating injection and production. Simultaneous injection and production involves designing the steam volume for each well based on the reservoir conditions and utilization status within the development unit. Multiple boilers are used for simultaneous steam injection, with wells requiring higher steam volumes injected first and having longer simmering times, while those requiring lower steam volumes are injected later and have shorter simmering times, before simultaneous production commencement. This reduces steam channeling, concentrates heat supply, increases temperature rise and heating range, and reduces dead oil zones. Alternating injection and production divides the development unit into several well rows, with simultaneous injection and production across alternating well rows. This creates a production pressure differential between well rows, promoting the overall migration of high-temperature fluids from high-pressure to low-pressure areas, providing a suitable reservoir environment for subsequent development. Table 5 shows the optimization results of the steam preheating methods. Comparatively, alternating injection and production steam preheating huff and puff methods show better development performance.

[0079] Table 6 Optimization of Preheated Steam Huff and Puff Method in Example 1 of Gas-Vapor Fusion Oil Recovery

[0080]

[0081]

[0082] The timing for ending preheating huff and puff depends on the reservoir preheating status. In Example 1, the well area had already averaged 15 huff and puff cycles. Two more rounds of combined huff and puff were conducted, resulting in a near-wellbore temperature of 87°C, crude oil viscosity of 75 mPa·s, and significantly improved rheological properties. The reservoir temperature was 61°C, and the crude oil viscosity was 531 mPa·s, meeting the conditions for gas-vapor fusion recovery. One more round of huff and puff did not significantly increase production (Table 7). It is recommended to switch to gas-vapor fusion recovery after two rounds of combined steam huff and puff.

[0083] Table 7 Example 1 Preheating Huff and Puff End Timing Optimization

[0084] Comparison Plan Oil-to-gas ratio (f) Air-to-fuel ratio (f) Recovery rate (%) <![CDATA[Net oil production (10 4 t)]]> 1 round of combined throughput 0.603 455 23.3 5.61 2-round combined throughput 0.612 505 27.1 6.43 3-round combined throughput 0.611 476 28.3 6.76

[0085] In the preheating steam injection stage, fewer cyclic steam injections result in shorter injection cycles and more cycles; more cyclic steam injections result in longer cycles and fewer cycles. With a suitable injection-production strategy, it is possible to achieve inter-well displacement, producing steam injection effects that cannot be achieved by elastic energy alone; however, excessive steam injection intensity will increase heat loss and reduce heat utilization. The optimal cyclic steam injection is 1560t. As steam dryness increases, the gas-steam fusion oil recovery development effect significantly improves. Based on existing process technology conditions, as long as the steam injection system is well designed, the bottom-hole steam dryness can reach over 50%. Therefore, it is recommended that the bottom-hole steam dryness in the gas-steam fusion oil recovery stage not be less than 50%. After steam injection, the well should be kept warm for a period of time to allow the heat of the injected steam to be fully transferred to the oil layer; however, the warming time should not be too long, otherwise excessive heat loss may lead to difficulties in recovery. In the example well area, the steam injection warming time in the preheating stage of gas-steam fusion oil recovery should be kept at around 3 days. The production-injection ratio determines how much heat is retained in the reservoir. For steam injection aimed at preheating the oil reservoir, the production-injection ratio should not be too high. The optimal production-injection ratio for steam injection before gas-steam fusion oil production is 1.0.

[0086] Rotating ignition wells for temperature control is a feasible way to maintain optimal fuel consumption and fully utilize the oxidative heat in the reservoir. The selection of rotation wells affects the uniformity of the displacement front and the direction of effectiveness. Studies have shown that selecting rotation wells along the depositional direction, so that the gas-vapor fusion production front extends along the depositional direction, yields the best development results (Table 8).

[0087] Table 8 Example 1: Optimal Selection of Gas-Vapor Fusion Oil Production Rotation Wells

[0088] Comparison Plan Oil-to-gas ratio (f) Air-to-fuel ratio (f) Recovery rate (%) <![CDATA[Net oil production (10 4 t)]]> Well selection along sedimentary direction 0.612 505 27.1 6.43 Well selection along the vertical sedimentation direction 0.562 550 24.9 5.77 Disordered well selection 0.486 634 21.6 4.78

[0089] Designing the rotation timing is crucial for achieving sufficient thermochemical displacement. Compared to a fixed rotation time, a sequence of air injection ignition – surrounding well production – rapid rise in oil well temperature and pressure followed by shut-in – gas injection well shutdown – well reopening and production up to the single well's maximum production is adopted. This fully considers the impact of reservoir and displacement heterogeneity on the effectiveness of each well, ensuring balanced gas-vapor fusion oil production across the entire well area (Table 9). The optimal rotation timing is affected by the advance rate of the high-temperature oxidation front in the target area; in Example 1, the rotation time for the well area is approximately 550 days.

[0090] Table 9 Example 1: Design of Gas-Vacuum Fusion Oil Recovery Rotation Timing

[0091] Comparison Plan Oil-to-gas ratio (f) Air-to-fuel ratio (f) Recovery rate (%) <![CDATA[Net oil production (10 4 t)]]> One round of 200 days 0.262 709 11.7 2.48 One round of 300 days 0.388 668 17.2 3.89 One round of 400 days 0.536 595 23.8 5.56 A round of 500 days 0.599 519 26.6 6.27 One round of 600 days 0.615 512 27.3 6.41 One round is when all oil wells are shut down once. 0.612 505 27.1 6.43

[0092] The rotation number design is another key parameter for achieving sufficient thermochemical displacement based on rotating ignition wells. According to the well area size, structural conditions, and development status in Example 1, rotating two ignition wells resulted in better development performance (Table 10).

[0093] Table 10 Example 1: Design of Gas-Vacuum Fusion Oil Recovery Rotation Frequency

[0094] Comparison Plan Oil-to-gas ratio (f) Air-to-fuel ratio (f) Recovery rate (%) No well replacement 0.241 457 10.7 Replace the ignition well 0.437 484 19.4 Replace two ignition wells 0.612 505 27.1 Replace three ignition wells 0.687 901 30.5 Replace four ignition wells 0.714 1029 31.7

[0095] In Example 1, after two well replacements in the well area, three wells with similar structural high locations and physical properties were selected for gas injection and ignition. The wells were then replaced using a linear well-drainage model until the wells were shut in, resulting in good development performance (Table 10).

[0096] Table 11 Example 1: Gas-vapor fusion oil recovery and displacement model design

[0097]

[0098] The design of the gas injection volume must be matched with the reservoir, pore volume, and crude oil flowability of the injection well to achieve better mixed gas sweep volume and scavenging ratio; at the same time, it must be matched with the oxygen consumption of the reservoir oxidation reaction to ensure that oxygen is consumed in the reservoir and to prevent the produced oxygen concentration from exceeding the standard. In Example 1, the optimal gas injection volume for gas-vapor fusion oil production in the well area, plus the gas produced by the oxidation reaction, is approximately 5.3 PV pore volume.

[0099] The gas injection rate design after successful ignition reflects the on-demand gas injection approach in gas-vapor fusion oil recovery. Optimization shows that when the gas injection rate is as suitable as possible for the oxidation reaction requirements of the reservoir crude oil, the oxidation reaction is sufficient, the temperature rises rapidly, the development effect is good, and the produced oxygen content is low.

[0100] Air injection and well shut-in are crucial steps to ensure sufficient oxygen oxidation for heat generation and to reduce oxygen production. However, excessive shut-in time increases heat loss between the top and bottom layers, hindering efficient heat utilization. In Example 1, during well rotation in gas-gas fusion oil production, the optimal shut-in time after air injection and ignition is 5-7 days. During implementation, close monitoring of wellhead pressure changes and produced gas oxygen content is essential, with timely adjustments to the shut-in time.

[0101] According to calculations, the gas-vapor fusion oil recovery in the well area of ​​Example 1 lasted 2408 days, with an air-to-oil ratio of 505, an oil-to-vapor ratio of 0.612, a stage recovery rate of 27.1%, and a final recovery rate of 57.3%.

[0102] Example 2

[0103] This example describes a heavy oil reservoir in Xinjiang, with a burial depth of 250m. The oil layer thickness is 10.5m, and under reservoir conditions, the degassed oil viscosity is 32900 mPa·s, the reservoir permeability is 415 mD, and the formation dip angle is 5-7°. There are a total of 40 wells in this well area (e.g., ...). Figure 3 As shown in the figure, since 2006, steam injection has been developed with an average of 13 injection cycles, a recovery rate of 33.8%, an oil-to-steam ratio of 0.228, and a production-to-injection ratio of 2.03.

[0104] Since the reservoir is a typical medium-porosity, medium-permeability sandstone-conglomerate reservoir with moderate to strong water and rate sensitivity, calculations show that the reservoir is not suitable for continued steam huff and puff or for development by steam drive, nor does it have the reservoir conditions for SAGD.

[0105] Reservoir oxidation kinetics experiments and reservoir engineering studies have shown that the heavy oil in a certain reservoir in Xinjiang has an ignition delay of less than 100ms in the temperature range below 1000K. It has good oxidation activity and short ignition delay time, and has the oxidation activity to cross the "valley of death". That is, it has the conditions to control the combustion temperature and is suitable for gas-vapor fusion oil recovery.

[0106] Experimental studies on optimal combustion temperature (Table 12) show that, similar to Example 1, the optimal combustion temperature of the heavy oil in Example 2 should be controlled at 500-550℃ and not higher than 600℃.

[0107] Table 12 Optimal Combustion Temperature Test Data for Heavy Oil in Example 2

[0108]

[0109]

[0110] Table 13 shows the predicted effects of gas-vapor fusion oil recovery and the results of the optimization study on start-up and displacement methods in Example 2. In Example 2, the crude oil viscosity in the well area was high, resulting in high fuel consumption without preheating and a small range of narrow flow lines for injection and production; after thermochemical preheating, the near-wellbore saturation was low, failing to meet the requirements of gas-vapor fusion oil recovery.

[0111] Gas-vapor fusion oil recovery produces less oil than fire-driven recovery, but has a higher net oil production. Rotating ignition wells reduces safety risks and solves the problem of difficulty in continuous ignition of the same well, making it technically feasible.

[0112] Table 13 Prediction of Gas-Vacuum Fusion Oil Recovery Effect and Optimization of Start-up and Displacement Methods in Example 2

[0113]

[0114] Example 2: The well area currently has 40 wells. Improving 8 wells to form a 70×100m reverse nine-spot well network can meet the requirements for gas-vapor fusion oil production. Infiltrating to a 50×70m reverse nine-spot well network increases oil production, but the net oil production remains the same, resulting in a higher input-output ratio. To fully capture movable oil within the area affected by the mixed gas, it is recommended to fully utilize existing wells in the surrounding area during implementation. Well pattern (Table 14).

[0115] Table 14 Example 2: Optimization of Well Spacing in Gas-Vapor Fusion Oil Production Network

[0116]

[0117] Similar to the well area in Example 1, the main oil layers in Example 2 lack interlayers. Selectively perforating the lower oil layers and sealing the original perforated sections will force the mixed gas into the poorly utilized area, lengthen the displacement flow line, and reduce crossflow (Tables 15 and 16).

[0118] Table 15 Example 2: Optimization of Perforation Method for Gas-Vacuum Fusion Oil Production Ignition Wells

[0119]

[0120]

[0121] Table 16 Example 2: Optimization of Perforation Methods in Gas-Vapor Fusion Oil Production Wells

[0122] Oil well perforation methods Oil-to-gas ratio (f) Air-to-fuel ratio (f) Recovery rate (%) Shoot open the upper half 0.370 1792 15.5 Shoot the lower 1 / 3 0.429 1546 17.9 Shoot the lower 1 / 2 0.469 1415 19.6 Full Shot 0.421 1578 17.6

[0123] Similar to Example 1, the suitable steam preheating huff and puff method for Example 2 is separate injection and intermittent oil production (Table 17).

[0124] Table 17 Optimization of Preheated Steam Huff and Puff Method in Example 2 of Gas-Steam Fusion Oil Recovery

[0125] Comparison items Oil-to-gas ratio (f) Air-to-fuel ratio (f) Recovery rate (%) disorder 0.353 1877 14.8 Same bet, same bet 0.461 1440 19.2 Alternate rows, same injection, same collection 0.469 1415 19.6

[0126] In Example 2, the well area has undergone an average of 13 cycles of huff and puff, and three more rounds of combined huff and puff are planned. The near-well temperature is 79°C, and the crude oil viscosity is 500 mPa·s, which preliminarily meets the conditions for gas-steam fusion oil recovery (Table 18). Optimization shows that the optimal cycle steam injection rate for preheated huff and puff is 97 t / m·ha, the bottom hole steam dryness should not be less than 50%, the well shut-in time is 3 days, and the production-injection ratio is 1.0.

[0127] Table 18 Example 2 Preheating Huff and Puff End Timing Optimization

[0128] Comparison Plan Oil-to-gas ratio (f) Air-to-fuel ratio (f) Recovery rate (%) <![CDATA[Net oil production (10 4 t)]]> 1 round of combined throughput 0.462 1275 16.9 7.60 3-round combined throughput 0.469 1415 19.6 7.44 5-wheel combined throughput 0.468 1399 20.5 6.94

[0129] In Example 2, the formation dip angle of the well area was relatively large and the physical properties were basically the same. Comparing the effects of selecting ignition wells parallel to and perpendicular to the contour lines, the rotation wells parallel to the contour lines can form a uniform displacement front in the gas-vapor fusion oil production stage, resulting in good development effect (Table 19).

[0130] Table 19 Example 2: Optimal Selection of Gas-Vapor Fusion Oil Production Rotation Wells

[0131] Comparison Plan Oil-to-gas ratio (f) Air-to-fuel ratio (f) Recovery rate (%) <![CDATA[Net oil production (10 4 t)]]> Well selection using parallel contour lines 0.469 1415 19.6 7.44 Well selection using vertical contour lines 0.431 1539 18.0 6.33 Disordered well selection 0.374 1775 15.6 4.65

[0132] Based on the scale and structure of the well area in Example 2, three central wells in the high part of the structure were selected as ignition wells. First, the middle well of the three central wells was ignited. After a rapid rise in temperature and pressure was observed around the well (the rotation time was 470 days, Table 20), the other two central wells were ignited (Table 21). The linear well bank was used to drive the displacement until all the wells in the first line were shut off. Then, the three central wells of the three well groups located in the downdip direction of the structure were ignited. Finally, the central wells of the three well groups located in the lower part of the structure were ignited (Table 22).

[0133] Table 20 Example 2: Design of Gas-Vacuum Fusion Oil Recovery Rotation Timing

[0134] Comparison Plan Oil-to-gas ratio (f) Air-to-fuel ratio (f) Recovery rate (%) <![CDATA[Net oil production (10 4 t)]]> One round of 100 days 0.203 1987 8.5 1.53 One round of 200 days 0.298 1872 12.4 3.19 One round of 300 days 0.412 1667 17.2 5.60 One round of 400 days 0.461 1454 19.2 7.15 A round of 500 days 0.473 1435 19.7 7.45 A complete cycle is defined as the shutdown of all oil wells. 0.469 1415 19.6 7.44

[0135] Table 21 Example 2: Design of Gas-Vapor Fusion Oil Recovery Rotation Frequency

[0136] Comparison Plan Oil-to-gas ratio (f) Air-to-fuel ratio (f) Recovery rate (%) <![CDATA[Net oil production (10 4 t)]]> No well replacement 0.185 1281 7.7 2.23 Replace with a fire well 0.336 1356 14.0 5.06 Replace two ignition wells 0.469 1415 19.6 7.44 Replace three ignition wells 0.528 1954 22.0 6.47 Replace four ignition wells 0.549 2083 22.9 6.26

[0137] Table 22 Example 2 Gas-vapor fusion oil recovery and displacement model design

[0138]

[0139] Example 2: The optimal gas injection rate for gas-vapor fusion oil production in the well area is 19519×104Sm3, and the optimal gas injection rate is 5000-10000-15000-20000 on-demand gas injection mode.

[0140] According to calculations, the gas-vapor fusion oil recovery in the well area of ​​Example 2 lasted 4292 days, with an air-to-oil ratio of 505, an oil-to-vapor ratio of 0.612, a stage recovery rate of 27.1%, and a final recovery rate of 57.3%.

[0141] Case 1 On-site Implementation Results

[0142] Since 2018, Example 1 has conducted two rounds of field tests on limited gas-steam fusion oil production (limited gas-steam fusion oil production refers to igniting and injecting gas to the design volume, then shutting the well for 5-7 days, and then producing to the single well's maximum production, without conducting gas-steam fusion oil production on linear wells), and achieved good results (Table 23).

[0143] Table 23 Comparison of injection and production indicators before and after the field test of limited gas-steam fusion oil production in the well area of ​​Example 1 since 2018

[0144]

[0145]

[0146] Analysis of the produced gas composition in the field test (Table 24) shows that the CO2 content in the gas produced by gas-vapor fusion recovery is lower than that in the previous fire-driven gas (Table 25). This indicates that the oxidation mechanism of gas-vapor fusion recovery is significantly different from that of previous fire-driven gas, and indirectly verifies that there is a three-stage crude oil oxidation process of low temperature oxidation, medium temperature oxidation and high temperature oxidation in the field production.

[0147] Table 24 Analysis of gas composition produced in the field test of limited gas-steam fusion oil recovery in Example 1 (2018)

[0148]

[0149] Table 25 Analysis of Gas Produced from the Hongqian 1 Fire-Driven Oilfield in Xinjiang Oilfield

[0150]

[0151] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Those skilled in the art can readily implement the present invention based on the accompanying drawings and the above description. However, any modifications, alterations, or variations made by those skilled in the art without departing from the scope of the present invention, utilizing the disclosed technical content, are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, or variations made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the present invention.

Claims

1. A gas-steam hybrid oil recovery method, characterized by, Includes the following steps: Based on the oxidation kinetics experiment of crude oil in the reservoir, the oxidation activity and ignition delay of heavy oil were obtained; Based on the oxidation activity and ignition delay of heavy oil, it is determined whether the heavy oil has the oxidation activity to cross the "valley of death". Specifically, if the ignition delay of heavy oil is less than 100ms in a temperature range below 1000K, then the heavy oil has the oxidation activity to cross the "valley of death". The "valley of death" is the stage in which the heavy oil cannot achieve high-temperature oxidation due to the ignition delay phenomenon. If the heavy oil has the oxidative activity to cross the valley of death, conduct an optimal combustion temperature experiment to obtain the optimal combustion temperature of the heavy oil. If it does not have this activity, improve the activity of the heavy oil until it has the oxidative activity to cross the valley of death. Steam is injected into the injection well for preheating and puffing until the average temperature between wells reaches the temperature corresponding to the second inflection point of the crude oil viscosity-temperature relationship curve, and the preheating treatment is completed; the injection well for injecting air and steam is ignited and the combustion temperature is controlled to the optimal combustion temperature, and the production wells around the injection well produce oil, thus realizing oil production; The method for controlling the combustion temperature to the optimal combustion temperature includes analyzing the heat retention rate of the burned zone, with the following steps: Based on the gas-vapor fusion oil production situation of the reservoir, control the gas injection rate of the injection well and / or intermittently inject air and / or rotate the ignition wells until the combustion temperature is the optimal combustion temperature.

2. The gas-hydrate production method according to claim 1, wherein Before the injection wells for igniting air and steam, the oil production and development area is divided into several well rows, with each well row producing and injecting air and steam simultaneously.

3. The gas-hydrate production method of claim 1, wherein During the preheating and injection operation, the steam dryness at the bottom of the injection well shall not be less than 50%.

4. The gas-vapor fusion oil recovery method according to claim 1, characterized in that, During the preheating and injection operation, the steam simmering time of the injection well is 2.5 to 3.5 days, and the production-injection ratio of the injection well is 0.8 to 1.

3.

5. The gas-hydrate production method of claim 1, wherein When rotating ignition wells, the ignition wells to be rotated are selected along the deposition direction and / or parallel to the contour lines.

6. The gas-hydrate production method of claim 1, wherein The timing for rotating ignition wells is as follows: following the sequence of air injection ignition, surrounding well production, rapid rise in oil well temperature and pressure, well shut-in, gas injection well shut-down, well opening and production up to the single well's maximum production, the timing for rotating ignition wells is when the temperature and pressure of oil wells around the ignition well rise rapidly.

7. The gas-hydrate production method of claim 1, wherein After several rotations, the rotating ignition wells will be ignited with gas at several wells located in the same structural high position and with the same physical properties. Then, the wells will be replaced in a linear well-deck pattern until they are shut in.

8. The gas-hydrate production method of claim 1, wherein The injection and production well network adopts a U-shaped well network.

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