Tight oil multi-well flooding elastic exploitation method

Abstract

The embodiment of the invention provides a tight oil multi-well flooding elastic mining method. The tight oil multi-well flooding elastic mining method comprises the steps that the maximum recovery ratio of a reservoir stratum is determined through a nuclear magnetic resonance experiment; a well pattern composed of at least one injection well and at least two production wells is arranged; a first working medium is injected into the reservoir through the injection well, and the bottom hole pressure of the production well after the first working medium is injected is obtained and serves as the original pressure of the reservoir; and the production well is subjected to depressurization production, when the reservoir pressure is reduced to the preset critical pressure, the production well is closed, the accumulative recovery rate of the current production round is obtained, a second working medium is injected into the reservoir through the injection well, so that the reservoir pressure is recovered to the energy injection pressure, and the recovery rate is increased. The recovery ratio difference value between the accumulated recovery ratio and the maximum recovery ratio is smaller than a preset recovery ratio threshold value; wherein the energy injection pressure is greater than the original pressure. According to the method provided by the embodiment of the invention, the mining cost and risk are reduced, and the mining scheme adaptability is enhanced.

Description

Technical Field

[0001] This invention relates to the field of petroleum extraction technology, and in particular to a multi-well permeation elastic extraction method for tight oil. Background Technology

[0002] Tight oil reservoirs refer to unconventional petroleum resources with a reservoir porosity of ≤10% and a permeability of ≤0.1mD.

[0003] Currently, tight oil development mainly relies on hydraulic fracturing to form an artificial fracture network. However, due to reservoir heterogeneity and rapid fracture closure, conventional water-drive or gas-drive development suffers from low recovery rates (usually <15%), rapid water cut increases, and high development costs.

[0004] Therefore, there is an urgent need for an efficient development method to improve tight oil recovery. Summary of the Invention

[0005] This invention provides a multi-well permeation elastic extraction method for tight oil to achieve efficient extraction of tight oil.

[0006] This invention provides a method for flexible multi-well drainage and seepage control of tight oil, comprising:

[0007] The maximum recovery rate of the reservoir was determined by nuclear magnetic resonance experiments.

[0008] A well network consisting of at least one injection well and at least two production wells shall be established;

[0009] The first working medium is injected into the reservoir through the injection well, and the bottom hole pressure of the production well after the injection of the first working medium is obtained as the original pressure of the reservoir.

[0010] The production well is depressurized and when the reservoir pressure drops to the preset critical pressure, the production well is closed and the cumulative recovery rate of the current production cycle is obtained. A second working medium is injected into the reservoir through the injection well to restore the reservoir pressure to the injection pressure until the recovery rate difference between the cumulative recovery rate and the maximum recovery rate is less than the preset recovery rate threshold; wherein, the injection pressure is greater than the original pressure.

[0011] Optionally, the maximum recovery rate of the reservoir can be determined by nuclear magnetic resonance experiments, including:

[0012] The reservoir rock samples were subjected to one round of elastic development simulation and at least one round of energy replenishment and seepage displacement simulation in sequence.

[0013] Obtain the nuclear magnetic resonance T2 spectrum after each round of simulation;

[0014] Based on the T2 spectrum data from the elastic development simulation and the energy replenishment and permeation simulation, the recovery rate after each round of simulation was calculated.

[0015] The maximum value among the recovery rates in each round is determined as the reservoir's maximum recovery rate.

[0016] Optionally, the reservoir rock samples are subjected to one round of elastic development simulation and at least one round of energy replenishment and seepage displacement simulation, including:

[0017] The rock samples were vacuum-treated and saturated with kerosene. After drying, they were pressurized and saturated with simulated formation water. Then, simulated oil was used for displacement to establish a state of oil-bound water.

[0018] The processed rock sample was placed in an online nuclear magnetic resonance analyzer. The experimental system pressure was adjusted to the original pressure. The inlet pressure was kept constant, and the outlet pressure was gradually reduced for elastic development. The pressure reduction was stopped when the outlet pressure dropped to the preset critical pressure, until no fluid was produced at the outlet.

[0019] After elastic development, the rock sample was placed in an online nuclear magnetic resonance analyzer. The experimental system pressure was adjusted to the energy injection pressure. The inlet pressure was kept constant, and the outlet pressure was gradually reduced to carry out energy replenishment and seepage removal. The pressure reduction was stopped when the outlet pressure dropped to the preset critical pressure, until no fluid was produced at the outlet.

[0020] Optionally, based on the T2 spectral data from the elastic development simulation and the supplementary energy diversion simulation, the recovery rate after each round of simulation is calculated, including:

[0021] Obtain the original oil saturation S0 of the rock sample;

[0022] Based on the T2 spectrum data after each round of simulation, the oil saturation S after that round of simulation is calculated. n ;

[0023] According to formula W n =(S0-S n ) / S0×100%, calculate the recovery rate W after each round of simulation. n .

[0024] Optionally, the original oil saturation S0 is obtained, including:

[0025] Obtain the first nuclear magnetic resonance T2 spectrum of the rock sample after vacuuming and saturating it with kerosene;

[0026] Obtain the second nuclear magnetic resonance T2 spectrum of the rock sample in the state of saturated oil-bound water;

[0027] The original oil saturation S0 was calculated based on the first and second nuclear magnetic resonance T2 spectra.

[0028] Optionally, the original oil saturation S is calculated based on the first and second NMR T2 spectra. o ,include:

[0029] Obtain the first total signal amplitude A1 of the first nuclear magnetic resonance T2 spectrum;

[0030] Obtain the second total signal amplitude A2 of the second nuclear magnetic resonance T2 spectrum;

[0031] The original oil saturation S0 is calculated using the formula S0 = (A2 / A1) × 100%.

[0032] Optionally, obtain the nuclear magnetic resonance T2 spectrum after each round of simulation, including:

[0033] Based on the T2 spectrum data after each round of simulation, the oil saturation S after that round of simulation is calculated. n Previously, it also included:

[0034] After each round of simulation, obtain the T2 NMR spectrum of the first preset spectral segment and the T2 NMR spectrum of the second preset spectral segment. The first preset spectral segment and the second preset spectral segment do not overlap.

[0035] Calculate the oil saturation S after each round of simulation. n ,include:

[0036] The first oil saturation S was obtained based on the nuclear magnetic resonance T2 spectrum of the first preset spectral band. n ';

[0037] The second oil saturation S was obtained based on the nuclear magnetic resonance T2 spectrum of the second preset spectral band. n ”;

[0038] According to formula S n =k1*S n '+k2*S n Calculate the oil saturation S n Among them, k1 and k2 are determined according to the number of simulation rounds.

[0039] Optionally, depressurization extraction can be performed on the production well, including:

[0040] During the depressurization mining process, the pressure difference between the bottom hole pressures of the production well and the injection well is obtained in real time;

[0041] The pressure difference is controlled within the preset pressure range.

[0042] Optionally, the pressure difference is controlled to be within a preset pressure range, including:

[0043] When the pressure difference is less than the lower limit of the preset pressure range, reduce the opening of the surface throttle valve of the production well;

[0044] When the pressure difference exceeds the upper limit of the preset pressure range, increase the opening of the surface throttle valve of the production well.

[0045] Optionally, a second working medium is injected into the reservoir through an injection well to restore the reservoir pressure to the injection pressure, including:

[0046] Determine the first distance between the injection well and the production well;

[0047] The second working medium is injected into the reservoir through the injection well. During the injection process, the formation pressure at a preset position in the production well is monitored in real time. The injection of the second working medium into the reservoir is stopped when the formation pressure at the preset position is greater than or equal to the energy injection pressure. The preset position is positively correlated with the first spacing.

[0048] This invention provides a multi-well flexible exploitation method for tight oil, comprising: determining the maximum recovery rate of the reservoir through nuclear magnetic resonance experiments to calibrate the upper limit of the crude oil extraction potential of the tight reservoir, avoiding over-exploitation leading to increased costs or under-exploitation leading to wasted resources; deploying a well network consisting of at least one injection well and at least two production wells to form a reservoir exploitation range with multi-directional pressure gradients, solving the problems of limited pressure transmission range and low crude oil accumulation efficiency in conventional single-well or dual-well exploitation; injecting a first working medium into the reservoir through the injection wells and obtaining the bottom hole pressure of the production wells after the injection of the first working medium as the original pressure of the reservoir, thereby expanding the rock fractures in the tight oil field and driving out the crude oil from the rock fractures. The production well undergoes depressurization extraction. When the reservoir pressure drops to a preset critical pressure, the production well is shut down, and the cumulative recovery rate of the current extraction cycle is obtained. A second working medium is then injected into the reservoir through an injection well to restore the reservoir pressure to the injection pressure. This process continues until the difference between the cumulative recovery rate and the maximum recovery rate is less than a preset recovery rate threshold. This difference is used as the criterion to ensure that the oilfield's extraction level approaches the maximum recovery rate. The method provided in this invention reduces extraction costs and risks, and enhances the adaptability of extraction schemes. Attached Figure Description

[0049] Figure 1 A flowchart of a multi-well seepage displacement elastic extraction method for tight oil provided in an embodiment of the present invention;

[0050] Figure 2 A schematic diagram of the pressure transmission direction of a well network under elastic development state is provided as an embodiment of the present invention;

[0051] Figure 3 This is a schematic diagram of the pressure transmission direction of a well network under recharge conditions, provided as an embodiment of the present invention.

[0052] Figure 4 A schematic diagram of the pressure transmission direction of a well network in a seepage-draining elastic state, provided as an embodiment of the present invention;

[0053] Figure 5A flowchart of another method for elastic extraction of tight oil through multiple wells provided in an embodiment of the present invention;

[0054] Figure 6 A flowchart of another method for elastic extraction of tight oil through multiple wells provided in this embodiment of the invention;

[0055] Figure 7 A flowchart of another method for elastic extraction of tight oil through multiple wells provided in this embodiment of the invention;

[0056] Figure 8 This is a schematic diagram illustrating the relationship between NMR-T2 spectral amplitude and relaxation time, provided as an embodiment of the present invention. Detailed Implementation

[0057] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0058] This invention provides a method for elastic extraction of tight oil through multi-well permeation. Figure 1 This is a flowchart illustrating a multi-well flexible exploitation method for tight oil production, provided by an embodiment of the present invention. Figure 2 This is a schematic diagram of the pressure transmission direction of a well network under elastic development state, provided by an embodiment of the present invention. Figure 3 This is a schematic diagram of the pressure transmission direction of a well network under recharge conditions, provided by an embodiment of the present invention. Figure 4 This is a schematic diagram illustrating the pressure transmission direction of a well network in a seepage-draining elastic state, provided as an embodiment of the present invention. (Reference) Figure 1 The mining method includes:

[0059] S110. The maximum recovery rate of the reservoir is determined by nuclear magnetic resonance experiments.

[0060] Maximum recovery rate can be understood as the highest percentage of crude oil that can be extracted from a reservoir rock sample under controlled laboratory conditions, relative to the original oil content of the rock sample, by simulating the core mechanisms of elastic development and energy replenishment and seepage dissipation in the actual mining process for a specific tight reservoir (porosity ≤ 10%, permeability ≤ 0.1mD).

[0061] Specifically, reservoir rock samples are preprocessed to establish a saturated oil-bound water model. Multiple rounds of production simulations are then conducted based on this model using a nuclear magnetic resonance (NMR) spectra. The NMR T2 spectra during the simulations are recorded, and the remaining oil saturation S for each round is calculated based on the corresponding T2 spectra. n Based on the remaining oil saturation S nThe recovery rate for each round is calculated based on the maximum oil saturation S0. Finally, the maximum value among all the recovery rates is selected as the maximum recovery rate of the reservoir.

[0062] S120. Deploy a well network consisting of at least one injection well and at least two production wells.

[0063] Among them, injection wells can be understood as wellbores used to inject working media into tight reservoirs; production wells can be understood as wellbores used to extract crude oil from tight reservoirs; horizontal wells extend along the principal stress direction, and vertical wells are distributed on both sides or above the horizontal wells.

[0064] For details, please refer to Figures 2-4 Based on reservoir geological exploration data, the thickness of the development interval, fracture orientation, and location of high-permeability bands are determined. Areas with uniform fractures and high permeability are selected as the center of the well network. According to the well network morphology and spacing, injection wells are placed at the center, with at least two production wells arranged around the injection wells. After determining the well network distribution, a complex fracture network is formed in the horizontal section through pre-fracturing acid fracturing or hydraulic fracturing. Combined with injection and production coordination using at least two production wells (horizontal, vertical / directional wells), oil is driven out using the reservoir's elastic expansion energy.

[0065] S130. Inject the first working medium into the reservoir through the injection well, and obtain the bottom hole pressure of the production well after the injection of the first working medium as the original pressure of the reservoir.

[0066] The first working medium can be understood as something injected into the tight reservoir at the beginning of mining to establish the initial pressure field, such as clean brine or acidic displacement fluid; the initial pressure can be understood as:

[0067] Specifically, by injecting the first working medium, the reservoir pores and fractures are rapidly filled, resulting in uniform and stable reservoir pressure. The determined initial pressure provides a numerical reference for subsequent pressure reduction and extraction. After injecting the first working medium into the reservoir, the pressure is stabilized for a period. When the bottomhole pressure fluctuation of the produced well is ≤0.5 MPa for 48 consecutive hours, the reservoir pressure is considered to have reached a stable state. The bottomhole pressure of the produced well is recorded as the initial pressure of the reservoir.

[0068] S140. Depressurize the production well. When the reservoir pressure drops to the preset critical pressure, close the production well and obtain the cumulative recovery rate of the current production cycle. Inject the second working medium into the reservoir through the injection well to restore the reservoir pressure to the injection pressure until the recovery rate difference between the cumulative recovery rate and the maximum recovery rate is less than the preset recovery rate threshold.

[0069] Among them, the preset critical pressure can be understood as the critical pressure determined by nuclear magnetic resonance experiments, at which the crude oil production will drop significantly (by more than 30% to 50%) when the reservoir pressure drops to this value, and further depressurization is no longer economically worthwhile; the cumulative recovery rate can be understood as the percentage of crude oil extracted from the reservoir in all extraction cycles from the start of extraction to the end of the current cycle, relative to the total original crude oil in the reservoir; the second working medium can be understood as a light gas (such as CO2, N2) or a chemical agent (such as a surfactant, nano-displacement agent); the injection pressure can be understood as the target pressure that needs to be reached when injecting the second working medium, which is higher than the original reservoir pressure; and the preset recovery rate threshold can be understood as a pre-set difference standard for judging whether to stop extraction.

[0070] For details, please refer to Figures 2-4 The production equipment in the production well is activated to gradually reduce the bottom hole pressure, creating a pressure difference between the injection well and the production well. During the depressurization process, reservoir pressure and crude oil production are monitored in real time. When the reservoir pressure drops to a preset critical pressure, the production well is shut down to stop production. The amount of crude oil produced in this cycle is calculated and combined with the original reservoir oil volume to determine the current cumulative recovery rate. If the difference between the current cumulative recovery rate and the maximum recovery rate is greater than the preset recovery rate threshold, it indicates that the reservoir has sufficient oil reserves and has not reached its economically viable limit. At this point, the injection equipment is activated to inject a second working medium into the reservoir through the injection well to increase the formation pressure. The production well is then reopened, and the depressurization, production, and well shutdown / recharge steps are repeated. After each cycle, the cumulative recovery rate is calculated and compared with the maximum recovery rate. This process continues until the difference between the cumulative recovery rate and the maximum recovery rate is less than the preset recovery rate threshold, indicating that the reservoir is nearing its maximum production potential and further production is no longer economically viable. At this point, the cycle is stopped, and tight oil production is complete.

[0071] This invention provides a multi-well flexible exploitation method for tight oil, comprising: determining the maximum recovery rate of the reservoir through nuclear magnetic resonance experiments to calibrate the upper limit of the crude oil extraction potential of the tight reservoir, avoiding over-exploitation leading to increased costs or under-exploitation leading to wasted resources; deploying a well network consisting of at least one injection well and at least two production wells to form a reservoir exploitation range with multi-directional pressure gradients, solving the problems of limited pressure transmission range and low crude oil accumulation efficiency in conventional single-well or dual-well exploitation; injecting a first working medium into the reservoir through the injection wells and obtaining the bottom hole pressure of the production wells after the injection of the first working medium as the original pressure of the reservoir, thereby expanding the rock fractures in the tight oil field and driving out the crude oil from the rock fractures. The production well undergoes depressurization extraction. When the reservoir pressure drops to a preset critical pressure, the production well is shut down, and the cumulative recovery rate of the current extraction cycle is obtained. A second working medium is then injected into the reservoir through an injection well to restore the reservoir pressure to the injection pressure. This process continues until the difference between the cumulative recovery rate and the maximum recovery rate is less than a preset recovery rate threshold. This difference is used as the criterion to ensure that the oilfield's extraction level approaches the maximum recovery rate. The method provided in this invention reduces extraction costs and risks, and enhances the adaptability of extraction schemes.

[0072] It should be noted that, Figure 2 This diagram illustrates the pressure transmission direction of a well network under flexible development conditions. At this point, the injection wells have completed the first injection of working medium and stopped injection. The production wells, acting as pressure release points, gradually reduce the bottomhole pressure through the opening of surface throttle valves, forming a radial pressure gradient with the injection wells as the "high-pressure end" and the production wells as the "low-pressure end." Due to the low porosity and permeability of tight reservoirs, crude oil flow resistance is high. Crude oil confined within the reservoir's micropores and fractures overcomes viscous resistance under the pressure difference, converging along the pressure transmission path towards the production wells and ultimately being extracted to the surface. Figure 3 This diagram illustrates the pressure transmission direction of a well network under recharge conditions. At this point, the injection well restarts, injecting a second working medium into the reservoir. The pressure transmission arrows in the diagram show a uniform diffusion pattern from the injection well outwards to the surrounding reservoir, and the diffusion range is significantly larger than [the previous diagram is missing from the original text]. Figure 2 By squeezing the reservoir pores with higher pressure, the second working medium is pushed into deep fractures and micropores to fill the pressure deficit area formed by previous depressurization mining, causing the residual oil originally adsorbed on the pore walls to fall off. Figure 4 This is a schematic diagram of the pressure transmission direction of the well network under the elastic state of seepage displacement. At this time, the second working medium has reduced the crude oil flow resistance in advance and expanded the pressure influence range. Under the same pressure difference, the crude oil flow rate is faster and the production well output is higher.

[0073] In an optional embodiment, depressurization extraction of the production well includes:

[0074] During the depressurization mining process, the pressure difference between the bottom hole pressures of the production well and the injection well is obtained in real time;

[0075] The pressure difference is controlled within the preset pressure range.

[0076] Specifically, pressure sensors are installed at the bottom of both injection and production wells. The preset pressure range is determined based on reservoir core experiments. For example, for reservoirs with permeability of 0.05-0.1 mD, the preset pressure range is usually set to 3-5 MPa. The lower limit of 3 MPa is used to ensure that crude oil can overcome the pore viscosity resistance and flow. The upper limit of 5 MPa is used to avoid reservoir skeleton stress overload leading to fracture closure or pore collapse.

[0077] In an optional embodiment, controlling the pressure difference to be within a preset pressure range includes:

[0078] When the pressure difference is less than the lower limit of the preset pressure range, reduce the opening of the surface throttle valve of the production well;

[0079] When the pressure difference exceeds the upper limit of the preset pressure range, increase the opening of the surface throttle valve of the production well.

[0080] Specifically, during the depressurization process, if the pressure difference is below 3 MPa, the opening of the surface throttle valve of the production well needs to be reduced to decrease the pressure release rate at the production end, thereby increasing the pressure difference. Conversely, if the pressure difference is above 5 MPa, the opening of the surface throttle valve of the production well should be increased to accelerate the pressure release at the production end and reduce the pressure difference, thus avoiding drastic pressure fluctuations that could impact the reservoir.

[0081] In an optional embodiment, injecting a second working medium into the reservoir via an injection well to restore the reservoir pressure to the injection pressure includes:

[0082] Determine the first distance L between the injection well and the production well;

[0083] The second working medium is injected into the reservoir through the injection well. During the injection process, the formation pressure at a preset position in the production well is monitored in real time. The injection of the second working medium into the reservoir is stopped when the formation pressure at the preset position is greater than or equal to the energy injection pressure. The preset position is positively correlated with the first spacing.

[0084] Specifically, the distance between the injection well and each production well is measured, i.e., the first spacing L. Based on the first spacing L, a preset monitoring position within the production well is determined; the two are positively correlated, such as L / 3. When the formation pressure at the preset position reaches or exceeds the injection pressure, it indicates that the second working medium has sufficiently diffused into the deep reservoir, and the pressure recovery range covers the main seepage channels between the injection and production wells.

[0085] Figure 5 This is a flowchart of another method for elastic extraction of tight oil through multi-well seepage control provided in an embodiment of the present invention, referred to [reference]. Figure 5Regarding the above embodiment, "S110, determining the maximum recovery rate of the reservoir through nuclear magnetic resonance experiments" can be further refined as follows:

[0086] Rock samples from the reservoir were subjected to one round of elastic development simulation and at least one round of energy replenishment and seepage displacement simulation.

[0087] Obtain the nuclear magnetic resonance T2 spectrum after each round of simulation.

[0088] Based on T2 spectrum data from elastic development simulation and energy replenishment and permeation simulation, the recovery rate after each round of simulation was calculated.

[0089] The maximum value among the recovery rates in each round is determined as the reservoir's maximum recovery rate.

[0090] For details not covered in this embodiment, please refer to the previous embodiment.

[0091] like Figure 5 As shown in the figure, another method for flexible exploitation of tight oil through multiple wells provided in this embodiment of the invention may include the following specific steps:

[0092] S210. Perform one round of elastic development simulation and at least one round of energy replenishment and seepage dispersal simulation on the reservoir rock samples in sequence.

[0093] Among them, elastic development simulation can be understood as the process in which a tight reservoir rock sample, after being injected with the first working medium, relies solely on its own elastic energy to drive crude oil production under laboratory conditions; energy replenishment and permeation can be understood as, after elastic development simulation, injecting a second working medium into the rock sample and increasing the pressure, using the displacement effect of the working medium to drive the flow of residual crude oil that was not extracted in the previous elastic development.

[0094] Specifically, reservoir rock samples undergo one round of elastic development simulation and at least one round of supplemental injection and permeation simulation. First, the rock samples are pretreated by vacuuming to remove air from the pores, followed by saturation with kerosene to simulate the original oil-bearing state of the reservoir. After drying, they are pressurized and saturated with simulated formation water to establish a bound water environment. Simulated oil is then used to displace the rock samples until they are saturated with oil and bound water. Next, elastic development simulation is performed. The pretreated rock samples are placed in a nuclear magnetic resonance (NMR) instrument, and the experimental system pressure is adjusted to the original reservoir pressure. The inlet pressure is kept stable, and a pressure difference is created by gradually reducing the outlet pressure, driving the crude oil in the rock samples to flow towards the outlet until the outlet pressure drops to a preset critical pressure and no fluid is produced, completing the elastic development simulation. Then, supplemental injection and permeation simulation is performed. The rock samples are kept in the instrument, and the system pressure is increased to the injection pressure, while the inlet pressure remains constant. The outlet pressure is then gradually reduced again until no fluid is produced at the outlet. If crude oil can still be extracted after one supplemental injection, the supplemental injection and permeation simulation can be repeated.

[0095] S220. Obtain the nuclear magnetic resonance T2 spectrum after each round of simulation.

[0096] Specifically, the rock sample is always placed inside the detection chamber of the online nuclear magnetic resonance analyzer. After each simulation stops, the T2 spectrum acquisition program is started, and a specific radio frequency pulse is applied to the rock sample to excite the hydrogen nuclei in the fluid to generate transverse relaxation signals. The signals are received by the detector and converted into T2 spectra.

[0097] For example, Figure 8 This diagram illustrates the relationship between NMR-T2 spectrum amplitude and relaxation time, as provided in this embodiment of the invention. The horizontal axis represents the T2 relaxation time in milliseconds (ms), and the vertical axis represents the signal amplitude, which is positively correlated with fluid content. The area enclosed by the curve and the horizontal axis represents the total amount of a specific fluid. The area between the curves visually reflects the amount of crude oil displaced in different simulation stages. The saturated oil-bound water T2 spectrum (T1 curve) before simulation represents the state with the highest oil content in the rock sample, and the total area enclosed by its curve and the horizontal axis corresponds to the original total oil content of the rock sample. After the elastic development simulation, the T2 spectrum (T2 curve) collected has a lower overall signal amplitude than the T1 curve because some crude oil has been displaced from the rock sample. The area between the two curves represents the amount of crude oil displaced during the elastic development stage. After the supplementary energy drainage simulation, the signal amplitude of the corresponding T2 spectrum (T3, T4, T5 curves) for each round further decreases: the area between the T3 and T2 curves represents the amount of crude oil displaced in the first round of supplementary energy drainage, and the area between the T4 and T3 curves represents the amount of crude oil displaced in the second round of supplementary energy drainage. As the number of cycles increases, the area gradually decreases, indicating that there is less and less crude oil that can be displaced, until the area approaches zero, at which point the reservoir crude oil is close to its extraction limit.

[0098] S230, based on T2 spectrum data from elastic development simulation and energy replenishment permeation simulation, calculate the recovery rate after each round of simulation.

[0099] Specifically, the T2 NMR spectrum of the rock samples is measured to calculate the initial oil saturation. After each round of development simulation, the T2 spectrum of the rock samples is measured to calculate the remaining oil saturation for that round. The recovery rate for each round is calculated using the initial oil saturation and the remaining oil saturation, and the recovery rate after each simulation is calculated separately.

[0100] S240. The maximum value among the recovery rates in each round is determined as the maximum recovery rate of the reservoir.

[0101] Specifically, from each round of simulated recovery rate calculated, the recovery rate with the largest value is selected and determined as the maximum recovery rate of the reservoir.

[0102] S250, Deploy a well network consisting of at least one injection well and at least two production wells.

[0103] S260. Inject the first working medium into the reservoir through the injection well, and obtain the bottom hole pressure of the production well after the injection of the first working medium as the original pressure of the reservoir.

[0104] S270. Depressurize the production well. When the reservoir pressure drops to a preset critical pressure, close the production well and obtain the cumulative recovery rate for the current production cycle. Inject a second working medium into the reservoir through the injection well to restore the reservoir pressure to the injection pressure, until the difference between the cumulative recovery rate and the maximum recovery rate is less than a preset recovery rate threshold.

[0105] Based on the above embodiments, this invention refines the process of determining reservoir maximum recovery rate using nuclear magnetic resonance experiments, thereby improving the accuracy and reliability of reservoir maximum recovery rate data.

[0106] In an optional embodiment, reservoir rock samples are sequentially subjected to one round of elastic development simulation and at least one round of energy replenishment and seepage dispersal simulation, including:

[0107] The rock samples were vacuum-treated and saturated with kerosene. After drying, they were pressurized and saturated with simulated formation water. Then, simulated oil was used for displacement to establish a state of oil-bound water.

[0108] Specifically, air is removed from the pores during the rock sample pretreatment stage to avoid interference with subsequent fluid saturation and NMR signals. Kerosene is used to saturate the rock sample pores, ensuring it fully fills the pores and simulates the original oil-bearing state of the reservoir. The sample is then dried until its mass is constant. Pressure saturation is applied to simulate formation water forming stable bound water in the pores. Simulated oil displacement is used to establish a saturated oil-bound water system consistent with the original reservoir state.

[0109] The processed rock sample was placed in an online nuclear magnetic resonance analyzer. The experimental system pressure was adjusted to the original pressure, the inlet pressure was kept constant, and the outlet pressure was gradually reduced for elastic development. The pressure reduction was stopped when the outlet pressure dropped to the preset critical pressure, until no fluid was produced at the outlet.

[0110] Specifically, during the elastic development simulation phase, pretreated rock samples are fixed in the high-pressure core holder of an online nuclear magnetic resonance (NMR) instrument. A first working medium is injected into the core holder via a pressure control system, slowly increasing the experimental system pressure to the original reservoir pressure, thus balancing the internal pressure of the rock sample with the system pressure. Subsequently, the outlet pressure is gradually reduced at a preset rate, and the fluid output at the outlet is recorded. When the outlet pressure drops to a preset critical pressure, the pressure reduction is stopped, and observation continues for a period of time. If no fluid is produced from the outlet during this period, the elastic development simulation is considered complete.

[0111] After elastic development, the rock sample was placed in an online nuclear magnetic resonance analyzer. The experimental system pressure was adjusted to the energy injection pressure. The inlet pressure was kept constant, and the outlet pressure was gradually reduced to carry out energy replenishment and seepage removal. The pressure reduction was stopped when the outlet pressure dropped to the preset critical pressure, until no fluid was produced at the outlet.

[0112] Specifically, a second working medium is injected into the core holder via a pressure control system, raising the system pressure to the injection pressure. This allows the second working medium to fully enter the pores of the rock sample, replenishing reservoir energy and establishing a new pressure gradient. The outlet pressure is then gradually reduced while recording the production rate until it drops to a preset critical pressure. After stopping the pressure reduction, observation continues for a period. If no fluid is produced at the outlet, one round of energy replenishment and seepage displacement simulation is complete. Similarly, second, third, and subsequent rounds of energy replenishment and seepage displacement simulations can be performed until the recovery rate of that round is less than 1%, at which point the simulation is stopped.

[0113] Figure 6 This is a flowchart of another method for elastic extraction of tight oil through multiple wells provided in this embodiment of the invention, referred to as [reference]. Figure 6 Regarding the above embodiment, "S230, based on the T2 spectrum data from the elastic development simulation and the energy replenishment and permeation simulation, calculate the recovery rate after each round of simulation," can be further refined as follows:

[0114] Obtain the original oil saturation S0 of the rock sample;

[0115] Based on the T2 spectrum data after each round of simulation, the oil saturation S after that round of simulation is calculated. n ;

[0116] According to formula W n =(S o -S n ) / S o ×100%, calculate the recovery rate W after each round of simulation. n .

[0117] like Figure 6 As shown in the figure, another method for elastic extraction of tight oil through multiple wells provided in this embodiment of the invention may include the following specific steps:

[0118] S310. Perform one round of elastic development simulation and at least one round of energy replenishment and seepage dispersal simulation on the reservoir rock samples in sequence.

[0119] S320: Obtain the nuclear magnetic resonance T2 spectrum after each round of simulation.

[0120] S330, Obtain the original oil saturation of the rock sample. o .

[0121] Specifically, the T2 spectrum under saturated water conditions can be used to characterize the pore volume (PV) of rocks. Under saturated oil-bound water conditions, the measured T2 spectrum signal amplitude, i.e., the integrated area under the spectral line, is proportional to the total amount of hydrogen-containing fluid (oil and bound water) in the rock sample pores. The ratio of the T2 spectrum signal amplitude under these conditions to that under saturated water conditions is the original oil saturation S0.

[0122] S340. Based on the T2 spectrum data after each round of simulation, calculate the oil saturation S after that round of simulation. n .

[0123] Specifically, after each round of elastic development or energy replenishment and seepage removal, nuclear magnetic resonance (NMR) tests are performed on the rock samples to obtain the T2 spectrum under that condition. The total signal amplitude A of this T2 spectrum is... n The remaining oil and bound water content is proportional to the total amount remaining after this simulation. The remaining oil saturation of the rock sample after the current simulation cycle is obtained by comparing the signal ratio of the current T2 spectrum with that of the T2 spectrum under saturated water conditions.

[0124] S350, according to formula W n =(S o -S n ) / S0×100%, calculate the recovery rate W after each round of simulation. n .

[0125] Specifically, first, S0 and S n The difference between the actual oil production and the original oil content in the simulation is calculated, and then divided by S0 to obtain the recovery rate W for each simulation. n .

[0126] S360. The maximum value among the recovery rates in each round is determined as the maximum recovery rate of the reservoir.

[0127] S370. Deploy a well network consisting of at least one injection well and at least two production wells.

[0128] S380. Inject the first working medium into the reservoir through the injection well and obtain the bottom hole pressure of the production well after the injection of the first working medium as the original pressure of the reservoir.

[0129] S390. Depressurize the production well. When the reservoir pressure drops to the preset critical pressure, close the production well, obtain the cumulative recovery rate of the current production cycle, and inject a second working medium into the reservoir through the injection well to restore the reservoir pressure to the injection pressure until the recovery rate difference between the cumulative recovery rate and the maximum recovery rate is less than the preset recovery rate threshold.

[0130] Based on the above embodiments, the embodiments of the present invention refine the process of calculating the recovery rate, improve the accuracy of the original oil saturation data and the rigor of the recovery rate calculation in each round.

[0131] In an optional embodiment, obtaining the nuclear magnetic resonance T2 spectrum after each round of simulation includes:

[0132] Based on the T2 spectrum data after each round of simulation, the oil saturation S after that round of simulation is calculated. n Previously, it also included:

[0133] After each round of simulation, obtain the T2 NMR spectrum of the first preset spectral segment and the T2 NMR spectrum of the second preset spectral segment. The first preset spectral segment and the second preset spectral segment do not overlap.

[0134] Calculate the oil saturation S after each round of simulation. n ,include:

[0135] The first oil saturation S was obtained based on the nuclear magnetic resonance T2 spectrum of the first preset spectral band. n ';

[0136] The second oil saturation S was obtained based on the nuclear magnetic resonance T2 spectrum of the second preset spectral band. n ”;

[0137] According to formula S n =k1*S n '+k2*S n Calculate the oil saturation S n Among them, k1 and k2 are determined according to the number of simulation rounds.

[0138] Specifically, the first preset spectral segment corresponds to the long relaxation time interval of crude oil in the T2 NMR spectrum, mainly reflecting the crude oil signal within large pores or fractures in the rock sample. The second preset spectral segment corresponds to the short relaxation time interval of crude oil, mainly reflecting the crude oil signal within small pores. The areas enclosed by the curves of the two preset spectral segments in the T2 spectrum after each round of simulation and the abscissa are extracted and compared with the first total signal amplitude A1 to obtain the first oil saturation S. n ' and second oil saturation S n "In the flexible development simulation phase, crude oil with large pores is more easily driven, so k1 is greater than k2. In the energy replenishment and permeation simulation phase, the proportion of crude oil with small and medium pores utilized increases, resulting in k1 being smaller and k2 being larger compared to the flexible development simulation phase."

[0139] For example, in the initial elastic displacement stage: more crude oil is extracted from larger pores (T2 spectrum 10-1000ms), and crude oil is extracted to a certain extent from smaller pores (T2 spectrum 0.5-10ms).

[0140] After the first round of energy replenishment and elastic permeation: mainly utilize crude oil in larger pores (T2 spectrum 10-1000ms);

[0141] After the second round of energy replenishment and elastic permeation: more crude oil was extracted from larger pores (T2 spectrum 10-1000ms), and crude oil was extracted to a certain extent from smaller pores (T2 spectrum 0.5-10ms);

[0142] After the third round of energy replenishment and elastic permeation: mainly utilize crude oil in larger pores (T2 spectrum 10-1000ms).

[0143] Figure 7 This is a flowchart of another method for elastic extraction of tight oil through multiple wells provided in this embodiment of the invention, referred to as [reference]. Figure 7 Regarding the above embodiment, "S330, obtaining the original oil saturation S0" can be further refined as follows:

[0144] Obtain the first nuclear magnetic resonance T2 spectrum of the rock sample after vacuuming and saturating it with kerosene;

[0145] Obtain the second nuclear magnetic resonance T2 spectrum of the rock sample in the state of saturated oil-bound water;

[0146] The original oil saturation S0 was calculated based on the first and second nuclear magnetic resonance T2 spectra.

[0147] like Figure 6 As shown in the figure, another method for elastic extraction of tight oil through multiple wells provided in this embodiment of the invention may include the following specific steps:

[0148] S410. Perform one round of elastic development simulation and at least one round of energy replenishment and seepage dispersal simulation on the reservoir rock samples in sequence.

[0149] S420: Obtain the nuclear magnetic resonance T2 spectrum after each round of simulation.

[0150] S431. Obtain the first nuclear magnetic resonance T2 spectrum of the rock sample after vacuuming and saturating it with kerosene.

[0151] Specifically, the rock sample is placed in a vacuum dryer to remove air from the pores. It is then transferred to a kerosene saturation device to completely fill all pores, achieving kerosene saturation. The kerosene-saturated rock sample is then placed in an online nuclear magnetic resonance (NMR) spectrometer. By applying a specific radio frequency pulse sequence to the rock sample, the hydrogen nuclei in the kerosene are excited to produce transverse relaxation signals. These signals are received by a detector and converted into a first NMR T2 spectrum.

[0152] S432. Obtain the second nuclear magnetic resonance (T2) spectrum of the rock sample under saturated bound water conditions.

[0153] Specifically, after the rock sample was saturated with kerosene under vacuum, it was dried and then pressurized with simulated formation water. This caused the formation water to form stable bound water in the pores, simulating the original oil-bearing state of the reservoir. The rock sample was then placed in an online nuclear magnetic resonance spectrometer to obtain the second nuclear magnetic resonance (T2) spectrum.

[0154] S433. Based on the first and second nuclear magnetic resonance T2 spectra, the original oil saturation S0 is calculated.

[0155] Specifically, the first total signal amplitude A1 (the total area enclosed by the first NMR T2 spectrum curve and the abscissa) is calculated by integrating the first NMR T2 spectrum. A1 corresponds to the total signal amount of 100% saturated crude oil in the rock sample pores, representing the maximum oil-bearing capacity of the rock sample. Similarly, the second NMR T2 spectrum corresponds to the mixed signal of crude oil and bound water. The curve corresponding to the crude oil spectral segment is extracted, and the total area enclosed by this curve and the abscissa is calculated to obtain the second total signal amplitude A2. The second total signal amplitude A2 reflects the actual oil content of the reservoir in its original state. By eliminating the influence of differences in the total porosity of individual rock samples through the ratio of A2 to A1, the original oil saturation S0 of the rock sample is obtained.

[0156] S440. Based on the T2 spectrum data after each round of simulation, calculate the oil saturation Sn after that round of simulation.

[0157] S450. Calculate the recovery rate Sn after each round of simulation using the formula Sn=(S0-Sn) / S0×100%.

[0158] S460. The maximum value among the recovery rates in each round is determined as the maximum recovery rate of the reservoir.

[0159] S470. Deploy a well network consisting of at least one injection well and at least two production wells.

[0160] S480. Inject the first working medium into the reservoir through the injection well and obtain the bottom hole pressure of the production well after the injection of the first working medium as the original pressure of the reservoir.

[0161] S490. Depressurize the production well. When the reservoir pressure drops to a preset critical pressure, close the production well and obtain the cumulative recovery rate for the current production cycle. Inject a second working medium into the reservoir through the injection well to restore the reservoir pressure to the injection pressure, until the difference between the cumulative recovery rate and the maximum recovery rate is less than a preset recovery rate threshold.

[0162] Based on the above embodiments, the embodiments of the present invention refine the process of calculating the original oil saturation, thereby improving the accuracy and reliability of the original oil saturation data.

[0163] In an optional embodiment, the original oil saturation S0 is calculated based on the first NMR T2 spectrum and the second NMR T2 spectrum, including:

[0164] Obtain the first total signal amplitude A1 of the first nuclear magnetic resonance T2 spectrum;

[0165] Obtain the second total signal amplitude A2 of the second nuclear magnetic resonance T2 spectrum;

[0166] The original oil saturation S0 is calculated using the formula S0 = (A2 / A1) × 100%.

[0167] Specifically, the first NMR T2 spectrum is the relaxation signal spectrum collected after the rock sample has been vacuum-treated and saturated with kerosene (100% oil filling the pores). Its first total signal amplitude, A1, is obtained by calculating the total area enclosed by the T2 spectrum curve and the abscissa; A1 reflects the maximum saturation amount of crude oil in the rock sample pores. The second NMR T2 spectrum is the relaxation signal spectrum collected after the rock sample has been pretreated to establish a saturated oil-bound water state (simulating the original oil-bearing state of the reservoir). Its second total signal amplitude, A2, is the total area of ​​the curve corresponding to the crude oil signal in this T2 spectrum, representing the oil content in the original reservoir state. The original oil saturation S0 can be quantified by calculating the ratio of A2 to A1.

[0168] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, combinations, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A method for elastic extraction of tight oil through multiple wells, characterized in that, include: The maximum recovery rate of the reservoir was determined by nuclear magnetic resonance experiments. A well network consisting of at least one injection well and at least two production wells shall be established; The first working medium is injected into the reservoir through the injection well, and the bottom hole pressure of the production well after the injection of the first working medium is obtained as the original pressure of the reservoir. The production well is depressurized and, when the reservoir pressure drops to a preset critical pressure, the production well is shut down. The cumulative recovery rate of the current production cycle is obtained. A second working medium is injected into the reservoir through the injection well to restore the reservoir pressure to the injection pressure, until the difference between the cumulative recovery rate and the maximum recovery rate is less than a preset recovery rate threshold; wherein, the injection pressure is greater than the original pressure.

2. The method for elastic extraction of tight oil through multiple wells according to claim 1, characterized in that, The maximum recovery rate of the reservoir was determined through nuclear magnetic resonance experiments, including: The rock samples from the reservoir were subjected to one round of elastic development simulation and at least one round of energy replenishment and seepage displacement simulation in sequence. Obtain the nuclear magnetic resonance T2 spectrum after each round of simulation; Based on the T2 spectrum data from the elastic development simulation and the energy replenishment and permeation simulation, the recovery rate after each round of simulation is calculated. The maximum value of the recovery rate in each round is determined as the maximum recovery rate of the reservoir.

3. The method for elastic extraction of tight oil through multiple wells according to claim 2, characterized in that, Rock samples from the reservoir were subjected to one round of elastic development simulation and at least one round of energy replenishment and permeation displacement simulation, including: The rock sample was vacuum-treated and saturated with kerosene. After drying, it was pressurized and saturated with simulated formation water. Then, simulated oil was used for displacement to establish a state of oil-bound water. The processed rock sample was placed in an online nuclear magnetic resonance analyzer. The pressure of the experimental system was adjusted to the original pressure. The inlet pressure was kept constant, and the outlet pressure was gradually reduced for elastic development. The pressure reduction was stopped when the outlet pressure dropped to the preset critical pressure, until no fluid was produced at the outlet. The rock sample after elastic development is placed in an online nuclear magnetic resonance analyzer. The experimental system pressure is adjusted to the energy injection pressure. The inlet pressure is kept constant, and the outlet pressure is gradually reduced to replenish energy and drive seepage. The pressure reduction is stopped when the outlet pressure drops to the preset critical pressure, until no fluid is produced at the outlet.

4. The method for elastic extraction of tight oil through multiple wells according to claim 2, characterized in that, Based on the T2 spectrum data from the aforementioned elastic development simulation and the aforementioned energy replenishment and permeation simulation, the recovery rate after each round of simulation is calculated, including: Obtain the original oil saturation S0 of the rock sample; Based on the T2 spectrum data after each round of simulation, the oil saturation S after that round of simulation is calculated. n ; According to formula W n =(S0-S n ) / S0×100%, calculate the recovery rate W after each round of simulation. n .

5. The method for elastic extraction of tight oil through multiple wells according to claim 4, characterized in that, Obtaining the original oil saturation S0 includes: Obtain the first nuclear magnetic resonance T2 spectrum of the rock sample after vacuuming and saturating it with kerosene; Obtain the second nuclear magnetic resonance T2 spectrum of the rock sample in a saturated oil-bound water state; The original oil saturation S0 was calculated based on the first and second nuclear magnetic resonance T2 spectra.

6. The method for elastic extraction of tight oil through multiple wells according to claim 5, characterized in that, Based on the first NMR T2 spectrum and the second NMR T2 spectrum, the original oil saturation S0 is calculated, including: Obtain the first total signal amplitude A1 of the first nuclear magnetic resonance T2 spectrum; Obtain the second total signal amplitude A2 of the second nuclear magnetic resonance T2 spectrum; The original oil saturation S0 is calculated using the formula S0 = (A2 / A1) × 100%.

7. The method for elastic extraction of tight oil through multiple wells according to claim 4, characterized in that, Obtain the nuclear magnetic resonance T2 spectrum after each round of simulation, including: Based on the T2 spectrum data after each round of simulation, the oil saturation S after that round of simulation is calculated. n Previously, it also included: After each round of simulation, obtain the T2 NMR spectrum of the first preset spectral segment and the T2 NMR spectrum of the second preset spectral segment, wherein the first preset spectral segment and the second preset spectral segment do not overlap. The calculation of the oil saturation S after each round of simulation n ,include: The first oil saturation S is obtained based on the nuclear magnetic resonance T2 spectrum of the first preset spectral band. n '; The second oil saturation S is obtained based on the nuclear magnetic resonance T2 spectrum of the second preset spectral band. n ”; According to formula S n =k1*S n '+k2*S n Calculate the oil saturation S n Among them, k1 and k2 are determined according to the number of simulation rounds.

8. The method for elastic extraction of tight oil through multiple wells according to claim 1, characterized in that, Depressurization mining of the produced well includes: During the depressurization mining process, the pressure difference between the bottom hole pressures of the production well and the injection well is acquired in real time. The pressure difference is controlled to be within a preset pressure range.

9. The method for elastic extraction of tight oil through multiple wells according to claim 8, characterized in that, Controlling the pressure difference to be within a preset pressure range includes: When the pressure difference is less than the lower limit of the preset pressure range, the opening of the surface throttle valve of the production well is reduced; When the pressure difference is greater than the upper limit of the preset pressure range, the opening of the surface throttle valve of the production well is increased.

10. The method for elastic extraction of tight oil through multiple wells according to claim 1, characterized in that, Injecting a second working medium into the reservoir through the injection well to restore the reservoir pressure to the injection pressure includes: Determine the first distance between the injection well and the production well; The second working medium is injected into the reservoir through the injection well. During the injection process, the formation pressure at a preset position in the production well is monitored in real time. The injection of the second working medium into the reservoir is stopped when the formation pressure at the preset position is greater than or equal to the energy injection pressure. The preset position is positively correlated with the first spacing.

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