Preparation method and system for rock cores with different fluid saturations and application of preparation method and system

Abstract

The invention discloses a preparation method and system for cores with different fluid saturations and application of the preparation method and system. The preparation method comprises the following steps: acquiring different types of core samples of a target reservoir; different types of core samples are connected in series according to the rock distribution condition of a target reservoir and placed in a core holder, and the core samples are vacuumized; performing constant-pressure water drive treatment on the vacuumized core samples until each core sample reaches a corresponding preset water saturation range; performing constant-pressure oil displacement water treatment on the core samples which meet the water saturation requirements and are arranged in series until no water flows out from the outlet end of the core holder, so as to obtain cores with different fluid saturations; the fluid comprises crude oil and water; according to the rock core preparation method, the transverse and longitudinal fluid distribution conditions of an original reservoir can be more truly reduced.

Description

Technical Field

[0001] The invention relates to the technical field of oilfield development, and in particular to a method and system for preparing cores with different fluid saturations and applications thereof. Background Art

[0002] In recent years, most oil fields have entered the medium-high water content period. After long-term water injection development, the pore structure of the reservoir has changed. Due to the heterogeneity of reservoir physical properties within the layer, between layers, and on the plane, the difference in the seepage process of the injected water has been caused, thus forming inefficient and invalid circulation strips between oil and water wells in some reservoirs, which is not conducive to improving the oil recovery efficiency. This has led to a large amount of injected water inefficiently circulating, making it difficult to expand the water drive swept volume, which in turn leads to high water content in the oil wells and reduces the oil well production. In order to improve the water injection effect of the oil field to achieve the purpose of stabilizing oil and controlling water, in order to solve the problem of inefficient and invalid circulation strips, it is necessary to first identify the inefficient and invalid circulation well layers in the reservoir, and then take measures such as profile adjustment and plugging to deal with the inefficient and invalid circulation well layers.

[0003] In order to solve the problems in oilfield development, such as identifying inefficient circulation wells as mentioned above, and finding exploitation measures for invalid and inefficient circulation wells, indoor flow simulation experiments are usually performed to simulate the real problems of underground oilfield reservoirs, and to find solutions to the problems encountered in oilfield development (i.e., indoor research on oilfield development problems). When conducting indoor flow simulation experiments, it is key to prepare core samples that meet the different fluid distributions in the reservoir and clarify the reservoir fluid distribution.

[0004] Since underground reservoirs are heterogeneous, there are many different types of cores in the reservoirs. In existing core preparation methods, different types of core samples are processed for fluid saturation separately to obtain cores with different fluid saturations. Summary of the invention

[0005] The inventors of the present application have discovered that in the prior art, the method of separately performing fluid saturation treatment on different types of core samples in the reservoir, due to the end face effect of the core, that is, the outlet end of the core holder is directly in contact with the atmosphere, which will cause the pressure gradient of the end face of the core sample close to the outlet end of the core holder to increase, thereby making the fluid saturation of the core sample at this location incomplete, and unable to truly reflect the fluid distribution of different types of core samples in the reservoir at different stages. Furthermore, when different types of core samples are separately saturated with fluid, the permeability difference between different types of core samples is not taken into account, and therefore the distribution of fluids at different stages of the reservoir cannot be accurately simulated.

[0006] In view of the above problems, the present invention is proposed to provide a method, system and application of core preparation with different fluid saturations that overcome the above problems or at least partially solve the above problems.

[0007] In a first aspect, an embodiment of the present invention provides a method for preparing cores with different fluid saturations, characterized by comprising:

[0008] Obtain different types of core samples from the target reservoir;

[0009] Connecting different types of core samples in series according to the rock distribution of the target reservoir, placing them in a core holder, and performing vacuum treatment on the core samples;

[0010] Performing constant pressure water flooding treatment on the core samples after vacuum treatment until each core sample reaches a corresponding preset water saturation range;

[0011] The core samples arranged in series after meeting the water saturation requirement are subjected to constant pressure oil-water drive treatment until no water flows out of the outlet of the core holder, so as to obtain cores with different fluid saturations; the fluids include crude oil and water.

[0012] In an optional embodiment, the serially connected core samples are placed along the direction from the injection end to the outlet end of the core holder.

[0013] In an optional embodiment, the core preparation method provided in the embodiment of the present invention further includes: using a nuclear magnetic resonance device to perform nuclear magnetic resonance detection on the obtained cores with different fluid saturations, and determining the distribution of the fluid in the core based on the nuclear magnetic resonance signals detected by the nuclear magnetic resonance device and the range of nuclear magnetic resonance signals corresponding to different fluids.

[0014] In an optional embodiment, the core preparation method provided in the embodiment of the present invention further includes: performing nuclear magnetic detection on the fluid using a nuclear magnetic device to calibrate the nuclear magnetic signal range of different fluids.

[0015] In an optional embodiment, the core preparation method provided in the embodiment of the present invention further includes: pre-processing different types of core samples, wherein the pre-processing includes: cleaning the core samples and drying the cleaned core samples.

[0016] In an optional embodiment, the core samples after vacuum treatment are subjected to constant pressure water flooding treatment until each core sample reaches a corresponding preset water saturation range; comprising:

[0017] The internal pressure of the core holder is set to the formation pressure of the target reservoir by using an injection pump, and the core samples after vacuum treatment are subjected to constant pressure water drive treatment. After reaching a preset treatment time, each core sample is subjected to nuclear magnetic resonance detection by using a nuclear magnetic resonance device to obtain the water saturation of each core sample;

[0018] Determine whether the difference between the water saturation of each core sample and the water saturation measured after the last preset processing time is within a preset difference range;

[0019] If yes, the constant pressure water flooding treatment is stopped to obtain a core sample that meets the water saturation requirements;

[0020] If not, continue to perform the constant pressure water flooding treatment step until a core sample that meets the water saturation requirement is obtained.

[0021] In an optional embodiment, after the difference between the water saturation of each core sample and the corresponding water saturation measured after the last preset processing time is within a preset difference range, the method further includes:

[0022] Calculate the permeability of the core sample after a preset treatment time;

[0023] Determine whether the difference between the permeability of the core sample and the permeability measured after the last preset processing time is within a preset difference range;

[0024] If not, continue with the steps of constant pressure water flooding treatment;

[0025] If yes, the constant pressure water flooding treatment is stopped to obtain a core sample that meets the water saturation requirements.

[0026] In an optional embodiment, the core samples after vacuum treatment are subjected to constant pressure water flooding treatment until each core sample reaches a corresponding preset water saturation range; comprising:

[0027] The pressure of the core holder is set to the formation pressure of the target reservoir, and the core sample after vacuum treatment is subjected to constant pressure water flooding treatment. After reaching a preset treatment time, the permeability of each core sample is calculated;

[0028] Determine whether the difference between the permeability of each core sample and the permeability measured after the last preset processing time is within a preset difference range;

[0029] If yes, the constant pressure water flooding treatment is stopped to obtain a core sample that meets the water saturation requirements;

[0030] If not, repeat the steps of constant pressure water flooding treatment until a core sample that meets the water saturation requirement is obtained.

[0031] In an optional embodiment, a constant-pressure oil-water drive treatment is performed on each core sample arranged in series after the water saturation requirement is met; including: determining the fluid injection pressure during the constant-pressure oil-water drive treatment according to the injection pressure of the target reservoir and the size of the core sample, and controlling the fluid to flow into the core clamp under the injection pressure during the constant-pressure oil-water drive treatment by an injection pump.

[0032] In a second aspect, an embodiment of the present invention further provides a core preparation system with different fluid saturations, which can implement the above-mentioned core preparation method with different fluid saturations, including: an injection pump, an intermediate container, a vacuum pump, an oil-water separator, a core holder, and a nuclear magnetic device;

[0033] The core holder is used to place core samples connected in series according to the rock distribution of the target reservoir;

[0034] The vacuum pump is connected to the core holder and is used to perform vacuum treatment on the core sample;

[0035] The intermediate container is used to contain the fluid, and the fluid includes: crude oil and water;

[0036] The injection pump is connected to the core holder to control the pressure of the core holder;

[0037] The injection pump, the intermediate container and the injection end of the core holder are connected in sequence, so that the fluid in the intermediate container is controlled by the injection pump to enter the core holder, so as to perform a constant pressure water drive treatment or a constant pressure oil drive water drive treatment on the core sample in the core holder;

[0038] The oil-water separator is connected to the outlet end of the core holder, and is used to receive the fluid flowing out of the outlet end of the core holder and to separate the fluid from oil and water;

[0039] The nuclear magnetic device is connected to the core holder and is used for real-time detection of the core sample.

[0040] In a third aspect, an embodiment of the present invention further provides an application of the above-mentioned method for preparing cores with different fluid saturations in the field of oilfield development technology.

[0041] The beneficial effects of the above technical solution provided by the embodiment of the present invention include at least:

[0042] The method for preparing cores with different fluid saturations provided by the embodiment of the present invention, when performing fluid saturation treatment on core samples of different types in the target reservoir, the core samples of different types in the target reservoir are connected in series according to the rock distribution of the target reservoir, and the core samples after the series connection are subjected to constant pressure water drive treatment in sequence, so that each core sample reaches the corresponding preset water saturation range, and the core samples arranged in series after meeting the water saturation requirements are subjected to constant pressure oil drive water treatment to obtain cores with different fluid saturations; the method for preparing cores with different fluid saturations provided by the embodiment of the present invention, when performing core preparation, the core samples are connected in series and then placed in a core holder, and only the core samples close to the outlet end of the core holder have an end face effect, thereby reducing the error caused by the core end face effect during the core preparation process. Different types of core samples are connected in series so that the fluid passes through each core sample in series to prepare cores with different fluid saturations. Compared with the method of separately processing the fluid saturation of different types of core samples, the flow of the fluid is more consistent with the actual flow in the reservoir. The core preparation method of the embodiment of the present invention can more realistically simulate the fluid distribution of different types of core samples in the reservoir at different stages.

[0043] Furthermore, the method for preparing cores with different fluid saturations provided in the embodiment of the present invention can use a nuclear magnetic resonance device to detect the obtained cores with different fluid saturations to obtain the distribution of the fluid in the prepared cores, that is, the nuclear magnetic resonance detection results can accurately locate the occurrence position of the fluid, providing important technical support for indoor flow simulation experiments, etc.

[0044] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description, claims, and drawings.

[0045] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0047] Figure 1 Flow chart of a core preparation method with different fluid saturations according to an embodiment of the present invention;

[0048] Figure 2 Schematic diagram of a portion of the structure of a core preparation system with different fluid saturations in an embodiment of the present invention. DETAILED DESCRIPTION

[0049] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0050] The inventors of the present application have discovered that in the prior art, the method of separately performing fluid saturation treatment on different types of core samples in the reservoir, due to the end face effect of the core, that is, the outlet end of the core holder is directly in contact with the atmosphere, which will cause the pressure gradient of the end face of the core sample close to the outlet end of the core holder to increase, thereby making the fluid saturation of the core sample at this location incomplete, and unable to truly reflect the fluid distribution of different types of core samples in the reservoir at different stages. Furthermore, when different types of core samples are separately saturated with fluid, the permeability difference between different types of core samples is not taken into account, and therefore the distribution of fluids at different stages of the reservoir cannot be accurately simulated.

[0051] The present invention provides a method for preparing cores with different fluid saturations, and the flow chart thereof is as follows: Figure 1 As shown, including:

[0052] Step S101: obtaining different types of core samples of the target reservoir;

[0053] Step S102: different types of core samples are connected in series according to the rock distribution of the target reservoir, and placed in a core holder, and the core samples are vacuumed;

[0054] Step S103: performing constant pressure water flooding treatment on the core samples after vacuum treatment until each core sample reaches a corresponding preset water saturation range;

[0055] Step S104: performing a constant pressure oil-water drive treatment on the core samples arranged in series after meeting the water saturation requirement until no water flows out of the core holder outlet, so as to obtain cores with different fluid saturations; the fluid includes crude oil and water.

[0056] The method for preparing cores with different fluid saturations provided by the embodiment of the present invention, when performing fluid saturation treatment on core samples of different types in the target reservoir, the core samples of different types in the target reservoir are connected in series according to the rock distribution of the target reservoir, and the core samples after the series connection are subjected to constant pressure water drive treatment in sequence, so that each core sample reaches the corresponding preset water saturation range, and the core samples arranged in series after meeting the water saturation requirements are subjected to constant pressure oil drive water treatment to obtain cores with different fluid saturations; the method for preparing cores with different fluid saturations provided by the embodiment of the present invention, when performing core preparation, the core samples are connected in series and then placed in a core holder, and only the core samples close to the outlet end of the core holder have an end face effect, thereby reducing the error caused by the core end face effect during the core preparation process. In addition, core samples of different types are connected in series so that the fluid passes through the core samples connected in series to prepare cores with different fluid saturations. Compared with the method of separately processing the fluid saturation of different types of core samples, the flow of the fluid is more consistent with the actual flow in the reservoir. The core preparation method of the embodiment of the present invention can more realistically simulate the fluid distribution of different types of core samples in the reservoir at different stages, and truly restore the horizontal and vertical fluid distribution of the original reservoir.

[0057] In step S101, the core sample obtained may be a natural core or an artificial core; preferably, the core sample is a natural core.

[0058] Furthermore, the core samples connected in series are placed along the injection end to the outlet end of the core holder. When constant pressure water drive treatment and constant pressure oil drive water treatment are performed, the fluid injected into the core holder flows through the core samples connected in series from the injection end to the outlet end in sequence. Compared with the process of treating the core samples individually, the flow path of the fluid is more consistent with the flow conditions in the formation, so the prepared cores with different fluid saturations can also more truly reflect the distribution of reservoir fluids.

[0059] Optionally, in step S102, different types of core samples are connected in series according to the rock distribution of the target reservoir, and before being placed in the core holder, the method further includes: pre-treating different types of core samples; wherein the pre-treating includes: cleaning the core samples, and drying the cleaned core samples; since there may be impurities on the surface of the core samples, especially natural cores, there may be impurities such as soil and drilling fluid on the surface, so when using core samples for indoor flow simulation experiments, the core samples must first be cleaned, such as oil washing, and the cleaned core samples must be dried for a preset time; wherein the preset drying time can be selected according to the experimental requirements, such as 24 hours. After drying the cleaned core samples, the dried core samples can also be dry-scanned using a nuclear magnetic device to determine whether the cleaned core samples are completely dried by the nuclear magnetic dry-scanning results, so as to avoid experimental errors caused by incomplete drying of the core samples.

[0060] At the same time, when pre-treating the core, the length and diameter of the core sample can also be measured to facilitate the calculation of some basic parameters such as the porosity and permeability of the core sample in subsequent flow simulation experiments.

[0061] In an optional embodiment, the core preparation method provided in the embodiment of the present invention further includes: using a nuclear magnetic resonance device to perform nuclear magnetic resonance detection on the obtained cores with different fluid saturations, and determining the distribution of the fluid in the core based on the nuclear magnetic resonance signals detected by the nuclear magnetic resonance device and the range of nuclear magnetic resonance signals corresponding to different fluids.

[0062] Specifically, when using a nuclear magnetic resonance detection device to perform nuclear magnetic resonance detection on cores with different fluid saturations, a T2 spectrum will be obtained. In the T2 spectrum, the horizontal axis relaxation time can reflect the size of the pores in the core sample, while the vertical axis can reflect the fluid content. In other words, the fluid content and the coverage area of ​​the voids represent the volume of fluid stored in this type of pores. Therefore, the T2 spectrum can determine the distribution of the fluid in the core.

[0063] The method for preparing cores with different fluid saturations provided in an embodiment of the present invention can use a nuclear magnetic resonance device to detect the obtained cores with different fluid saturations to obtain the distribution of the fluid in the prepared cores. The nuclear magnetic resonance detection results can accurately locate the occurrence position of the fluid, providing important technical support for indoor flow simulation experiments, etc.

[0064] In an optional embodiment, the core preparation method of the embodiment of the present invention, before using the nuclear magnetic device to perform nuclear magnetic detection on the obtained cores with different fluid saturations, further includes: using the nuclear magnetic device to perform nuclear magnetic detection on the used fluid to calibrate the nuclear magnetic signal range of different fluids, so as to facilitate fluid identification according to the nuclear magnetic signal range corresponding to different fluids during the core preparation process. And when calibrating the nuclear magnetic signal range of different fluids, parameters can be adjusted, such as: nuclear magnetic detection interval time, etc., so that the nuclear magnetic device can achieve the best effect when performing nuclear magnetic detection on the fluid (that is, it can more clearly distinguish different fluids).

[0065] In an optional embodiment, in step S103, the core samples after vacuum treatment are subjected to constant pressure water flooding treatment until each core sample reaches a corresponding preset water saturation range; including:

[0066] The internal pressure of the core holder is set to the formation pressure of the target reservoir by using an injection pump, and the core samples after vacuum treatment are subjected to constant pressure water drive treatment. After reaching the preset treatment time, each core sample is subjected to nuclear magnetic resonance detection by using a nuclear magnetic resonance device to obtain the water saturation of each core sample;

[0067] Determine whether the difference between the water saturation of each core sample and the water saturation measured after the last preset processing time is within a preset difference range;

[0068] If yes, the constant pressure water flooding treatment is stopped to obtain a core sample that meets the water saturation requirements;

[0069] If not, the constant pressure water flooding treatment step is repeated until a core sample that meets the water saturation requirement is obtained.

[0070] Among them, after the core sample is vacuumed and before the constant pressure water drive treatment, the core sample after vacuuming can be subjected to nuclear magnetic detection by using a nuclear magnetic device to detect whether the core sample is completely vacuumed. At the same time, the set vacuuming treatment time, the preset treatment time of the constant pressure water drive treatment, and the preset difference range of water saturation between two adjacent preset treatment times can be designed according to specific needs, and the embodiment of the present invention does not make specific limitations. For example, the preset treatment time can be 48 hours, the preset difference range of water saturation can be less than 1%, and the vacuuming treatment time can be 24-48 hours.

[0071] Specifically, after the constant-pressure water drive treatment for the pretreatment time, each core sample in series is subjected to nuclear magnetic detection by a nuclear magnetic device to obtain a nuclear magnetic signal corresponding to each core sample, and the water saturation of each core sample is calculated by the nuclear magnetic signal. After each preset treatment time, each core sample can obtain the water saturation after the preset treatment time, and the water saturation difference after two adjacent preset treatment times can be obtained based on the water saturation after the preset treatment time and the water saturation after the previous preset treatment time. When the water saturation difference is less than the preset difference range, it is judged that the water saturation of each core sample meets the preset saturation range. At this time, it can be judged that each core sample arranged in series meets the water saturation requirement.

[0072] When calculating the water saturation of each core sample through nuclear magnetic signal, it is also necessary to determine the relationship between the nuclear magnetic signal and the volume of the fluid (water); specifically, the corresponding relationship between the measured nuclear magnetic signal and the fluid volume of the core sample is determined based on the difference in the fluid volume before and after a period of processing of the core sample, and the difference in the nuclear magnetic signal before and after the processing time.

[0073] For example, when performing oil-driven water treatment, after a period of treatment time, the difference of the nuclear magnetic signal output by the nuclear magnetic device for nuclear magnetic detection is 200, and the oil-water separator arranged at the outlet end of the core holder is used to receive the fluid flowing out of the outlet end of the core holder during the treatment time, and after oil-water separation of the fluid, it is found that the volume of water corresponding to the nuclear magnetic signal with a difference of 200 during the treatment time is 10 ml, that is, the corresponding relationship between the nuclear magnetic signal and the volume of water can be determined.

[0074] Therefore, when the oil saturation or water saturation of the core sample is subsequently calculated, the calculation can be performed based on the detected nuclear magnetic signal and the corresponding relationship between the nuclear magnetic signal and the volume of water to achieve quantification of the oil / water saturation. Compared with the calculation of the water saturation or oil saturation of the core sample using an oil-water separator, the measured water saturation or oil saturation is more accurate.

[0075] It should be noted that the specific method for calculating the water saturation / oil saturation corresponding to each core sample using the nuclear magnetic resonance signal of each core sample detected can refer to the existing technology, and the embodiment of the present invention will not be elaborated in detail here.

[0076] Furthermore, the core sample preparation method provided in the embodiment of the present invention further includes: after the difference between the water saturation of each core sample and the water saturation measured after the last preset processing time corresponding thereto is within a preset difference range, that is, after the water saturation of the core sample obtained by the nuclear magnetic resonance device meets the water saturation requirement, the method further includes:

[0077] Calculate the permeability of the core sample after a preset treatment time;

[0078] Determine whether the difference between the permeability of the core sample and the permeability measured after the last preset processing time is within a preset difference range;

[0079] If not, continue with the steps of constant pressure water flooding treatment;

[0080] If yes, the constant pressure water flooding treatment is stopped to obtain a core sample that meets the water saturation requirements.

[0081] The method provided in the embodiment of the present invention determines whether the water saturation of the core sample meets the requirement. After using the nuclear magnetic resonance detection technology to determine whether the core sample meets the water saturation requirement, further judgment can be made by calculating the permeability of the core sample after a preset processing time. After two adjacent preset processing times, when the permeability difference of the core sample is within the preset difference range, it indicates that the fluid forms a stable flow in the core sample, and it can be determined that the core sample has reached the preset water saturation requirement.

[0082] In an optional embodiment, the method provided in the embodiment of the present invention performs constant pressure water flooding treatment on the core samples after vacuum treatment until each core sample reaches the corresponding preset water saturation range; comprising:

[0083] The pressure of the core holder is set to the formation pressure of the target reservoir, and the core samples after vacuum treatment are subjected to constant pressure water flooding treatment. After reaching the preset treatment time, the permeability of each core sample is calculated;

[0084] Determine whether the difference between the permeability of each core sample and the permeability measured after the last preset processing time is within a preset difference range;

[0085] If yes, the constant pressure water flooding treatment is stopped to obtain a core sample that meets the water saturation requirements;

[0086] If not, repeat the steps of constant pressure water flooding treatment until a core sample that meets the water saturation requirement is obtained.

[0087] That is, when judging whether the water saturation of the core sample meets the preset saturation requirement, the core preparation method of the embodiment of the present invention can be judged by performing nuclear magnetic resonance detection on the core sample after the preset processing time, and calculating the water saturation of the core sample according to the nuclear magnetic resonance detection result, or by calculating the permeability of the core sample after the preset processing time; it can also be judged by jointly judging whether the water saturation of the core sample meets the preset water saturation requirement by the nuclear magnetic resonance detection result and the calculated permeability;

[0088] Preferably, the water saturation of the core sample is determined by the nuclear magnetic resonance test results and the calculated permeability to determine whether it meets the preset water saturation requirements. After the nuclear magnetic resonance test results and the permeability meet the preset conditions, it is determined that the water saturation of the core sample meets the preset water saturation requirements, so that the measured water saturation can be determined with higher accuracy.

[0089] It should be noted that the specific method for calculating the permeability of each core sample can refer to the prior art, and the embodiment of the present invention will not be elaborated in detail here.

[0090] Among them, the nuclear magnetic resonance device used in the core preparation method provided in the embodiment of the present invention can be a high-precision nuclear magnetic resonance device.

[0091] In an optional embodiment, in step S104, a constant pressure oil-water displacement treatment is performed on each core sample arranged in series after the water saturation requirement is met; comprising:

[0092] The fluid injection pressure during constant pressure oil-water drive treatment is determined by the injection pressure of the target reservoir and the size of the core sample. The fluid flows into the core holder under the injection pressure during the constant pressure oil-water drive treatment process through the injection pump.

[0093] Specifically, the injection pressure of the fluid during constant-pressure oil-water drive treatment can be determined based on the size ratio between the core sample and the target reservoir, and the speed and flow rate of the fluid flowing into the core holder during constant-pressure oil-water drive treatment can be controlled by an injection pump, thereby preparing a core sample with controllable saturation.

[0094] The following examples are used to illustrate the fluid distribution of the core prepared by the core preparation method of the present invention as follows:

[0095] Example 1:

[0096] The inventors of the present application used artificial cores with permeabilities of 1500mD, 700mD and 100mD as core samples for core preparation experiments. The core samples were all dense sandstones with a length of 50cm and a diameter of 4.5cm. The experimental oil was simulated water and simulated oil of the Daqing formation. The experimental pressure was 2MPa and the experimental period was 4 days.

[0097] When the core preparation method provided by the embodiment of the present invention is used to connect the artificial cores in series according to the rock distribution of the reservoir and then conduct an oil saturation experiment, after the experiment, the oil saturations of the three cores obtained are 78.4%, 75.8% and 56.6% respectively.

[0098] Under the same experimental conditions, when the three core samples were subjected to oil saturation experiments separately, the oil saturation of the three core samples obtained was all above 75%, which was quite different from the oil volume and distribution of the reservoir under formation conditions.

[0099] Example 2:

[0100] The inventors of the present application used artificial cores with permeabilities of 1500mD, 700mD, 350mD and 100mD as core samples for core preparation experiments. The core samples were all dense sandstones with a length of 50cm and a diameter of 4.5cm. The experimental oil was simulated water and simulated oil of the Daqing formation. The experimental pressure was 2MPa and the experimental period was 4 days.

[0101] When the core preparation method provided in the embodiment of the present invention is used to connect the artificial cores in series according to the rock distribution of the reservoir and then conduct an oil saturation experiment, after the experiment, the oil saturations of the four cores obtained are 69.5%, 67.4%, 58.2% and 56.65% respectively.

[0102] Under the same experimental conditions, when four core samples were subjected to oil saturation experiments separately, the oil saturation of the four core samples was all above 70%, which was quite different from the oil volume and distribution of the reservoir under formation conditions.

[0103] Due to the strong underground heterogeneity, the fluid distribution degree is high in the area with higher underground permeability, and vice versa in the area with lower permeability; therefore, it can be further seen from the above embodiments that, compared with the cores with different fluid saturations obtained by processing the core samples alone, the cores obtained by the core preparation method provided in the embodiment of the present invention can more truly restore the lateral and vertical distribution of the original reservoir fluid.

[0104] The core preparation method provided in the embodiment of the present invention performs multi-stage series connection on core samples of different types, adjusts parameters such as flow rate and pressure through injection pumps, simulates the distribution of fluids in core samples at different stages, and truly restores the lateral and vertical distribution of fluids in the original reservoir; and the method can be combined with high-resolution nuclear magnetic resonance real-time monitoring: nuclear magnetic resonance detection is performed on rock samples at each stage, oil / water saturation is quantified, and combined with two-dimensional nuclear magnetic resonance, the occurrence position of the fluid is accurately located, providing important technical support for indoor core simulation experimental research.

[0105] Based on the same inventive concept, the embodiment of the present invention also provides a system that can implement the above-mentioned different fluid core preparation methods, referring to Figure 2 As shown, including:

[0106] It includes: an injection pump, an intermediate container, a vacuum pump (not shown in the figure), an oil-water separator, a core holder and a nuclear magnetic device;

[0107] Among them, the core holder is used to place core samples that are connected in series according to the rock distribution of the target reservoir;

[0108] The vacuum pump is connected to the core holder and is used to evacuate the core sample;

[0109] The intermediate container is used to hold fluid, and the fluid includes: crude oil and water;

[0110] The injection pump is connected to the core holder to control the pressure of the core holder;

[0111] The injection pump, the intermediate container and the injection end of the core holder are connected in sequence, so that the fluid in the intermediate container is controlled by the injection pump to enter the core holder, so as to perform a constant pressure water drive treatment or a constant pressure oil drive water drive treatment on the core sample in the core holder;

[0112] The oil-water separator is connected to the outlet end of the core holder and is used to receive the fluid flowing out of the outlet end of the core holder and to separate the oil and water in the fluid;

[0113] The nuclear magnetic resonance device is connected to the core holder and is used to perform real-time detection of core samples.

[0114] Specifically, the injection pump is a double-cylinder pump, one end of which is connected to the core clamp for controlling the pressure of the core clamp, thereby making the pressure of the core sample arranged in the core clamp at a preset pressure. At the same time, a pressure sensor can be arranged on the connecting pipeline between the core clamp and the double-cylinder pump to detect the pressure value of the core clamp; for example: when the core sample is subjected to constant-pressure water drive treatment, the pressure of the core sample is controlled to be the formation pressure by the injection pump to simulate the reservoir environment.

[0115] The other end of the double-cylinder pump is connected to the injection end of the intermediate container and the core holder in sequence, so that the fluid in the intermediate container can be controlled to enter the core holder through the double-cylinder pump when the core sample is subjected to constant pressure oil-water treatment.

[0116] Optionally, the core holder is a diffusion coefficient dedicated holder.

[0117] Among them, the specific use process of each device in the system in the core preparation method has been described in detail in the above-mentioned core preparation method, and will not be described in detail here.

[0118] The embodiment of the present invention adopts a method of serial simulation sample preparation and combines it with a high-resolution nuclear magnetic resonance real-time detection system to perform multi-stage serial connection on different types of rock samples. By adjusting the system's parameters such as flow rate and pressure, the distribution of fluids in the rock samples at different stages is simulated. This can easily and quickly prepare core samples with controllable saturation, truly restore the horizontal and vertical distribution of fluids in the original reservoir, and accurately locate the occurrence position of the fluid.

[0119] The core preparation method of the embodiment of the present invention is suitable for the preparation of conventional and unconventional rock samples with different fluid saturations, and the devices used in the method are simple and are the most commonly used devices in indoor research of oilfield development, and have high universality.

[0120] Based on the same inventive concept, an embodiment of the present invention also provides an application of the above-mentioned method for preparing cores with different fluid saturations in the field of oilfield development technology.

[0121] It should be understood that the specific order or hierarchy of steps in the disclosed process is an example of an exemplary method. Based on design preferences, it should be understood that the specific order or hierarchy of steps in the process can be rearranged without departing from the scope of protection of the present disclosure. The attached method claims present the elements of the various steps in an exemplary order and are not intended to be limited to the specific order or hierarchy described.

[0122] The above description includes examples of one or more embodiments. Of course, it is impossible to describe all possible combinations of components or methods for the purpose of describing the above embodiments, but it should be recognized by those skilled in the art that the various embodiments may be further combined and arranged. Therefore, the embodiments described herein are intended to cover all such changes, modifications and variations that fall within the scope of protection of the appended claims. In addition, with respect to the term "comprising" used in the specification or claims, the word is covered in a manner similar to the term "including", just as "including," is explained as a transitional word in the claims. In addition, any term "or" used in the specification of the claims is intended to mean "non-exclusive or".

[0123] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for preparing cores with different fluid saturations, characterized in that: include: Obtain different types of core samples from the target reservoir; Connecting different types of core samples in series according to the rock distribution of the target reservoir, placing them in a core holder, and performing vacuum treatment on the core samples; Performing constant pressure water flooding treatment on the core samples after vacuum treatment until each core sample reaches a corresponding preset water saturation range; The core samples arranged in series after meeting the water saturation requirement are subjected to constant pressure oil-water drive treatment until no water flows out of the outlet of the core holder, so as to obtain cores with different fluid saturations; the fluids include crude oil and water.

2. The method according to claim 1, characterized in that The core samples connected in series are placed along the direction from the injection end to the outlet end of the core holder.

3. The method according to claim 1, characterized in that Also includes: The obtained cores with different fluid saturations are subjected to nuclear magnetic detection using a nuclear magnetic device, and the distribution of the fluid in the core is determined based on the nuclear magnetic signals detected by the nuclear magnetic device and the ranges of nuclear magnetic signals corresponding to different fluids.

4. The method for preparing cores with different fluid saturations according to claim 3, characterized in that: Also includes: The fluid is tested by nuclear magnetic resonance (NMR) device to calibrate the NMR signal range of different fluids.

5. The method for preparing cores with different fluid saturations according to claim 1, characterized in that: Also includes: Pre-process different types of core samples; The pretreatment includes: cleaning the core sample and drying the cleaned core sample.

6. The method for preparing cores with different fluid saturations according to claim 1, characterized in that: The core samples after vacuum treatment are subjected to constant pressure water flooding treatment until each core sample reaches a corresponding preset water saturation range; including: The internal pressure of the core holder is set to the formation pressure of the target reservoir by using an injection pump, and the core samples after vacuum treatment are subjected to constant pressure water drive treatment. After reaching a preset treatment time, each core sample is subjected to nuclear magnetic resonance detection by using a nuclear magnetic resonance device to obtain the water saturation of each core sample; Determine whether the difference between the water saturation of each core sample and the water saturation measured after the last preset processing time is within a preset difference range; If yes, the constant pressure water flooding treatment is stopped to obtain a core sample that meets the water saturation requirements; If not, continue to perform the constant pressure water flooding treatment step until a core sample that meets the water saturation requirement is obtained.

7. The method for preparing cores with different fluid saturations according to claim 6, characterized in that: The difference between the water saturation of each core sample and the water saturation measured after the last preset processing time corresponding thereto within the preset difference range also includes: Calculate the permeability of the core sample after a preset treatment time; Determine whether the difference between the permeability of the core sample and the permeability measured after the last preset processing time is within a preset difference range; If not, continue with the steps of constant pressure water flooding treatment; If yes, the constant pressure water flooding treatment is stopped to obtain a core sample that meets the water saturation requirements.

8. The method for preparing cores with different fluid saturations according to claim 1, characterized in that: The core samples after vacuum treatment are subjected to constant pressure water flooding treatment until each core sample reaches a corresponding preset water saturation range; including: The pressure of the core holder is set to the formation pressure of the target reservoir, and the core sample after vacuum treatment is subjected to constant pressure water flooding treatment. After reaching a preset treatment time, the permeability of each core sample is calculated; Determine whether the difference between the permeability of each core sample and the permeability measured after the last preset processing time is within a preset difference range; If yes, the constant pressure water flooding treatment is stopped to obtain a core sample that meets the water saturation requirements; If not, repeat the steps of constant pressure water flooding treatment until a core sample that meets the water saturation requirement is obtained.

9. The method for preparing cores with different fluid saturations according to claim 1, characterized in that: The core samples arranged in series after meeting the water saturation requirements are subjected to constant pressure oil-water drive treatment; the process includes: determining the fluid injection pressure during the constant pressure oil-water drive treatment according to the injection pressure of the target reservoir and the size of the core sample, and controlling the fluid to flow into the core holder under the injection pressure during the constant pressure oil-water drive treatment by an injection pump.

10. A core preparation system with different fluid saturations, characterized in that: A method for preparing cores with different fluid saturations as described in any one of claims 1 to 9 can be implemented, comprising: an injection pump, an intermediate container, a vacuum pump, an oil-water separator, a core holder and a nuclear magnetic device; The core holder is used to place core samples connected in series according to the rock distribution of the target reservoir; The vacuum pump is connected to the core holder and is used to perform vacuum treatment on the core sample; The intermediate container is used to contain the fluid, and the fluid includes: crude oil and water; The injection pump is connected to the core holder to control the pressure of the core holder; The injection pump, the intermediate container and the injection end of the core holder are connected in sequence, so that the fluid in the intermediate container is controlled by the injection pump to enter the core holder, so as to perform a constant pressure water drive treatment or a constant pressure oil drive water drive treatment on the core sample in the core holder; The oil-water separator is connected to the outlet end of the core holder, and is used to receive the fluid flowing out of the outlet end of the core holder and to separate the oil and water in the fluid; The nuclear magnetic device is connected to the core holder and is used for real-time detection of the core sample.

11. An application of the method for preparing cores with different fluid saturations as claimed in any one of claims 1 to 9 in the field of oilfield development technology.

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