A fracturing process for tight oil horizontal wells

Abstract

The present invention relates to the field of oil production engineering technology, and in particular to a fracturing process for tight oil horizontal wells, comprising: obtaining geological data information; determining the state of the rock formation based on a porosity reference value and the richness of tight oil in the area to be constructed, and determining a target layer setting method based on the rock formation state; perforating the toe of the horizontal well, and performing a fracturing operation on each target layer after the toe perforation of the horizontal well is completed; determining the injection amount of CO2 fracturing fluid based on a reference oil-bearing sandstone length, and determining the thickener content based on the reservoir pressure; if the fracture density is less than a preset fracture density, determining the fracturing fluid adjustment method for the post-target layer based on the gravel state of the proppant, such as determining an optimization method based on the difference in gravel particle size or adjusting the injection pressure of the CO2 fracturing fluid; after the injection of the CO2 fracturing fluid in the entire well section is completed, determining the well blocking time based on a comprehensive reference value; and drilling out the bridge plug. The present invention can improve the fracturing effect and improve the production efficiency of tight oil horizontal wells.

Description

Technical Field

[0001] The present invention relates to the technical field of oil production engineering, and in particular to a fracturing process for tight oil horizontal wells. Background Art

[0002] Because CO2 can be in a supercritical state under reservoir conditions, its fluidity and diffusivity are extremely strong, making it the primary medium for enhancing oil production in unconventional reservoirs. However, during CO2 fracturing, CO2 is primarily pumped in during a single pre-fluid stage, resulting in incomplete CO2 diffusion, short contact time with the formation crude oil, and insufficient displacement. Furthermore, due to the short interval between CO2 pumping into the formation and the main fracturing operation, the CO2 cannot be fully embedded in the complex fractures formed by the main fracturing, reducing the effectiveness of CO2 fracturing. Therefore, improving the effectiveness of CO2 fracturing and increasing the efficiency of tight oil horizontal well production is a technical problem that urgently needs to be addressed by those skilled in the art.

[0003] Chinese Patent Publication No. CN109538177A discloses a new supercritical carbon dioxide fracturing process, comprising the following steps: (1) well cleaning, (2) perforating, (3) fracturing treatment, (4) proppant injection, (5) staged fracturing, (6) isolation treatment, (7) wellbore treatment, and (8) post-fracturing blowback. It can be seen that the above technical solution has the following problems: it does not improve the CO2 fracturing effect, and the production efficiency of tight oil horizontal wells is poor. Summary of the Invention

[0004] To this end, the present invention provides a fracturing process for tight oil horizontal wells to overcome the problem in the prior art that the CO2 fracturing effect is not improved and the tight oil horizontal well production efficiency is poor.

[0005] To achieve the above object, the present invention provides a fracturing process for a tight oil horizontal well, comprising:

[0006] Obtain geological data information;

[0007] Determine the rock formation status based on the porosity reference value and tight oil richness of the area to be constructed;

[0008] The target layer setting method is to determine the target layer length according to the rock layer evaluation coefficient or to determine the length of the first target layer according to the pore reference value and determine the length of each second target layer according to the pore length difference of the previous target layer;

[0009] Perforate the toe of the horizontal well, and then perform fracturing operations on each target layer after the perforation of the toe of the horizontal well is completed;

[0010] When performing a fracturing operation on a single target layer, the target layer is perforated and, upon completion of perforation, CO2 fracturing fluid and proppant are injected into the target layer, wherein the injection amount of the CO2 fracturing fluid is determined based on the reference oil-bearing sandstone length, and the thickener content is determined based on the reservoir pressure;

[0011] After the injection of proppant into a single target layer is completed, the fracture density of the target layer is detected. If the fracture density is less than the preset fracture density, the fracturing fluid adjustment method for the target layer is determined based on the gravel state of the proppant. This includes optimizing the method based on the difference in gravel particle size or adjusting the injection pressure of the CO2 fracturing fluid.

[0012] The optimization method is to adjust the injection temperature of the CO2 fracturing fluid, or to adjust the thickener content or the injection rate of the CO2 fracturing fluid according to the apparent viscosity of the CO2 fracturing fluid;

[0013] After the CO2 fracturing fluid injection is completed in the entire well section, the well is blocked, and the blocking time is determined according to the comprehensive reference value;

[0014] The well is blocked and the bridge plug is drilled out.

[0015] Furthermore, the formation state is determined based on the porosity reference value and the tight oil richness. The formation state includes:

[0016] a first rock formation state in which the pore reference value is greater than a preset pore reference value and the tight oil richness is greater than a preset tight oil richness;

[0017] A second rock formation state in which the pore reference value is less than or equal to a preset pore reference value or the tight oil richness is less than or equal to a preset tight oil richness.

[0018] Furthermore, the target layer setting method is determined according to the rock layer state;

[0019] In the first rock layer state, the target layer is set by determining the target layer length according to the rock layer evaluation coefficient;

[0020] In the second rock layer state, the target layer is set in such a way that the length of the first target layer is determined according to the pore reference value, and the length of each second target layer is determined according to the pore length difference of the preceding target layer.

[0021] Furthermore, the target layer length is determined based on the rock layer evaluation coefficient;

[0022] The relationship between the target layer length and the rock formation evaluation coefficient is a negative correlation.

[0023] Furthermore, the calculation formula of the rock formation evaluation coefficient τ is:

[0024]

[0025] Where φ is the pore reference value, H is the tight oil richness, ε1 is the first coefficient, and ε2 is the second coefficient.

[0026] Furthermore, in the second rock layer state, the length of the first target layer is determined according to the pore reference value, and the length of each second target layer is determined according to the pore length difference of the preceding target layer;

[0027] If the hole length difference is less than the preset hole length difference, the length of the second target layer is the standard length;

[0028] If the hole length difference is greater than or equal to the preset hole length difference, the length of the second target layer is reduced;

[0029] The relationship between the pore reference value and the length of the first target layer is a positive correlation;

[0030] The first target layer is the target layer closest to the toe of the horizontal well, and the second target layer is all target layers except the first target layer.

[0031] Furthermore, when injecting CO2 fracturing fluid into the target layer, the injection amount of CO2 fracturing fluid corresponding to the target layer is determined according to the reference oil-bearing sandstone length of the target layer;

[0032] The injection volume of the CO2 fracturing fluid is positively correlated with the length of the reference oil-bearing sandstone.

[0033] Further, the thickener content of the target layer is determined according to the reservoir pressure of the target layer;

[0034] The relationship between the reservoir pressure and the thickener content is a negative correlation.

[0035] Furthermore, when the injection of proppant into a single target layer is completed, the fracture density of the target layer is detected. If the fracture density is less than the preset fracture density, the fracturing fluid adjustment method for the subsequent target layer of the target layer is determined according to the gravel state of the proppant;

[0036] In the first gravel state, the fracturing fluid adjustment method is to determine the optimization method according to the difference in gravel particle size;

[0037] In the second gravel state, the fracturing fluid adjustment method is to adjust the injection pressure of the CO2 fracturing fluid.

[0038] Furthermore, the gravel state is determined according to the average gravel particle size of the proppant, and the gravel state includes:

[0039] A first gravel state in which the average gravel particle size is greater than or equal to a preset average gravel particle size;

[0040] A second gravel state in which the average gravel particle size is smaller than a preset average gravel particle size.

[0041] Furthermore, if the fracture density of a target layer is less than the preset fracture density and the gravel state of the proppant is the first gravel state, the optimization method is determined according to the difference in gravel particle size;

[0042] If the difference in gravel particle size is greater than or equal to the preset difference in gravel particle size, the optimization method is to reduce the injection temperature of the CO2 fracturing fluid corresponding to the subsequent target layer of the target layer;

[0043] If the difference in gravel particle size is less than the preset difference in gravel particle size, the optimization method is to adjust the thickener content or carbon dioxide injection rate corresponding to the target layer after the target layer according to the apparent viscosity of the CO2 fracturing fluid;

[0044] The relationship between the reduction value of the injection temperature of the CO2 fracturing fluid and the fracture density is positively correlated.

[0045] Further, if the difference in the gravel particle size is less than the preset difference in the gravel particle size, the apparent viscosity of the CO2 fracturing fluid is detected;

[0046] If the apparent viscosity is greater than or equal to the preset apparent viscosity, the injection rate of the CO2 fracturing fluid corresponding to the target layer after the target layer is reduced;

[0047] If the apparent viscosity is less than the preset apparent viscosity, the thickener content corresponding to the subsequent target layer of the target layer is increased;

[0048] The relationship between the reduction value of the injection rate of the CO2 fracturing fluid and the fracture density is positively correlated;

[0049] The relationship between the increase in the thickener content and the crack density is positively correlated.

[0050] Furthermore, if the fracture density of a target layer is less than the preset fracture density and the gravel state of the proppant is the second gravel state, the injection pressure of the CO2 fracturing fluid corresponding to the subsequent target layer of the target layer is increased and adjusted;

[0051] The increase in the injection pressure of the CO2 fracturing fluid is positively correlated with the fracture density.

[0052] Furthermore, after the CO2 fracturing fluid injection is completed in the entire well section, the well blocking time is determined based on the comprehensive reference value;

[0053] The calculation formula of the comprehensive reference value γ is: γ=lnα ω1 +lnβ ω2 , where α is the reservoir pressure, β is the horizontal well diameter, ω1 is the first weight coefficient, and ω2 is the second weight coefficient;

[0054] The relationship between the well blocking time and the comprehensive reference value is a negative correlation.

[0055] Furthermore, an annular sand fracturing method is used for the target layer into which CO2 fracturing fluid has been injected.

[0056] Compared with the prior art, the beneficial effect of the present invention lies in that the technical solution of the present invention effectively reflects the current rock formation state through the pore reference value and the tight oil richness, and then selects different target layer setting methods according to actual conditions, so that the selection of the target layer setting method is more in line with the actual working scenario, avoiding the problem of poor fracturing effect caused by the inability to select a suitable target layer setting method according to the rock formation conditions, thereby improving the efficiency of tight oil horizontal well production.

[0057] Furthermore, the present invention effectively reflects the current rock formation characteristics and the degree of tight oil enrichment based on the rock formation evaluation coefficient, and then determines the target layer length according to the actual situation, so that the setting of the target layer length is more in line with the actual situation of the rock formation, avoiding the problem of poor fracturing effect caused by setting the target layer length too large, thereby improving the efficiency of tight oil horizontal well production.

[0058] Furthermore, the present invention effectively reflects the pore conditions of the current formation through the pore reference value, and then determines the length of the first target layer through the pore reference value, so that the setting of the first target layer is more in line with the actual working scenario, and then determines the length of the second target layer according to the pore length difference of the previous target layer, and effectively reflects the uniformity of the length of the mapping hole through the pore length difference of the previous target layer, and then determines the length of the second target layer according to the actual situation, so that the setting of the length of the second target layer is more in line with the actual application scenario, avoiding the problem of unreasonable setting of the target layer length due to formation changes, and thus improving the fracturing effect.

[0059] Furthermore, the present invention determines the injection amount of CO2 fracturing fluid corresponding to the target layer based on the reference length of the oil-bearing sandstone. By referring to the length of the oil-bearing sandstone, the current reservoir state is effectively reflected, and the injection amount of CO2 fracturing fluid can be determined according to the actual situation of the reservoir, avoiding the problems of excessive fracturing fluid injection increasing operating costs and insufficient fracturing fluid injection resulting in poor fracturing effect, thereby improving the production efficiency of tight oil horizontal wells.

[0060] Furthermore, the present invention effectively reflects the storage state of the target layer through the reservoir pressure of the target layer, and then determines the thickener content of the target layer according to the reservoir pressure of the target layer, thereby avoiding the problem of reduced viscosity and fluidity of the CO2 fracturing fluid under high-pressure environment, resulting in poor sand carrying capacity, thereby ensuring the stability of the CO2 fracturing fluid performance and improving the fracturing effect.

[0061] Furthermore, the present invention determines the fracturing fluid adjustment method of the post-target layer according to the gravel state of the proppant. The gravel state of the proppant reflects the particle length state of the gravel, and then different fracturing fluid adjustment methods are selected according to the gravel state, so that the selection of the fracturing fluid adjustment method is more in line with the actual working scenario, avoiding the problem of poor CO2 fracturing effect caused by too small crack density, thereby improving the production efficiency of tight oil horizontal wells.

[0062] Furthermore, when the fracture density of the target layer is less than the preset fracture density and the gravel state of the proppant is the first gravel state, the present invention determines the optimization method according to the gravel particle size difference. The gravel particle size difference reflects the degree of difference in the gravel particle size, and then different optimization methods are selected according to the gravel particle size difference, so that the selection of the optimization method is more in line with the actual working scenario, avoiding the problem of poor CO2 fracturing effect due to excessive gravel particle size, thereby improving the production efficiency of tight oil horizontal wells.

[0063] Furthermore, when the difference in gravel particle size is less than a preset difference in gravel particle size, the present invention effectively reflects the sand-carrying capacity of the CO2 fracturing fluid through the apparent viscosity of the CO2 fracturing fluid, and then determines different adjustment methods through the apparent viscosity of the CO2 fracturing fluid, so that the selection of the adjustment method is more in line with the actual working scenario, avoiding the problem of poor CO2 fracturing effect caused by too small fracture density, and thus improving the production efficiency of tight oil horizontal wells.

[0064] Furthermore, the present invention effectively reflects the horizontal well diameter and storage pressure status based on the comprehensive reference value, and then determines the well blocking time according to the actual situation, so that the determination of the well blocking time is more in line with the time working scenario, avoiding the problem of incomplete diffusion of carbon dioxide in the formation when the horizontal well diameter is too large and the reservoir pressure is too high, increasing the contact time with the formation crude oil, and thus improving the horizontal well production efficiency of tight oil.

[0065] Furthermore, the present invention adopts an annular sand fracturing method for the target layer into which CO2 fracturing fluid has been injected, which can significantly improve the conductivity of the fractures, allowing tight oil and CO2 to flow more smoothly through the fractures, thereby enhancing formation stability and reducing the risk of formation pressure drop and tight oil production drop due to fracture closure. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 Schematic diagram of the fracturing process for tight oil horizontal wells according to the present invention;

[0067] Figure 2 This is a flow chart of the present invention for determining the state of a rock formation based on a pore reference value and tight oil richness;

[0068] Figure 3 This is a flow chart of the present invention for determining the target layer setting method according to the rock layer state;

[0069] Figure 4 This is a flow chart of the present invention for determining a fracturing fluid adjustment method for a subsequent target layer according to the gravel state of the proppant;

[0070] Figure 5 is a schematic diagram of a tight oil horizontal well according to the present invention;

[0071] In the figure: horizontal well toe 1, bridge plug 2, target layer 3, hole 4. DETAILED DESCRIPTION

[0072] In order to make the objects and advantages of the present invention more clearly understood, the present invention is further described below in conjunction with embodiments; it should be understood that the specific embodiments described herein are merely used to explain the present invention and are not intended to limit the present invention.

[0073] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0074] It should be noted that, in the description of the present invention, terms such as "up", "down", "left", "right", "inside", and "outside" indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings. This is only for the convenience of description and does not indicate or imply that the device or element must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on the present invention.

[0075] Furthermore, it should be noted that, in the description of the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0076] See also Figures 1 to 4 As shown, the present invention provides a fracturing process for a tight oil horizontal well, comprising:

[0077] Obtain geological data information;

[0078] Determine the rock formation status based on the porosity reference value and tight oil richness of the area to be constructed;

[0079] The target layer setting method is to determine the target layer length according to the rock layer evaluation coefficient or to determine the length of the first target layer according to the pore reference value and determine the length of each second target layer according to the pore length difference of the previous target layer;

[0080] Perforate the toe of the horizontal well, and then perform fracturing operations on each target layer after the perforation of the toe of the horizontal well is completed;

[0081] When performing a fracturing operation on a single target layer, the target layer is perforated and, upon completion of perforation, CO2 fracturing fluid and proppant are injected into the target layer, wherein the injection amount of the CO2 fracturing fluid is determined based on the reference oil-bearing sandstone length, and the thickener content is determined based on the reservoir pressure;

[0082] After the injection of proppant into a single target layer is completed, the fracture density of the target layer is detected. If the fracture density is less than the preset fracture density, the fracturing fluid adjustment method for the target layer is determined based on the gravel state of the proppant. This includes optimizing the method based on the difference in gravel particle size or adjusting the injection pressure of the CO2 fracturing fluid.

[0083] The optimization method is to adjust the injection temperature of the CO2 fracturing fluid, or to adjust the thickener content or the injection rate of the CO2 fracturing fluid according to the apparent viscosity of the CO2 fracturing fluid;

[0084] After the CO2 fracturing fluid injection is completed in the entire well section, the well is blocked, and the blocking time is determined according to the comprehensive reference value;

[0085] The well is blocked and the bridge plug is drilled out.

[0086] The geological data information in the present invention includes pore reference values ​​and tight oil richness. The area to be constructed is the area where the horizontal well is located. The present invention uses a continuous oil pipe to transport the perforating gun to the toe of the horizontal well during perforation at the toe end of the horizontal well. The toe end perforation layer should select Class II reservoirs and Class III reservoirs with poor reservoir development to balance the production pressure difference, protect high-quality reservoirs and reduce mining risks. At the same time, it can leave a liquid inlet channel when the bridge plug fracturing tool is lowered, which is convenient for the implementation of the bridge-shot combined operation process. This is content that is easy to understand for those skilled in the art and will not be elaborated here.

[0087] For a single target layer, the target layer that is closest to the target layer and is located farthest from the toe of the horizontal well relative to the target layer is recorded as the subsequent target layer.

[0088] The present invention performs staged fracturing on horizontal wells, wherein the horizontal section of the horizontal well subjected to each fracturing is recorded as a target layer, wherein a bridge plug is provided between two adjacent target layers in the horizontal well to isolate the target layer into which proppant has been injected, and a bridge-shooting combined operation process is adopted for perforating each target layer, wherein the bridge plug and the perforator are sent into the wellbore by means of continuous tubing, and the setting of the bridge plug and the perforating operation are achieved through ground control.

[0089] The components of CO2 fracturing fluid include: supercritical CO2, thickener and additives. The thickener can be guar gum, siloxane, carboxymethyl cellulose, ND-PAM or ZJ-PAM. The additive can be a bactericide, corrosion inhibitor, resistance reducer or drainage agent. The proppant is ceramsite proppant. Users can choose the types of thickeners and additives according to the actual needs of the scenario. There is no specific restriction and users can choose according to their actual needs.

[0090] Specifically, the formation state is determined based on the porosity reference value and tight oil richness. The formation state includes:

[0091] a first rock formation state in which the pore reference value is greater than a preset pore reference value and the tight oil richness is greater than a preset tight oil richness;

[0092] A second rock formation state in which the pore reference value is less than or equal to a preset pore reference value or the tight oil richness is less than or equal to a preset tight oil richness.

[0093] Starting from the ground, a detection point is set every 0.5 m on the horizontal well wall. The calculation formula of the pore reference value Φ is: Where N is the number of detection points, x i is the porosity of the i-th detection point; the detection method of the porosity of each detection point includes but is not limited to the borehole logging method, density logging method or sonic logging method, and the user can choose according to the needs. This is content that is easy to understand for those skilled in the art and is not elaborated here.

[0094] The tight oil richness is the total length of oil-bearing sandstone encountered during the drilling process. The method for confirming the total length of oil-bearing sandstone is to conduct real-time measurement of the formation through natural gamma logging technology, and draw a logging curve with the natural gamma value as the vertical coordinate and the drilling length as the horizontal coordinate. The total length of the logging curve where the natural gamma value is less than the preset natural gamma value is the total length of the oil-bearing sandstone; the value of the preset natural gamma value can be determined by the user based on historical construction records. A preset natural gamma value is provided to detect the rock formation positions in the historical construction records whose oil content can meet the user's needs, and the average value of the natural gamma values ​​corresponding to each rock formation position is recorded as the preset natural gamma value.

[0095] The preset pore reference value and the preset tight oil enrichment value can be set by the user according to the actual application scenario. The greater the user's need to improve the fracturing effect, the larger the preset pore reference value and the preset tight oil enrichment value will be. Provided are the preset pore reference value and the preset tight oil enrichment value. The preset pore reference value is 60%, and the preset tight oil enrichment is 70% of the horizontal well length.

[0096] Specifically, the target layer setting method is determined according to the rock layer status;

[0097] In the first rock layer state, the target layer is set by determining the target layer length according to the rock layer evaluation coefficient;

[0098] In the second rock layer state, the target layer is set in such a way that the length of the first target layer is determined according to the pore reference value, and the length of each second target layer is determined according to the pore length difference of the preceding target layer.

[0099] Among them, for a single target layer, perforation is performed to obtain a number of holes, and the hole length of each hole is detected. The hole length difference = maximum hole length - minimum hole length. The hole length detection method is to lower the downhole imaging equipment into the horizontal well and locate it at the perforation section. The depth of each hole in the perforation section is detected and recorded as the hole length of each hole. This is easy for technicians in this field to understand and will not be elaborated here.

[0100] The target layer length is the length of the target layer in a direction perpendicular to the ground.

[0101] Specifically, the target layer length is determined based on the rock layer evaluation coefficient;

[0102] The relationship between the target layer length and the rock formation evaluation coefficient is a negative correlation.

[0103] Specifically, the calculation formula of the rock formation evaluation coefficient τ is:

[0104]

[0105] Where φ is the pore reference value, H is the tight oil richness, ε1 is the first coefficient, and ε2 is the second coefficient.

[0106] It is understandable that users can learn from historical records through deep learning convolutional neural networks to analyze the influence of the porosity reference value and tight oil richness on the target layer length setting, and then determine the values ​​of the first coefficient and the second coefficient, where ε1+ε2=1, and provide a value of ε1 and ε2, ε1=0.5, ε2=0.5.

[0107] Specifically, in the second rock layer state, the length of the first target layer is determined according to the pore reference value, and the length of each second target layer is determined according to the pore length difference of the previous target layer;

[0108] If the hole length difference is less than the preset hole length difference, the length of the second target layer is the standard length;

[0109] If the hole length difference is greater than or equal to the preset hole length difference, the length of the second target layer is reduced;

[0110] The relationship between the pore reference value and the length of the first target layer is a positive correlation;

[0111] The first target layer is the target layer closest to the toe of the horizontal well, and the second target layer is all target layers except the first target layer.

[0112] Among them, the value of the preset hole length difference can be set by the user according to the actual application scenario. The greater the user's demand for improving the carbon dioxide fracturing effect, the smaller the value of the preset hole length difference is. A value of the preset hole length difference is provided, and the preset hole length difference is 30%.

[0113] The standard length is the same as the length of the first target layer, and the length of the second target layer is negatively correlated with the hole length difference.

[0114] Specifically, when injecting CO2 fracturing fluid into the target layer, the injection amount of CO2 fracturing fluid corresponding to the target layer is determined according to the reference oil-bearing sandstone length of the target layer;

[0115] The injection volume of the CO2 fracturing fluid is positively correlated with the length of the reference oil-bearing sandstone.

[0116] The reference oil-bearing sandstone length is determined by taking the total length of the target layer in the well logging curve where the natural gamma value is less than the preset natural gamma value within the length interval of the target layer as the reference oil-bearing sandstone length.

[0117] The injection volume of CO2 fracturing fluid is the total amount of CO2 fracturing fluid injected into a single target layer, with the unit of t. The calculation formula of the injection volume Q of CO2 fracturing fluid is: Q = δ × h, where h is the reference oil-bearing sandstone length and δ is the reference coefficient. A value of the reference coefficient δ is provided, δ = 25t / m.

[0118] Specifically, the thickener content of the target layer is determined according to the reservoir pressure of the target layer;

[0119] The relationship between the reservoir pressure and the thickener content is a negative correlation.

[0120] The reservoir pressure is confirmed by, for a single target layer, recording the target layer as a reference target layer, using a pressure sensor, lowering the pressure sensor to the two end points and the midpoint of the reference target layer for measurement, and recording the pressure at each position detected by the pressure sensor as the reference pressure. The reservoir pressure is the average of the three reference pressures.

[0121] The method for confirming the thickener content is to record the amount of thickener in the CO2 fracturing fluid corresponding to a single target layer as the thickener content, in kg.

[0122] Specifically, when the injection of proppant into a single target layer is completed, the fracture density of the target layer is detected. If the fracture density is less than the preset fracture density, the fracturing fluid adjustment method for the subsequent target layer of the target layer is determined according to the gravel state of the proppant;

[0123] In the first gravel state, the fracturing fluid adjustment method is to determine the optimization method according to the difference in gravel particle size;

[0124] In the second gravel state, the fracturing fluid adjustment method is to adjust the injection pressure of the CO2 fracturing fluid.

[0125] For a single target layer, the target layer is recorded as the reference target layer, and the fracture density = the number of fractures in the reference target layer / the volume of the reference target layer. The number of fractures in the reference target layer is the number of fractures generated after the CO2 fracturing fluid and proppant are injected into the reference target layer. The number of fractures in the reference target layer can be detected by microseismic monitoring technology. This is easy to understand for those skilled in the art and will not be described in detail. The calculation formula for the volume V of the reference target layer is: Where D is the diameter of the tight oil horizontal well, H0 is the length of the reference target layer;

[0126] The value of the preset fracture density can be determined by the user according to the actual application scenario. The greater the user's demand for a good fracturing effect of the CO2 fracturing fluid, the larger the value of the preset fracture density. A value of the preset fracture density is provided, and the fracture density of horizontal wells whose fracturing effect meets the user's demand in the historical construction records is detected, and the average value of each fracture density is recorded as the preset fracture density.

[0127] Specifically, the gravel state is determined according to the average gravel particle size of the proppant, and the gravel state includes:

[0128] A first gravel state in which the average gravel particle size is greater than or equal to a preset average gravel particle size;

[0129] A second gravel state in which the average gravel particle size is smaller than a preset average gravel particle size.

[0130] Among them, W gravels are randomly selected from the proppant used in the present invention, and the calculation formula for the mean gravel particle size R0 is: Where, f = 1, 2, 3, ..., W, W is the number of selected gravels, R f is the particle size of the fth gravel, R f The calculation formula is: R f =(long axis length of the fth gravel + short axis length of the fth gravel) / 2, the long axis length of the fth gravel is the length of the fth gravel in the maximum extension direction, and the short axis length of the fth gravel is the length of the fth gravel in the minimum extension direction. It can be understood that the higher the user's demand for the accuracy of the mean gravel particle size, the larger the value of W is. A value of W is provided, W=100.

[0131] The value of the preset mean gravel particle size can be set by the user according to the actual application scenario. The greater the user's demand for the CO2 fracturing fluid to have better sand suspension ability, the smaller the value of the preset mean gravel particle size will be. A value of the preset mean gravel particle size is provided, and the preset mean gravel particle size is 3mm.

[0132] Specifically, if the fracture density of a target layer is less than the preset fracture density and the gravel state of the proppant is the first gravel state, the optimization method is determined according to the difference in gravel particle size;

[0133] If the difference in gravel particle size is greater than or equal to the preset difference in gravel particle size, the optimization method is to reduce the injection temperature of the CO2 fracturing fluid corresponding to the subsequent target layer of the target layer;

[0134] If the difference in gravel particle size is less than the preset difference in gravel particle size, the optimization method is to adjust the thickener content or carbon dioxide injection rate corresponding to the target layer after the target layer according to the apparent viscosity of the CO2 fracturing fluid;

[0135] The relationship between the reduction value of the injection temperature of the CO2 fracturing fluid and the fracture density is positively correlated.

[0136] Among them, the injection temperature of the CO2 fracturing fluid is the initial temperature when the CO2 fracturing fluid is injected, the gravel particle size difference = (maximum gravel particle size - minimum gravel particle size) / maximum gravel particle size, the maximum gravel particle size is the maximum gravel particle size among several gravels arbitrarily selected from the proppant used in the present invention, and the minimum gravel particle size is the minimum gravel particle size among several gravels arbitrarily selected from the proppant used in the present invention, wherein, gravel particle size = (long axis length of gravel + short axis length of gravel) / 2, the long axis length of gravel is the length of gravel in the maximum extension direction, and the short axis length of gravel is the length of gravel in the minimum extension direction.

[0137] The preset value of the gravel particle size difference can be set by the user according to the actual application scenario. The greater the user's demand for a good fracturing effect of the CO2 fracturing fluid, the smaller the preset value of the gravel particle size difference. A preset value of the gravel particle size difference is provided, and the preset gravel particle size difference is 20%;

[0138] It is understandable that reducing the injection temperature of the CO2 fracturing fluid in the adjacent target layer can increase the apparent viscosity of the CO2 fracturing fluid, allowing a large number of gravel particles to be suspended in the CO2 fracturing fluid, thereby increasing the fracture density.

[0139] Specifically, if the difference in the sand and gravel particle sizes is less than a preset difference in the sand and gravel particle sizes, the apparent viscosity of the CO2 fracturing fluid is detected;

[0140] If the apparent viscosity is greater than or equal to the preset apparent viscosity, the injection rate of the CO2 fracturing fluid corresponding to the target layer after the target layer is reduced;

[0141] If the apparent viscosity is less than the preset apparent viscosity, the thickener content corresponding to the subsequent target layer of the target layer is increased;

[0142] The relationship between the reduction value of the injection rate of the CO2 fracturing fluid and the fracture density is positively correlated;

[0143] The relationship between the increase in the thickener content and the crack density is positively correlated.

[0144] The apparent viscosity of the CO2 fracturing fluid is tested using a viscometer. The model of the viscometer is not specifically limited, as long as it meets the user's needs.

[0145] The value of the preset apparent viscosity can be set by the user according to the actual application scenario. The greater the user's demand for a good fracturing effect of the CO2 fracturing fluid, the larger the value of the preset apparent viscosity. A value of the preset apparent viscosity is provided, and the apparent viscosity of the CO2 fracturing fluid whose fracturing effect meets the user's demand is detected in the historical construction records. The average value of the apparent viscosity of each CO2 fracturing fluid is recorded as the preset apparent viscosity;

[0146] It is understandable that reducing the injection rate of the CO2 fracturing fluid corresponding to the target layer after the target layer is helpful to expand the cracks and form more cracks, thereby increasing the crack density.

[0147] Specifically, if the fracture density of a target layer is less than the preset fracture density and the gravel state of the proppant is the second gravel state, the injection pressure of the CO2 fracturing fluid corresponding to the subsequent target layer of the target layer is increased and adjusted;

[0148] The increase in the injection pressure of the CO2 fracturing fluid is positively correlated with the fracture density.

[0149] Among them, increasing the injection pressure of the CO2 fracturing fluid corresponding to the target layer after the target layer can increase the number of fractures and thus increase the fracture density. It should be noted that during the injection of the CO2 fracturing fluid, the injection pressure of the CO2 fracturing fluid and the reservoir conditions should be monitored in real time, and the injection parameters should be adjusted in time according to the monitoring results to ensure that the injection pressure of the CO2 fracturing fluid remains in a safe range to avoid excessive injection pressure of the CO2 fracturing fluid causing formation rupture.

[0150] Specifically, after the CO2 fracturing fluid injection is completed in the entire well section, the well blocking time is determined based on the comprehensive reference value;

[0151] The calculation formula of the comprehensive reference value γ is: γ=lnα ω1 +lnβ ω2 , where α is the reservoir pressure, β is the horizontal well diameter, ω1 is the first weight coefficient, and ω2 is the second weight coefficient;

[0152] The relationship between the well blocking time and the comprehensive reference value is a negative correlation.

[0153] Among them, the well shut-down time refers to the period of time after the CO2 fracturing fluid injection is completed in the entire well section, when the wellhead is closed to allow the CO2 fracturing fluid to fully act underground;

[0154] It can be understood that users can learn from historical records through deep learning convolutional neural networks to analyze the influence of the first weight coefficient and the second weight coefficient on the well blocking time, and then determine the values ​​of the first weight coefficient and the second weight coefficient, where ω1+ω2=1, and provide a value of ω1 and ω2, ω1=0.5, ω2=0.5.

[0155] Specifically, the annular sand fracturing method is used for the target layer into which CO2 fracturing fluid has been injected.

[0156] Among them, the annular sand fracturing method uses a high-pressure pump to inject fracturing fluid into the annular space between the wellbore and the casing. Through the pressure of the fracturing fluid, cracks are formed in the formation and expanded. There is no specific restriction on the model of the high-pressure pump, as long as it meets the user's needs.

[0157] See also Figure 5 As shown, it is a schematic structural diagram of a tight oil horizontal well according to the present invention;

[0158] In the present invention, the toe 1 of the horizontal well is the farthest area of ​​the horizontal well extending in the horizontal direction during the drilling process of the horizontal well. The horizontal well is subjected to staged fracturing, and the horizontal section of the horizontal well subjected to each fracturing is recorded as a target layer 3. The bridge plug 2 is set between two adjacent target layers 3 in the horizontal well to isolate the target layer 3 into which the proppant has been injected. After perforating the toe 1 of the horizontal well or the target layer 3, a number of holes 4 can be obtained.

[0159] Thus far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art may make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will fall within the scope of protection of the present invention.

[0160] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A fracturing process for tight oil horizontal wells, characterized in that: include: Obtain geological data information; Determine the rock formation status based on the porosity reference value and tight oil richness of the area to be constructed; The target layer setting method is to determine the target layer length according to the rock layer evaluation coefficient or to determine the length of the first target layer according to the pore reference value and determine the length of each second target layer according to the pore length difference of the previous target layer; Perforate the toe of the horizontal well, and then perform fracturing operations on each target layer after the perforation of the toe of the horizontal well is completed; When performing a fracturing operation on a single target layer, the target layer is perforated and, upon completion of perforation, CO2 fracturing fluid and proppant are injected into the target layer, wherein the injection amount of the CO2 fracturing fluid is determined based on the reference oil-bearing sandstone length, and the thickener content is determined based on the reservoir pressure; After the injection of proppant into a single target layer is completed, the fracture density of the target layer is detected. If the fracture density is less than the preset fracture density, the fracturing fluid adjustment method for the target layer is determined based on the gravel state of the proppant. This includes optimizing the method based on the difference in gravel particle size or adjusting the injection pressure of the CO2 fracturing fluid. The optimization method is to adjust the injection temperature of the CO2 fracturing fluid, or to adjust the thickener content or the injection rate of the CO2 fracturing fluid according to the apparent viscosity of the CO2 fracturing fluid; After the CO2 fracturing fluid injection is completed in the entire well section, the well is blocked, and the blocking time is determined according to the comprehensive reference value; The well is blocked and the bridge plug is drilled out; The formation state is determined based on the porosity reference value and tight oil richness. The formation state includes: a first rock formation state in which the pore reference value is greater than a preset pore reference value and the tight oil richness is greater than a preset tight oil richness; a second rock formation state in which the pore reference value is less than or equal to a preset pore reference value or the tight oil richness is less than or equal to a preset tight oil richness; Determine the target layer setting method based on the rock formation status; In the first rock layer state, the target layer is set by determining the target layer length according to the rock layer evaluation coefficient; In the second rock layer state, the target layer is set in such a way that the length of the first target layer is determined according to the pore reference value, and the length of each second target layer is determined according to the pore length difference of the previous target layer; The calculation formula of the rock formation evaluation coefficient τ is: ； Where φ is the pore reference value, H is the tight oil richness, ε1 is the first coefficient, and ε2 is the second coefficient; After the CO2 fracturing fluid injection is completed in the entire well section, the well blocking time is determined based on the comprehensive reference value; The calculation formula of the comprehensive reference value γ is: , where α is the reservoir pressure, β is the horizontal well diameter, ω1 is the first weight coefficient, and ω2 is the second weight coefficient; The relationship between the well blocking time and the comprehensive reference value is a negative correlation.

2. The fracturing process for tight oil horizontal wells according to claim 1, characterized in that: Determine the target layer length based on the rock formation evaluation coefficient; The relationship between the target layer length and the rock formation evaluation coefficient is a negative correlation.

3. The fracturing process for tight oil horizontal wells according to claim 1, characterized in that: In the second rock layer state, the length of the first target layer is determined according to the pore reference value, and the length of each second target layer is determined according to the pore length difference of the previous target layer; If the hole length difference is less than the preset hole length difference, the length of the second target layer is the standard length; If the hole length difference is greater than or equal to the preset hole length difference, the length of the second target layer is reduced; The relationship between the pore reference value and the length of the first target layer is a positive correlation; The first target layer is the target layer closest to the toe of the horizontal well, and the second target layer is all target layers except the first target layer.

4. The fracturing process for tight oil horizontal wells according to claim 3, characterized in that: When injecting CO2 fracturing fluid into the target layer, the injection amount of CO2 fracturing fluid corresponding to the target layer is determined according to the reference oil-bearing sandstone length of the target layer; The injection volume of the CO2 fracturing fluid is positively correlated with the length of the reference oil-bearing sandstone.

5. The fracturing process for tight oil horizontal wells according to claim 4, characterized in that: Determine the thickener content of the target layer according to the reservoir pressure of the target layer; The relationship between the reservoir pressure and the thickener content is a negative correlation.

6. The fracturing process for tight oil horizontal wells according to claim 5, characterized in that: When the injection of proppant into a single target layer is completed, the fracture density of the target layer is detected. If the fracture density is less than the preset fracture density, the fracturing fluid adjustment method for the subsequent target layer of the target layer is determined according to the gravel state of the proppant; In the first gravel state, the fracturing fluid adjustment method is to determine the optimization method according to the difference in gravel particle size; In the second gravel state, the fracturing fluid adjustment method is to adjust the injection pressure of the CO2 fracturing fluid.

7. The fracturing process for tight oil horizontal wells according to claim 6, characterized in that: The gravel state is determined according to the average gravel particle size of the proppant, and the gravel state includes: A first gravel state in which the average gravel particle size is greater than or equal to a preset average gravel particle size; A second gravel state in which the average gravel particle size is smaller than a preset average gravel particle size.

8. The fracturing process for tight oil horizontal wells according to claim 7, characterized in that: If the fracture density of a target layer is less than the preset fracture density and the gravel state of the proppant is the first gravel state, an optimization method is determined according to the difference in gravel particle size; If the difference in gravel particle size is greater than or equal to the preset difference in gravel particle size, the optimization method is to reduce the injection temperature of the CO2 fracturing fluid corresponding to the subsequent target layer of the target layer; If the difference in gravel particle size is less than the preset difference in gravel particle size, the optimization method is to adjust the thickener content or carbon dioxide injection rate corresponding to the target layer after the target layer according to the apparent viscosity of the CO2 fracturing fluid; The relationship between the reduction value of the injection temperature of the CO2 fracturing fluid and the fracture density is positively correlated.

9. The fracturing process for tight oil horizontal wells according to claim 8, characterized in that: If the difference in the sand and gravel particle sizes is less than the preset difference in the sand and gravel particle sizes, the apparent viscosity of the CO2 fracturing fluid is tested; If the apparent viscosity is greater than or equal to the preset apparent viscosity, the injection rate of the CO2 fracturing fluid corresponding to the target layer after the target layer is reduced; If the apparent viscosity is less than the preset apparent viscosity, the thickener content corresponding to the subsequent target layer of the target layer is increased; The relationship between the reduction value of the injection rate of the CO2 fracturing fluid and the fracture density is positively correlated; The relationship between the increase in the thickener content and the crack density is positively correlated.

10. The fracturing process for tight oil horizontal wells according to claim 6, characterized in that: If the fracture density of a target layer is less than the preset fracture density and the gravel state of the proppant is the second gravel state, the injection pressure of the CO2 fracturing fluid corresponding to the subsequent target layer of the target layer is increased and adjusted; The increase in the injection pressure of the CO2 fracturing fluid is positively correlated with the fracture density.

11. The fracturing process for tight oil horizontal wells according to claim 1, characterized in that: The annular sand fracturing method is used for the target layer that has been injected with CO2 fracturing fluid.

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