Fracturing process for tight oil horizontal well

Abstract

The invention relates to the technical field of oil production engineering, in particular to a fracturing process for a tight oil horizontal well, which comprises the following steps: acquiring geological data information; determining a rock stratum state according to the pore reference value of the to-be-constructed area and the tight oil enrichment degree, and determining a target stratum setting mode according to the rock stratum state; perforation is conducted on the toe end of the horizontal well, and fracturing operation is conducted on all target layers after perforation of the toe end of the horizontal well is completed; the injection amount of CO2 fracturing fluid is determined according to the length of the reference oil-containing sandstone, and the content of a thickening agent is determined according to the reservoir pressure; if the fracture density is smaller than the preset fracture density, it is determined that the fracturing fluid adjusting mode of the rear target layer is an optimization mode determined according to the gravel particle size difference degree or adjustment is conducted according to the injection pressure of CO2 fracturing fluid according to the gravel state of the proppant; after the CO2 fracturing fluid is injected into the whole well section, the well closing time is determined according to the comprehensive reference value; and drilling and removing the bridge plug. The fracturing effect can be improved, and the exploitation efficiency of the tight oil horizontal well is improved.

Description

Technical Field

[0001] The 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] Due to CO 2 Under reservoir conditions, it can be in a supercritical state, with extremely strong fluidity and diffusivity, and is currently the main medium for energy enhancement and recovery in unconventional reservoirs. 2 During the fracturing process, CO is mainly pumped into the single-stage pre-fluid stage. 2 , leading to CO 2 The diffusion is not thorough, the contact time with the formation crude oil is short, and the displacement is not sufficient. At the same time, due to the CO 2 The interval between pumping into the formation and the main fracturing operation is short, CO 2 It cannot be fully laid into the complex fractures formed by the main fracturing, reducing CO 2 Therefore, how to improve CO 2 Improving the fracturing effect and improving the production efficiency of tight oil horizontal wells are technical problems that need to be solved urgently by those skilled in the art.

[0003] Chinese patent publication number CN109538177A discloses a new process of supercritical carbon dioxide fracturing, including the following steps: (1) well cleaning, (2) perforation, (3) fracturing treatment, (4) injection of proppant, (5) staged fracturing, (6) isolation treatment, (7) well blocking treatment, and (8) post-fracturing blowdown and backflow. It can be seen that the above technical solution has the following problems: it does not improve CO 2 The fracturing effect and the production efficiency of tight oil horizontal wells are 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 that the prior art does not improve CO 2 The fracturing effect and the poor production efficiency of tight oil horizontal wells.

[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 setting method of determining the target layer according to the rock layer state 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 to 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 after the perforation of the toe of the horizontal well is completed, perform fracturing operations on each target layer;

[0010] When a single target layer is subjected to fracturing, perforation is performed on the target layer and CO is injected into the target layer after perforation is completed. 2 Fracturing fluid, proppant injection, wherein CO is determined based on the reference oil-bearing sandstone length 2 The injection volume of fracturing fluid and the thickener content are determined according to 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 according to the gravel state of the proppant. The optimization method is determined according to the difference in gravel particle size or the CO 2 Adjust the injection pressure of the fracturing fluid;

[0012] The optimization method is to target CO 2 The injection temperature of the fracturing fluid is adjusted, or, according to the CO 2 The apparent viscosity of the fracturing fluid is specific to the thickener content or CO 2 Adjust the injection rate of the fracturing fluid;

[0013] Full well section CO 2 After the fracturing fluid is injected, the well is sealed, wherein the well sealing time is determined according to the comprehensive reference value;

[0014] The well is blocked and the bridge plug is removed by drilling.

[0015] Furthermore, the formation state is determined based on the porosity reference value and the tight oil abundance, and 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 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] Further, 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] Further, the target layer length is determined according to 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] Among them, φ is the pore reference value, H is the richness of tight oil, ε1 is the first coefficient, and ε2 is the second coefficient.

[0026] Further, 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;

[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 and adjusted;

[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, CO is injected into the target layer. 2 When fracturing fluid is used, the CO corresponding to the target layer is determined according to the reference oil-bearing sandstone length of the target layer. 2 The amount of fracturing fluid injected;

[0032] The CO 2 There is a positive correlation between the injection volume of the fracturing fluid and 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, and if the fracture density is less than the preset fracture density, the fracturing fluid adjustment method of the target layer after 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 target CO 2The injection pressure of the fracturing fluid is adjusted.

[0038] Further, the gravel state is determined according to the mean value of the gravel particle size of the proppant, and the gravel state includes:

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

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

[0041] Further, 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 the gravel particle size;

[0042] If the difference in the sand and gravel particle size is greater than or equal to the preset difference in the sand and gravel particle size, the optimization method is to target the CO corresponding to the target layer after the target layer. 2 The injection temperature of the fracturing fluid is reduced and adjusted;

[0043] If the difference in the size of the gravel particles is less than the preset difference in the size of the gravel particles, the optimization method is to use CO 2 The apparent viscosity of the fracturing fluid is adjusted according to the thickener content or carbon dioxide injection rate corresponding to the target layer behind the target layer;

[0044] The CO 2 The decrease in injection temperature of the fracturing fluid is positively correlated with the fracture density.

[0045] Furthermore, if the difference in the size of the gravel particles is less than the preset difference in the size of the gravel particles, the CO 2 The apparent viscosity of the fracturing fluid;

[0046] If the apparent viscosity is greater than or equal to the preset apparent viscosity, the CO corresponding to the post-target layer of the target layer 2 The injection rate of the fracturing fluid is reduced and adjusted;

[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 and adjusted;

[0048] The CO 2 The decrease in the injection rate of the fracturing fluid is positively correlated with the fracture density;

[0049] The increase in the thickener content is positively correlated with the crack density.

[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 CO corresponding to the subsequent target layer of the target layer is 2 The injection pressure of the fracturing fluid is increased and adjusted;

[0051] The CO 2 The increase in injection pressure of the fracturing fluid is positively correlated with the fracture density.

[0052] Furthermore, the whole well section CO 2 After the fracturing fluid is injected, 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, for the injected CO 2 The target layer of the fracturing fluid adopts the annular sand fracturing method.

[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 the actual situation, 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 according to 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 production efficiency of tight oil horizontal wells.

[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 CO corresponding to the target layer according to the length of the reference oil-bearing sandstone. 2The injection volume of the fracturing fluid can effectively reflect the current reservoir state by referring to the length of the oil-bearing sandstone, and can then determine the CO2 injection volume according to the actual reservoir conditions. 2 The injection volume of fracturing fluid avoids the problem of increasing operating costs due to excessive injection of fracturing fluid and poor fracturing effect due to insufficient injection of fracturing fluid, 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 CO 2 The viscosity and fluidity of the fracturing fluid decrease under high pressure, resulting in poor sand carrying capacity, thus ensuring the CO 2 The stability of fracturing fluid performance improves the fracturing effect.

[0061] Furthermore, the present invention determines the fracturing fluid adjustment mode of the post-target layer according to the gravel state of the proppant, and the gravel state of the proppant reflects the grain length state of the gravel, and then selects different fracturing fluid adjustment modes according to the gravel state, so that the selection of the fracturing fluid adjustment mode is more in line with the actual working scene, avoiding the CO 2 The problem of poor fracturing effect has been solved, 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 difference in gravel particle size, and the difference in gravel particle size reflects the difference in gravel particle size, and then selects different optimization methods according to the difference in gravel particle size, so that the selection of the optimization method is more in line with the actual working scene, avoiding the CO 2 The problem of poor fracturing effect has been solved, thereby improving the production efficiency of tight oil horizontal wells.

[0063] Furthermore, when the difference in the size of the gravel particles is less than the preset difference in the size of the gravel particles, the present invention uses CO 2 The apparent viscosity of the fracturing fluid effectively reflects the CO 2 The sand-carrying capacity of the fracturing fluid, and then through CO 2 The apparent viscosity of the fracturing fluid determines different adjustment methods, making the selection of adjustment methods more in line with the actual working scenario and avoiding the CO 2 The problem of poor fracturing effect has been solved, thereby improving the production efficiency of tight oil horizontal wells.

[0064] Furthermore, the present invention effectively reflects the horizontal well diameter and storage pressure status according to 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 has injected CO 2 The target layer of the fracturing fluid adopts the annular sand fracturing method, which can significantly improve the conductivity of the fracture, making the tight oil and CO 2 The ability to flow more smoothly through fractures can enhance formation stability and reduce the risk of formation pressure drop and tight oil production decline due to fracture closure. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 It is a schematic diagram of the fracturing process for tight oil horizontal wells of the present invention;

[0067] Figure 2 A flow chart of determining the state of a rock formation according to a pore reference value and tight oil richness in the present invention;

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

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

[0070] Figure 5 is a schematic diagram of a horizontal tight oil well of 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 only used to explain the present invention and are not used 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 protection scope 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 drawings. This is merely 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] In addition, it should be noted that in the description of the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to 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 setting method of determining the target layer according to the rock layer state 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 to 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 after the perforation of the toe of the horizontal well is completed, perform fracturing operations on each target layer;

[0081] When a single target layer is subjected to fracturing, perforation is performed on the target layer and CO is injected into the target layer after perforation is completed. 2 Fracturing fluid, proppant injection, wherein CO is determined based on the reference oil-bearing sandstone length 2 The injection volume of fracturing fluid and the thickener content are determined according to 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 according to the gravel state of the proppant. The optimization method is determined according to the difference in gravel particle size or the CO 2 Adjust the injection pressure of the fracturing fluid;

[0083] The optimization method is to target CO 2 The injection temperature of the fracturing fluid is adjusted, or, according to the CO2 The apparent viscosity of the fracturing fluid is specific to the thickener content or CO 2 Adjust the injection rate of the fracturing fluid;

[0084] Full well section CO 2 After the fracturing fluid is injected, the well is sealed, wherein the well sealing time is determined according to the comprehensive reference value;

[0085] The well is blocked and the bridge plug is removed by drilling.

[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 toe perforation. The toe perforation layer section 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-shooting joint operation process. This is content that is easy to understand for technicians in this field 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 post-target layer.

[0088] The present invention performs staged fracturing on a horizontal well, wherein the horizontal section of the horizontal well to be fractured each time is recorded as a target layer, wherein a bridge plug is arranged between two adjacent target layers in the horizontal well to seal the target layer into which proppant has been injected, and a bridge-shooting joint operation process is adopted for perforating each target layer, wherein the bridge-shooting joint operation process utilizes a continuous oil pipe to send the bridge plug and the perforator into the wellbore, and the setting and perforating operations of the bridge plug are realized through ground control.

[0089] The ingredients 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, drag reducer or drainage agent. The proppant is ceramsite proppant. The types of thickener and additives can be selected by users according to the actual needs of the scene. 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 the tight oil richness, and 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 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 Ф is: Where N is the number of detection points, x i is the porosity of the ith detection point; the detection method of the porosity of each detection point includes but is not limited to borehole logging, density logging or sonic logging, and the user can choose according to the needs. This is easy to understand for technicians in this field and will not be 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 the 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 whose 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, and 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 are. 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 to the perforation section, and detect the depth of each hole in the perforation section, which is recorded as the hole length of each hole. This is easy for technical personnel 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] Among them, φ is the pore reference value, H is the richness of tight oil, ε1 is the first coefficient, and ε2 is the second coefficient.

[0106] It is understandable that the user can learn from historical records through a deep learning convolutional neural network to analyze the influence of the porosity reference value and the 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 and adjusted;

[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, CO is injected into the target layer. 2 When fracturing fluid is used, the CO corresponding to the target layer is determined according to the reference oil-bearing sandstone length of the target layer. 2 The amount of fracturing fluid injected;

[0115] The CO 2 There is a positive correlation between the injection volume of the fracturing fluid and the length of the reference oil-bearing sandstone.

[0116] The reference oil-bearing sandstone length is confirmed in the following manner: for a single target layer, the total length of the target layer in the length interval in the logging curve where the natural gamma value is less than the preset natural gamma value is the reference oil-bearing sandstone length;

[0117] CO 2 The injection volume of fracturing fluid is the CO injected into a single target layer. 2 Total amount of fracturing fluid, in tons, CO 2 The calculation formula for the injection volume Q of the fracturing fluid is: Q=δ×h, where h is the reference oil-bearing sandstone length and δ is the reference coefficient. A value of a 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 method for confirming the reservoir pressure is as follows: for a single target layer, the target layer is recorded as a reference target layer, and a pressure sensor is used to be lowered to the two end points and the midpoint of the reference target layer for measurement, and the pressure at each position detected by the pressure sensor is recorded 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 convert the CO 2 The amount of thickener in the fracturing fluid is recorded 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 of 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 target CO 2 The injection pressure of the fracturing fluid is adjusted.

[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 in the reference target layer after CO is injected into the reference target layer. 2The number of cracks generated after fracturing fluid and proppant, the number of cracks in the reference target layer can be detected by microseismic monitoring technology, which 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, and H0 is the length of the reference target layer;

[0126] The preset crack density value can be determined by the user according to the actual application scenario. 2 The greater the demand for good fracturing effect of the 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 mean value of the gravel particle size is greater than or equal to a preset mean value of the gravel particle size;

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

[0130] Among them, W gravels are randomly selected from the proppant used in the present invention, and the calculation formula for the mean value of the 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: 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. A value of W is provided, W=100.

[0131] The value of the average gravel particle size can be preset, and users can set it according to the actual application scenario. 2 The greater the demand for better sand suspension capacity of the fracturing fluid, the smaller the value of the preset mean gravel particle size. A value of the preset mean gravel particle size is provided, and the preset mean gravel particle size is 3 mm.

[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 the gravel particle size;

[0133] If the difference in the sand and gravel particle size is greater than or equal to the preset difference in the sand and gravel particle size, the optimization method is to target the CO corresponding to the target layer after the target layer. 2 The injection temperature of the fracturing fluid is reduced and adjusted;

[0134] If the difference in the size of the gravel particles is less than the preset difference in the size of the gravel particles, the optimization method is to use CO 2 The apparent viscosity of the fracturing fluid is adjusted according to the thickener content or carbon dioxide injection rate corresponding to the target layer behind the target layer;

[0135] The CO 2 The decrease in injection temperature of the fracturing fluid is positively correlated with the fracture density.

[0136] Among them, CO 2 The injection temperature of the fracturing fluid is CO 2 The initial temperature when the fracturing fluid is injected, the difference in gravel particle size = (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 randomly selected from the proppant used in the present invention, and the minimum gravel particle size is the minimum gravel particle size among several gravels randomly 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 value of the preset gravel particle size difference can be set by the user according to the actual application scenario. 2 The greater the requirement for the fracturing fluid to have a good fracturing effect, the smaller the value of the preset gravel particle size difference is, and a value of the preset gravel particle size difference is provided, and the preset gravel particle size difference is 20%;

[0138] It is understandable that for the adjacent target layer CO 2 The fracturing fluid injection temperature can be reduced to increase CO 2 The apparent viscosity of the fracturing fluid allows a large amount of sand and gravel particles to be suspended in the CO 2 The fracturing fluid increases the density of the fractures.

[0139] Specifically, if the difference in the size of the gravel particles is less than the preset difference in the size of the gravel particles, the CO 2 The apparent viscosity of the fracturing fluid;

[0140] If the apparent viscosity is greater than or equal to the preset apparent viscosity, the CO corresponding to the post-target layer of the target layer 2 The injection rate of the fracturing fluid is reduced and adjusted;

[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 and adjusted;

[0142] The CO 2 The decrease in the injection rate of the fracturing fluid is positively correlated with the fracture density;

[0143] The increase in the thickener content is positively correlated with the crack density.

[0144] Among them, CO 2 The apparent viscosity of the fracturing fluid is tested by a viscometer. The model of the viscometer is not specifically limited, as long as it meets the needs of the user;

[0145] The value of the preset apparent viscosity can be set by the user according to the actual application scenario. 2 The greater the demand for good fracturing effect of the fracturing fluid, the greater the value of the preset apparent viscosity. A preset apparent viscosity value is provided to detect the CO2 content in the historical construction records that the fracturing effect meets the user's needs. 2 The apparent viscosity of the fracturing fluid is 2 The average value of the apparent viscosity of the fracturing fluid is recorded as the preset apparent viscosity;

[0146] It can be understood that the CO corresponding to the post-target layer of the target layer 2 Reducing the injection rate of the fracturing fluid helps 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 CO corresponding to the subsequent target layer of the target layer 2 The injection pressure of the fracturing fluid is increased and adjusted;

[0148] The CO 2 The increase in injection pressure of the fracturing fluid is positively correlated with the fracture density.

[0149] Among them, the CO corresponding to the post-target layer of the target layer 2 Increasing the injection pressure of the fracturing fluid can increase the number of fractures and thus the fracture density. 2 During the injection of fracturing fluid, CO 2 The injection pressure of the fracturing fluid and the reservoir conditions are monitored, and the injection parameters are adjusted in a timely manner according to the monitoring results to ensure that CO 2 The injection pressure of the fracturing fluid is kept within a safe range to avoid CO 2 The injection pressure of the fracturing fluid is too high, causing the formation to rupture.

[0150] Specifically, the whole well section CO 2 After the fracturing fluid is injected, 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 blocking time refers to the time after the completion of the whole well section CO 2 After the fracturing fluid is injected, the wellhead is closed to allow the CO 2 The period of time during which the fracturing fluid is fully active in the ground;

[0154] It is understandable that the user 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-clogging time, and then determine the values ​​of the first weight coefficient and the second weight coefficient, where ω1+ω2=1, and one value of ω1 and ω2 is provided, ω1=0.5, ω2=0.5.

[0155] Specifically, the injected CO 2 The target layer of the fracturing fluid adopts the annular sand fracturing method.

[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 diagram of the structure of a tight oil horizontal well of 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 of the horizontal well. The horizontal well is subjected to staged fracturing, and the horizontal section of the horizontal well subjected to fracturing each time is recorded as a target layer 3. The bridge plug 2 is arranged 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 plurality of holes 4 can be obtained.

[0159] So far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

[0160] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope 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 setting method of determining the target layer according to the rock layer state 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 to 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 after the perforation of the toe of the horizontal well is completed, perform fracturing operations on each target layer; When a fracturing operation is performed on a single target layer, perforation is performed on the target layer and CO2 fracturing fluid and proppant are injected into the target layer after perforation is completed, wherein the injection amount of CO2 fracturing fluid is determined according to the reference oil-bearing sandstone length, and the thickener content is determined according to 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 according to the gravel state of the proppant, such as determining the optimization method according to 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 speed 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 sealed, wherein the sealing time is determined according to the comprehensive reference value; The well is blocked and the bridge plug is removed by drilling.

2. The fracturing process for tight oil horizontal wells according to claim 1, characterized in that: The formation state is determined based on the porosity reference value and the 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 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.

3. The fracturing process for tight oil horizontal wells according to claim 2, characterized in that: Determine the target layer setting method according to 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 preceding target layer.

4. The fracturing process for tight oil horizontal wells according to claim 3, characterized in that: Determine the target layer length according to the rock formation evaluation coefficient; The relationship between the target layer length and the rock formation evaluation coefficient is a negative correlation.

5. The fracturing process for tight oil horizontal wells according to claim 4, characterized in that: The calculation formula of the rock formation evaluation coefficient τ is: Among them, φ is the pore reference value, H is the richness of tight oil, ε1 is the first coefficient, and ε2 is the second coefficient.

6. The fracturing process for tight oil horizontal wells according to claim 5, 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 and adjusted; 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.

7. The fracturing process for tight oil horizontal wells according to claim 6, 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 amount of the CO2 fracturing fluid is positively correlated with the length of the reference oil-bearing sandstone.

8. The fracturing process for tight oil horizontal wells according to claim 7, characterized in that: Determining 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.

9. The fracturing process for tight oil horizontal wells according to claim 8, 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 of 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.

10. The fracturing process for tight oil horizontal wells according to claim 9, 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 mean value of the gravel particle size is greater than or equal to a preset mean value of the gravel particle size; A second gravel state in which the average gravel particle size is smaller than a preset gravel particle size average.

11. The fracturing process for tight oil horizontal wells according to claim 9, 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 the gravel particle size; If the difference in the sand and gravel particle size is greater than or equal to the preset difference in the sand and gravel particle size, the optimization method is to reduce the injection temperature of the CO2 fracturing fluid corresponding to the post-target layer of the target layer; If the difference in the sand and gravel particle sizes is less than the preset difference in the sand and gravel particle sizes, the optimization method is to adjust the thickener content or the carbon dioxide injection rate corresponding to the post-target layer of the target layer according to the apparent viscosity of the CO2 fracturing fluid; The decrease in injection temperature of the CO2 fracturing fluid is positively correlated with the fracture density.

12. The fracturing process for tight oil horizontal wells according to claim 11, 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 and adjusted; The decrease in injection speed of the CO2 fracturing fluid is positively correlated with the fracture density; The increase in the thickener content is positively correlated with the crack density.

13. The fracturing process for tight oil horizontal wells according to claim 9, 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 injection pressure of the CO2 fracturing fluid is positively correlated with the fracture density.

14. The fracturing process for tight oil horizontal wells according to claim 13, characterized in that: 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: 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; The relationship between the well blocking time and the comprehensive reference value is a negative correlation.

15. 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 into which CO2 fracturing fluid has been injected.

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