A reservoir protection method based on solid-free low-activity drilling fluid

Abstract

The present invention relates to the field of drilling technology, and in particular to a reservoir protection method based on solid-free, low-activity drilling fluid, comprising: obtaining geological parameters of a target area and constructing a parameter evaluation model; determining a drilling fluid ratio based on the parameter evaluation model, and preparing solid-free, low-activity drilling fluid based on the drilling fluid ratio; detecting characteristic parameters of the solid-free, low-activity drilling fluid, wherein the characteristic parameters include density, viscosity, and fluid loss; determining a target drilling pressure and a target drilling rate during the drilling process based on the characteristic parameters, and determining a drilling fluid adjustment method based on the determined target drilling pressure and target drilling rate; drilling based on the target drilling pressure, target drilling rate, and drilling fluid adjustment method, and determining whether the target drilling pressure and target drilling rate need to be adjusted based on the thickness and porosity of the mud cake during the drilling process. The present invention can reduce damage to the reservoir and improve drilling efficiency.

Description

Technical Field

[0001] The present invention relates to the field of drilling technology, and in particular to a reservoir protection method based on solid-phase-free low-activity drilling fluid. Background Art

[0002] Horizontal openhole completions are often used to increase single-well productivity, but this technology places extremely high demands on reservoir protection. The drilling fluid is the first fluid to contact the reservoir, and parameters such as the solids composition, physicochemical properties, and particle size distribution within the fluid profoundly impact the reservoir. Solids (barite, bentonite) in traditional drilling fluids can damage the reservoir and are difficult to remove, leading to significant declines in oil and gas production. To address these issues, solids-free drilling fluids are being used for reservoir drilling. These are a new type of drilling fluid developed based on low-solids drilling fluids. They do not contain clay, but only incorporate organic polymers as viscosifiers and inorganic chemical treatment agents, minimizing the damage caused by artificial clay minerals. Currently studied solids-free drilling fluids offer advantages such as wellbore stability, resistance to mudstone contamination, ease of degradation, and low biotoxicity. However, their drawback is that the drilling fluid colloids can clog reservoir fractures and are difficult to break down, compromising reservoir protection.

[0003] Chinese patent publication number CN102410022B discloses a fractured carbonate reservoir protection method, comprising: fractured carbonate reservoir protection material: composed of 0.5-20 parts by mass of carbon material, 70-85 parts by mass of special fiber colloid new material and 5-10 parts by mass of surfactant; solid-free low-damage drilling fluid completion fluid formula: 100 parts of water, 1-2 parts of sulfonated asphalt, 0.5-3 parts of methyl formate, 0.1-0.3 parts of carboxymethyl Cellulose, 1-2 parts of sulfonated phenolic resin, 1-2 parts of modified starch and 3 parts of fractured carbonate reservoir protection material, sodium formate is added to adjust the density to 1-1.36g / cm3; when serious leakage is expected, solid-free low-damage drilling fluid and completion fluid are added to the mud to increase the pump pressure, fully open the fractures, squeeze in the fracture layer, and form a plug to strengthen the formation; it can prevent the extension of fractures and make the formation withstand pressure higher than the fracture gradient without causing mud leakage.

[0004] It can be seen that the above invention has the following problems: only by adding solid-free low-damage drilling fluid completion fluid into the mud to form a plugging layer to prevent the extension of cracks, it will cause greater damage to the reservoir and low drilling efficiency. Summary of the Invention

[0005] To this end, the present invention provides a reservoir protection method based on a solid-free low-activity drilling fluid to overcome the problems in the prior art of significant damage to the reservoir during the drilling process and low drilling efficiency.

[0006] To achieve the above objectives, the present invention provides a reservoir protection method based on a solid-free low-activity drilling fluid, comprising:

[0007] Step S1, obtaining geological parameters of the target area and constructing a parameter evaluation model; the geological parameters include formation hardness, formation pressure, formation structure and reservoir characteristics;

[0008] Step S2, determining a drilling fluid ratio based on the parameter evaluation model, and preparing a solid-free low-activity drilling fluid based on the drilling fluid ratio;

[0009] Step S3, detecting characteristic parameters of the solid-free low-activity drilling fluid; the characteristic parameters include density, viscosity, and fluid loss;

[0010] Step S4, determining a target drilling pressure and a target drilling rate during the drilling process based on the characteristic parameters, and determining a drilling fluid adjustment method according to the determined target drilling pressure and target drilling rate;

[0011] Step S5: Drilling is performed based on the target drilling pressure, the target drilling rate, and the drilling fluid adjustment method, and whether the target drilling pressure and the target drilling rate need to be adjusted is determined according to the thickness and porosity of the mud cake during drilling.

[0012] Furthermore, in the step S1, it includes:

[0013] Step S11, constructing a geological parameter model according to the geological parameters of the target area, and determining key geological parameters based on the geological parameter model;

[0014] Step S12: establishing parameter influence indexes of the key geological parameters and various geological parameters, and constructing a parameter evaluation model based on the parameter influence indexes and preset evaluation criteria.

[0015] Furthermore, in step S2, it includes:

[0016] Step S21, determining a parameter evaluation characteristic value based on the parameter evaluation model;

[0017] Step S22: determining the drilling fluid ratio according to the parameter evaluation characteristic value.

[0018] Furthermore, in the step S4, it includes:

[0019] Step S41, determining a comprehensive parameter influencing factor based on the characteristic parameters;

[0020] Step S42: determining a target drilling pressure according to the comprehensive parameter influencing factor and a preset drilling pressure, and determining a target drilling rate according to the comprehensive parameter influencing factor and a preset drilling rate.

[0021] Furthermore, in the step S4, it further includes:

[0022] Comparing the target drilling pressure with the actual drilling pressure, and determining a flow adjustment method for the drilling fluid according to the comparison result;

[0023] The target drilling rate is compared with the actual drilling rate, and a flow rate adjustment method of the drilling fluid is determined based on the comparison result.

[0024] Furthermore, in the step S4, it further includes:

[0025] determining a first comparison value according to a difference between the target drilling pressure and the actual drilling pressure, and determining a flow adjustment amount of the drilling fluid based on the first comparison value and a standard drilling fluid flow rate;

[0026] A second comparison value is determined according to the difference between the target drilling rate and the actual drilling rate, and a drilling fluid flow rate adjustment amount is determined based on the second comparison value and a standard drilling fluid flow rate.

[0027] Furthermore, in the step S5, it includes:

[0028] Obtaining the thickness and porosity of the mud cake after a preset drilling time period, and determining whether the target drilling pressure and the target drilling rate need to be adjusted based on the thickness and the porosity;

[0029] If the thickness is less than a preset thickness threshold, and the porosity is less than a preset porosity threshold, it is determined that there is no need to adjust the target drilling pressure and the target drilling rate;

[0030] If the thickness is greater than or equal to a preset thickness threshold and / or the porosity is greater than or equal to a preset porosity threshold, it is determined that the target drilling pressure and the target drilling rate need to be adjusted.

[0031] Furthermore, in the step S5, it further includes:

[0032] If the thickness of the mud cake is greater than or equal to a preset thickness threshold, determining an adjustment amount for the target drilling pressure based on a comparison result between the thickness and the preset thickness threshold;

[0033] If the porosity of the mud cake is greater than or equal to a preset porosity threshold, an adjustment amount of the target drilling speed is determined according to a comparison result of the porosity with the preset porosity threshold.

[0034] Furthermore, in step S22, the comparison characteristic values ​​of the drilling fluid ratio comparison table are determined based on the correlation between the key geological parameters and the characteristic parameters of the drilling fluid, and the drilling fluid ratio is determined according to the comparison characteristic values ​​and the parameter evaluation characteristic values.

[0035] Furthermore, the drilling fluid components include organic salts, cellulose polysaccharides, hydrophobic temporary plugging agents, plugging agents, activity regulators and water.

[0036] Compared with the prior art, the beneficial effect of the present invention is that the present invention constructs a parameter evaluation model based on the geological parameters of the target area to determine the drilling fluid ratio, which can adapt to the geological conditions of the target area, obtain ideal drilling effects, and improve drilling efficiency. In addition, the application of solid-free low-activity drilling fluid can reduce damage to the reservoir and achieve reservoir protection. Determining the target drilling pressure and target drilling rate during the drilling process based on the characteristic parameters of the solid-free low-activity drilling fluid can improve drilling efficiency and maintain wellbore stability. Determining the drilling fluid adjustment method based on the determined target drilling pressure and target drilling rate can improve drilling efficiency and drilling effects by adjusting the drilling fluid, and reduce damage to the reservoir caused by the drilling fluid.

[0037] Furthermore, the present invention constructs a geological parameter model based on the geological parameters of the target area to determine the key geological parameters more accurately. By establishing parameter influence indexes of key geological parameters and various geological parameters, the accuracy and efficiency of the constructed parameter evaluation model can be improved.

[0038] Furthermore, the present invention determines the parameter evaluation characteristic value based on the parameter evaluation model, and determines the drilling fluid ratio according to the parameter evaluation characteristic value and the preset drilling fluid ratio comparison table, which can improve the efficiency of determining the drilling fluid ratio, and can make the determined drilling fluid ratio adapt to the geological parameters of the target area, improve the drilling effect, and reduce damage to the reservoir.

[0039] Furthermore, the present invention determines the comprehensive parameter influencing factor based on the characteristic parameters of the solid-free low-activity drilling fluid, which can characterize the performance characteristics of the solid-free low-activity drilling fluid. Different drilling fluid properties have an impact on drilling pressure and drilling rate. By determining the target drilling pressure and target drilling rate respectively by combining the comprehensive parameter influencing factor with the preset drilling pressure and preset drilling rate, the drilling efficiency can be improved and leakage can be reduced.

[0040] Furthermore, the present invention determines the drilling fluid flow adjustment method and the drilling fluid flow rate adjustment method according to the target drilling pressure and the target drilling rate, respectively, which can reduce the loss of drilling fluid and reduce damage to the reservoir.

[0041] Furthermore, the drilling fluid of the present invention uses a solid-free low-activity drilling fluid system, which can reduce damage to the reservoir due to solid phase invasion and improve drilling efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a flow chart of a reservoir protection method based on a solid-free low-activity drilling fluid according to an embodiment of the present invention;

[0043] Figure 2Schematic diagram of the process of step S1 of the embodiment of the present invention;

[0044] Figure 3 Schematic diagram of the process of step S2 of an embodiment of the present invention;

[0045] Figure 4 Schematic diagram of the process of step S4 of the embodiment of the present invention;

[0046] Figure 5 This is a flow chart of determining whether to adjust the target drilling pressure and target drilling rate according to an embodiment of the present invention. DETAILED DESCRIPTION

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] See also Figure 1 As shown, it is a flow chart of a reservoir protection method based on a solid-free low-activity drilling fluid according to an embodiment of the present invention. An embodiment of the present invention provides a reservoir protection method based on a solid-free low-activity drilling fluid, comprising:

[0052] Step S1, obtaining geological parameters of the target area and constructing a parameter evaluation model; the geological parameters include formation hardness, formation pressure, formation structure and reservoir characteristics;

[0053] It can be understood that the target area is the drilling area, the stratigraphic structure includes rock folds, fault structures, inclined structures, etc., and the reservoir characteristics include rock type, reservoir porosity, permeability, throat type, etc. Those skilled in the art know that any method and equipment in the prior art that can detect the geological parameters of the target area, such as: multi-scale CT scanning technology, micro-area scanning electron microscope imaging technology, etc., fall within the scope of protection of the present invention and will not be repeated here.

[0054] See also Figure 2 , which is a flow chart of step S1 of an embodiment of the present invention; specifically, step S1 includes:

[0055] Step S11, constructing a geological parameter model according to the geological parameters of the target area, and determining key geological parameters based on the geological parameter model;

[0056] Step S12: establishing parameter influence indexes of the key geological parameters and various geological parameters, and constructing a parameter evaluation model based on the parameter influence indexes and preset evaluation criteria.

[0057] During implementation, the correlation coefficients between various geological parameters can be determined through correlation analysis, a geological parameter model can be constructed based on the correlation relationship between the parameters, and geological parameters whose correlation coefficients with other geological parameters are greater than the correlation coefficient threshold are determined as key geological parameters; among them, the actual implementers can determine the correlation coefficient threshold based on the mean of the correlation coefficients between various geological parameters in historical data. Preferably, the correlation coefficient threshold range is 0.3 to 0.5, or the geological parameters corresponding to the top 5 to 7 in the correlation coefficient sorting from large to small are determined as key geological parameters.

[0058] It can be understood that the ratio of the correlation coefficient between the key geological parameter and other geological parameters to the correlation coefficient threshold is determined as the parameter influence index of the key geological parameter and the corresponding geological parameter. The actual implementer can determine the preset evaluation standard based on the correlation between the geological parameters of the drilling area that has passed the qualification test in the historical data and the performance of different drilling fluids. According to the parameter influence index and the preset evaluation standard, data fitting is performed or based on the expert system to construct a parameter evaluation model, which will not be elaborated here.

[0059] The present invention constructs a geological parameter model based on the geological parameters of the target area to determine the key geological parameters more accurately. By establishing the parameter influence index of the key geological parameters and various geological parameters, the accuracy and efficiency of the constructed parameter evaluation model can be improved.

[0060] Step S2, determining a drilling fluid ratio based on the parameter evaluation model, and preparing a solid-free low-activity drilling fluid based on the drilling fluid ratio;

[0061] See also Figure 3 , which is a flow chart of step S2 of an embodiment of the present invention; specifically, in step S2, it includes:

[0062] Step S21, determining a parameter evaluation characteristic value based on the parameter evaluation model;

[0063] In implementation, each geological parameter is input into the parameter evaluation model respectively, the output results of the parameter evaluation model are subjected to regression analysis, and the parameter evaluation characteristic value is determined based on the regression analysis results.

[0064] Step S22: determining the drilling fluid ratio according to the parameter evaluation characteristic value.

[0065] Specifically, in step S22, the comparison characteristic values ​​of the drilling fluid ratio comparison table are determined based on the correlation between the key geological parameters and the characteristic parameters of the drilling fluid, and the drilling fluid ratio is determined according to the comparison characteristic values ​​and the parameter evaluation characteristic values.

[0066] It is understandable that different drilling fluid formulations have different drilling properties, such as good rheological properties, strong high-temperature resistance, good fluid loss reduction, and good plugging performance. The geological parameters of the drilling area are correlated with the drilling performance. Selecting an appropriate drilling fluid based on the geological parameters of the drilling area can not only improve drilling efficiency but also improve drilling quality. In practice, implementers can determine parameter evaluation characteristic values ​​based on the geological parameters of the drilling area in historical data, and determine the corresponding drilling fluid properties based on the parameter evaluation characteristic values, thereby determining the drilling fluid formulation. Correlation analysis can be performed on the characteristic parameters of several drilling fluid ratios corresponding to the drilling fluid formulation and various geological parameters to determine the correlation between the geological parameters and each characteristic parameter. Based on the correlation between the characteristic parameters corresponding to each drilling fluid ratio and the various geological parameters, a reference characteristic value for each drilling fluid ratio is determined. In this way, a drilling fluid ratio reference table is constructed, including the drilling fluid formulation, several drilling fluid ratios corresponding to each drilling fluid formulation, and the reference characteristic value corresponding to each drilling fluid ratio.

[0067] In a specific embodiment, the drilling fluid density (any characteristic parameter) during several drilling processes in the historical data is obtained as Y1, Y2, ..., Y j ,…,Y m , and the corresponding several sub-stratum hardnesses (any geological parameter) are E1, E2, ..., E j ,…,E m , then the correlation Q between drilling fluid density and formation hardness is: Q=((∑ m j=1 (Y j -Y))×(∑ m j=1 (E j-E))) / ((sqrt(∑ m j=1 (Y j -Y) 2 ))×(sqrt(∑ m j=1 (E j -E) 2 ))), where j = 1, 2, ..., m; m is the number of times, Y j is the drilling fluid density during the jth drilling process, E j is the formation hardness of the jth drilling area, Y is the actual value of the drilling fluid density during the drilling process in the target area, and E is the actual value of the formation hardness during the drilling process in the target area. Similarly, the correlation between the key geological parameters and the characteristic parameters of the drilling fluid is calculated, and the mean of each correlation is calculated to determine the control characteristic value.

[0068] The present invention determines parameter evaluation characteristic values ​​based on a parameter evaluation model, and determines the drilling fluid ratio according to the parameter evaluation characteristic values ​​and a preset drilling fluid ratio comparison table. This can improve the efficiency of determining the drilling fluid ratio, and can adapt the determined drilling fluid ratio to the geological parameters of the target area, thereby improving the drilling effect and reducing damage to the reservoir.

[0069] Specifically, the drilling fluid components include organic salts, cellulose polysaccharides, hydrophobic temporary plugging agents, plugging agents, activity regulators and water.

[0070] It is understandable that the use of organic salts in drilling fluids can adjust the density of drilling fluids, improve the rheological properties of drilling fluids, effectively inhibit the hydration and expansion of clay minerals in the formation, reduce damage to oil and gas layers, effectively control well wall penetration, reduce formation invasion, improve well wall stability, reduce the risk of leakage, and improve the protection of reservoirs; cellulose polysaccharides are made by modifying natural materials and have the physical and chemical properties of heteropolysaccharides and cellulose. As an environmentally friendly drilling fluid treatment agent, cellulose polysaccharides have good filtration loss reduction performance. They can resist saturation and form organic compounds in drilling fluids. The effective colloid structure reduces liquid loss, thereby protecting the oil and gas layer, reducing the damage of drilling fluid to the formation, effectively inhibiting the hydration expansion of clay minerals in the formation, reducing damage to the oil and gas layer, maintaining the stability of the well wall, and adjusting the rheological properties of the drilling fluid to make it have better rock carrying capacity and the ability to suspend rock cuttings, thereby improving drilling efficiency; the hydrophobic temporary plugging agent is formed by self-blocking hydrophobic temporary plugging technology, reasonably matching the solid phase particle size of the drilling fluid, and can effectively form a dense mud cake, thereby forming a stable hydrophobic channel in the drilling fluid mud cake, and reducing the resistance to water. It has a large diameter and low resistance to oil, and can block pores of different particle sizes in heterogeneous reservoirs, effectively preventing solid particles and filtrate in the drilling fluid from invading the oil and gas layer. During the drilling process, it can reduce the damage of the drilling fluid to the oil and gas layer and improve the recovery rate of core permeability. The hydrophobic temporary plugging agent is biodegradable, and its degradation rate in the soil can reach more than 50% in 90 days, which is friendly to the environment. The plugging agent can fill the pores in the formation and form a plugging layer on the wellbore wall, thereby increasing the anti-seepage ability of the well wall, preventing the drilling fluid from penetrating and leaking into the formation, and reducing the penetration of the drilling fluid into the formation. Permeability is destroyed; the use of activity regulators in drilling fluids can reduce the water activity of the drilling fluid, creating an activity difference between the downhole and the surrounding rock. The water activity can reach 0.9-0.95, and the membrane efficiency can reach 9.4%-9.5%. This can reduce the migration of water molecules in the drilling fluid to the wellbore wall, improve the membrane efficiency of the shale formation, slow the osmotic hydration of the shale, reduce the damage of the drilling fluid to the reservoir, and maintain the stability of the wellbore wall. The water in the drilling fluid serves as a base fluid, which can adjust the density and viscosity of the drilling fluid to adapt to different drilling conditions and geological environments. Preferably, the drilling fluid composition includes water, organic salts, 4%-5% cellulose polysaccharide, 0.5%-1% hydrophobic temporary plugging agent, 1%-2% activity regulator, and 1%-2% multi-graded plugging agent. The cellulose polysaccharide can be modified alkyl cellulose polysaccharide, modified plant cellulose polysaccharide, etc., and the activity regulator can be a modified polyhydroxy polymer.

[0071] The drilling fluid of the present invention adopts a solid-phase-free low-activity drilling fluid system, which can reduce the damage to the reservoir due to solid phase invasion and improve drilling efficiency.

[0072] Step S3, detecting characteristic parameters of the solid-free low-activity drilling fluid; the characteristic parameters include density, viscosity, and fluid loss;

[0073] Step S4, determining a target drilling pressure and a target drilling rate during the drilling process based on the characteristic parameters, and determining a drilling fluid adjustment method according to the determined target drilling pressure and target drilling rate;

[0074] See also Figure 4 , which is a flow chart of step S4 of an embodiment of the present invention; specifically, in step S4, it includes:

[0075] Step S41, determining a comprehensive parameter influencing factor based on the characteristic parameters;

[0076] Step S42: determining a target drilling pressure according to the comprehensive parameter influencing factor and a preset drilling pressure, and determining a target drilling rate according to the comprehensive parameter influencing factor and a preset drilling rate.

[0077] In the implementation, each characteristic parameter is compared with the corresponding parameter threshold to determine the ratio of each characteristic parameter to the corresponding parameter threshold, and the product of all ratios is calculated to obtain the comprehensive parameter influence factor, where the density threshold value range is set to 1.1g / cm 3 ~1.4g / cm 3 ; The viscosity threshold value range is set to 40s~60s, and the filtration loss threshold value range is set to 5mL~10mL.

[0078] It can be understood that the target drilling pressure is determined according to the product of the comprehensive parameter influencing factor and the preset drilling pressure, and the target drilling speed is determined according to the product of the comprehensive parameter influencing factor and the preset drilling speed. The actual implementers can set the preset drilling pressure according to the actual situation or based on the average of the drilling pressures that have passed the qualification test in the historical data. The actual implementers can set the preset drilling speed according to the actual situation or based on the average of the drilling speeds that have passed the qualification test in the historical data. Preferably, the preset drilling pressure value range is set to 1.0MPa~2.0MPa, and the preset drilling speed value range is set to 1.5m / h~3m / h.

[0079] The present invention determines the comprehensive parameter influencing factors based on the characteristic parameters of the solid-free low-activity drilling fluid, which can characterize the performance characteristics of the solid-free low-activity drilling fluid. Different drilling fluid properties have an impact on drilling pressure and drilling rate. The target drilling pressure and target drilling rate are determined by combining the comprehensive parameter influencing factors with the preset drilling pressure and preset drilling rate, respectively, which can improve drilling efficiency and reduce leakage.

[0080] Specifically, in step S4, the following is also included:

[0081] Comparing the target drilling pressure with the actual drilling pressure, and determining a flow adjustment method for the drilling fluid according to the comparison result;

[0082] The target drilling rate is compared with the actual drilling rate, and a flow rate adjustment method of the drilling fluid is determined based on the comparison result.

[0083] It can be understood that the drilling fluid flow rate is the volume of drilling fluid flowing into the wellhead per unit time, and the drilling fluid flow rate is the speed at which the drilling fluid flows underground. During the actual drilling process, the actual drilling pressure and the target drilling pressure, as well as the target drilling rate and the actual drilling rate may differ due to measurement factors or external factors. The drilling pressure directly affects the bottom hole pressure, and different drilling pressures require different drilling fluid flow rates to ensure that the pressure on the well wall is stable; the speed of drilling directly affects the efficiency of the entire drilling operation. Changes in drilling speed require corresponding adjustments to the drilling fluid flow rate to ensure that the rock-carrying capacity of the drilling fluid is in a stable state.

[0084] The present invention determines the drilling fluid flow adjustment mode and the drilling fluid flow rate adjustment mode according to the target drilling pressure and the target drilling rate, respectively, which can reduce the loss of drilling fluid and reduce the damage to the reservoir.

[0085] Specifically, in step S4, the following is also included:

[0086] determining a first comparison value according to a difference between the target drilling pressure and the actual drilling pressure, and determining a flow adjustment amount of the drilling fluid based on the first comparison value and a standard drilling fluid flow rate;

[0087] A second comparison value is determined according to the difference between the target drilling rate and the actual drilling rate, and a drilling fluid flow rate adjustment amount is determined based on the second comparison value and a standard drilling fluid flow rate.

[0088] In implementation, a first coefficient is determined by the ratio of the first comparison value to the target drilling pressure, and the drilling fluid flow adjustment is determined based on the product of the first coefficient and the standard drilling fluid flow rate. A second coefficient is determined by the ratio of the second comparison value to the target drilling speed, and the drilling fluid flow rate adjustment is determined based on the product of the second coefficient and the standard drilling fluid flow rate. Practical implementation personnel may set the standard drilling fluid flow rate based on actual conditions or based on the average of drilling fluid flow rates that have passed qualification tests in historical data. Preferably, the standard drilling fluid flow rate is set to a value range of 20 L / s to 30 L / s, and the standard drilling fluid flow rate is set to a value range of 0.5 m / s to 1.0 m / s.

[0089] See also Figure 5As shown in FIG, it is a logic judgment diagram for determining whether the target drilling pressure and the target drilling rate need to be adjusted according to an embodiment of the present invention; Step S5, drilling is performed based on the target drilling pressure, the target drilling rate and the drilling fluid adjustment method, and whether the target drilling pressure and the target drilling rate need to be adjusted is determined according to the thickness and porosity of the mud cake during the drilling process.

[0090] Specifically, step S5 includes:

[0091] Obtaining the thickness and porosity of the mud cake after a preset drilling time period, and determining whether the target drilling pressure and the target drilling rate need to be adjusted based on the thickness and the porosity;

[0092] If the thickness is less than a preset thickness threshold, and the porosity is less than a preset porosity threshold, it is determined that there is no need to adjust the target drilling pressure and the target drilling rate;

[0093] If the thickness is greater than or equal to a preset thickness threshold and / or the porosity is greater than or equal to a preset porosity threshold, it is determined that the target drilling pressure and the target drilling rate need to be adjusted.

[0094] It is understandable that excessive mud cake thickness and porosity will damage the oil and gas formations, increase weak interfaces during cementing, affect the wellbore stress field, reduce the strength and toughness of the mud cake, affect the rock-carrying capacity of the drilling fluid and the cleanliness of the bottom hole, thereby reducing drilling efficiency. Therefore, it is necessary to adjust the target drilling pressure and the target drilling rate.

[0095] Specifically, in step S5, the following is also included:

[0096] If the thickness of the mud cake is greater than or equal to a preset thickness threshold, determining an adjustment amount for the target drilling pressure based on a comparison result between the thickness and the preset thickness threshold;

[0097] If the porosity of the mud cake is greater than or equal to a preset porosity threshold, an adjustment amount of the target drilling speed is determined according to a comparison result of the porosity with the preset porosity threshold.

[0098] In implementation, the adjustment amount of the target drilling pressure is determined based on the product of the ratio of the thickness to the preset thickness threshold and the target drilling pressure, and the adjustment amount of the target drilling speed is determined based on the product of the ratio of the porosity to the preset porosity threshold and the target drilling speed.

[0099] It is understandable that the actual implementers may set the preset thickness threshold according to the actual situation or based on the minimum thickness of the mud cake that has passed the qualification test in the historical data. The actual implementers may set the preset porosity threshold according to the actual situation or based on the minimum porosity of the mud cake that has passed the qualification test in the historical data. Preferably, the preset thickness threshold value range is set to 6 mm to 10 mm; the preset porosity threshold value range is set to 25% to 35%.

[0100] The present invention constructs a parameter evaluation model based on the geological parameters of the target area to determine the drilling fluid ratio, which can adapt to the geological conditions of the target area, obtain ideal drilling results, and improve drilling efficiency. The application of solid-free low-activity drilling fluid can reduce damage to the reservoir and achieve reservoir protection. The target drilling pressure and target drilling rate during the drilling process are determined based on the characteristic parameters of the solid-free low-activity drilling fluid, which can improve drilling efficiency and maintain wellbore stability. The drilling fluid adjustment method is determined based on the determined target drilling pressure and target drilling rate, which can improve drilling efficiency and drilling results by adjusting the drilling fluid, and reduce damage to the reservoir caused by the drilling fluid.

[0101] 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.

Claims

1. A reservoir protection method based on a solid-free low-activity drilling fluid, characterized in that: include: Step S1, obtaining geological parameters of the target area and constructing a parameter evaluation model, wherein the geological parameters include formation hardness, formation pressure, formation structure and reservoir characteristics; Step S2, determining a drilling fluid ratio based on the parameter evaluation model, and preparing a solid-free low-activity drilling fluid based on the drilling fluid ratio; Step S3, detecting characteristic parameters of the solid-free low-activity drilling fluid; The characteristic parameters include density, viscosity and fluid loss; Step S4, determining a target drilling pressure and a target drilling rate during the drilling process based on the characteristic parameters, and determining a drilling fluid adjustment method according to the determined target drilling pressure and target drilling rate; Step S5, drilling based on the target drilling pressure, the target drilling rate, and the drilling fluid adjustment method, and determining whether to adjust the target drilling pressure and the target drilling rate according to the thickness and porosity of the mud cake during drilling; In the step S4, it further includes: Comparing the target drilling pressure with the actual drilling pressure, and determining a flow adjustment method for the drilling fluid according to the comparison result; Comparing the target drilling rate with the actual drilling rate, and determining a flow rate adjustment method for the drilling fluid based on the comparison result; In the step S4, it further includes: determining a first comparison value according to a difference between the target drilling pressure and the actual drilling pressure, and determining a flow adjustment amount of the drilling fluid based on the first comparison value and a standard drilling fluid flow rate; determining a second comparison value according to a difference between the target drilling rate and the actual drilling rate, and determining a drilling fluid flow rate adjustment amount based on the second comparison value and a standard drilling fluid flow rate; In the step S5, it includes: Obtaining the thickness and porosity of the mud cake after a preset drilling time period, and determining whether the target drilling pressure and the target drilling rate need to be adjusted based on the thickness and the porosity; If the thickness is less than a preset thickness threshold, and the porosity is less than a preset porosity threshold, it is determined that there is no need to adjust the target drilling pressure and the target drilling rate; If the thickness is greater than or equal to a preset thickness threshold and / or the porosity is greater than or equal to a preset porosity threshold, it is determined that the target drilling pressure and the target drilling rate need to be adjusted; In the step S5, it further includes: If the thickness of the mud cake is greater than or equal to a preset thickness threshold, determining an adjustment amount for the target drilling pressure based on a comparison result between the thickness and the preset thickness threshold; If the porosity of the mud cake is greater than or equal to a preset porosity threshold, an adjustment amount of the target drilling speed is determined according to a comparison result of the porosity with the preset porosity threshold.

2. The reservoir protection method based on solid-free low-activity drilling fluid according to claim 1, characterized in that: In the step S1, it includes: Step S11, constructing a geological parameter model according to the geological parameters of the target area, and determining key geological parameters based on the geological parameter model; Step S12: establishing parameter influence indexes of the key geological parameters and various geological parameters, and constructing a parameter evaluation model based on the parameter influence indexes and preset evaluation criteria.

3. The reservoir protection method based on solid-free low-activity drilling fluid according to claim 2, characterized in that: In the step S2, it includes: Step S21, determining a parameter evaluation characteristic value based on the parameter evaluation model; Step S22: determining the drilling fluid ratio according to the parameter evaluation characteristic value.

4. The reservoir protection method based on solid-free low-activity drilling fluid according to claim 3, characterized in that: In the step S4, it includes: Step S41, determining a comprehensive parameter influencing factor based on the characteristic parameters; Step S42: determining a target drilling pressure according to the comprehensive parameter influencing factor and a preset drilling pressure, and determining a target drilling rate according to the comprehensive parameter influencing factor and a preset drilling rate.

5. The reservoir protection method based on solid-free low-activity drilling fluid according to claim 4, characterized in that: In step S22, the comparison characteristic values ​​of the drilling fluid ratio comparison table are determined based on the correlation between the key geological parameters and the characteristic parameters of the drilling fluid, and the drilling fluid ratio is determined according to the comparison characteristic values ​​and the parameter evaluation characteristic values.

6. The reservoir protection method based on solid-free low-activity drilling fluid according to claim 5, characterized in that: The drilling fluid components include organic salt, cellulose polysaccharide, hydrophobic temporary plugging agent, plugging agent, activity regulator and water.

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