Quantitative regulation and control method for performance of oil-based drilling fluid polluted by fracturing fluid

Abstract

The invention relates to the field of oil and gas drilling, and particularly provides a quantitative regulation and control method for the performance of an oil-based drilling fluid polluted by fracturing fluid. According to the method, key performance parameters, including apparent viscosity, plastic viscosity, dynamic shearing force, density, oil-water ratio and internal phase water activity, of the polluted oil-based drilling fluid are obtained in real time through a monitoring system, and whether fracturing fluid invasion exists or not is judged according to the key performance parameters. Calculating the supplementary oil quantity according to the oil-water ratio change so as to recover the original oil-water ratio; and determining the calcium chloride solid supplementing amount according to the internal phase water activity in combination with an empirical formula and the oil supplementing amount. According to a regional drilling fluid formula, fracturing fluid is adopted as internal phase slurry preparation, additives such as an emulsifier, a filtrate reducer and a plugging agent are combined, a drilling fluid formula with performance close to that of an original system is formed, and the density is further adjusted to stabilize a stratum. Quantitative monitoring, regulation and control of the drilling fluid performance are achieved, the field emergency response efficiency is improved, the cost is effectively controlled, the underground operation safety is guaranteed, and high practical value and popularization prospects are achieved.

Description

Technical Field

[0001] The present invention specifically relates to a method for quantitatively controlling the rheological characteristics and stability performance of an oil-based drilling fluid after it is contaminated by a fracturing fluid in a complex downhole environment. Background Art

[0002] With the continuous development of unconventional oil and gas resources, oil-based drilling fluids, as key working fluids in unconventional oil and gas wellbore operations, have been widely used in the drilling process of low-permeability reservoirs such as shale gas and deep tight sandstone. This is mainly due to the excellent wettability, plugging, anti-pollution ability and performance advantages of oil-based drilling fluids in maintaining wellbore stability, which can effectively cope with complex formation environments and ensure the smooth progress of drilling operations. In the completion stage, horizontal well volume fracturing technology is widely used to improve reservoir transformation efficiency and enhance oil and gas permeability, thereby releasing reservoir potential and increasing single well production capacity. However, under the dense well network development model, multi-well parallel fracturing, repeated fracturing and other operations are frequently carried out, and the resulting fracturing crosstalk phenomenon is becoming increasingly prominent. Fracturing crosstalk refers to the process of fracturing, in which the fracturing fluid seeps along natural fractures, induced fractures or through high-permeability channels, and invades adjacent wellbores that are being drilled or to be completed, thereby causing a series of wellbore fluid contamination and downhole safety issues. Once the fracturing fluid invades the operating wellbore, it is easy to cause significant changes in the performance of the oil-based drilling fluid, including emulsification destruction, rheological property degradation, increased filtration, etc., which may lead to complex downhole problems such as lost circulation, well kick, well wall collapse, and even overflow, seriously threatening the safety and stability of drilling and subsequent production operations. Therefore, how to deal with and regulate the performance changes of oil-based drilling fluid after being contaminated by fracturing fluid has become a key technical issue that needs to be solved urgently.

[0003] When fracturing crosstalk occurs at the drilling site, it is usually first evaluated by monitoring the changes in the circulation tank volume and combining it with the logging information to determine whether the fracturing fluid has entered the wellbore, causing the mud volume in the wellbore to change. However, there is a certain error in the monitoring of the circulation tank volume change, because the compressibility of the oil-based drilling fluid and the throughput of the mud are difficult to eliminate, and the intrusion phenomenon can often only be discovered and dealt with when it is already serious. When treating contaminated oil-based drilling fluid on site, it is usually taken to directly add mud, emulsifiers and barite to restore the drilling fluid performance and stabilize the formation. However, it is difficult to restore the drilling fluid performance without a certain guidance method. At the same time, due to the high viscosity of the fracturing fluid itself, the viscosity of the drilling fluid after additional weighting is further increased, resulting in an increase in the circulation pressure loss, which is easy to induce well leakage, thereby increasing the difficulty of subsequent treatment.

[0004] Monitoring technology helps to monitor the performance changes of oil-based drilling fluids after being contaminated by fracturing fluids in real time, and to achieve a quantitative assessment of the degree of contamination. Quantitative control methods can combine monitoring data with empirical experiments to quickly formulate drilling fluid control plans and complete adjustments in a very short time to ensure that the drilling fluid system maintains excellent performance under complex working conditions, thereby effectively improving wellbore stability, reducing the incidence of complex situations downhole, and optimizing drilling operation efficiency. At present, general monitoring technology and quantitative control solutions have provided an efficient solution path for the performance control of oil-based drilling fluids under fracturing crosstalk conditions. Summary of the invention

[0005] The present invention aims to provide a performance control scheme for oil-based drilling fluid contaminated by fracturing fluid. Based on the monitoring system for basic data collection and combined with empirical experiments, a set of quantitative control schemes for oil-based drilling fluid is established to control the performance of drilling fluid within the range of engineering design requirements and reduce the probability of complex occurrence.

[0006] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0007] A method for controlling the performance of an oil-based drilling fluid contaminated by a fracturing fluid comprises the following steps:

[0008] S1: Based on the monitoring system, the basic properties of the contaminated oil-based drilling fluid, such as apparent viscosity, plastic viscosity, dynamic shear force, density, oil-water ratio, and internal phase water activity, are tested to determine whether fracturing interference occurs;

[0009] S2: Based on the oil-water ratio measurement, the amount of fracturing fluid invasion is determined and the amount of supplementary oil required to restore the drilling fluid oil-water ratio is calculated;

[0010] S3: Based on the internal phase water activity test, the amount of calcium chloride to be supplemented is calculated according to the empirical formula of calcium chloride addition and water activity value;

[0011] S4: Using the same drilling fluid formula, replace CaCl2 with fracturing fluid to prepare the slurry. The amount of calcium chloride added in this system is calculated by the amount of calcium chloride added calculated in S3 and the amount of calcium chloride added in the original system. Then, additional drilling fluid additives such as emulsifiers, filtrate reducers, plugging agents, calcium oxide, and organic soil are added, and the amount of organic soil and plugging agents is appropriately reduced, so that the performance of this system is similar to that of the original system.

[0012] S5: Based on S4, a drilling fluid formula with fracturing fluid as the internal phase can be derived. The amount of fracturing fluid invasion and the volume of contaminated well slurry can be used to derive a quantitative control method.

[0013] S6: Adjust the density of the drilling fluid and control the density of the drilling fluid within the range that can stabilize the formation.

[0014] Beneficial effects:

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] 1. The monitoring system can obtain key parameters of drilling fluid performance in real time, determine whether fracturing fluid intrusion occurs, achieve quantitative assessment of the degree of contamination, and provide accurate data support for subsequent regulation.

[0017] 2. The present invention uses monitoring data and empirical formulas to establish a quantitative control method, calculate the amount of oil replenishment required for oil-water ratio recovery and the amount of calcium chloride required for water activity adjustment, and combines the drilling fluid formula used on site to supplement key treatment agents such as emulsifiers and filtration reducers to form a quantitative control method, improve control efficiency and accuracy, and significantly shorten emergency treatment time.

[0018] 3. Using the invaded fracturing fluid as a partial additive for slurry preparation can utilize on-site resources, reduce the use of new drilling fluid additives, appropriately reduce the cost of drilling fluid, and have certain on-site adaptability and economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a flow chart of the method for quantitatively controlling the performance of oil-based drilling fluid contaminated by fracturing fluid according to the present invention. DETAILED DESCRIPTION

[0020] In order to make the features of the present invention easier to understand, the present invention is further described in detail below in conjunction with the accompanying drawings and specific examples. It should be noted that the exemplary features described herein are only used to illustrate and explain the present invention, and do not limit the present invention.

[0021] Example:

[0022] S1: Based on the monitoring system, the basic properties of the contaminated oil-based drilling fluid, such as apparent viscosity, plastic viscosity, dynamic shear force, density, oil-water ratio, and internal phase water activity, are tested to determine whether fracturing interference occurs;

[0023] S2: Based on the oil-water ratio measurement, the amount of fracturing fluid invasion is determined and the amount of supplementary oil required to restore the drilling fluid oil-water ratio is calculated;

[0024] S3: Based on the internal phase water activity test, the amount of calcium chloride to be supplemented is calculated according to the empirical formula of calcium chloride addition and water activity value;

[0025] S4: Using the same drilling fluid formula, replace CaCl with fracturing fluid 2 The amount of calcium chloride added in this system is calculated by the amount of calcium chloride added in S3 and the amount of calcium chloride added in the original system, and then additional drilling fluid additives such as emulsifiers, filtrate reducers, plugging agents, calcium oxide, and organic soil are added, and the amount of organic soil and plugging agents is appropriately reduced, so that the performance of this system is similar to that of the original system.

[0026] S5: Based on S4, a drilling fluid formula with fracturing fluid as the internal phase can be derived. The amount of fracturing fluid invasion and the volume of contaminated well slurry can be used to derive a quantitative control method.

[0027] S6: Adjust the density of the drilling fluid and control the density of the drilling fluid within the range that can stabilize the formation.

[0028] Embodiment 1:

[0029] 1. According to the density tested in Table 1, it is 1.4g / cm 3 , six speeds: >360 / 240 / 191 / 130 / 35 / 30, G' / G": 15 / 19Pa, ES: 174V, water activity: 0.782, oil-water ratio: 17.4:21.4. The comprehensive judgment is that the fracturing fluid invades and contaminates the oil-based drilling fluid, and the invasion amount of the fracturing fluid is 31.2%.

[0030] 2. Based on the oil-water ratio of the contaminated oil-based drilling fluid, the amount of white oil added is 93.6%.

[0031] 3. According to the value of the internal phase water activity, the internal phase calcium chloride concentration is 23%, and an additional 7% of calcium chloride solids need to be added. Subsequently, the internal phase water activity of the test system is 0.647. Then, 30% of the calcium chloride solids of the drilling fluid system configured with additional supplementary oil are weighed, which is the total amount of calcium chloride that needs to be supplemented.

[0032] The oil-water ratio is 75:25, the basic calcium chloride addition is 30%, and after fracturing fluid and water invasion, the empirical formula for internal phase activity is as follows:

[0033] Empirical formula for the change of internal phase water activity after water invasion:

[0034] y=-0.0005x 2 +0.0063x+0.6532

[0035] Empirical formula for the change of internal phase water activity after fracturing fluid invasion:

[0036] y=-0.0005x 2 +0.0063x+0.6532

[0037] Table 1 Optimization results

[0038]

[0039] 4. The optimization plan is as follows:

[0040] Regional drilling fluid formula: 75:25 (white oil: 30% CaCl 2solution) + 3.5% primary emulsifier + 3.5% secondary emulsifier + 1.5% wetting agent + 3% organic soil + 2.5% fluid loss reducer + 1.5% CaO + 2% plugging agent + barite

[0041] According to the drilling fluid formula in the above area, considering that the fracturing fluid invasion volume is 31.2%, the volume of 400mL contaminated slurry fracturing is 124.8mL, and the following optimization scheme is set: 400mL contaminated well slurry + 374.4mL white oil + 17.4g primary emulsifier + 17.4g auxiliary emulsifier + 7.5g wetting agent + 10g organic soil + 12.5g filtration reducer + 7.5g CaO + 7.5g plugging agent + barite + 188g CaCl 2 (Solid). The optimized drilling fluid properties are shown in Table 1, which are close to the rheological properties of the original system drilling fluid.

[0042] 5. The formula is as follows: If the amount of fracturing fluid intrusion is a%, the contaminated well slurry bm 3 , the optimization solution is 3ab%m 3 White oil + 0.14ab%kg primary emulsifier + 0.14ab%kg auxiliary emulsifier + 0.06ab%kg wetting agent + 0.08ab%kg organic soil + 0.1ab%kg fluid loss reducer + 0.06ab%kg CaO + 0.06ab%kg plugging agent + barite (density 1.5g / cm 3 )+(49b+9ab) / 700CaCl 2 (Solid). The above is the quantitative processing solution.

[0043] The above description is not intended to impose any form of limitation on the present invention. Although the present invention has been disclosed through the above embodiments, it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A method for quantitatively controlling the performance of oil-based drilling fluid contaminated by fracturing fluid, characterized in that: The following steps are involved: S1. The method detects the performance of the oil-based drilling fluid through a monitoring system to determine whether the fracturing fluid crosstalk phenomenon occurs; S2: Based on the oil-water ratio measurement, the amount of fracturing fluid invasion is determined and the amount of supplementary oil required to restore the drilling fluid oil-water ratio is calculated; S3: Based on the internal phase water activity test, the amount of calcium chloride to be supplemented is calculated according to the empirical formula of calcium chloride addition and water activity value; S4: Prepare a system according to the drilling fluid formula of the block, with the internal phase being the fracturing fluid in the block. Calculate the amount of calcium chloride added in the system by the amount of calcium chloride added calculated in S3 and the amount of calcium chloride added in the original system, and then add additional drilling fluid additives to make the performance of the system close to that of the original system. S5: Based on S4, a drilling fluid formula with fracturing fluid as the internal phase can be obtained. Based on S2, the fracturing fluid invasion amount and the contaminated well slurry volume can be calculated, and a quantitative control formula can be obtained. S6: Adjust the density of the drilling fluid and control the density of the drilling fluid within the range that can stabilize the formation.

2. The method for controlling the performance of oil-based drilling fluid according to claim 1, characterized in that: In step S1, the monitoring system includes key parameters such as apparent viscosity, plastic viscosity, dynamic shear force, density, oil-water ratio, demulsification voltage, internal phase water activity and conductivity; the oil-water ratio test adopts centrifugal separation method, and the separated water phase is tested for the water activity of the separated liquid phase through a resistance sensor.

3. The method for controlling the performance of oil-based drilling fluid according to claim 1, characterized in that: The determination of the crosstalk phenomenon of the fracturing fluid is achieved as follows: After the liquid phase invades the wellbore, for every 5% increase in the amount of liquid phase invasion, the apparent viscosity of the drilling fluid increases by 3-7%, the plastic viscosity increases by 2-8.5%, the dynamic shear force increases by 2-6%, the density decreases by 0.28-0.4%, and the demulsification voltage decreases by 7-15%; The conductivity of the drilling fluid system suddenly increases, and the oil-water ratio decreases significantly. By analyzing the oil-water ratio, the proportion of non-oil phase invasion can be determined; After the non-oil phase invades the wellbore, after the non-oil phase is mixed with the calcium chloride solution, the water activity of the internal phase of the oil-based drilling fluid is significantly greater than the water activity value during water invasion. The invading phase can be judged as fracturing fluid by the water activity of the internal phase. Determine whether it is fracturing fluid invasion based on the data.

4. According to the method for quantitatively controlling the performance of oil-based drilling fluid contaminated by fracturing fluid as claimed in claim 1, in step S2, the amount of supplementary oil phase is calculated based on the oil-water ratio measurement result and the oil-water ratio of the original drilling fluid.

5. The method for quantitatively controlling the performance of oil-based drilling fluid contaminated by fracturing fluid according to claim 1, characterized in that: The empirical formula of the calcium chloride dosage and water activity value is: y=-0.0002x 2 -0.0057x+0.9941 Where y is water activity, x is CaCl2 concentration, and the empirical formula is obtained by fitting the laboratory experimental results.

6. The method for quantitatively controlling the performance of oil-based drilling fluid contaminated by fracturing fluid according to claim 1, characterized in that: In step S3, the determination of calcium chloride addition is achieved by: According to the empirical formula described in claim 6 and the measured internal phase water activity value, the equivalent CaCl2 concentration of the contaminated drilling fluid internal phase at this time can be determined and the amount of supplementary CaCl2 can be calculated.

7. According to the method for quantitatively controlling the performance of oil-based drilling fluid contaminated by fracturing fluid as claimed in claim 1, in step S4, the method for controlling the performance of drilling fluid contaminated by fracturing fluid is specifically implemented as follows: After the fracturing fluid invaded the drilling fluid, the additional fracturing fluid components were introduced into the system, which caused the drilling fluid performance to change. That is, the fracturing fluid was used to replace the CaCl2 solution, and combined with the viscosity-increasing characteristics of the fracturing fluid, the amount of viscosity-increasing agent added was appropriately reduced on the basis of the original regional drilling fluid system, and the drilling fluid system was re-formulated.

8. The supplementary amount of the drilling fluid additive according to claim 8, characterized in that: The emulsifier is 100% of the original formula, the filtrate reducer is 100% of the original formula, the organic soil is 60-70% of the original formula, the plugging agent is 70-80% of the original formula, the wetting agent is 100% of the original formula, and the CaO is 100% of the original formula. The final drilling fluid control plan guides the control of drilling fluid performance in a quantitative form.

9. The drilling fluid system according to claim 8, characterized in that: The method of controlling the density of drilling fluid is to add barite to increase the density by 0.02-0.05g / cm 3 , real-time regulation according to well depth and real-time formation pore pressure.

10. The method according to claim 1, characterized in that The method is applicable to fracturing fluids mainly consisting of water-based fracturing fluids, the main components of which are water, tackifiers and other fracturing fluid additives.

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