A method for evaluating the sealing performance of drilling fluid in the uncased section of the annulus

Abstract

The present invention relates to a method for evaluating the sealing performance of drilling fluid in an unsealed section of an annulus, which comprises: taking the drilling fluid used in oil and gas wells and aging it, loading it into a settling tank to the top zero mark and sealing it, heating the settling tank to the actual wellbore temperature, introducing gas into the settling tank and pressurizing it to the actual wellbore pressure, letting it stand to room temperature, and taking out the settling tank; scanning the drilling fluid in the settling tank, and dividing the drilling fluid into three areas from top to bottom according to the different transmittances of the drilling fluid, and calculating the heights of the three areas; pumping the drilling fluid in the liquid separation area and the solidified mud area into a storage tank, and pressurizing the gas into the tank from the lower vent pipe of the settling tank, and obtaining the breakthrough pressure when the gas passes through the lower solidified accumulation area of ​​the drilling fluid; similarly obtaining the breakthrough pressure when the gas passes through the lower solidified accumulation area of ​​the drilling fluid and the middle solidified mud area; calculating the total breakthrough pressure of the drilling fluid in the unsealed section of the annulus in the actual wellbore; and evaluating the wellbore sealing ability of the unsealed section. The present invention does not require downhole measurement and can achieve accurate evaluation.

Description

Technical Field

[0001] The invention relates to a wellbore sealing evaluation technology for oil wells, in particular to a drilling fluid sealing performance evaluation method suitable for an annulus unsealed section. Background Art

[0002] In order to save costs, major oil fields often only return cement to 100~300m above the top of the oil layer during well cementing construction. That is, the annulus section from 100~300m above the top of the oil layer to the wellhead is not cemented. The main medium of the unsealed section of the annulus is the drilling fluid used during drilling. Since cementing is a one-time operation, the drilling fluid in the unsealed section of the annulus will remain in the annulus permanently for a long period from the completion of the well to the abandonment. Due to the continuous changes in injection and production scheme adjustments, corrosion, temperature, pressure, etc. during the production and long-term abandonment of oil wells, abandoned wells and even many active production wells have experienced casing misalignment, corrosion perforation or cement sealing failure in the sealing section. Underground oil and gas enter the unsealed section of the annulus along the misaligned parts of the casing, holes formed by corrosion or cement rings with failed seals, and flow upward along the long-term abandoned drilling fluid in the unsealed section to the drinking water layer and the wellhead, causing oil and gas leakage, which will not only cause blowouts and bring safety risks, but also pollute the soil, water bodies and ecology. At present, there are a large number of oil wells in various oil fields with unsealed sections. Whether they are active production wells or abandoned wells, the unsealed sections filled with drilling fluid are the weakest part of the entire oil well barrier system and the main risk source for oil and gas leakage. At present, the number of oil wells where oil and gas flow to the ground along the unsealed sections of the annulus is still increasing.

[0003] For the above-mentioned oil wells with unsealed annulus sections, they can only be treated by secondary cementing. The premise is to re-perforate to establish an annulus circulation channel to remove the original aged drilling fluid. This removal method can only be achieved through fluid displacement. Due to the significant changes in the properties of drilling fluid after aging under long-term conditions, some of them even solidify. Therefore, the process of fluid displacement of aged drilling fluid is often more complicated and more costly than drilling a new well. Therefore, if all the oil wells with unsealed annulus sections are re-sealed, the economic cost and the resulting oil well shutdown will cause the oil field to be overwhelmed. The most practical method at present is to evaluate the sealing performance of the drilling fluid in the unsealed annulus section, identify the risk of oil and gas upward movement based on the evaluation results, and only perform secondary cementing and sealing on the oil wells with the risk of oil and gas upward movement. This can not only reduce the blindness of secondary cementing and prevent the safety risks and environmental pollution caused by oil and gas upward movement, but also reduce the cost of treatment as much as possible. Therefore, evaluating the sealing performance of the drilling fluid in the unsealed annulus section under long-term downhole working conditions is the core of judging whether the unsealed section of the oil well needs to be treated.

[0004] At present, there is no literature report on the evaluation method of the sealing ability of drilling fluid in the unsealed section of the annulus. In order to improve the pertinence and effectiveness of secondary cementing and reduce the cost of secondary cementing, a scientific and reasonable evaluation method for the sealing performance of drilling fluid in the unsealed section of the annulus under long-term aging conditions is urgently needed. Summary of the invention

[0005] The purpose of the present invention is to provide a method for evaluating the sealing performance of drilling fluid in an unsealed section of an annulus. The method is used to solve the problem that abandoned wells in oil fields and in-service production wells may have underground oil and gas flowing upward along the unsealed section of the oil well to the drinking water layer and the wellhead, causing oil and gas leakage, which will not only cause blowouts, but also pollute soil and water bodies.

[0006] The technical solution adopted by the present invention to solve the technical problem is: the drilling fluid sealing performance evaluation method applicable to the unsealed section of the annulus comprises the following steps:

[0007] Step 1: Take the drilling fluid used in the oil and gas wells and put it into an aging tank and place it in a roller furnace for rolling aging for 16 hours;

[0008] Step 2: Take out the drilling fluid after aging in step 1 and put it into a measuring bottle. The height of the drilling fluid in the measuring bottle is 43mm. Measure the curve of the drilling fluid stability index over time and record the time when the stability index tends to be stable. t ;

[0009] Step 3: Take out the drilling fluid aged in step 1, put it into the settling tank to the top zero mark and seal it. The total height of the drilling fluid column is recorded as h， The temperature of the sedimentation tank is raised to the actual wellbore temperature. Gas is introduced into the sedimentation tank through the upper ventilation pipe to pressurize it to the actual wellbore pressure. The constant temperature time is 1000× h × t / 43 and then cooled to room temperature, took out the sedimentation tank and placed it on a storage rack;

[0010] Step 4: Scan the drilling fluid in the settling tank from top to bottom starting from the zero scale line at the top of the observation port of the settling tank, and record the relationship curve between the scale and the transmittance of the drilling fluid. The drilling fluid in the settling tank is divided into three areas from top to bottom according to the different transmittances of the drilling fluid: when the transmittance is 100%, it is the liquid separation area, when the transmittance is between 5%-100%, it is the solidified mud area, and when the transmittance is between 0%-5%, it is the solidified accumulation area. Calculate the heights of the three areas; record them as h 上 , h 中 , h 下 , h 上 + h 中 +h 下 = h ;

[0011] Step 5: Extend the drilling fluid extraction pipe into the drilling fluid along the inner wall of the sedimentation tank, and draw the drilling fluid from the liquid separation area and the solidified mud area into the storage tank, leaving only the solidified accumulation area in the sedimentation tank. Turn on the upper and lower ventilation pipe switches, connect the bottom of the sedimentation tank to the pressure supply system, and pressurize the tank from the lower ventilation pipe of the sedimentation tank. When the gas flow meter on the upper sealing cover shows the reading, record the reading of the ventilation pipe pressure gauge, which is the breakthrough pressure when the gas passes through the lower solidified accumulation area, recorded as P 1 , P 1 / h 下 is the breakthrough pressure of the drilling fluid solidification accumulation zone at unit height;

[0012] Step 6: Repeat steps 1 to 4, turn on the upper and lower ventilation pipe switches, connect the bottom of the sedimentation tank to the pressure supply system, and pressurize the tank from the lower ventilation pipe of the sedimentation tank. When the gas flow meter on the upper sealing cover shows the reading, record the reading of the ventilation pipe pressure gauge, which is the breakthrough pressure of the gas when it passes through the lower solidified accumulation area of ​​the drilling fluid and the solidified mud area in the middle layer, recorded as P 2 (MPa), P 2 - P 1 ) / h 中 is the breakthrough pressure of the solidified mud zone in the middle layer of drilling fluid at unit height;

[0013] Step 7: Calculate the total breakthrough pressure of the drilling fluid in the unsealed section of the annulus in the actual wellbore P 总 ;

[0014] Step 8: Evaluate the sealing ability of the unsealed section of the wellbore: When the total breakthrough pressure of the drilling fluid in the unsealed section of the annulus in the actual wellbore is greater than the formation pore pressure, the sealing performance of the drilling fluid in the unsealed section of the annulus is good; otherwise, make a plan for secondary cementing to prevent underground oil and gas from rising through the drilling fluid in the unsealed section of the annulus to the upper shallow water layer or the ground, causing oil and gas pollution.

[0015] Step 7 in the above scheme is specifically:

[0016] Assume that the total height of drilling fluid in the annulus in the actual wellbore is H , then the actual height of the solidified accumulation area of ​​the lower layer of drilling fluid in the wellbore is h 下 × H / h , the breakthrough pressure is ( P1 / h 下 )×( h 下 × H / h ); The actual height of the solidified mud zone in the middle layer of drilling fluid in the wellbore is h 中 × H / h , the breakthrough pressure is ( P 2 - P 1 ) / h 中 ×( h 中 × H / h ); The upper layer of the drilling fluid in the actual wellbore does not have a breakthrough pressure;

[0017] The total breakthrough pressure of drilling fluid in the unsealed section of the annulus in the actual wellbore is as follows:

[0018] P 总 =( P 1 / h 下 )×( h 下 × H / h )+( P 2 - P 1 ) / h 中 ×( h 中 × H / h ) (1-1)

[0019] Where: P 总 is the total breakthrough pressure of drilling fluid in the unsealed section of the annulus in the actual wellbore, MPa; P 1 is the gas breakthrough pressure in the solidified accumulation area under the drilling fluid in the settling tank, MPa; P 2 The sum of the gas breakthrough pressures of the lower and middle layers of the drilling fluid in the settling tank, MPa; H is the total height of drilling fluid in the annulus in the actual wellbore, m; h is the total height of drilling fluid in the settling tank, m; h 下 is the height of the lower solidification accumulation area in the settling tank, m; h中 is the gas breakthrough pressure of the solidified mud zone in the middle layer of drilling fluid in the settling tank, m;

[0020] Simplifying formula (1-1), the total breakthrough pressure of drilling fluid in the unsealed section of the annulus in the actual wellbore is obtained as follows:

[0021] P 总 = P 2 ×( H / h ) (1-2)

[0022] Where: P 总 is the total breakthrough pressure of drilling fluid in the unsealed section of the annulus in the actual wellbore, MPa; P 2 The sum of the gas breakthrough pressures of the lower and middle layers of the drilling fluid in the settling tank, MPa; H is the total height of drilling fluid in the annulus in the actual wellbore, m; h is the total height of drilling fluid in the settling tank, m.

[0023] In the above scheme, the top of the sedimentation tank is composed of an upper sealing cover sealed at the upper port of the tank body, a high-temperature resistant annular sealing ring is arranged between the upper sealing cover and the upper port of the tank body, an upper ventilation pipe is arranged on the top of the tank, an upper ventilation pipe switch, a gas flow meter and a pressure gauge are arranged on the upper ventilation pipe, and the upper ventilation pipe is connected to the gas compression pump through a ventilation pipeline; the bottom of the sedimentation tank is composed of a lower sealing cover sealed at the lower port of the tank body, a high-temperature resistant annular sealing ring is arranged between the lower sealing cover and the lower port of the tank body, a lower ventilation pipe is arranged on the bottom of the tank, and a lower ventilation pipe switch and a pressure gauge are arranged on the lower ventilation pipe; the tank body is provided with a transparent window and a scale, and the transparent window and the scale are arranged correspondingly.

[0024] Step 3 in the above scheme is specifically: take out the aged drilling fluid and put it into the settling tank to the top zero mark, and the total height of the drilling fluid column is recorded as h， After the settling tank is sealed, place the settling tank in a heating furnace, with the upper and lower ventilation pipes extending from the heating furnace. The heating furnace is equipped with a temperature sensor and a temperature display instrument. An insulation layer is provided outside the heating furnace. The heating furnace is turned on to heat the settling tank to the actual wellbore temperature, and gas is introduced into the settling tank through the upper ventilation pipe on the top of the settling tank to pressurize it to the actual wellbore pressure. The settling tank is kept at a constant temperature for 1000× h × t / 43, cool to room temperature, then slowly take out the sedimentation tank from the heating furnace and place it on the storage rack.

[0025] In the above scheme, step 4 of scanning the drilling fluid in the settling tank is performed using an automatic identification and zoning system for the settling section. The automatic identification and zoning system for the settling section is a spectrophotometer scanning device, which includes a light source, a monochromator, a detector, a signal processor and a calculator. The light source emits a continuous spectrum within the required wavelength range. The monochromator decomposes the continuous spectrum emitted by the light source into monochromatic light and accurately focuses it on the drilling fluid in the settling tank to detect the stratification of the drilling fluid in the tank. The detector uses the photoelectric effect to convert light energy into electrical signals and transmits the electrical signals to the computer after amplification, filtering and numerical calculation by the signal processor to obtain the transmittance of the drilling fluid at different positions, and divides the drilling fluid in the settling tank from top to bottom into a liquid separation zone, a solidified mud zone and a solidified accumulation zone according to the different transmittances.

[0026] Step 2 in the above scheme is specifically as follows: 20 mL of the aged drilling fluid is taken out and put into a measuring bottle, the height of the drilling fluid in the measuring bottle is about 43 mm, and a stability analyzer is used to measure the curve of the drilling fluid stability index changing with time. The smaller the stability index, the more stable the drilling fluid system is; when the curve tends to be stable, the sedimentation, flocculation, aggregation and liquid separation processes of the drilling fluid system are completed, and the time t when the stability index tends to be stable is recorded, which is used as a reference for the standing time of the drilling fluid in step 3. Beneficial Effects

[0027] 1. The present invention provides an evaluation method for the sealing performance of drilling fluid in an unsealed section of an annulus. The method obtains the relationship between the height of drilling fluid in a settling tank and the light transmittance and the gas breakthrough pressure under the unit height of drilling fluid in different partitions based on the indoor experimental results, and can predict the gas breakthrough pressure of drilling fluid in the unsealed section of the actual wellbore annulus under long-term aging conditions, and then judge whether the unsealed section needs secondary cementing. No downhole measurement is required, the method is simple and easy to use, and is convenient for practical application.

[0028] 2. The sealing performance evaluation method of drilling fluid in the unsealed section of the annulus provided by the present invention is generally applicable, and can realize the accurate identification of oil wells with the risk of oil and gas upward movement in the unsealed section, provide a basis for the selection of oil wells that need secondary cementing and sealing and the formulation of treatment measures, reduce the blindness of sealing all wells, prevent oil and gas leakage and protect the environment while minimizing the huge economic losses caused by the treatment of the unsealed section, and improve the effectiveness and economy of secondary cementing.

[0029] 3. The present invention is used to fill the gap in the existing evaluation method of the sealing ability of drilling fluid under long-term aging conditions. The risk of oil and gas upward movement is identified based on the evaluation results, and secondary cementing and sealing are only performed on wells with the risk of oil and gas upward movement, thereby achieving accurate identification of oil wells with the risk of oil and gas upward movement in the unsealed sections, providing a basis for the selection of oil wells that require secondary cementing and sealing and the formulation of treatment measures, and is particularly suitable for the sealing detection of drilling fluid in the unsealed section of the oil well annulus under long-term aging conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the structure of the device of the present invention;

[0031] Figure 2 The figure is a flow chart of the evaluation method of the present invention.

[0032] In the figure: 1 transparent window 2 upper sealing cover 3 high temperature resistant annular sealing ring 4 heating furnace 5 insulation layer 6 lower sealing cover 7 upper ventilation pipe 8 upper ventilation pipe switch 9 upper ventilation pipe pressure gauge 10 gas flow meter 11 gas compression pump 12 temperature display instrument 13 temperature sensor 14 ventilation pipeline 15 lower ventilation pipe 16 lower ventilation pipe switch 17 lower ventilation pipe pressure gauge. DETAILED DESCRIPTION

[0033] The present invention will be further described below in conjunction with the accompanying drawings:

[0034] Combination Figure 1-2 As shown in FIG. 1 , the evaluation method for the sealing performance of drilling fluid in the unsealed section of the annulus includes the following steps:

[0035] Step 1: Take the drilling fluid used in oil and gas wells and put it into an aging tank. Place it in a roller furnace for rolling aging for 16 hours to make the components evenly mixed.

[0036] Step 2: Take out 20mL of the aged drilling fluid and put it into a measuring bottle (the height of the drilling fluid in the measuring bottle is about 43mm). Use a stability analyzer to measure the curve of the drilling fluid stability index over time (the smaller the stability index, the more stable the drilling fluid system; when the curve tends to be stable, the sedimentation, flocculation, aggregation and liquid separation process of the drilling fluid system ends), and record the time when the stability index tends to be stable t (h) and use it as a reference for the drilling fluid standing time in step 3.

[0037] Step 3: Take out the aged drilling fluid and put it into the drilling fluid settling tank to the top zero mark. The total height of the drilling fluid column is recorded as h(m), after the settling tank is sealed, turn on the heating furnace to heat the drilling fluid settling tank to the actual wellbore temperature, and turn on the upper ventilation pipe switch, and introduce gas into the settling tank through the upper ventilation pipe to pressurize it to the actual wellbore pressure (used to simulate the formation pressure, and the upper ventilation pipe is the air inlet pipe at this time), and let it stand at a constant temperature of 1000× h × t / 43 (h) and then cool to room temperature, then slowly take out the sedimentation tank from the heating furnace and place it on the storage rack.

[0038] Step 4: Turn on the spectrophotometer scanning device, scan the drilling fluid in the settling tank from top to bottom starting from the zero scale line at the top of the observation port of the settling tank, and record the relationship curve between the scale and the drilling fluid transmittance. The drilling fluid in the settling tank is divided into three areas from top to bottom according to the different transmittances of the drilling fluid: when the transmittance is 100%, it is the liquid separation area (note: the liquid separation area is liquid and there is no gas breakthrough pressure), between 5%-100% is the solidified mud area, and between 0%-5% is the solidified accumulation area formed by the dense phase accumulation of weighted materials. The heights of the three areas are calculated by the range of transmittance, which are recorded as h 上 (m), h 中 (m), h 下 (m), h 上 + h 中 + h 下 = h (m).

[0039] Step 5: Extend the drilling fluid extraction pipe into the drilling fluid along the inner wall of the settling tank, and use a pump to pump the upper liquid area and the middle solidified mud area into the drilling fluid storage tank, leaving only the lower solidified accumulation area in the settling tank. Turn on the upper and lower vent pipe switches, connect the bottom of the settling tank to the pressure supply system, and pressurize the tank from the lower vent pipe of the settling tank (to measure the breakthrough pressure, at this time, the upper vent pipe is used for air outlet and the lower vent pipe is used for air intake). When the gas flow meter on the upper sealing cover shows a reading, record the reading of the vent pipe pressure gauge, which is the breakthrough pressure when the gas passes through the lower solidified accumulation area, recorded as P 1 , P 1 / h 下 is the breakthrough pressure of the drilling fluid solidification accumulation zone at unit height; , records the breakthrough pressure when the gas passes through the lower solidification accumulation zone, recorded as P 1 (MPa). P 1 / h 下It is the breakthrough pressure of the drilling fluid solidification accumulation area at unit height.

[0040] Step 6: Repeat steps 1 to 4. In this step, drilling fluid is not extracted from the sedimentation tank, but all drilling fluid is retained in the sedimentation tank. Open the upper and lower ventilation pipe switches, connect the bottom of the sedimentation tank to the pressure supply system, and pressurize the tank from the lower ventilation pipe of the sedimentation tank. When the gas flow meter on the upper sealing cover shows the reading, record the reading of the ventilation pipe pressure gauge, which is the breakthrough pressure when the gas passes through the lower and middle layers of the drilling fluid, recorded as P 2 (MPa). P 2 - P 1 ) / h 中 It is the breakthrough pressure of the solidified mud zone in the middle layer of drilling fluid at unit height.

[0041] Step 7: Calculate the total breakthrough pressure of the drilling fluid in the unsealed section of the annulus in the actual wellbore P 总 (MPa), specifically:

[0042] Assume that the total height of drilling fluid in the annulus in the actual wellbore is H (m), the actual height of the solidified accumulation area of ​​the lower layer of drilling fluid in the wellbore is h 下 × H / h (m), the breakthrough pressure is ( P 1 / h 下 )×( h 下 × H / h ); The actual height of the solidified mud zone in the middle layer of drilling fluid in the wellbore is h 中 × H / h (m), the breakthrough pressure is ( P 2 - P 1 ) / h 中 ×( h 中 × H / h ); The upper layer of drilling fluid in the actual wellbore does not have a breakthrough pressure.

[0043] The total breakthrough pressure of drilling fluid in the unsealed section of the annulus in the actual wellbore is shown in Formula 1-1:

[0044] P总 =( P 1 / h 下 )×( h 下 × H / h )+( P 2 - P 1 ) / h 中 ×( h 中 × H / h ) (1-1)

[0045] Where: P 总 is the total breakthrough pressure of drilling fluid in the unsealed section of the annulus in the actual wellbore, MPa; P 1 is the gas breakthrough pressure in the solidified accumulation area under the drilling fluid in the settling tank, MPa; P 2 The sum of the gas breakthrough pressures of the lower and middle layers of the drilling fluid in the settling tank, MPa; H is the total height of drilling fluid in the annulus in the actual wellbore, m; h is the total height of drilling fluid in the settling tank, m; h 下 is the height of the lower solidification accumulation area in the settling tank, m; h 中 is the gas breakthrough pressure of the solidified mud zone in the middle layer of drilling fluid in the settling tank, m.

[0046] By simplifying the above formula, the total breakthrough pressure of the drilling fluid in the unsealed section of the annulus in the actual wellbore is obtained, see formula 1-2:

[0047] P 总 = P 2 ×( H / h ) (1-2)

[0048] Where: P 总 is the total breakthrough pressure of drilling fluid in the unsealed section of the annulus in the actual wellbore, MPa; P 2 The sum of the gas breakthrough pressures of the lower and middle layers of the drilling fluid in the settling tank, MPa; H is the total height of drilling fluid in the annulus in the actual wellbore, m; h is the total height of drilling fluid in the settling tank, m.

[0049] Step 8: Evaluate the wellbore sealing ability of the unsealed section: When the total breakthrough pressure of the drilling fluid in the annulus of the actual wellbore in the unsealed section is greater than the formation pore pressure, the sealing performance of the drilling fluid in the annulus of the unsealed section is good; otherwise, a plan needs to be formulated for secondary cementing to prevent underground oil and gas from flowing up through the drilling fluid in the annulus of the unsealed section to the upper shallow water layer or the ground, causing oil and gas pollution.

[0050] The present invention uses a drilling fluid sealing performance measuring device to evaluate the sealing performance of the drilling fluid in the annulus of the unsealed section. The drilling fluid sealing performance measuring device includes a settling tank, a temperature and pressure control and measurement system, a settling section automatic identification and zoning system, and a drilling fluid separation device.

[0051] The settling tank is a cylindrical container made of alloy-glass material encapsulation. The container can withstand a temperature of 300 °C and a pressure of 200 MPa. The settling tank is 1 m high and 0.25 m in inner diameter. A transparent window 1 made of glass material is provided on the side of the tank body for subsequent measurement of the sedimentation and stratification status of the drilling fluid in the tank. A scale is provided on the outside of the tank for reading the volume of the drilling fluid in the tank. Sealing covers with ventilation pipes (upper ventilation pipe 7 and lower ventilation pipe 15) and ventilation pipe switches (upper ventilation pipe switch 8 and lower ventilation pipe switch 16) are provided at the upper and lower ends of the settling tank. The upper sealing cover 2 and the lower sealing cover 6 are hermetically connected to the cylindrical container through a high-temperature resistant annular sealing ring 3.

[0052] The temperature and pressure control and measurement system includes a temperature control and measurement part and a pressure supply and measurement part. The temperature control and measurement part includes a heating furnace 4, a heat preservation layer 5, a temperature sensor 13, and a temperature display instrument 12. The heating furnace is used to heat the settling tank, and the temperature sensor and the display instrument are used to measure and display the temperature of the settling tank; the pressure supply and measurement part includes a gas compression pump 11, an upper ventilation pipe pressure gauge 9, an upper ventilation pipe pressure gauge 17, and a gas flowmeter 10. The gas compression pump provides high-pressure gas, which is connected to the settling tank through a ventilation pipeline 14, an upper ventilation pipe, and a lower ventilation pipe respectively. Pressure gauges are provided on the ventilation pipes at the top and bottom of the settling tank to measure and display the gas pressure flowing through the ventilation pipes. The gas flowmeter is provided on the upper ventilation pipe of the settling tank to determine whether there is gas flowing through the ventilation pipe, so as to determine the breakthrough pressure of the drilling fluid.

[0053] The automatic identification and zoning system of the settling section involves a spectrophotometer scanning device, which mainly includes a light source, a monochromator, a detector, a signal processor and a calculator. The device emits a continuous spectrum within the required wavelength range from the light source, and the monochromator decomposes the continuous spectrum emitted by the light source into monochromatic light and accurately focuses it on the drilling fluid in the settling tank, and detects the stratification of the drilling fluid in the tank based on the different absorption amounts of monochromatic light or penetration intensity of the drilling fluid at different concentrations. The detector uses the photoelectric effect to convert light energy into electrical signals, and transmits the electrical signals to the computer after amplification, filtering and numerical calculation by the signal processor, so that the transmittance of the drilling fluid at different positions can be directly obtained, and the drilling fluid in the settling tank can be divided from top to bottom according to the different transmittances, including the liquid separation area, the solidified mud area and the solidified accumulation area.

[0054] The drilling fluid separation device involves a drilling fluid extraction pipe, a pump and a storage tank. The drilling fluid extraction pipe extends into the drilling fluid along the inner wall of the settling tank, and the drilling fluid in the settling tank is pumped into the storage tank through the pump. Example

[0055] This indoor evaluation method for the sealing performance of drilling fluid in the unsealed section of the annulus of an oil well includes the following steps:

[0056] Step 1: Take the drilling fluid used in oil and gas wells and put it into an aging tank, place it in a roller furnace for rolling aging for 16 hours to make the components evenly mixed;

[0057] Step 2: Take out 20 mL of the aged drilling fluid and put it into a measuring bottle (the height of the drilling fluid in the measuring bottle is about 43 mm). Use a stability analyzer to measure the curve of the drilling fluid stability index changing with time (the smaller the stability index, the more stable the drilling fluid system; when the curve tends to be stable, the sedimentation, flocculation, aggregation and liquid separation process of the drilling fluid system is completed). Record the time when the stability index tends to be stable, which is 4 hours, and use it as a reference for the standing time of the drilling fluid in step 3.

[0058] Step 3: Take out the aged drilling fluid and put it into the drilling fluid settling tank to the top zero mark. The total height of the drilling fluid column is recorded as 1m. ， After the settling tank is sealed, turn on the heating furnace to heat the drilling fluid settling tank to the actual wellbore temperature, and introduce gas into the settling tank through the upper valve stem to pressurize it to the actual wellbore pressure. After standing at a constant temperature for 93 hours under temperature and pressure conditions, cool it to room temperature, and then slowly take out the settling tank from the heating furnace and place it on the storage rack.

[0059] Step 4: Turn on the spectrophotometer scanning device, scan the drilling fluid in the settling tank from top to bottom starting from the zero scale line at the top of the observation port of the settling tank, and record the relationship curve between the scale and the transmittance of the drilling fluid. The drilling fluid in the settling tank is divided into three areas from top to bottom according to the different transmittances of the drilling fluid: when the transmittance is 100%, it is the liquid separation area (note: the liquid separation area is liquid and there is no gas breakthrough pressure), between 5%-100% is the solidified mud area, and between 0%-5% is the solidified accumulation area formed by the dense phase accumulation of weighted materials. The heights of the three areas are calculated by the range of transmittance, which are recorded as 0.02m, 0.93m, and 0.05m respectively, 0.02+0.93+0.05=1 (m).

[0060] Step 5: Extend the drilling fluid extraction pipe into the drilling fluid along the inner wall of the sedimentation tank, and use a pump to pump the upper chromatographic liquid area and the middle layer solidified mud area into the drilling fluid storage tank, leaving only the lower solidified accumulation area in the sedimentation tank. Turn on the upper and lower ventilation pipe switches, connect the bottom of the sedimentation tank to the pressure supply system, turn on the gas compression pump to pressurize the gas into the tank from the lower ventilation pipe of the sedimentation tank, and when the gas flow meter on the upper sealing cover shows the indication, record the reading of the ventilation pipe pressure gauge, which is the breakthrough pressure when the gas passes through the lower solidified accumulation area, recorded as 0.55kPa. 0.55 / 0.05=11 (kPa) is the breakthrough pressure of the drilling fluid solidified accumulation area at a unit height;

[0061] Step 6: Repeat steps 1 to 4 to retain all the drilling fluid. Turn on the upper and lower vent pipe switches, connect the bottom of the sedimentation tank to the pressure supply system, and pressurize the tank from the lower vent pipe of the sedimentation tank. When the gas flow meter on the upper sealing cover shows the reading, record the reading of the vent pipe pressure gauge, which is the breakthrough pressure when the gas passes through the lower and middle layers of the drilling fluid, recorded as 9.52kPa. (9.52-0.55) / 0.93=9.65 (kPa) is the breakthrough pressure of the solidified mud zone in the middle layer of the drilling fluid at a unit height;

[0062] Step 7: Calculate the total breakthrough pressure of the drilling fluid in the unsealed section of the annulus in the actual wellbore P 总 (MPa), specifically:

[0063] Assuming that the total height of the drilling fluid in the annulus in the actual wellbore is 1000m, the height of the solidified accumulation area of ​​the lower layer of drilling fluid in the actual wellbore is h 下 × H / h= 0.05×1000 / 1=50 (m), the breakthrough pressure is ( P 1 / h 下 )×( h 下 × H / h ) = 11 × 50 = 550 (kPa); the actual height of the solidified mud zone in the middle layer of drilling fluid in the wellbore is h 中 × H / h= 0.93×1000 / 1=930 (m), the breakthrough pressure is ( P 2 - P 1 ) / h 中 ×( h 中 × H / h )=9.65×930=8974.5 (kPa); The upper stratum fluid zone of the drilling fluid in the actual wellbore does not have a breakthrough pressure.

[0064] The total breakthrough pressure of drilling fluid in the unsealed section of the annulus in the actual wellbore P 总 =( P 1 / h 下 )×( h 下 × H / h )+( P 2 - P 1 ) / h 中 ×( h 中 × H / h ) = 550 + 8974.5 = 9524.5 (kPa). By simplifying the above formula, the total breakthrough pressure of the drilling fluid in the unsealed section of the annulus in the actual wellbore is obtained. P 总 About 9.52MPa.

[0065] Step 8: Evaluate the wellbore sealing ability of the unsealed section: The actual formation pore pressure at 1000m in the wellbore is about 11.1MPa, which is greater than the total breakthrough pressure of the drilling fluid in the unsealed section of the annulus 9.52MPa. The drilling fluid in the unsealed section of the annulus has poor sealing performance, and there is a risk of underground oil and gas rising to the upper shallow water layer or the ground through the unsealed section of the annulus. A plan needs to be made to carry out secondary cementing before leakage occurs.

Claims

1. A method for evaluating the sealing performance of drilling fluid in an unsealed section of an annulus, characterized in that The steps include: Step 1: Take the drilling fluid used in the oil and gas wells and put it into an aging tank and place it in a roller furnace for rolling aging for 16 hours; Step 2: Take out the aged drilling fluid in step 1 and put it into a measuring bottle. The height of the drilling fluid in the measuring bottle is 43 mm. Measure the curve of the drilling fluid stability index over time and record the time t when the stability index tends to be stable. Step 3: Take out the drilling fluid aged in step 1, put it into the settling tank to the top zero mark and seal it. The total height of the drilling fluid column is recorded as h， The temperature of the sedimentation tank is raised to the actual wellbore temperature. Gas is introduced into the sedimentation tank through the upper ventilation pipe to pressurize it to the actual wellbore pressure. The constant temperature time is 1000× h × t / 43 and then cooled to room temperature, took out the sedimentation tank and placed it on a storage rack; Step 4: Scan the drilling fluid in the settling tank from top to bottom starting from the zero scale line at the top of the observation port of the settling tank, and record the relationship curve between the scale and the transmittance of the drilling fluid. The drilling fluid in the settling tank is divided into three areas from top to bottom according to the different transmittances of the drilling fluid: when the transmittance is 100%, it is the liquid separation area, when the transmittance is between 5%-100%, it is the solidified mud area, and when the transmittance is between 0%-5%, it is the solidified accumulation area. Calculate the heights of the three areas; record them as h 上 , h 中 , h 下 , h 上 + h 中 + h 下 = h ; Step 5: Extend the drilling fluid extraction pipe into the drilling fluid along the inner wall of the settling tank, and draw the drilling fluid from the liquid separation area and the solidified mud area into the storage tank. Open the upper and lower ventilation pipe switches, and pressurize the gas from the lower ventilation pipe into the settling tank. When the gas flow meter shows the indication, record the reading of the ventilation pipe pressure gauge, which is the breakthrough pressure when the gas passes through the lower solidified accumulation area, recorded as P 1, P 1 / h 下 is the breakthrough pressure of the drilling fluid solidification accumulation zone at unit height; Step 6: Repeat steps 1 to 4, and add gas pressure to the tank from the lower vent pipe of the settling tank. When the gas flow meter shows the indication, record the reading of the vent pipe pressure gauge, which is the breakthrough pressure of the gas when it passes through the lower solidified accumulation area of ​​the drilling fluid and the solidified mud area in the middle layer, recorded as P 2, ( P 2- P 1) / h 中 is the breakthrough pressure of the solidified mud zone in the middle layer of drilling fluid at unit height; Step 7: Calculate the total breakthrough pressure of the drilling fluid in the unsealed section of the annulus in the actual wellbore P 总 ; Step 8: Evaluate the sealing ability of the uncemented section of the wellbore: When the total breakthrough pressure of the drilling fluid in the uncemented section of the annulus in the actual wellbore is greater than the formation pore pressure, the sealing performance of the drilling fluid in the uncemented section of the annulus is good; otherwise, make a plan for secondary cementing.

2. The method for evaluating the sealing performance of drilling fluid in an unsealed section of an annulus according to claim 1, characterized in that: The step 7 is specifically as follows: Assume that the total height of drilling fluid in the annulus in the actual wellbore is H , then the actual height of the solidified accumulation area of ​​the lower layer of drilling fluid in the wellbore is h 下 × H / h , the breakthrough pressure is ( P 1 / h 下 )×( h 下 × H / h ); The actual height of the solidified mud zone in the middle layer of drilling fluid in the wellbore is h 中 × H / h , the breakthrough pressure is ( P 2- P 1) / h 中 ×( h 中 × H / h ); The upper layer of drilling fluid in the actual wellbore does not have a breakthrough pressure; The total breakthrough pressure of drilling fluid in the unsealed section of the annulus in the actual wellbore is as follows: P 总 =（ P 1 / h 下 ）×（ h 下 × H / h ）+（ P 2- P 1） / h 中 ×（ h 中 × H / h ） （1-1） Where: P 总 is the total breakthrough pressure of drilling fluid in the unsealed section of the annulus in the actual wellbore, MPa; P 1 is the gas breakthrough pressure in the solidified accumulation area of ​​the lower layer of drilling fluid in the settling tank, MPa; P 2 is the sum of the gas breakthrough pressures of the lower and middle layers of the drilling fluid in the settling tank, MPa; H is the total height of drilling fluid in the annulus in the actual wellbore, m; h is the total height of drilling fluid in the settling tank, m; h 下 is the height of the lower solidification accumulation area in the settling tank, m; h 中 is the gas breakthrough pressure of the solidified mud zone in the middle layer of drilling fluid in the settling tank, m; Simplifying formula (1-1), the total breakthrough pressure of drilling fluid in the unsealed section of the annulus in the actual wellbore is obtained as follows: P 总 = P 2×（ H / h ） （1-2） Where: P 总 is the total breakthrough pressure of drilling fluid in the unsealed section of the annulus in the actual wellbore, MPa; P 2 is the sum of the gas breakthrough pressures of the lower and middle layers of the drilling fluid in the settling tank, MPa; H is the total height of drilling fluid in the annulus in the actual wellbore, m; h is the total height of drilling fluid in the settling tank, m.

3. The method for evaluating the sealing performance of drilling fluid in an unsealed section of an annulus according to claim 2, characterized in that: The top of the sedimentation tank is composed of an upper sealing cover sealed at the upper port of the tank body, a high-temperature resistant annular sealing ring is arranged between the upper sealing cover and the upper port of the tank body, an upper ventilation pipe is arranged on the top of the tank, an upper ventilation pipe switch, a gas flow meter and a pressure gauge are arranged on the upper ventilation pipe, and the upper ventilation pipe is connected to the gas compression pump through a ventilation pipeline; the bottom of the sedimentation tank is composed of a lower sealing cover sealed at the lower port of the tank body, a high-temperature resistant annular sealing ring is arranged between the lower sealing cover and the lower port of the tank body, a lower ventilation pipe is arranged on the bottom of the tank, and a lower ventilation pipe switch and a pressure gauge are arranged on the lower ventilation pipe; the tank body is provided with a transparent window and a scale, and the transparent window and the scale are arranged correspondingly.

4. The method for evaluating the sealing performance of drilling fluid in an unsealed section of an annulus according to claim 3, characterized in that: The step 3 is specifically as follows: the aged drilling fluid is taken out and loaded into the settling tank to the top zero mark, and the total height of the drilling fluid column is recorded as h， After the settling tank is sealed, place the settling tank in a heating furnace, with the upper and lower ventilation pipes extending from the heating furnace. The heating furnace is equipped with a temperature sensor and a temperature display instrument. An insulation layer is provided outside the heating furnace. The heating furnace is turned on to heat the settling tank to the actual wellbore temperature, and gas is introduced into the settling tank through the upper ventilation pipe on the top of the settling tank to pressurize it to the actual wellbore pressure. The settling tank is kept at a constant temperature for 1000× h × t / 43, cool to room temperature, then slowly take out the sedimentation tank from the heating furnace and place it on the storage rack.

5. The method for evaluating the sealing performance of drilling fluid in an unsealed section of an annulus according to claim 4, characterized in that: The step 4 scans the drilling fluid in the settling tank using an automatic identification and zoning system for the settling section. The automatic identification and zoning system for the settling section is a spectrophotometer scanning device, which includes a light source, a monochromator, a detector, a signal processor and a computer. The light source emits a continuous spectrum within a required wavelength range. The monochromator decomposes the continuous spectrum emitted by the light source into monochromatic light and accurately focuses it on the drilling fluid in the settling tank to detect the stratification of the drilling fluid in the tank. The detector uses the photoelectric effect to convert light energy into an electrical signal, and transmits the electrical signal to the computer after amplification, filtering and numerical calculation by the signal processor to obtain the transmittance of the drilling fluid at different positions, and divides the drilling fluid in the settling tank from top to bottom into a liquid separation zone, a solidified mud zone and a solidified accumulation zone according to the different transmittances.

6. The method for evaluating the sealing performance of drilling fluid in an unsealed section of an annulus according to claim 5, characterized in that: The step 2 is specifically as follows: 20 mL of the aged drilling fluid is taken out and put into a measuring bottle, the height of the drilling fluid in the measuring bottle is about 43 mm, and a stability analyzer is used to measure the curve of the drilling fluid stability index changing with time. The smaller the stability index is, the more stable the drilling fluid system is; when the curve tends to be stable, the sedimentation, flocculation, aggregation and liquid separation process of the drilling fluid system is completed, and the time when the stability index tends to be stable is recorded. t , which will be used as a reference for the drilling fluid standing time in step 3.

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