CN112780257A - Drilling fluid leakage monitoring system and monitoring method based on distributed optical fiber sensing - Google Patents
Drilling fluid leakage monitoring system and monitoring method based on distributed optical fiber sensing Download PDFInfo
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Abstract
The invention provides a drilling fluid leakage monitoring system and a monitoring method based on distributed optical fiber sensing.A borehole is provided with an armored optical cable, the armored optical cable contains a special optical fiber or an armored optical cable of a single-mode optical fiber with high temperature resistance and high sensitivity and a multimode optical fiber with high temperature resistance and high sensitivity, and the armored optical cable also comprises a DAS/DTS composite modulation and demodulation instrument placed near a wellhead; the DAS/DTS composite modulation and demodulation instrument has DAS signal ports connected to single mode fiber in armored cable and two DTS signal ports connected to multimode fiber in armored cable. The invention can measure and monitor the condition of the drilling fluid leakage point in the drilling hole in time, evaluate the leakage strength of the drilling fluid leakage point, design the technical scheme and measures for leakage stoppage in time and protect the safety of the drilling hole and the drilling machine.
Description
Technical Field
The invention belongs to the technical field of drilling, and particularly relates to a drilling fluid loss monitoring system and method based on distributed optical fiber sensing.
Background
The lost circulation is a complex underground condition that various working fluids (including drilling fluid, well cementing cement slurry, well repairing fluid, completion fluid and other fluids) in a shaft directly leak into a stratum under the action of pressure difference in underground operations such as drilling, well cementation, testing or well repairing of exploration and development of petroleum and natural gas. Lost circulation includes permeability, fracture, and karst cave losses. The visual performance of the well leakage is that no drilling fluid returns (lost return) from the well mouth, and the well mouth drilling fluid return is less than the drilling fluid discharge.
The well leakage has the hazards of incapability of maintaining drilling, large drilling fluid loss, drilling time loss, lost plugging material consumption, influence on geological logging, incapability of acquiring qualified geological data and other underground complex conditions such as well collapse, drilling sticking, blowout and the like.
The reason for lost circulation is that lost circulation channels, such as pores, cracks or karsts, exist in the formation and the drilling process is not proper. If the drilling fluid is high in density and pressure, a positive pressure difference exists.
The reason for the occurrence of the lost circulation is that natural leakage passages capable of enabling the drilling fluid to flow exist in drilled stratums, such as pores, cracks, karst caves, high-permeability stratums, fractured stratums and karst caves; the drilling process measures are improper, the drilling fluid performance is not good or a leakage channel is artificially generated due to improper operation; the pressure of the drilled stratum is deficient, or the density of the drilling fluid is too high, and the pressure is too high, so that a large positive pressure difference is generated; the viscosity shear force of the drilling fluid is too large, so that the pump-on pressure is too large, and pressure excitation is generated to suppress and leak the stratum; the drilling fluid has poor sand carrying performance, unclean well wall, or excessive water loss and thick filter cake, and pressure excitation is generated due to improper operations such as drilling down, pump starting and the like.
The optical fiber sensing technology started in 1977 and developed rapidly along with the development of the optical fiber communication technology, and the optical fiber sensing technology is an important mark for measuring the informatization degree of a country. The optical fiber sensing technology is widely applied to the fields of military affairs, national defense, aerospace, industrial and mining enterprises, energy environmental protection, industrial control, medicine and health, metering test, building, household appliances and the like, and has a wide market. There are hundreds of fiber sensing technologies in the world, and physical quantities such as temperature, pressure, flow, displacement, vibration, rotation, bending, liquid level, speed, acceleration, sound field, current, voltage, magnetic field, radiation and the like realize sensing with different performances.
The downhole optical fiber sensing system can be used for measuring pressure, temperature, noise, vibration, sound wave, seismic wave, flow, component analysis, electric field and magnetic field downhole. The system is based on a full armored optical cable structure, and the sensor and the connecting and data transmission cable are all made of optical fibers. At present, there are various underground armored optical cables, such as those placed in an underground control pipeline, placed in a coiled tubing, directly integrated into the wall of the coiled tubing made of composite material, bound and fixed outside the coiled tubing, placed in a casing, bound and fixed outside the casing and permanently fixed with well-cementing cement.
When drilling fluid leaks in a drill hole, a drilling engineer can roughly or qualitatively judge whether the drilling fluid leaks in the drill hole or not according to the difference between the discharge amount of the drilling fluid and the return amount of the wellhead drilling fluid, but cannot accurately judge the position or the depth of a drilling fluid leakage point, cannot quantitatively evaluate the strength and the speed of the drilling fluid leakage, and cannot determine the number of the drilling fluid leakage points in the drill hole. The method is one of the difficulties in timely and accurate judgment and evaluation of drilling fluid loss in the current drilling construction.
Disclosure of Invention
The invention provides a drilling fluid leakage measuring and monitoring system and a monitoring method in a drill hole based on distributed optical fiber sensing, aiming at overcoming the difficulties that the position or the depth of a drilling fluid leakage point cannot be accurately judged, the strength and the speed of the drilling fluid leakage cannot be quantitatively evaluated, and the number of the drilling fluid leakage points in the drill hole cannot be determined.
In order to achieve the purpose, the specific technical scheme of the invention is as follows:
based on a distributed optical fiber sensing drilling fluid loss monitoring system, a drilling hole is drilled in a drilling hole, drilling fluid loss points are likely to appear in the drilling hole, an armored optical cable is arranged in the drilling hole, the armored optical cable contains special optical fibers or armored optical cables of single-mode optical fibers with high temperature resistance and high sensitivity and multimode optical fibers with high temperature resistance and high sensitivity, and the system further comprises a DAS/DTS composite modulation and demodulation instrument placed near a wellhead;
the DAS/DTS composite modulation and demodulation instrument has DAS signal ports connected to single mode fiber in armored cable and two DTS signal ports connected to multimode fiber in armored cable.
The single-mode optical fiber and the multimode optical fiber are externally provided with at least one layer of continuous metal tubule for packaging, and the continuous metal tubule is externally provided with at least one layer of armored steel wire for packaging.
The tail end of the single-mode optical fiber is provided with an extinction device, and the tail ends of the multi-mode optical fiber are welded together in a U shape at the bottom of the well and are used for being connected to two double-end signal input ports of two DTS signals of the DAS/DTS composite modulation and demodulation instrument.
The drilling fluid leakage monitoring system based on the distributed optical fiber sensing further comprises a drill rod, when a drilling fluid leakage point is measured and monitored in horizontal well drilling, the armored optical cable is placed in the drill rod and is brought into a horizontal well section and is arranged behind a drill bit, and the drill rod is used for protecting the armored optical cable from being damaged during drilling operation.
The monitoring method based on the distributed optical fiber sensing drilling fluid loss monitoring system comprises the following steps:
(1) when drilling fluid loss occurs in the drilling hole, if the well condition is stable, namely no drill rod or drill bit exists underground, the well wall cannot collapse, and the armored optical cable with the tail end connected with the counterweight rod is slowly lowered into a borehole of an open hole from a well head;
(2) connecting the single-mode optical fiber and the multi-mode optical fiber in the armored optical cable to DAS and DTS signal input ends of a DAS/DTS composite modulation and demodulation instrument at a wellhead respectively;
(3) after the armored optical cable is put down to the well bottom, a DAS/DTS composite modulation and demodulation instrument near the well top is started, and single mode optical fibers in the armored optical cable are used for carrying out real-time measurement and monitoring on the underground noise of the whole well section; the migration process and the state of the drilling fluid in the shaft can be reflected by the change of the noise distribution of the whole well section; the abnormal noise position measured along the armored optical cable is a drilling fluid leakage point where well leakage occurs; the amount of the drilling fluid leaking into the stratum and the leakage speed can be analyzed and judged according to the noise change around the drilling fluid leakage point; the DAS data can reflect that the larger the noise is, the larger the drilling fluid loss at the drilling fluid loss part is represented;
(4) synchronously measuring and monitoring the underground temperature change of the whole well section in real time by utilizing the multimode optical fiber in the armored optical cable; the temperature change of the whole well section can reflect the migration process and state of the drilling fluid in the shaft; the abnormal temperature position measured along the armored optical cable is a drilling fluid leakage point where well leakage occurs; the amount of the drilling fluid leaking into the stratum and the leakage speed can be analyzed and judged according to the temperature change around the drilling fluid leakage point; the lower the temperature can be reflected from the DTS data, the larger the drilling fluid loss at the drilling fluid loss point is represented;
(5) and (4) establishing a real-time shaft temperature model according to the temperature value of the whole well section measured in the step (4), comparing the real-time shaft temperature model with the shaft temperature model calculated according to the geothermal gradient of the well drilling area, carrying out integral optimization through continuous iteration, and quantitatively estimating the leakage or injection profile of the well by applying an optimization theoretical model. This optimization is obtained by comparing the measured temperature data in the well of the instrument with the theoretical calculation data of the temperature model in the well at the response location. Successive iterations are performed in the calculation until the best match is obtained between the theoretical wellbore temperature model and the wellbore measured temperature data.
(6) Comparing the temperature and pressure data of underground measurement with a theoretical temperature and pressure curve calculated by a shaft model, setting an initial value of shaft temperature, calculating a shaft temperature profile by an optimization algorithm by using the established shaft temperature model, and enabling the mean square error to be minimum to realize the calculation of the temperature profile:
wherein x2: mean square error; y isa,th: tool values predicted by the model; y isa,exp(ii) a Measuring a tool value; sigmaa: measuring errors by an instrument; the concrete solving steps of the optimal calculation are as follows:
the specific solution of the optimal calculation comprises the following sub-steps:
(1) preparing parameters required by calculation, including oil deposit parameters, fluid physical property parameters, production system parameters and thermodynamic parameters of a shaft;
(2) initializing reservoir pressure and temperature;
(3) calculating the pressure distribution of the shaft according to a pressure formula, comparing the calculated pressure with the measured pressure, if the iteration limiting condition is not met, recalculating the calculated value as a new initial value until the condition is met, and then continuing to solve;
(4) and calculating the temperature distribution flowing into the shaft according to the shaft temperature model, comparing the calculated shaft temperature with the measured shaft temperature, and if the iteration limit condition is not met, recalculating the calculated value as a new initial value until the condition is met and then continuing to solve.
(8) And by analyzing the single-phase or multiphase flow state in the shaft, considering the influence of factors such as friction and gravity on pressure, and establishing a shaft temperature model under a steady state condition by utilizing the mass and energy conservation law, the relation between the leakage of the drilling fluid and the temperature is obtained. According to the mass conservation law, the mass flowing in a unit area is equal to the mass flowing out, and under the stable condition, the mass conservation equation in the shaft is as follows:
where ρ isiThe density of each phase; gamma is the area of the drilling fluid loss point and the surface area ratio of the shaft; v is the flow rate; y isiThe retention rate is determined; r is the radius of a shaft; p: a pressure value; dx is the differential or step size along the well trajectory direction x.
(9) And performing joint inversion processing by using noise and temperature abnormal values measured in real time at the drilling fluid loss points of the well in the well according to the total drilling fluid discharge capacity, the drilling fluid loss amount or the loss volume and the drilling fluid loss speed measured at the well mouth, so as to quantitatively calculate the specific drilling fluid loss amount or the loss volume and the loss speed at each drilling fluid loss point in the shaft.
(10) According to the time of DAS noise at the drilling fluid leakage point in the armored optical cable reaching the DAS/DTS composite modulation and demodulation instrument and the propagation speed of light in the optical fiber, the depth of the drilling fluid leakage point from a wellhead can be calculated, the leakage strength of the drilling fluid leakage point can be evaluated by combining the specific drilling fluid leakage amount or leakage volume and the leakage speed of each drilling fluid leakage point in the shaft calculated in the step (9), the technical scheme and the measures for leakage stoppage are designed in time, and the safety of drilling holes and drilling machines is protected.
The invention provides a drilling fluid leakage monitoring system and a monitoring method based on distributed optical fiber sensing, wherein an armored optical cable is placed in an open hole drill hole with drilling fluid leakage or is placed in a drill rod and is brought to the bottom of a horizontal well by the drill rod and a drilling tool, and an underground sensing unit capable of measuring and monitoring a drilling fluid leakage point in real time is constructed. The DAS/DTS composite modulation and demodulation instrument on the wellhead ground is connected with an underground armored optical cable to form a drilling fluid leakage measuring and monitoring system based on distributed optical fiber sensing, the condition of a drilling fluid leakage point in a drill hole is measured and monitored in time, the leakage strength of the drilling fluid leakage point is evaluated, the technical scheme and measures for leakage stoppage are designed in time, and the safety of the drill hole and a drilling machine is protected.
Drawings
FIG. 1 is a schematic diagram of the structure and downhole layout of a distributed optical fiber sensing based drilling fluid loss monitoring system of the present invention;
FIG. 2 is a schematic diagram of a horizontal downhole deployment of an embodiment of a distributed optical fiber sensing based drilling fluid loss monitoring system;
fig. 3 is an optimum calculation flowchart of the embodiment.
Detailed Description
In order to facilitate an understanding of the invention, the invention is described in more detail below with reference to the accompanying drawings and specific examples. Preferred embodiments of the present invention are shown in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete. They are not to be construed as limiting the invention but merely as exemplifications, while the advantages thereof will be more clearly understood and appreciated by way of illustration.
The invention relates to a specific implementation mode of a drilling fluid loss monitoring system based on distributed optical fiber sensing, which is shown in figure 1:
the optical cable comprises a drilling hole 1 which is drilled in the open hole, a drilling fluid leakage point 2 in the drilling hole, an armored optical cable 3 containing a special optical fiber or a high-temperature-resistant high-sensitivity single-mode optical fiber 4 and a high-temperature-resistant high-sensitivity multi-mode optical fiber 5, and a DAS/DTS composite modulation and demodulation instrument 8 which is arranged near a wellhead;
the DAS/DTS composite modulation and demodulation instrument 8 has DAS signal ports connected to the single-mode optical fiber 4 in the armored optical cable 3, and the two DTS signal ports of the DAS/DTS composite modulation and demodulation instrument 8 are connected to the multimode optical fiber 5 in the armored optical cable 3.
At least one layer of continuous metal thin tube is arranged outside the single-mode optical fiber 4 and the multimode optical fiber 5 to encapsulate the same, and at least one layer of armored steel wire is arranged outside the continuous metal thin tube to encapsulate the same.
The tail end of the single-mode optical fiber 4 is provided with an extinction device 6, the tail ends of the multimode optical fibers 5 are welded together in a U-shaped 7 mode at the bottom of the well and are used for being connected to two DTS signal double-end signal input ports of a DAS/DTS composite modulation and demodulation instrument 8.
As shown in fig. 2, when the drilling fluid loss point 2 is measured and monitored in the horizontal well drilling process, the armored optical cable 2 cannot be placed at the bottom of the horizontal well by means of the counterweight, and the well wall of the horizontal well is very unstable due to the huge pressure of the overlying stratum, the armored optical cable 3 can only be placed in the drill rod 9 and brought into the horizontal well section and is arranged behind the drill bit 10, and the drill rod 9 is used for protecting the armored optical cable 3 from being damaged during the drilling operation.
The monitoring method based on the distributed optical fiber sensing drilling fluid loss monitoring system comprises the following steps:
(a) when drilling fluid loss occurs in the borehole 1, if the well conditions are stable, namely no drill rod 9 or drill bit 10 exists underground, the borehole wall cannot collapse, and the armored optical cable 3 with the tail end connected with the counterweight rod is slowly lowered into a borehole of an open hole from a wellhead;
(b) connecting a single-mode optical fiber 4 and a multi-mode optical fiber 5 in the armored optical cable 3 to DAS and DTS signal input ends of a DAS/DTS composite modulation and demodulation instrument 8 at a wellhead respectively;
(c) after the armored optical cable 3 is lowered to the well bottom, a DAS/DTS composite modulation and demodulation instrument 8 near the well top is started, and single mode optical fibers 4 in the armored optical cable 3 are used for carrying out real-time measurement and monitoring on the whole well section underground noise; the migration process and the state of the drilling fluid in the shaft can be reflected by the change of the noise distribution of the whole well section; the abnormal noise position measured along the armored optical cable 3 is a drilling fluid leakage point 2 where well leakage occurs; the amount of liquid leaking into the stratum and the leakage speed of the drilling fluid can be analyzed and judged according to the noise change around the drilling fluid leakage point 2; the DAS data can reflect that the larger the noise is, the larger the drilling fluid loss at the drilling fluid loss point 2 is;
(d) synchronously carrying out real-time measurement and monitoring of the underground temperature change of the whole well section by utilizing the multimode optical fiber 5 in the armored optical cable 3; the temperature change of the whole well section can reflect the migration process and state of the drilling fluid in the shaft; the abnormal temperature position measured along the armored optical cable 3 is a drilling fluid leakage point 2 where well leakage occurs; the amount of the drilling fluid leaking into the stratum and the leakage speed can be analyzed and judged according to the temperature change around the drilling fluid leakage point 2; the lower the temperature can be reflected from the DTS data, the larger the drilling fluid loss at the drilling fluid loss point 2 is represented;
(e) and (d) establishing a real-time shaft temperature model according to the temperature value of the whole well section measured in the step (d), comparing the real-time shaft temperature model with the shaft temperature model calculated according to the geothermal gradient of the well drilling area, carrying out integral optimization through continuous iteration, and quantitatively estimating the leakage or injection profile of the well by applying an optimization theoretical model. This optimization is obtained by comparing the measured data of the instrument with the theoretical calculated data of the temperature model in the well at the response location. Successive iterations are performed in the calculation until the best match is obtained between the theoretical temperature model of the wellbore and the measured temperature data of the wellbore.
(f) Comparing the temperature and pressure data of underground measurement with a theoretical temperature and pressure curve calculated by a shaft model, setting an initial value of shaft temperature, calculating a shaft temperature profile by an optimization algorithm by using the established shaft temperature model, and enabling the mean square error to be minimum to realize the calculation of the temperature profile:
wherein x2: mean square error; y isa,th: tool value of model prediction；Ya,exp(ii) a Measuring a tool value; sigmaa: measuring errors by an instrument;
as shown in fig. 3, the specific solution of the optimal calculation includes the following sub-steps:
(1) preparing parameters required by calculation, including oil deposit parameters, fluid physical property parameters, production system parameters and thermodynamic parameters of a shaft;
(2) initializing reservoir pressure and temperature;
(3) calculating the pressure distribution of the shaft according to a pressure formula, comparing the calculated pressure with the measured pressure, if the iteration limiting condition is not met, recalculating the calculated value as a new initial value until the condition is met, and then continuing to solve;
(4) and calculating the temperature distribution flowing into the shaft according to the shaft temperature model, comparing the calculated shaft temperature with the measured shaft temperature, and if the iteration limit condition is not met, recalculating the calculated value as a new initial value until the condition is met and then continuing to solve.
(g) And by analyzing the single-phase or multiphase flow state in the shaft, considering the influence of factors such as friction and gravity on pressure, and establishing a shaft temperature model under a steady state condition by utilizing the mass and energy conservation law, the relation between the leakage of the drilling fluid and the temperature is obtained. According to the mass conservation law, the mass flowing in a unit area is equal to the mass flowing out, and under the stable condition, the mass conservation equation in the shaft is as follows:
where ρ isiThe density of each phase; gamma is the area of the drilling fluid loss point 2 and the surface area ratio of the shaft; v is the flow rate; y isiThe retention rate is determined; r is the radius of a shaft; p: a pressure value; dx is the differential or step size along the well trajectory direction x.
(h) And performing joint inversion processing by using noise and temperature abnormal values measured in real time at the drilling fluid leakage point 2 of the well in the well according to the total drilling fluid discharge capacity, the drilling fluid leakage amount or the leakage volume and the drilling fluid leakage speed measured at the well mouth, and quantitatively calculating the specific drilling fluid leakage amount or the leakage volume and the leakage speed at each drilling fluid leakage point 2 in the shaft.
(i) According to the time of DAS noise at the drilling fluid leakage point 2 in the armored optical cable reaching the DAS/DTS composite modulation and demodulation instrument 8 and the propagation speed of light in the optical fiber, the depth of the drilling fluid leakage point 2 from a wellhead can be calculated, the leakage strength of the drilling fluid leakage point 2 can be evaluated by combining the specific drilling fluid leakage amount or the leakage volume and the leakage speed of each drilling fluid leakage point 2 in the shaft calculated in the step (h), the technical scheme and the measures for leaking stoppage are designed in time, and the safety of drilling and drilling machines is protected.
Claims (6)
1. The drilling fluid loss monitoring system based on distributed optical fiber sensing is characterized by comprising an armored optical cable (3) arranged in a drilling hole (1) which is drilled in a drilling manner, wherein the armored optical cable (3) contains a high-temperature-resistant high-sensitivity single-mode optical fiber (4) and a high-temperature-resistant high-sensitivity multi-mode optical fiber (5), and further comprises a DAS/DTS composite modulation and demodulation instrument (8) placed near a wellhead;
the DAS/DTS composite modulation and demodulation instrument (8) is characterized in that a DAS signal port is connected with a single mode optical fiber (4) in an armored optical cable (3), and two DTS signal ports of the DAS/DTS composite modulation and demodulation instrument (8) are connected with a multimode optical fiber (5) in the armored optical cable (3).
2. The system for monitoring the loss of drilling fluid based on the distributed optical fiber sensing of claim 1, wherein at least one layer of continuous metal tubule is arranged outside the single-mode optical fiber (4) and the multi-mode optical fiber (5) to encapsulate the single-mode optical fiber and the multi-mode optical fiber, and at least one layer of armored steel wire is arranged outside the continuous metal tubule to encapsulate the continuous metal tubule.
3. The system for monitoring the loss of drilling fluid based on the distributed optical fiber sensing of claim 1, wherein an extinction device (6) is installed at the tail end of the single-mode optical fiber (4), and the tail ends of the multimode optical fiber (5) are welded together in a U-shaped manner (7) at the bottom of a well and are used for being connected to two DTS signal double-end signal input ports of a DAS/DTS composite modulation and demodulation instrument (8).
4. The drilling fluid loss monitoring system based on the distributed optical fiber sensing is characterized by further comprising a drill rod (9), when the drilling fluid loss point (2) is measured and monitored in horizontal well drilling, the armored optical cable (3) is placed in the drill rod (9) and is brought into a horizontal well section, the armored optical cable (3) is arranged behind the drill bit (10), and the drill rod (9) is used for protecting the armored optical cable (3) from being damaged during drilling operation.
5. The method for monitoring the loss of drilling fluid based on the distributed optical fiber sensing is characterized in that the system for monitoring the loss of drilling fluid based on the distributed optical fiber sensing as claimed in any one of claims 1 to 4 is adopted, and comprises the following steps:
(a) when drilling fluid loss occurs in the drilling hole (1), if the well condition is stable, namely no drill rod (9) and drill bit (10) exist underground, the well wall cannot collapse, and the armored optical cable (3) with the tail end connected with the counterweight rod is slowly lowered into a borehole of an open hole from a well head;
(b) the single-mode optical fiber (4) and the multi-mode optical fiber (5) in the armored optical cable (3) are respectively connected to DAS and DTS signal input ends of a DAS/DTS composite modulation and demodulation instrument (8) at a wellhead;
(c) after the armored optical cable (3) is lowered to the well bottom, a DAS/DTS composite modulation and demodulation instrument (8) near the well top is started, and single-mode optical fibers (4) in the armored optical cable (3) are used for carrying out real-time measurement and monitoring on the whole well section underground noise; the migration process and the state of the drilling fluid in the shaft can be reflected by the change of the noise distribution of the whole well section; the abnormal noise position measured along the armored optical cable (3) is a drilling fluid leakage point (2) where well leakage occurs; the amount of liquid leaking into the stratum and the leakage speed of the drilling fluid can be analyzed and judged according to the noise change around the drilling fluid leakage point (2); the DAS data can reflect that the larger the noise is, the larger the drilling fluid loss at the drilling fluid loss point (2) is;
(d) synchronously measuring and monitoring the underground temperature change of the whole well section in real time by using the multimode optical fiber (5) in the armored optical cable (3); the temperature change of the whole well section can reflect the migration process and state of the drilling fluid in the shaft; the abnormal temperature position measured along the armored optical cable (3) is a drilling fluid leakage point (2) with the well leakage; the amount of liquid leaking into the stratum by the drilling fluid can be analyzed and judged at the leakage speed according to the temperature change around the drilling fluid leakage point (2); the lower the temperature can be reflected from the DTS data, the larger the drilling fluid loss at the drilling fluid loss point (2) is represented;
(e) establishing a real-time shaft temperature model according to the temperature value of the whole well section measured in the step (d), comparing the real-time shaft temperature model with a temperature model calculated according to the geothermal gradient of a drilling area, carrying out integral optimization through continuous iteration, and quantitatively estimating the leakage or injection profile of the well by applying an optimization theoretical model; the optimization is obtained by comparing the measured data of the instrument with the theoretical calculation data of the model in the well at the response position; when calculating, continuous iteration is executed until the best matching is obtained between the theoretical model and the measured data;
(f) comparing the temperature and pressure data measured underground with a theoretical temperature and pressure curve calculated by a shaft model, setting an initial value of shaft temperature, calculating a shaft temperature profile by an optimization algorithm by using the established shaft temperature model, and enabling the mean square error to be minimum to realize the calculation of the temperature profile:
wherein x2: mean square error; y isa,th: tool values predicted by the model; y isa,exp(ii) a Measuring a tool value; sigmaa: measuring errors by an instrument;
(g) the method comprises the following steps of (1) establishing a shaft temperature model under a steady state condition by analyzing the single-phase or multi-phase flow state in a shaft and considering the influence of friction and gravity factors on pressure and utilizing the mass and energy conservation law to obtain the relation between the leakage of drilling fluid and temperature; according to the mass conservation law, the mass flowing in a unit area is equal to the mass flowing out of the unit area, and under the stable condition, the mass conservation equation in the shaft is as follows:
where ρ isiThe density of each phase; gamma is the area of the drilling fluid loss point (2) and the surface area ratio of the shaft; v is the flow rate; y isiThe retention rate is determined; r is the radius of a shaft; p: a pressure value; dx is the differential or step length along the well trajectory direction x;
(h) performing joint inversion processing by using noise and temperature abnormal values measured in real time at the drilling fluid loss point (2) of the well in the well according to the total drilling fluid discharge capacity, the drilling fluid loss amount or the loss volume and the drilling fluid loss speed measured at the well mouth, and quantitatively calculating the specific drilling fluid loss amount or the loss volume and the loss speed at each drilling fluid loss point (2) in the shaft;
(i) according to the time of DAS noise at the drilling fluid leakage point (2) in the armored optical cable reaching the DAS/DTS composite modulation and demodulation instrument (8) and the propagation speed of light in the optical fiber, the depth of the drilling fluid leakage point (2) from a wellhead can be calculated, the leakage strength of the drilling fluid leakage point (2) can be evaluated by combining the specific drilling fluid leakage amount or leakage volume and the leakage speed of each drilling fluid leakage point (2) in the shaft calculated in the step (h), the technical scheme and the measures for leakage stoppage are designed in time, and the safety of drilling holes and drilling machines is protected.
6. The distributed optical fiber sensing-based drilling fluid loss monitoring method according to claim 1, wherein the concrete solution of the optimal calculation in the step (f) comprises the following sub-steps:
(1) preparing parameters required by calculation, including oil deposit parameters, fluid physical property parameters, production system parameters and thermodynamic parameters of a shaft;
(2) initializing reservoir pressure and temperature;
(3) calculating the pressure distribution of the shaft according to a pressure formula, comparing the calculated pressure with the measured pressure, if the iteration limiting condition is not met, recalculating the calculated value as a new initial value until the condition is met, and then continuing to solve;
(4) and calculating the temperature distribution flowing into the shaft according to the shaft temperature model, comparing the calculated shaft temperature with the measured shaft temperature, and if the iteration limit condition is not met, recalculating the calculated value as a new initial value until the condition is met and then continuing to solve.
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