Multipoint pressure optical fiber long-acting monitoring system for offshore oilfield heavy oil thermal production well

Abstract

The invention discloses a multipoint pressure optical fiber long-acting monitoring system for a heavy oil thermal production well of an offshore oilfield. The multipoint pressure optical fiber long-acting monitoring system comprises an underground process pipe column and a plurality of high-temperature optical fiber pressure sensors arranged in the underground process pipe column. The high-temperature optical fiber pressure sensor is connected with a pressure demodulator arranged on the ground through an underground monitoring optical cable; the high-temperature optical fiber pressure sensor is a single-end optical fiber pressure sensor or a double-end optical fiber pressure sensor; and the integration mode of the underground process pipe column and the underground monitoring optical cable is an out-pipe binding mode or an out-pipe to in-pipe mode. The temperature-resistant and pressure-resistant grade of the optical fiber pressure gauge is improved, the structural design of the single-end optical fiber pressure sensor and the double-end optical fiber pressure sensor is adopted, the series-parallel connection integration mode of a monitoring optical cable and the pressure gauge is achieved, the time division multiplexing demodulation mode and the wavelength division multiplexing demodulation mode of a ground pressure demodulator are matched, and real-time and online long-term monitoring of underground multipoint pressure is achieved; two kinds of process pipe columns are configured, and the requirements for annular multi-point pressure monitoring in an underground oil pipe are met respectively.

Description

Technical Field

[0001] The invention belongs to the technical field of offshore heavy oil thermal recovery, and in particular relates to a multi-point pressure optical fiber long-term monitoring system for heavy oil thermal recovery wells in an offshore oil field. Background Art

[0002] With the deepening of the development of offshore heavy oil thermal recovery wells, it is necessary to monitor the real-time data of multiple parameters such as downhole temperature and pressure during the production process of thermal recovery wells to reflect the production status of heavy oil thermal recovery wells, so as to improve the production efficiency. Parameter monitoring work runs through the entire life cycle of heavy oil thermal recovery wells from measures, heat injection, well shut-down, and blowout, and is a key link and basic work in the development of heavy oil thermal recovery. However, during the heat injection period, heavy oil thermal recovery wells are subject to harsh conditions such as high temperature, high pressure, and corrosion, which brings great technical difficulties to the downhole multi-parameter monitoring work. At present, the relatively mature applications of long-term downhole pressure monitoring technologies for heavy oil thermal recovery wells include high-temperature storage pressure testing and capillary pressure testing. However, due to the influence of wellbore conditions, the high-temperature storage test and capillary test processes are subject to certain limitations in the implementation of heavy oil thermal recovery wells, such as depth measurement restrictions, temperature resistance level restrictions, short single test time, and low test accuracy.

[0003] Fiber optic sensing testing technology is very suitable for monitoring heavy oil thermal recovery wells due to its inherent safety, high precision, anti-electromagnetic interference, and corrosion resistance. In particular, fiber optic pressure testing technology has quasi-distributed characteristics, so it can achieve simultaneous online and long-term monitoring of multiple pressure points in the well.

[0004] In view of the current lack of long-term pressure measurement technology in offshore heavy oil thermal recovery wells, how to combine the characteristics of fiber optic sensor pressure measurement technology such as high temperature resistance, high pressure resistance, corrosion resistance, and multi-point monitoring to effectively solve the technical limitations of the existing single technical parameters of offshore heavy oil thermal recovery monitoring is an urgent problem that needs to be solved. Summary of the invention

[0005] The present invention is proposed to solve the problem that the optical fiber pressure testing technology in the prior art cannot meet the high temperature and high pressure working conditions of heavy oil thermal recovery wells, especially the technical difficulties in integration mode, connection process, etc. for realizing long-term downhole multi-point pressure testing in offshore oil fields. Its purpose is to provide a multi-point pressure optical fiber long-term monitoring system for heavy oil thermal recovery wells in offshore oil fields.

[0006] The present invention is achieved through the following technical solutions:

[0007] A multi-point pressure optical fiber long-term monitoring system for heavy oil thermal recovery wells in an offshore oil field, comprising a downhole process pipe string and a plurality of high-temperature optical fiber pressure sensors arranged in the downhole process pipe string; the high-temperature optical fiber pressure sensor is connected to a pressure demodulator arranged on the ground through a downhole monitoring optical cable; the high-temperature optical fiber pressure sensor is a single-ended optical fiber pressure sensor or a double-ended optical fiber pressure sensor; when the high-temperature optical fiber pressure sensor is a single-ended optical fiber pressure sensor, the downhole monitoring optical cable and the single-ended optical fiber pressure sensor are integrated in parallel; when the high-temperature optical fiber pressure sensor is a double-ended optical fiber pressure sensor, the downhole monitoring optical cable and the double-ended optical fiber pressure sensor are integrated in series; the downhole process pipe string and the downhole monitoring optical cable are integrated in an outside-pipe bundling method or an outside-pipe-inside-pipe transfer method.

[0008] In the above technical scheme, the single-ended optical fiber pressure sensor includes a single-ended sealed body, a single-ended optical fiber pressure-sensing component arranged inside the single-ended sealed body, and an optical fiber lead-out component; the single-ended sealed body includes a single-ended connecting steel pipe, a single-ended annular end cover, and a single-ended pressure-conducting end head connected in sequence; the single-ended pressure-conducting end head is a hollow cylindrical structure with one end open, and its closed end forms a pressure-sensitive chip hole; the single-ended annular end cover is a hollow truncated cone with two ends open, its large-diameter end is connected to the single-ended pressure-conducting end head, and its small-diameter end is connected to the single-ended connecting steel pipe; the single-ended optical fiber pressure-sensing component includes a single-ended pressure-sensing diaphragm, a single-ended Single-mode optical fiber, single-ended temperature-measuring optical fiber Bragg grating and single-ended pressure-measuring optical fiber Bragg grating; the single-ended pressure-sensitive diaphragm is arranged in the cavity of the single-ended pressure-conducting end; one end of the single-ended single-mode optical fiber is connected to the single-ended pressure-sensitive diaphragm, and the other end extends out of the single-ended connecting steel pipe to the single-ended sealing body; the single-ended single-mode optical fiber and the single-ended pressure-sensitive diaphragm are connected through the single-ended temperature-measuring optical fiber Bragg grating and the single-ended pressure-measuring optical fiber Bragg grating; the optical fiber lead-out assembly is arranged between the single-ended single-mode optical fiber and the single-ended connecting steel pipe, and the optical fiber lead-out assembly includes a single-ended capillary glass tube sleeved on the outside of the single-ended single-mode optical fiber and a single-ended soft metal sealing ring sleeved on the outside of the single-ended capillary glass tube.

[0009] In the above technical solution, the single-end annular end cover is connected to the single-end pressure-conducting end head and the single-end connecting steel pipe by threaded connection, and secondary sealing is performed at the connection by laser welding technology.

[0010] In the above technical solution, the single-ended pressure-sensitive diaphragm is a rectangular plate-like structure, both ends of which extend outward along the axis to form convex strips, forming a single-ended pressure-sensitive cavity in the middle, and the convex strips on the pressure-conducting end side extend into the pressure-sensitive chip hole of the single-ended pressure-conducting end; the convex strips on the pressure-conducting end side form a single-ended pressure-conducting hole opened along the axial direction, and the single-ended pressure-conducting hole is connected to the single-ended pressure-sensitive cavity.

[0011] In the above technical scheme, the single-ended temperature-measuring fiber Bragg grating and the single-ended pressure-measuring fiber Bragg grating are both fixed to the single-ended pressure-sensitive diaphragm by bonding; the single-ended temperature-measuring fiber Bragg grating and the single-ended pressure-measuring fiber Bragg grating are both etched on the single-ended single-mode optical fiber by femtosecond laser writing technology; the single-ended temperature-measuring fiber Bragg grating is arranged above the single-ended pressure-sensing cavity, and the single-ended pressure-measuring fiber Bragg grating is arranged on the side convex strip of the pressure-conducting end of the single-ended pressure-sensitive diaphragm.

[0012] In the above technical solution, the double-ended optical fiber pressure sensor comprises a double-ended sealed body, a double-ended optical fiber pressure sensing component arranged inside the double-ended sealed body, and an optical fiber lead-out component;

[0013] The double-end sealing body comprises a double-end pressure-conducting end head, a double-end annular end caps arranged at both ends of the double-end pressure-conducting end head, and a double-end connecting steel pipe connected to the double-end annular end caps; the double-end optical fiber pressure-sensing assembly comprises a double-end pressure-sensing diaphragm, a double-end single-mode optical fiber, a double-end temperature-measuring optical fiber grating, and a double-end pressure-measuring optical fiber grating; the double-end pressure-sensing diaphragm is an inverted T-shaped structure, the horizontal section forms a double-end pressure-sensing cavity, the vertical section forms a double-end pressure-conducting hole, the double-end pressure-conducting hole is connected to the double-end pressure-sensing cavity, and the vertical section of the double-end pressure-sensing diaphragm is a double-end pressure-sensing cavity. The section extends into the pressure-sensitive chip hole of the double-ended pressure-conducting end; the side of the horizontal section of the double-ended pressure-sensitive diaphragm away from the vertical section extends to the side of any double-ended connected steel pipe to form a convex strip, the double-ended temperature-measuring fiber grating is arranged corresponding to the double-ended pressure-sensing cavity, and the double-ended pressure-measuring fiber grating is arranged on the convex strip of the double-ended pressure-sensitive diaphragm; an optical fiber lead-out assembly is arranged between the double-ended single-mode optical fiber and the double-ended connected steel pipe, and the structure of the optical fiber lead-out assembly is exactly the same as the structure and connection method of the optical fiber lead-out assembly in the single-ended optical fiber pressure sensor.

[0014] In the above technical scheme, the double-ended pressure-conducting end head is a sleeve structure with two ends open, and a pressure-sensitive chip hole is formed on the wall of the sleeve; the double-ended annular end cap has the same structure as the single-ended annular end cap, and the double-ended connecting steel pipe has the same structure as the single-ended connecting steel pipe; the connection method between the double-ended annular end cap and the double-ended pressure-conducting end head and the double-ended connecting steel pipe is the same as the connection method between the single-ended annular end cap and the single-ended pressure-conducting end head and the single-ended connecting steel pipe; the connection method between the double-ended temperature-measuring fiber grating and the double-ended pressure-measuring fiber grating and the double-ended pressure-sensitive diaphragm and the double-ended single-mode optical fiber is the same as the connection method between the temperature-measuring fiber grating and the pressure-measuring fiber grating belt in the single-ended optical fiber pressure sensor;

[0015] In the above technical solution, the downhole monitoring optical cable includes a high-temperature optical fiber and an outer armored protective tube arranged inside and outside; when the high-temperature optical fiber pressure sensor is a single-ended optical fiber pressure sensor, the downhole monitoring optical cable and the single-ended optical fiber pressure sensor are integrated in parallel; the high-temperature optical fiber built into the downhole monitoring optical cable is an N-core single-mode modified polyimide optical fiber, where N is the number of single-ended optical fiber pressure sensors; when the high-temperature optical fiber pressure sensor is a double-ended optical fiber pressure sensor, the downhole monitoring optical cable and the double-ended optical fiber pressure sensor are integrated in series, and the high-temperature optical fiber built into the downhole monitoring optical cable is a 1-core single-mode modified polyimide optical fiber.

[0016] In the above technical scheme, the downhole process tubing string includes an upper oil pipe, a penetrable packer, an electric pump Y-joint, a tubing nipple, a lower oil pipe, a buckle and a perforated oil pipe which are connected in sequence from top to bottom; a penetrable packer is sleeved on the outside of the upper oil pipe above the electric pump Y-joint; the electric pump unit is connected to another interface of the electric pump Y-joint; and a round plug is provided at the end of the perforated oil pipe.

[0017] In the above technical scheme, when the high-temperature optical fiber pressure sensor is a single-ended optical fiber pressure sensor, the downhole monitoring optical cable and the downhole process pipe are integrated in an outside-pipe bundling manner; the single-ended optical fiber pressure sensor is arranged on the outside of the perforated oil pipe near the round plug, and the downhole monitoring optical cable is arranged on the outside of the oil pipe and connected to the oil pipe through a cable tie; when the high-temperature optical fiber pressure sensor is a double-ended optical fiber pressure sensor, the downhole monitoring optical cable and the downhole process pipe are integrated in an outside-pipe bundling manner or an outside-pipe-inside-pipe transfer manner; when the outside-pipe bundling manner is adopted for integration, the integration manner is the same as that of the single-ended optical fiber pressure sensor; when the outside-pipe-inside-pipe transfer manner is adopted, the downhole process pipe also includes a Y-type crossing device, which is arranged between the buckle and the perforated oil pipe; the double-ended optical fiber pressure sensor is arranged on the inside of the perforated oil pipe near the round plug, and the downhole monitoring optical cable above the Y-type crossing device is arranged on the outside of the oil pipe, and the downhole monitoring optical cable passes through the Y-type crossing device and extends into the perforated oil pipe.

[0018] The beneficial effects of the present invention are:

[0019] The present invention provides a multi-point pressure optical fiber long-term monitoring system for heavy oil thermal recovery wells in offshore oil fields, comprising a high-temperature optical fiber pressure sensor with a temperature resistance of 370°C and a pressure resistance of 26MPa, a downhole monitoring optical cable, a ground pressure demodulator, and a process pipe string; wherein the high-temperature optical fiber pressure sensor is optimized and improved in terms of a pressure measuring optical fiber unit and a sealing structure, so that the temperature and pressure resistance levels of the optical fiber pressure gauge are greatly improved; at the same time, according to different monitoring process requirements, two innovative structures of single-end and double-end optical fiber pressure sensors are proposed, which respectively realize the series-parallel integration of the monitoring optical cable and the pressure gauge, and are equipped with a time division and wavelength division multiplexing demodulation mode of a ground pressure demodulator, so that real-time, online and long-term monitoring of multi-point pressure in the downhole is realized; and according to different monitoring requirements, two process pipe strings are designed to respectively meet the requirements for multi-point pressure monitoring in the downhole oil pipe and the annulus. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the structure of a single-ended optical fiber pressure sensor in the present invention;

[0021] Figure 2 It is a schematic diagram of the structure of the double-ended optical fiber pressure sensor of the present invention;

[0022] Figure 3 It is a structural schematic diagram of the downhole process pipe string and the downhole monitoring optical cable in the present invention when they are integrated by bundling outside the pipe;

[0023] Figure 4 It is a structural schematic diagram of the downhole process pipe string and the downhole monitoring optical cable in the present invention when they are integrated by adopting the method of transferring from outside the pipe to inside the pipe.

[0024] in:

[0025] 1. High temperature optical fiber pressure sensor;

[0026] 11. Single-ended optical fiber pressure sensor;

[0027] 111. Single-ended pressure-conducting terminal; 112. Single-ended annular end cap; 113. Single-ended connecting steel pipe; 114. Single-ended pressure-sensitive diaphragm; 1141. Single-ended pressure-sensitive cavity; 1142. Single-ended pressure-conducting hole; 115. Single-ended single-mode optical fiber; 116. Single-ended temperature-measuring optical fiber Bragg grating; 117. Single-ended pressure-measuring optical fiber Bragg grating; 118. Single-ended capillary glass tube; 119. Single-ended soft metal sealing ring;

[0028] 12. Double-ended optical fiber pressure sensor;

[0029] 121. Double-ended pressure-conducting terminal; 122. Double-ended annular end cap; 123. Double-ended connecting steel pipe; 124. Double-ended pressure-sensitive diaphragm; 1241. Double-ended pressure-sensitive cavity; 1242. Double-ended pressure-conducting hole; 125. Double-ended single-mode optical fiber; 126. Double-ended temperature-measuring optical fiber Bragg grating; 127. Double-ended pressure-measuring optical fiber Bragg grating; 128. Double-ended capillary glass tube; 129. Double-ended soft metal sealing ring;

[0030] 2. Downhole monitoring optical cable;

[0031] 3. Pressure demodulator;

[0032] 41. Upper oil pipe; 42. Traversable packer; 43. Electric pump Y-joint; 44. Oil pipe nipple; 45. Electric pump unit; 46. Lower oil pipe; 47. Variable buckle; 48. Oil pipe with holes; 49. Round plug; 410. Y-type crossing device.

[0033] For ordinary technicians in this field, other relevant drawings can be obtained based on the above drawings without any creative work. DETAILED DESCRIPTION

[0034] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0035] like Figures 1 to 4 As shown, a multi-point pressure optical fiber long-term monitoring system for heavy oil thermal recovery wells in offshore oil fields includes a downhole process pipe string and a plurality of high-temperature optical fiber pressure sensors arranged in the downhole process pipe string; the high-temperature optical fiber pressure sensor 1 is connected to a pressure demodulator 3 arranged on the ground through a downhole monitoring optical cable 2; the high-temperature optical fiber pressure sensor 1 is a single-ended optical fiber pressure sensor 11 or a double-ended optical fiber pressure sensor 12;

[0036] The single-ended optical fiber pressure sensor 11 comprises a single-ended sealed body, a single-ended optical fiber pressure sensing component arranged inside the single-ended sealed body, and an optical fiber lead-out component;

[0037] The single-end sealing body comprises a single-end connecting steel pipe 113, a single-end annular end cover 112 and a single-end pressure-conducting end head 111 which are connected in sequence; the single-end pressure-conducting end head 111 is a hollow cylindrical structure with one end open, and a pressure-sensitive chip hole is formed at its closed end; the single-end annular end cover 112 is a hollow truncated cone with two ends open, and its large-diameter end is connected to the single-end pressure-conducting end head 111, and its small-diameter end is connected to the single-end connecting steel pipe 113; the single-end annular end cover 112 is threadedly connected to the single-end pressure-conducting end head 111 and the single-end connecting steel pipe 113, and secondary sealing is performed at the connection by laser welding technology; laser welding between the single-end annular end cover 112 and the single-end connecting steel pipe 113 is performed after the pressure gauge is sealed and packaged as a whole;

[0038] The single-ended optical fiber pressure-sensing assembly includes a single-ended pressure-sensing diaphragm 114, a single-ended single-mode optical fiber 115, a single-ended temperature-measuring optical fiber Bragg grating 116 and a single-ended pressure-measuring optical fiber Bragg grating 117;

[0039] The single-ended pressure-sensitive diaphragm 114 is arranged in the cavity of the single-ended pressure-conducting terminal 111. Both ends of the single-ended pressure-sensitive diaphragm 114 along the axis extend outward to form convex strips, and a single-ended pressure-sensitive cavity 1141 is formed in the middle. The convex strips on the pressure-conducting terminal side extend into the pressure-sensitive chip hole of the single-ended pressure-conducting terminal 111 and are fixed by laser welding. The convex strips on the pressure-conducting terminal side form a single-ended pressure-conducting hole 1142 opened along the axial direction, and the single-ended pressure-conducting hole 1142 is connected to the single-ended pressure-sensitive cavity 1141.

[0040] The single-ended temperature-measuring fiber grating 116 and the single-ended pressure-measuring fiber grating 117 are both etched on the single-ended single-mode optical fiber 115 by femtosecond laser writing technology, and the etching position is located at one end of the single-mode optical fiber 115 close to the single-ended pressure-conducting port; the other end of the single-mode optical fiber 115 extends out of the single-ended sealing body from the single-ended connecting steel pipe 113; the single-ended temperature-measuring fiber grating 116 is used to make temperature compensation for the single-ended pressure-measuring fiber grating 117, and the single-ended pressure-measuring fiber grating 117 is used as a pressure sensor; the single-ended temperature-measuring fiber grating 116 and the single-ended pressure-measuring fiber grating 117 are both fixed to the single-ended pressure-sensitive diaphragm 114 by bonding; the single-ended temperature-measuring fiber grating 116 is arranged above the single-ended pressure-sensitive cavity 1141, and the single-ended pressure-measuring fiber grating 117 is arranged on the convex strip on the pressure-conducting end of the single-ended pressure-sensitive diaphragm 114;

[0041] The working principle of the optical fiber pressure sensing assembly is as follows: the single-ended pressure-conducting hole 1142 is a through hole, which is used to transmit the external pressure to the single-ended pressure-sensitive diaphragm 114 through the single-ended pressure-sensitive cavity 1141; the single-ended pressure-sensitive diaphragm 114 is axially deformed after being in direct contact with the external medium, causing the single-ended pressure-measuring optical fiber Bragg grating 117 attached to the single-ended pressure-sensitive diaphragm 114 to deform, thereby causing the grating fringes to change periodically;

[0042] The optical fiber lead-out assembly is arranged between the single-ended single-mode optical fiber 115 and the single-ended connecting steel tube 113, and the optical fiber lead-out assembly includes a single-ended capillary glass tube 118 sleeved on the outside of the single-ended single-mode optical fiber 115 and a single-ended soft metal sealing ring 119 sleeved on the outside of the single-ended capillary glass tube 118; the single-ended single-mode optical fiber 115 is welded to the single-ended capillary glass tube 118; the optical fiber lead-out assembly realizes the sealing between the single-ended single-mode optical fiber 115 and the single-ended annular end cover 112;

[0043] Since the optical fiber is made of glass and the annular end cap is made of metal, sealants are currently widely used to achieve sealing between the two, including epoxy resin glue and inorganic glue. The maximum temperature resistance of this type of sealant is 300°C. If the temperature exceeds 300°C, it will not be able to perform the sealing and isolation functions.

[0044] The double-ended optical fiber pressure sensor 12 comprises a double-ended sealed body, a double-ended optical fiber pressure sensing component disposed inside the double-ended sealed body, and an optical fiber lead-out component;

[0045] The double-end sealing body comprises a double-end pressure-conducting end head 121, a double-end annular end cap 122 arranged at both ends of the double-end pressure-conducting end head 121, and a double-end connecting steel pipe 123 connected to the double-end annular end cap 122; the double-end pressure-conducting end head 121 is a sleeve structure with open ends, and a pressure-sensitive chip hole is formed on the wall of the sleeve; the double-end annular end cap 122 has the same structure as the single-end annular end cap 112, and the double-end connecting steel pipe 123 has the same structure as the single-end connecting steel pipe 113; the connection method between the double-end annular end cap 122 and the double-end pressure-conducting end head 121 and the double-end connecting steel pipe 123 is the same as the connection method between the single-end annular end cap 112 and the single-end pressure-conducting end head 111 and the single-end connecting steel pipe 113;

[0046] The double-ended optical fiber pressure-sensing assembly includes a double-ended pressure-sensing diaphragm 124, a double-ended single-mode optical fiber 125, a double-ended temperature-measuring optical fiber Bragg grating 126 and a double-ended pressure-measuring optical fiber Bragg grating 127;

[0047] The double-ended pressure-sensitive diaphragm 124 is an inverted T-shaped structure, wherein the horizontal section forms a double-ended pressure-sensitive cavity 1241, and the vertical section forms a double-ended pressure-conducting hole 1242, the double-ended pressure-conducting hole 1242 is connected to the double-ended pressure-sensitive cavity 1241, and the vertical section of the double-ended pressure-sensitive diaphragm 124 extends into the pressure-sensitive chip hole of the double-ended pressure-conducting terminal 121; the horizontal section of the double-ended pressure-sensitive diaphragm 124 extends from one side of the vertical section to any double-ended connecting steel pipe 123 to form a convex strip, the double-ended temperature-measuring fiber grating 126 is arranged corresponding to the double-ended pressure-sensitive cavity 1241, and the double-ended pressure-measuring fiber grating 127 is arranged on the convex strip of the double-ended pressure-sensitive diaphragm 124; the connection method of the double-ended temperature-measuring fiber grating 126 and the double-ended pressure-measuring fiber grating 127 to the double-ended pressure-sensitive diaphragm 124 and the double-ended single-mode optical fiber 125 is the same as the connection method of the temperature-measuring fiber grating and the pressure-measuring fiber grating belt in the single-ended optical fiber pressure sensor 11;

[0048] An optical fiber lead-out assembly is arranged between the double-ended single-mode optical fiber 125 and the double-ended connecting steel pipe 123. The structure and connection method of the optical fiber lead-out assembly are exactly the same as those of the optical fiber lead-out assembly in the single-ended optical fiber pressure sensor 11.

[0049] The downhole monitoring optical cable 2 is used for downhole pressure signal transmission, and includes high-temperature optical fibers and an outer armored protection tube.

[0050] When the high-temperature optical fiber pressure sensor 1 is a single-ended optical fiber pressure sensor 11, the downhole monitoring optical cable 2 and the single-ended optical fiber pressure sensor 11 are integrated in parallel; the high-temperature optical fiber built into the downhole monitoring optical cable 2 is an N-core single-mode modified polyimide optical fiber, where N is the number of single-ended optical fiber pressure sensors; the length of each single-mode modified polyimide optical fiber corresponds to the depth of the measured pressure point, and after each single-ended optical fiber pressure sensor is connected to the corresponding single-mode modified polyimide optical fiber, the optical fiber at the remaining depth continues to be transmitted along the optical cable, and the connection position between the downhole monitoring optical cable 2 and the single-ended optical fiber pressure sensor is protected by a Y-type protector, and the downhole monitoring optical cable 2, the Y-type protector and the single-ended optical fiber pressure sensor are all connected by laser welding;

[0051] When the high-temperature optical fiber pressure sensor 1 is a double-ended optical fiber pressure sensor 12, the downhole monitoring optical cable 2 and the double-ended optical fiber pressure sensor 12 are integrated in series, the high-temperature optical fiber built into the downhole monitoring optical cable 2 is a single-core single-mode modified polyimide optical fiber, and the double-ended single-mode optical fiber 125 of each double-ended optical fiber pressure sensor 12 is respectively connected to the built-in high-temperature optical fiber of the downhole monitoring optical cable 2, and the connection position is protected by a conventional optical fiber connection point protection method, wherein the downhole monitoring optical cable 2, the double-ended optical fiber pressure sensor 12 and the sheath are connected by laser welding;

[0052] The downhole monitoring optical cable 2 and the pressure demodulator 3 are connected via a pigtail.

[0053] The pressure demodulator 3 (SmartScan) is used to convert the downhole pressure signal into an electrical signal and then demodulate and output it into pressure data;

[0054] The integration method of the downhole process pipe string and the downhole monitoring optical cable 2 is an outside-pipe bundling method or an outside-pipe-inside-pipe transfer method;

[0055] The downhole process string includes an upper oil pipe 41, a penetrable packer 42, an electric pump Y joint 43, an oil pipe short joint 44, a lower oil pipe 46, a buckle 47 and a perforated oil pipe 48 which are connected in sequence from top to bottom; the penetrable packer 42 is sleeved on the outer surface of the upper oil pipe 41 above the electric pump Y joint 43; the electric pump unit 45 is connected to another interface of the electric pump Y joint 43; and a round plug 49 is provided at the end of the perforated oil pipe 48;

[0056] When the high-temperature optical fiber pressure sensor 1 is a single-ended optical fiber pressure sensor 11, the downhole monitoring optical cable 2 and the downhole process pipe string are integrated in an external bundling manner; the single-ended optical fiber pressure sensor 11 is arranged outside the perforated oil pipe 48 near one end of the round plug 49, and the downhole monitoring optical cable 2 is arranged outside the oil pipe and connected to the oil pipe by a cable tie;

[0057] When the high-temperature optical fiber pressure sensor 1 is a double-ended optical fiber pressure sensor 12, the downhole monitoring optical cable 2 and the downhole process pipe string are integrated in an external pipe bundling method or an external pipe to internal pipe transfer method;

[0058] When the integration is performed by bundling outside the tube, the integration method is the same as that of the single-ended optical fiber pressure sensor 11;

[0059] When the outside-to-inside integration method is adopted, the downhole process pipe string further includes a Y-shaped crossing device 410, which is arranged between the buckle 47 and the perforated oil pipe 48;

[0060] The double-ended optical fiber pressure sensor 12 is arranged inside the perforated oil pipe 48 near one end of the round plug 49, and the downhole monitoring optical cable 2 above the Y-shaped crossing device 410 is arranged outside the oil pipe. The downhole monitoring optical cable 2 passes through the Y-shaped crossing device 410 and then extends into the perforated oil pipe 48.

[0061] Working principle of the present invention:

[0062] Aiming at the demand of long-term monitoring of multiple points of pressure in the wells of offshore heavy oil thermal recovery, the present invention innovatively designs a multi-point pressure optical fiber long-term monitoring system for offshore heavy oil thermal recovery wells. A single-end / double-end optical fiber pressure sensor is proposed from the aspects of temperature and pressure resistance, integration mode, and well entry process. The optical fiber pressure sensor adopts the optical fiber grating pressure sensing principle. When the external medium exerts force on the pressure sensing cavity, the pressure sensing diaphragm in the pressure sensing cavity is deformed due to the force, causing the optical fiber grating attached to the pressure sensing diaphragm to deform, thereby changing the grating grid period, resulting in a change in the central wavelength of the grating. The test of the external pressure is realized by demodulating the change of the central wavelength of the grating through the ground pressure demodulator. The optical fiber multi-point pressure monitoring system for offshore heavy oil thermal recovery wells adopts parallel and series integration of monitoring optical cables and optical fiber pressure sensors to realize multi-point pressure monitoring in the wells. At the same time, aiming at the temperature and pressure resistance level of the optical fiber pressure sensor, the optical fiber pressure sensing unit, the optical fiber-metal sealing mode, etc. are optimized and improved to improve its temperature and pressure resistance performance to meet the monitoring needs of thermal recovery wells during heat injection.

[0063] The present invention combines the complex working conditions of offshore heavy oil thermal recovery wells such as high temperature and high pressure, as well as the demand for multi-point pressure monitoring, and innovatively designs a high-temperature optical fiber pressure sensor with a temperature resistance of 370°C and a pressure resistance of 26MPa. The pressure sensor can be divided into a single-end structure and a double-end structure according to the integration method; the single-end optical fiber pressure sensor realizes downhole multi-point pressure measurement through a parallel integration method, and the double-end optical fiber pressure sensor realizes it through a series integration method; compared with the traditional optical fiber pressure sensor, the high-temperature optical fiber pressure sensor of the present invention is optimized and improved in the design of the optical fiber pressure measurement unit and the overall sealing method design of the pressure gauge, and the overall temperature and pressure resistance level of the optical fiber pressure gauge is improved, which solves the problem of the difficulty of downhole pressure monitoring during the heat injection period of heavy oil thermal recovery wells; and the downhole monitoring cables and ground demodulators of different structures are matched to form a high-temperature optical fiber pressure monitoring system. At the same time, for the complex process string structure of high-temperature injection and production integration of offshore heavy oil wells, two string lowering processes are designed without changing the existing process and tool working conditions, respectively realizing the demand for pressure monitoring in the oil pipe and the annulus of the oil casing in offshore heavy oil thermal recovery wells.

[0064] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and the like are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0065] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0066] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A multi-point pressure optical fiber long-term monitoring system for heavy oil thermal recovery wells in offshore oil fields, characterized by: The invention comprises a downhole process pipe string and a plurality of high-temperature optical fiber pressure sensors arranged in the downhole process pipe string; the high-temperature optical fiber pressure sensor (1) is connected to a pressure demodulator (3) arranged on the ground through a downhole monitoring optical cable (2); the high-temperature optical fiber pressure sensor (1) is a single-ended optical fiber pressure sensor (11) or a double-ended optical fiber pressure sensor (12); when the high-temperature optical fiber pressure sensor (1) is a single-ended optical fiber pressure sensor (11), the downhole monitoring optical cable (2) and the single-ended optical fiber pressure sensor (11) are integrated in parallel; when the high-temperature optical fiber pressure sensor (1) is a double-ended optical fiber pressure sensor (12), the downhole monitoring optical cable (2) and the double-ended optical fiber pressure sensor (12) are integrated in series; the downhole process pipe string and the downhole monitoring optical cable (2) are integrated in an external-pipe bundling manner or an external-pipe-inside-pipe transfer manner.

2. The multi-point pressure optical fiber long-term monitoring system for heavy oil thermal recovery wells in offshore oil fields according to claim 1 is characterized by: The single-ended optical fiber pressure sensor (11) comprises a single-ended sealed body, a single-ended optical fiber pressure sensing component arranged inside the single-ended sealed body, and an optical fiber lead-out component; The single-end sealing body comprises a single-end connecting steel pipe (113), a single-end annular end cover (112) and a single-end pressure-conducting end head (111) which are connected in sequence; the single-end pressure-conducting end head (111) is a hollow cylindrical structure with one end open, and a pressure-sensitive chip hole is formed at its closed end; the single-end annular end cover (112) is a hollow truncated cone structure with two ends open, and its large-diameter end is connected to the single-end pressure-conducting end head (111), and its small-diameter end is connected to the single-end connecting steel pipe (113); The single-ended optical fiber pressure-sensing component comprises a single-ended pressure-sensing diaphragm (114), a single-ended single-mode optical fiber (115), a single-ended temperature-measuring optical fiber Bragg grating (116) and a single-ended pressure-measuring optical fiber Bragg grating (117); the single-ended pressure-sensing diaphragm (114) is arranged in the cavity of the single-ended pressure-conducting terminal (111). One end of the single-ended single-mode optical fiber (115) is connected to the single-ended pressure-sensitive diaphragm (114), and the other end extends out of the single-ended sealing body from the single-ended connecting steel pipe (113); the single-ended single-mode optical fiber (115) and the single-ended pressure-sensitive diaphragm (114) are connected via a single-ended temperature-measuring optical fiber grating (116) and a single-ended pressure-measuring optical fiber grating (117); the optical fiber lead-out assembly is arranged between the single-ended single-mode optical fiber (115) and the single-ended connecting steel pipe (113), and the optical fiber lead-out assembly comprises a single-ended capillary glass tube (118) sleeved on the outside of the single-ended single-mode optical fiber (115) and a single-ended soft metal sealing ring (119) sleeved on the outside of the single-ended capillary glass tube (118).

3. The multi-point pressure optical fiber long-term monitoring system for heavy oil thermal recovery wells in offshore oil fields according to claim 2 is characterized by: The single-end annular end cover (112) is connected to the single-end pressure-conducting end head (111) and the single-end connecting steel pipe (113) by threaded connection, and secondary sealing is performed at the connection point by laser welding technology.

4. The multi-point pressure optical fiber long-term monitoring system for heavy oil thermal recovery wells in offshore oil fields according to claim 2 is characterized by: The single-ended pressure-sensitive diaphragm (114) extends outward at both ends along the axis to form convex strips, forming a single-ended pressure-sensitive cavity (1141) in the middle, and the convex strips on the pressure-conducting end side extend into the pressure-sensitive chip hole of the single-ended pressure-conducting end (111); the convex strips on the pressure-conducting end side form a single-ended pressure-conducting hole (1142) opened along the axial direction, and the single-ended pressure-conducting hole (1142) is connected to the single-ended pressure-sensitive cavity (1141).

5. The multi-point pressure optical fiber long-term monitoring system for heavy oil thermal recovery wells in offshore oil fields according to claim 2 is characterized by: The single-ended temperature-measuring optical fiber Bragg grating (116) and the single-ended pressure-measuring optical fiber Bragg grating (117) are both fixed to the single-ended pressure-sensitive diaphragm (114) by bonding; the single-ended temperature-measuring optical fiber Bragg grating (116) and the single-ended pressure-measuring optical fiber Bragg grating (117) are both etched on the single-ended single-mode optical fiber (115) by femtosecond laser writing technology; the single-ended temperature-measuring optical fiber Bragg grating (116) is arranged above the single-ended pressure-sensitive cavity (1141), and the single-ended pressure-measuring optical fiber Bragg grating (117) is arranged on the convex strip on the pressure-conducting end side of the single-ended pressure-sensitive diaphragm (114).

6. The multi-point pressure optical fiber long-term monitoring system for heavy oil thermal recovery wells in offshore oil fields according to claim 1 is characterized by: The double-ended optical fiber pressure sensor (12) comprises a double-ended sealed body, a double-ended optical fiber pressure sensing component arranged inside the double-ended sealed body, and an optical fiber lead-out component; The double-end sealing body comprises a double-end pressure-conducting end head (121), a double-end annular end cover (122) arranged at both ends of the double-end pressure-conducting end head (121), and a double-end connecting steel pipe (123) connected to the double-end annular end cover (122); The double-ended optical fiber pressure-sensing component comprises a double-ended pressure-sensing diaphragm (124), a double-ended single-mode optical fiber (125), a double-ended temperature-measuring optical fiber Bragg grating (126) and a double-ended pressure-measuring optical fiber Bragg grating (127); The double-end pressure-sensitive diaphragm (124) is an inverted T-shaped structure, the horizontal section forms a double-end pressure-sensitive cavity (1241), the vertical section forms a double-end pressure-conducting hole (1242), the double-end pressure-conducting hole (1242) is connected with the double-end pressure-sensitive cavity (1241), and the vertical section of the double-end pressure-sensitive diaphragm (124) extends into the pressure-sensitive chip hole of the double-end pressure-conducting terminal (121); the side of the horizontal section of the double-end pressure-sensitive diaphragm (124) away from the vertical section extends toward any double-end connecting steel pipe (123) to form a convex strip, the double-end temperature measurement optical fiber Bragg grating (126) is arranged corresponding to the double-end pressure-sensitive cavity (1241), and the double-end pressure measurement optical fiber Bragg grating (127) is arranged on the convex strip of the double-end pressure-sensitive diaphragm (124); An optical fiber lead-out assembly is arranged between the double-ended single-mode optical fiber (125) and the double-ended connecting steel pipe (123), and the structure and connection method of the optical fiber lead-out assembly are completely the same as those of the optical fiber lead-out assembly in the single-ended optical fiber pressure sensor (11).

7. The multi-point pressure optical fiber long-term monitoring system for heavy oil thermal recovery wells in offshore oil fields according to claim 6 is characterized by: The double-ended pressure-conducting end head (121) is a sleeve structure with two ends open, and a pressure-sensitive chip hole is formed on the wall of the sleeve; the double-ended annular end cap (122) has the same structure as the single-ended annular end cap (112), and the double-ended connecting steel pipe (123) has the same structure as the single-ended connecting steel pipe (113); the connection method between the double-ended annular end cap (122) and the double-ended pressure-conducting end head (121) and the double-ended connecting steel pipe (123) is the same as the connection method between the single-ended annular end cap (112) and the single-ended pressure-conducting end head (111) and the single-ended connecting steel pipe (113); the connection method between the double-ended temperature-measuring optical fiber grating (126) and the double-ended pressure-measuring optical fiber grating (127) and the double-ended pressure-sensitive diaphragm (124) and the double-ended single-mode optical fiber (125) is the same as the connection method between the temperature-measuring optical fiber grating and the pressure-measuring optical fiber grating belt in the single-ended optical fiber pressure sensor (11).

8. The multi-point pressure optical fiber long-term monitoring system for heavy oil thermal recovery wells in offshore oil fields according to claim 1 is characterized by: The downhole monitoring optical cable (2) comprises a high-temperature optical fiber and an outer armored protective tube. When the high-temperature optical fiber pressure sensor (1) is a single-ended optical fiber pressure sensor (11), the downhole monitoring optical cable (2) and the single-ended optical fiber pressure sensor (11) are integrated in parallel. The high-temperature optical fiber built into the downhole monitoring optical cable (2) is an N-core single-mode modified polyimide optical fiber, where N is the number of single-ended optical fiber pressure sensors. When the high-temperature optical fiber pressure sensor (1) is a double-ended optical fiber pressure sensor (12), the downhole monitoring optical cable (2) and the double-ended optical fiber pressure sensor (12) are integrated in series, and the high-temperature optical fiber built into the downhole monitoring optical cable (2) is a 1-core single-mode modified polyimide optical fiber.

9. The multi-point pressure optical fiber long-term monitoring system for heavy oil thermal recovery wells in offshore oil fields according to claim 1, characterized in that: The downhole process pipe string comprises an upper oil pipe (41), a penetrable packer (42), an electric pump Y-joint (43), an oil pipe short joint (44), a lower oil pipe (46), a buckle (47) and a perforated oil pipe (48) which are connected in sequence from top to bottom; the penetrable packer (42) is sleeved on the outer portion of the upper oil pipe (41) above the electric pump Y-joint (43); the electric pump unit (45) is connected to another interface of the electric pump Y-joint (43); and a round plug (49) is provided at the end of the perforated oil pipe (48).

10. The multi-point pressure optical fiber long-term monitoring system for heavy oil thermal recovery wells in offshore oil fields according to claim 1, characterized in that: When the high-temperature optical fiber pressure sensor (1) is a single-ended optical fiber pressure sensor (11), the downhole monitoring optical cable (2) and the downhole process pipe column are integrated in an external bundling manner; the single-ended optical fiber pressure sensor (11) is arranged outside the perforated oil pipe (48) near one end of the round plug (49), and the downhole monitoring optical cable (2) is arranged outside the oil pipe and connected to the oil pipe by a cable tie; when the high-temperature optical fiber pressure sensor (1) is a double-ended optical fiber pressure sensor (12), the downhole monitoring optical cable (2) and the downhole process pipe column are integrated in an external bundling manner or an external-to-internal-pipe method; when the When the outside-pipe bundling method is used for integration, the integration method is the same as that of the single-ended optical fiber pressure sensor (11); when the outside-pipe-inside-pipe integration method is used, the downhole process pipe string also includes a Y-shaped crossing device (410), and the Y-shaped crossing device (410) is arranged between the buckle (47) and the perforated oil pipe (48); the double-ended optical fiber pressure sensor (12) is arranged inside the perforated oil pipe (48) near one end of the round plug (49), and the downhole monitoring optical cable (2) above the Y-shaped crossing device (410) is arranged outside the oil pipe, and the downhole monitoring optical cable (2) passes through the Y-shaped crossing device (410) and then extends into the perforated oil pipe (48).

Images