Large-scale fracturing operation method for offshore oil and gas field

Abstract

The invention relates to a large-scale fracturing operation method for an offshore oil and gas field. The large-scale fracturing operation method comprises the following steps that fracturing operation of a movable fracturing device and drilling and completion operation of a drilling machine are carried out alternately; fracturing, flowback and production are carried out in a multi-well batch continuous fracturing operation mode; on the basis of fracturing, flowback and production in a multi-well batch continuous fracturing operation mode, the fracturing and production integrated pipe column is adopted for fracturing, flowback and production; on the basis that the fracturing production integrated pipe column is used for fracturing, flowback and production, the fracturing flowback fluid is treated by adopting a fracturing flowback fluid on-site low-cost environment-friendly treatment technology. The technical problems of high comprehensive cost caused by occupation of a drilling machine by fracturing, insufficient capacity release caused by small transformation scale, low operation efficiency caused by limited equipment capability and the like can be solved.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas exploitation, and in particular to a large-scale fracturing operation method for offshore oil and gas fields. Background Art

[0002] Offshore low-permeability oil and gas fields have low natural productivity, and reservoir transformation measures are necessary for economic development.

[0003] After years of exploration and practice, a fracturing model based on offshore drilling platforms, wellhead platforms or tugboats has been formed. However, the scale of fracturing operations, technological level, operating efficiency, reservoir protection, and production increase effects are still unsatisfactory, mainly reflected in: ① The offshore platform site is limited, resulting in a small scale of fracturing; ② Drilling, fracturing, and flowback on the same platform are difficult to carry out in an interlaced manner, resulting in low operating efficiency, high comprehensive operating costs, and a long operating cycle that is not conducive to reservoir protection; ③ The post-fracturing production capacity is lower than expected, and the effective period of fracturing is short.

[0004] Therefore, a large-scale fracturing operation method for offshore oil and gas fields is urgently needed to break the dilemma and promote the effective development of offshore low-permeability reserves. It is necessary to fully consider the special operating environment conditions at sea, form applicable fracturing technology and operation mode, and ensure the economy of offshore fracturing operations. Summary of the invention

[0005] In view of the above problems, the purpose of the present invention is to provide a large-scale fracturing operation method for offshore oil and gas fields, which can solve the technical problems such as high comprehensive cost caused by fracturing occupying drilling rigs, insufficient production capacity release caused by small transformation scale, and inefficient operation caused by limited equipment capacity.

[0006] To achieve the above object, the present invention adopts the following technical solutions: The offshore oil and gas field large-scale fracturing operation method of the present invention comprises the following steps: The fracturing operation using a mobile fracturing device is carried out alternately with the drilling and completion operation of the drilling rig; On the basis of the fracturing operation of the mobile fracturing device and the drilling and completion operation of the drilling rig, a multi-well batch continuous fracturing operation mode is adopted for fracturing, flowback and production; On the basis of fracturing, flowback and production in batch continuous fracturing operation mode of multiple wells, fracturing, flowback and production are carried out by using integrated fracturing and production string; On the basis of adopting integrated fracturing and production tubing for fracturing, flowback and production, the fracturing flowback fluid is treated by adopting low-cost on-site environmentally friendly treatment technology for fracturing flowback fluid.

[0007] The offshore oil and gas field large-scale fracturing operation method preferably adopts a multi-well batch continuous fracturing operation mode to perform fracturing, flowback and production, specifically comprising the following steps: The oil wells to be operated are numbered and grouped, with each group including a number of oil wells; Several groups of oil wells are drilled, completed, fractured, flowed back and produced alternately so that the operations of each group of oil wells do not interfere with each other.

[0008] In the offshore oil and gas field large-scale fracturing operation method, preferably, the integrated fracturing production string is a string of "in-pipe packer + ball-throwing sleeve" fracturing method, including a bottom fracturing string string and an upper string string; The bottom fracturing string includes a first tail pipe, a first float shoe, a wellbore isolation valve, a toe end sliding sleeve, a ball-dropping sliding sleeve, a segmented packer and a bottom tubing; The first tail pipe, the first float shoe and the wellbore isolation valve are connected to the tail end of the bottom oil pipe in sequence from bottom to top; A plurality of segmented packers are arranged at intervals on the bottom oil pipe, and the toe end sliding sleeve is arranged on the bottom oil pipe between the first segmented packer and the second segmented packer from the tail to the front; The ball-throwing sleeves are respectively arranged between the remaining segmented packers and on the bottom oil pipe at the front end of the segmented packer at the front end; The upper tubular string includes an upper tubing, an automatic guiding and deflecting device, a suspension packer, a ratchet anchoring and positioning seal, a tubing hydraulic anchor, a circulating sleeve, a safety valve and a flow collar, a casing and a tie-back tubing; The lower end of the upper oil pipe is connected to the upper end of the bottom oil pipe; The automatic guiding and deflecting device, hanging packer, ratchet anchoring and positioning seal, oil pipe hydraulic anchor, circulating sleeve, safety valve and flow joint hoop are arranged on the upper oil pipe in sequence from bottom to top, the return oil pipe is connected to the top of the upper oil pipe, and the casing is sleeved outside the return oil pipe.

[0009] The offshore oil and gas field large-scale fracturing operation method preferably adopts the fracturing production integrated tubing string of the "in-pipe packer + ball-throwing sliding sleeve" fracturing method to perform fracturing, flowback and production, including the following steps: Before fracturing begins, perforate the target oil and gas layer in advance; When fracturing begins, the integrated fracturing production string is lowered, and the fracturing pump delivers fracturing fluid and carries proppant into the formation; The first stage of fracturing is carried out by toe-end sliding sleeve fracturing, which is carried out by pressurizing the wellbore and opening the toe-end sliding sleeve; the subsequent fracturing layers are successively injected with soluble balls to open the ball-injection sliding sleeve for fracturing; During the flowback and production stage after fracturing, the integrated fracturing and production string will continue to be used for flowback and production operations, and no string replacement operations will be performed.

[0010] The offshore oil and gas field large-scale fracturing operation method preferably adopts the fracturing production integrated tubing string of the "in-pipe packer + ball-throwing sliding sleeve" fracturing method to perform fracturing, flowback and production, and further includes the following steps: The number of sliding sleeves to be lowered is determined according to the number of reservoir layers vertically transformed. In layers close to bottom water or where no fracturing is required, perforation and ball injection can be performed without fracturing. In layers with poor physical properties, ball injection and fracturing can be performed after the ball injection sliding sleeve is opened. After gas breakthrough or water production occurs in the corresponding layer, selective production is achieved by closing the ball-dropping sleeve of the layer.

[0011] In the offshore oil and gas field large-scale fracturing operation method, preferably, the integrated fracturing production string is a "bridge plug perforation joint operation" fracturing string, including: a second float shoe, a second tail pipe, a toe rupture valve, a tail pipe hanger, a tieback casing, a downhole safety valve and a hydraulic control pipeline; The second float shoe is disposed at the bottom of the second tail pipe; A plurality of toe-end rupture valves are arranged on the second tail pipe near the second float shoe; A tail pipe hanger is provided at the upper end of the second tail pipe for hanging the second tail pipe; The tie-back sleeve is connected to the top of the second tail pipe; A downhole safety valve is provided on the tieback casing, and the downhole safety valve is connected to the fracturing wellhead through the hydraulic control pipeline.

[0012] The offshore oil and gas field large-scale fracturing operation method preferably adopts a fracturing production integrated string of "bridge plug perforation joint operation" fracturing method to perform fracturing, flowback and production, including the following steps: Before fracturing, tie back the tieback casing to the fracturing wellhead; At the beginning of fracturing, the first stage is to pressurize the wellbore to open the toe-end rupture valve reserved on the second tail pipe, and keep the first stage open smoothly; if the toe-end rupture valve fails to open or the displacement cannot be established after opening, the coiled tubing is used for perforation, pressurized detonation, and the perforating gun is pulled out after perforation to conduct the tail pipe injection pressure drop test to determine whether the reservoir is perforated; The subsequent fracturing layers are put into the "soluble bridge plug and perforation" service tool by cable transmission. After reaching the target layer, the plug is set, the plug is released, the perforation is performed, and the matching soluble ball is used for fracturing. During the flowback and production phase after fracturing, the downhole passage can be closed in an emergency through the matching downhole safety valve installed on the tieback casing; For fracturing wells with high pressure coefficient and self-flowing period, the fracturing string is used for flowback and self-flowing production in the early stage of fracturing; after the production decreases, the string above the tail pipe hanger can be taken out and a special production string can be lowered.

[0013] The offshore oil and gas field large-scale fracturing operation method preferably adopts a multi-well batch continuous fracturing operation mode to perform fracturing, flowback and fracturing in production in the following manner: The mobile fracturing device is equipped with a seawater pump and a seawater filtration device, and is equipped with a buffer tank, continuous mixing, liquid addition skid, sand mixing skid, sand tank, and fracturing pump. The mobile fracturing device can be used to realize fracturing construction using seawater-based fracturing fluid. The fracturing well group on the wellhead platform shares a set of wellhead fracturing manifolds and emergency blowdown processes. Each well is equipped with a hydraulic plug valve to achieve switching between fracturing and post-fracturing flowback processes. After the mobile fracturing device prepares the fracturing materials at the dock, it sails to the wellhead platform and takes position. The wellhead fracturing manifold of the wellhead platform has been pre-installed in the middle deck area of ​​the platform; the mobile fracturing device is connected to the hose hanger of the wellhead platform through its own high-pressure fracturing hose; after the pipeline is installed, the pipeline pressure test is carried out; after the pressure test is qualified, the mobile fracturing device carries out continuous sand fracturing work on each well in turn; after the fracturing operation is completed, the high-pressure hose of the mobile fracturing device is released from the platform hose hanger and evacuated.

[0014] The offshore oil and gas field large-scale fracturing operation method is preferably arranged differently in terms of spatial heights to ensure that the fracturing operation of the mobile fracturing device and the drilling and completion operation of the drilling rig are performed in an intersecting manner without interfering with each other, specifically: The drilling rig is positioned in the well slot area on the upper deck of the wellhead platform and starts drilling and completion operations; The fracturing manifold and wellhead hanger for fracturing are arranged on the middle deck for fracturing construction; The crane is arranged under the upper deck and is used to fix the fracturing pipeline during fracturing. In order to ensure that fracturing operations are all carried out on the middle deck, a riser must be connected to the Christmas tree. The length of the riser is determined according to the height difference between the middle deck and the Christmas tree operating deck.

[0015] The offshore oil and gas field large-scale fracturing operation method, preferably, the fracturing flowback fluid is treated by using a low-cost on-site environmentally friendly treatment technology for the fracturing flowback fluid, and the specific steps are: A flowback device is used for flowback, wherein the flowback device includes two modules: a flowback control system and a flowback liquid treatment system, wherein the flowback liquid control system includes a ball catcher, a cyclone desander, a nozzle manifold, a heater, and a three-phase separator; the Christmas tree is connected to the ball catcher and the cyclone desander in sequence through pipelines, and then connected to the nozzle manifold, after the outlet of the nozzle manifold is connected to the three-phase separator through a pipeline, the oil phase outlet of the three-phase separator is connected to the dirty oil tank; the liquid phase outlet of the three-phase separator is connected to the mud pool, and the mud pool is connected to the flowback liquid treatment system; the flowback liquid in the Christmas tree passes through the ball catcher, and then passes through the cyclone desander to remove sand before entering the nozzle manifold, the flowback liquid flows out from the nozzle manifold outlet, is heated by the heater, and then enters the three-phase separator for separation, the separated natural gas is used for combustion, the dirty oil separated at the initial stage of flowback flows into the dirty oil tank, the separated liquid phase enters the mud pool, and then is pumped into the flowback liquid treatment system; The return liquid treatment system includes an oil-water separator, an oil dehydrator, an advanced oxidizer, a primary flocculator, a secondary flocculator, an oil filter, a precision filter and a microfilter. The water phase outlet of the oil-water separator is connected to the oil dehydrator, the water phase outlet of the oil dehydrator is connected to the waste oil tank, the oil phase outlets of the oil-water separator and the oil dehydrator are respectively connected to the advanced oxidizer, the advanced oxidizer is connected to the primary flocculator, the solid phase outlet of the primary flocculator is connected to the sludge tank, the outlet of the sludge tank is connected to the solid-liquid separator, the solid phase outlet of the solid-liquid separator discharges sludge, and its liquid phase outlet is connected to the The inlet of the first-stage flocculator; the liquid phase outlet of the first-stage flocculator is connected to the second-stage flocculator, the solid phase outlet of the second-stage flocculator is connected to the sludge tank, and the liquid phase outlet of the second-stage flocculator is connected to the oil filter, precision filter and microfilter in sequence and then to the production water system; the return liquid pumped in from the mud pool is separated from oil and water, and the oil in the initial return oil tank is transported back to land for treatment. The polymer in the return liquid after oil and water separation is oxidized by advanced catalysis and degraded into small molecular polymers, and then after adding flocculants, flocculation and sedimentation, and solid-liquid separation, the return water is filtered and enters the platform production water process.

[0016] The present invention adopts the above technical solution, which has the following advantages: (1) The multi-well batch fracturing operation mode is adopted without occupying drilling rigs, which enables the cross-processing of drilling and completion operations and fracturing operations, greatly saving the expensive rental costs of offshore drilling platforms and accelerating the production progress; (2) The integrated fracturing and production string is used to achieve refined transformation of the reservoir through layered fracturing. At the same time, it can be backflowed and self-flowing after fracturing, saving the production string construction time; (3) By temporarily placing flowback treatment equipment on the platform, a post-fracturing flowback fluid control and treatment process technology was developed to meet the needs of on-site treatment of post-fracturing flowback fluid on a large scale at sea. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Throughout the accompanying drawings, the same reference numerals are used to represent the same components. In the accompanying drawings: Figure 1 This is a flow chart of multi-well batch continuous fracturing operation of the present invention; Figure 2 It is a schematic diagram of the batch fracturing construction process of the mobile fracturing device of the present invention; Figure 3 It is a schematic diagram of the layout of the batch fracturing construction pipeline of the mobile fracturing device of the present invention; Figure 4 It is a structural schematic diagram of the integrated fracturing production string of the "in-pipe packer + ball-throwing sliding sleeve" fracturing method of the present invention; Figure 5 It is a structural schematic diagram of the integrated fracturing production string of the "bridge plug and perforation combined operation" fracturing method of the present invention; Figure 6 It is a flow chart of the flowback control system and the flowback fluid treatment system.

[0018] The reference numerals in the figures are: 1-first tail pipe; 2-first float shoe; 3-wellbore isolation valve; 4-toe end sliding sleeve; 5-ball sliding sleeve; 6-segmented packer; 7-bottom tubing; 8-upper tubing; 9-automatic guiding and deflecting; 10-hanging packer; 11-ratchet anchoring and positioning seal; 12-tubing hydraulic anchor; 13-circulating sliding sleeve; 14-safety valve and flow collar; 15-casing; 16-return tubing; 17-second float shoe; 18-second tail pipe; 19-toe end rupture valve; 20-tail pipe hanger; 21-return casing; 22-downhole safety valve; 23-hydraulic control pipeline. DETAILED DESCRIPTION

[0019] The exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0020] The present invention provides a large-scale fracturing operation method for offshore oil and gas fields. Through a mobile fracturing device multi-well batch continuous fracturing operation mode and an on-site low-cost environmentally friendly treatment technology for fracturing return fluid, the invention focuses on offshore fracturing concepts and methods, fracturing operation modes, fracturing equipment and tools, etc., innovates the offshore low-permeability fracturing concept, changes the traditional two-high and one-low (high viscosity, high sand ratio and low displacement) mode to two-low and one-high (low viscosity, low sand ratio and high displacement), and realizes the integration of offshore low-permeability seam network fracturing and energy storage; adopts a batch fracturing scheme that does not occupy a drilling rig, realizes the parallel operation of fracturing and drilling and completion on the same platform, and speeds up the production progress while saving the expensive offshore drilling platform costs; adopts a mobile fracturing device for construction, greatly improving the fracturing scale and operation efficiency; adopts a seawater-based integrated variable viscosity fracturing fluid system, simplifies on-site material preparation work, and reduces material costs.

[0021] The invention provides a method for large-scale fracturing operation in offshore oil and gas fields, comprising the following steps: S1. The fracturing operation is carried out alternately with the drilling and completion operation of the drilling rig by using a mobile fracturing device; S2. On the basis of the fracturing operation of the mobile fracturing device and the drilling and completion operation of the drilling rig, a multi-well batch continuous fracturing operation mode is adopted for fracturing, flowback and production; S3. On the basis of fracturing, flowback and production in a multi-well batch continuous fracturing operation mode, an integrated fracturing and production string is used for fracturing, flowback and production; S4. On the basis of adopting integrated fracturing production tubing for fracturing, flowback and production, the fracturing flowback fluid is treated by adopting on-site low-cost environmentally friendly treatment technology.

[0022] In the above embodiment, preferably, Figure 1 As shown, the multi-well batch continuous fracturing operation mode is used for fracturing, flowback and production, which specifically includes the following steps: The oil wells to be operated are numbered and grouped, with each group including a number of oil wells; Several groups of oil wells are drilled, completed, fractured, flowed back and produced alternately so that the operations of each group of oil wells do not interfere with each other.

[0023] In the above embodiment, preferably, Figure 4 As shown, the integrated fracturing production string is a string of "in-pipe packer + ball-throwing sliding sleeve" fracturing method, including a bottom fracturing string string and an upper string string; The bottom fracturing string includes a first tail pipe 1, a first float shoe 2, a wellbore isolation valve 3, a toe end sliding sleeve 4, a ball-dropping sliding sleeve 5, a segmented packer 6 and a bottom tubing 7; The first tail pipe 1, the first float shoe 2 and the wellbore isolation valve 3 are connected to the tail end of the bottom oil pipe 7 in sequence from bottom to top; A plurality of segmented packers 6 are arranged at intervals on the bottom oil pipe 7, and a toe end sliding sleeve 4 is arranged on the bottom oil pipe 7 between the first segmented packer 6 and the second segmented packer 6 from the tail to the front; Ball-throwing sleeves 5 are respectively arranged between the remaining segmented packers 6 and on the bottom oil pipe 7 at the front end of the frontmost segmented packer 6; The upper tubing string includes an upper tubing 8, an automatic guiding and deflecting device 9, a suspension packer 10, a ratchet anchoring and positioning seal 11, a tubing hydraulic anchor 12, a circulating sleeve 13, a safety valve and a flow collar 14, a casing 15 and a tie-back tubing 16; The lower end of the upper oil pipe 8 is connected to the upper end of the bottom oil pipe 7; The automatic guiding and deflecting device 9, the hanging packer 10, the ratchet anchoring and positioning seal 11, the tubing hydraulic anchor 12, the circulating sleeve 13, the safety valve and the flow joint hoop 14 are arranged on the upper tubing 8 in sequence from bottom to top, the return tubing 16 is connected to the top of the upper tubing 8, and the casing 15 is sleeved outside the return tubing 16.

[0024] In the above embodiment, preferably, the fracturing, flowback and production of the integrated fracturing and production string using the "in-pipe packer + ball-throwing sleeve" fracturing method includes the following steps: Before fracturing begins, perforate the target oil and gas layer in advance; When fracturing begins, the integrated fracturing production string is lowered, and the fracturing pump delivers fracturing fluid and carries proppant into the formation; The first stage of fracturing is carried out by toe-end sliding sleeve fracturing, which is carried out by pressurizing the wellbore and opening the toe-end sliding sleeve; the subsequent fracturing layers are successively injected with soluble balls to open the ball-injection sliding sleeve for fracturing; During the flowback and production stage after fracturing, the integrated fracturing and production string continues to be used for flowback and production operations, and no string replacement operations are performed.

[0025] In the above embodiment, preferably, the fracturing and production integrated tubing string using the "in-pipe packer + ball-throwing sleeve" fracturing method for fracturing, flowback and production also includes the following steps: The number of sliding sleeves to be lowered is determined according to the number of reservoir layers vertically transformed. In layers close to bottom water or where no fracturing is required, perforation and ball injection can be performed without fracturing. In layers with poor physical properties, ball injection and fracturing can be performed after the ball injection sliding sleeve is opened. After gas breakthrough or water production occurs in the corresponding layer, selective production can be achieved by closing the ball-dropping sleeve of the layer.

[0026] In the above embodiment, preferably, Figure 5As shown, the integrated fracturing production string is a string of "bridge plug perforation" fracturing method, including: a second float shoe 17, a second tail pipe 18, a toe end rupture valve 19, a tail pipe hanger 20, a tie-back casing 21, a downhole safety valve 22 and a hydraulic control pipeline 23; The second float shoe 17 is disposed at the bottom of the second tail pipe 18; A plurality of toe-end rupture valves 19 are provided on the second tail pipe 18 near the second float shoe 17; A tail pipe hanger 20 is provided at the upper end of the second tail pipe 18 for hanging the second tail pipe 18; The tie-back sleeve 21 is connected to the top of the second tail pipe 18; A downhole safety valve 22 is provided on the tieback casing 21 , and the downhole safety valve 22 is connected to the fracturing wellhead through a hydraulic control pipeline 23 .

[0027] In the above embodiment, preferably, the fracturing, flowback and production of the integrated fracturing and production string using the "bridge plug perforation" fracturing method includes the following steps: Before fracturing, tie back the tieback casing to the fracturing wellhead; At the beginning of fracturing, the first stage is to open the toe-end rupture valve reserved on the second tail pipe by pressurizing the wellbore to keep the first stage open smoothly; if the toe-end rupture valve fails to open or the displacement cannot be established after opening, the coiled tubing is used for perforation, pressurized detonation, and the perforating gun is pulled out after perforation to conduct the injection pressure drop test of the second tail pipe to determine whether the reservoir is perforated; The subsequent fracturing layers are put into the "soluble bridge plug and perforation" service tool by cable transmission. After reaching the target layer, the plug is set, the plug is released, the perforation is performed, and the matching soluble ball is used for fracturing. During the flowback and production phase after fracturing, the downhole passage can be closed in an emergency through the matching downhole safety valve installed on the tieback casing; For fracturing wells with high pressure coefficient and self-flowing period, the fracturing string is used for flowback and self-flowing production in the early stage of fracturing; after the production decreases, the string above the tail pipe hanger can be taken out and a special production string can be lowered.

[0028] In the above embodiment, preferably, Figure 2 As shown in the figure, fracturing, flowback and fracturing in production using a multi-well batch continuous fracturing operation mode are carried out in the following ways: The mobile fracturing device is equipped with a seawater pump and a seawater filtration device, and is equipped with a buffer tank, continuous mixing, liquid addition skid, sand mixing skid, sand tank, and fracturing pump. The mobile fracturing device can be used to realize fracturing construction using seawater-based fracturing fluid. The fracturing well group on the wellhead platform shares a set of wellhead fracturing manifolds and emergency blowdown processes. Each well is equipped with a hydraulic plug valve to achieve switching between fracturing and post-fracturing flowback processes. After the mobile fracturing device prepares the fracturing materials at the dock, it sails to the wellhead platform and takes position. The wellhead fracturing manifold of the wellhead platform has been pre-installed in the middle deck area of ​​the platform; the mobile fracturing device is connected to the hose hanger of the wellhead platform through its own high-pressure fracturing hose; after the pipeline is installed, the pipeline pressure test is carried out; after the pressure test is qualified, the mobile fracturing device carries out continuous sand fracturing work on each well in turn; after the fracturing operation is completed, the high-pressure hose of the mobile fracturing device is released from the platform hose hanger and evacuated.

[0029] In the above embodiment, preferably, Figure 3 As shown, in order to ensure that the fracturing operation of the mobile fracturing device and the drilling and completion operation of the drilling rig are carried out alternately so as not to interfere with each other, the wellhead platform is arranged differently in terms of spatial height, specifically: The drilling rig is positioned in the well slot area on the upper deck of the wellhead platform and starts drilling and completion operations; The fracturing manifold and wellhead hanger for fracturing are arranged on the middle deck for fracturing construction; The crane is arranged under the upper deck and is used to fix the fracturing pipeline during fracturing. In order to ensure that fracturing operations are all carried out on the middle deck, a riser must be connected to the Christmas tree. The length of the riser is determined according to the height difference between the middle deck and the Christmas tree operating deck.

[0030] In the above embodiment, preferably, Figure 6 As shown, the fracturing flowback fluid is treated by using a low-cost on-site environmentally friendly fracturing flowback fluid treatment technology, and the specific steps are: A backflow device is used for backflow, wherein the backflow device includes two modules, a backflow control system and a backflow liquid treatment system, wherein the backflow liquid control system includes a ball catcher, a cyclone desander, a nozzle manifold, a heater, and a three-phase separator; the Christmas tree is connected to the ball catcher and the cyclone desander in sequence through pipelines, and then to the nozzle manifold, the outlet of the nozzle manifold is connected to the three-phase separator through a pipeline, and then to the three-phase separator, the oil phase outlet of the three-phase separator is connected to the dirty oil tank; the liquid phase outlet of the three-phase separator is connected to the mud pool, and the mud pool is connected to the backflow liquid treatment system; the backflow liquid in the Christmas tree passes through the ball catcher, and then passes through the cyclone desander to remove sand, and then enters the nozzle manifold. The backflow liquid flows out from the nozzle manifold outlet, is heated by the heater, and then enters the three-phase separator for separation, the separated natural gas is used for combustion, the separated oil phase flows into the dirty oil tank, the separated liquid phase enters the mud pool, and then is pumped into the backflow liquid treatment system; The return liquid treatment system includes an oil-water separator, an oil dehydrator, an advanced oxidizer, a primary flocculator, a secondary flocculator, an oil filter, a precision filter and a microfilter. The water phase outlet of the oil-water separator is connected to the oil dehydrator, the water phase outlet of the oil dehydrator is connected to the waste oil tank, the oil phase outlets of the oil-water separator and the oil dehydrator are respectively connected to the advanced oxidizer, the advanced oxidizer is connected to the primary flocculator, the solid phase outlet of the primary flocculator is connected to the sludge tank, the outlet of the sludge tank is connected to the solid-liquid separator, the solid phase outlet of the solid-liquid separator discharges sludge, and its liquid phase outlet is connected to the The inlet of the first-stage flocculator; the liquid phase outlet of the first-stage flocculator is connected to the second-stage flocculator, the solid phase outlet of the second-stage flocculator is connected to the sludge tank, and the liquid phase outlet of the second-stage flocculator is connected to the oil filter, precision filter and microfilter in sequence and then to the production water system; the return liquid pumped in from the mud pool is separated from oil and water, and the oil in the initial return oil tank is transported back to land for treatment. The polymer in the return liquid after oil and water separation is oxidized by advanced catalysis and degraded into small molecular polymers, and then after adding flocculants, flocculation and sedimentation, and solid-liquid separation, the return water is filtered and enters the platform production water process.

[0031] Embodiment 1: Take the "in-pipe packer + ball-throwing sleeve" fracturing method as an example: Before the fracturing operation, the target fracturing well has completed the liner cementing, scraping, cementing quality testing, perforation and other work. The fracturing string is lowered in two trips. The first trip is the fracturing string below the suspension packer, which mainly consists of the suspension packer, the sliding sleeve and the layered in-pipe packer. After the first trip and release, the second trip string is lowered. The second trip string is the production string with a downhole safety valve, and the oil pipe is connected back to the fracturing wellhead. In the layer that needs to be increased and reformed, the target layer is opened by throwing a ball, and then the fracturing fluid is pumped for fracturing construction. In the layer that is only perforated but not fractured, the sliding sleeve is opened by throwing a ball.

[0032] Before the fracturing operation is ready, skid-mounted equipment such as the flowback control system and the flowback fluid treatment system have been placed in the upper deck area of ​​the platform. After the mobile fracturing device is in place, it is connected to the wellhead hanger on the middle deck through a high-pressure hose, and the wellhead hanger is connected to the platform fracturing manifold. The fracturing manifolds are all placed on the middle deck. Since most offshore Christmas trees are arranged in two layers, it is necessary to connect the flange surface of the fracturing well to the riser, so that all fracturing wells are constructed on the middle deck. The riser is connected to the middle deck, and the upper part of the riser is connected to the six-way fracturing pipe. The fracturing pipes are connected to the fracturing pipelines and connected to the fracturing manifold on the middle deck.

[0033] After the fracturing manifold and wellhead pressure test are qualified, fracturing operations can be carried out. Taking the drilling, completion and fracturing operations of 4 wells as an example, wells 1 and 2 are the first group, and wells 3 and 4 are the second group. When the fracturing operation of the first group of wells is carried out, the first group of wells has completed perforation, integrated tubing, and installation of the Christmas tree. The mobile fracturing device starts its own fracturing equipment and carries out sand fracturing operations. At this time, the drilling rig is in place in the well slot area of ​​the upper deck, and perforation, integrated tubing and other operations are carried out on the second group of wells. The drilling, completion and fracturing operations do not interfere with each other. The fracturing operations of the first group of wells are carried out in sequence. When the sand fracturing operation is completed in well 1, the hydraulic plug valve on the Christmas tree of well 1 is closed. The backflow of well 1 after pressure is discharged from the Christmas tree wing valve and enters the backflow control system. At this time, the hydraulic plug valve on well 2 is opened to start the fracturing operation of the second well.

[0034] After the fracturing of two wells is completed, there is a situation where both wells flow back at the same time. The flowback control system is equipped with a corresponding number of ground safety valves, ball catchers, sand removers, oil nozzle manifolds and other equipment according to the actual number of fracturing flowback wells. When multiple wells flow back, heaters and three-phase separation equipment are shared by multiple wells. The construction site chooses to end the flowback and switch the production process in a timely manner based on the flowback rate, oil content, and water quality indicators after the flowback fluid is treated.

[0035] When the flowback of the first group of fracturing wells was completed, the second group of wells had completed drilling and completion operations, and fracturing operations were carried out according to the above process.

[0036] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for large-scale fracturing operation in offshore oil and gas fields, characterized in that: The steps include: The fracturing operation using a mobile fracturing device is carried out alternately with the drilling and completion operation of the drilling rig; On the basis of the fracturing operation of the mobile fracturing device and the drilling and completion operation of the drilling rig, a multi-well batch continuous fracturing operation mode is adopted for fracturing, flowback and production; On the basis of fracturing, flowback and production in batch continuous fracturing operation mode of multiple wells, fracturing, flowback and production are carried out by using integrated fracturing and production string; On the basis of adopting integrated fracturing and production tubing for fracturing, flowback and production, the fracturing flowback fluid is treated by adopting low-cost on-site environmentally friendly treatment technology for fracturing flowback fluid.

2. The offshore oil and gas field large-scale fracturing operation method according to claim 1, characterized in that: The method of adopting a multi-well batch continuous fracturing operation mode to perform fracturing, flowback and production specifically includes the following steps: The oil wells to be operated are numbered and grouped, with each group including a number of oil wells; Several groups of oil wells are drilled, completed, fractured, flowed back and produced alternately so that the operations of each group of oil wells do not interfere with each other.

3. The offshore oil and gas field large-scale fracturing operation method according to claim 1, characterized in that: The integrated fracturing production string is a string of "in-pipe packer + ball-throwing sleeve" fracturing method, including a bottom fracturing string string and an upper string string; The bottom fracturing string includes a first tail pipe, a first float shoe, a wellbore isolation valve, a toe end sliding sleeve, a ball-dropping sliding sleeve, a segmented packer and a bottom tubing; The first tail pipe, the first float shoe and the wellbore isolation valve are connected to the tail end of the bottom oil pipe in sequence from bottom to top; A plurality of segmented packers are arranged at intervals on the bottom oil pipe, and the toe end sliding sleeve is arranged on the bottom oil pipe between the first segmented packer and the second segmented packer from the tail to the front; The ball-throwing sleeves are respectively arranged between the remaining segmented packers and on the bottom oil pipe at the front end of the segmented packer at the front end; The upper tubular string includes an upper tubing, an automatic guiding and deflecting device, a suspension packer, a ratchet anchoring and positioning seal, a tubing hydraulic anchor, a circulating sleeve, a safety valve and a flow collar, a casing and a tie-back tubing; The lower end of the upper oil pipe is connected to the upper end of the bottom oil pipe; The automatic guiding and deflecting device, hanging packer, ratchet anchoring and positioning seal, oil pipe hydraulic anchor, circulating sleeve, safety valve and flow joint hoop are arranged on the upper oil pipe in sequence from bottom to top, the return oil pipe is connected to the top of the upper oil pipe, and the casing is sleeved outside the return oil pipe.

4. The offshore oil and gas field large-scale fracturing operation method according to claim 3, characterized in that: The fracturing, flowback and production of the integrated fracturing and production string using the "in-pipe packer + ball-throwing sleeve" fracturing method include the following steps: Before fracturing begins, perforate the target oil and gas layer in advance; When fracturing begins, the integrated fracturing production string is lowered, and the fracturing pump delivers fracturing fluid and carries proppant into the formation; The first stage of fracturing is carried out by toe-end sliding sleeve fracturing, which is carried out by pressurizing the wellbore and opening the toe-end sliding sleeve; the subsequent fracturing layers are successively injected with soluble balls to open the ball-injection sliding sleeve for fracturing; During the flowback and production stage after fracturing, the integrated fracturing and production string will continue to be used for flowback and production operations, and no string replacement operations will be performed.

5. The offshore oil and gas field large-scale fracturing method according to claim 4, characterized in that: The fracturing, flowback and production of the integrated fracturing and production string using the "in-pipe packer + ball-throwing sleeve" fracturing method also includes the following steps: The number of sliding sleeves to be lowered is determined according to the number of reservoir layers vertically transformed. In layers close to bottom water or where no fracturing is required, perforation and ball injection can be performed without fracturing. In layers with poor physical properties, ball injection and fracturing can be performed after the ball injection sliding sleeve is opened. After gas breakthrough or water production occurs in the corresponding layer, selective production is achieved by closing the ball-dropping sleeve of the layer.

6. The offshore oil and gas field large-scale fracturing method according to claim 1, characterized in that: The integrated fracturing production string is a "bridge plug perforation" fracturing string, including: a second float shoe, a second tail pipe, a toe-end rupture valve, a tail pipe hanger, a tieback casing, a downhole safety valve and a hydraulic control pipeline; The second float shoe is disposed at the bottom of the second tail pipe; A plurality of toe-end rupture valves are arranged on the second tail pipe near the second float shoe; A tail pipe hanger is provided at the upper end of the second tail pipe for hanging the second tail pipe; The tie-back sleeve is connected to the top of the second tail pipe; A downhole safety valve is provided on the tieback casing, and the downhole safety valve is connected to the fracturing wellhead through the hydraulic control pipeline.

7. The offshore oil and gas field large-scale fracturing method according to claim 6, characterized in that: The fracturing, flowback and production of the integrated fracturing and production string using the "bridge plug perforation" fracturing method include the following steps: Before fracturing, tie back the tieback casing to the fracturing wellhead; At the beginning of fracturing, the first stage is to pressurize the wellbore to open the toe-end rupture valve reserved on the second tail pipe, and keep the first stage open smoothly; if the toe-end rupture valve fails to open or the displacement cannot be established after opening, the coiled tubing is used for perforation, pressurized detonation, and the perforating gun is pulled out after perforation to conduct the tail pipe injection pressure drop test to determine whether the reservoir is perforated; The subsequent fracturing layers are put into the "soluble bridge plug and perforation" service tool by cable transmission. After reaching the target layer, the plug is set, the plug is released, the perforation is performed, and the matching soluble ball is used for fracturing. During the flowback and production phase after fracturing, the downhole passage can be closed in an emergency through the matching downhole safety valve installed on the tieback casing; For fracturing wells with high pressure coefficient and self-flowing period, the fracturing string is used for flowback and self-flowing production in the early stage of fracturing; after the production decreases, the string above the tail pipe hanger can be taken out and a special production string can be lowered.

8. The offshore oil and gas field large-scale fracturing method according to claim 1, characterized in that: The fracturing, flowback and production fracturing in multi-well batch continuous fracturing operation mode are carried out in the following ways: The mobile fracturing device is equipped with a seawater pump and a seawater filtration device, and is equipped with a buffer tank, continuous mixing, liquid addition skid, sand mixing skid, sand tank, and fracturing pump. The mobile fracturing device can be used to realize fracturing construction using seawater-based fracturing fluid. The same fracturing well group on the wellhead platform shares a set of wellhead fracturing manifolds and emergency blowdown processes, and each well is equipped with a hydraulic plug valve to achieve switching between fracturing and post-fracturing flowback processes; After the mobile fracturing device prepares the fracturing materials at the dock, it sails to the wellhead platform and takes position. The wellhead fracturing manifold of the wellhead platform has been pre-installed in the middle deck area of ​​the platform; the mobile fracturing device is connected to the hose hanger of the wellhead platform through its own high-pressure fracturing hose; after the pipeline is installed, the pipeline pressure test is carried out; after the pressure test is qualified, the mobile fracturing device carries out continuous sand fracturing work on each well in turn; after the fracturing operation is completed, the high-pressure hose of the mobile fracturing device is released from the platform hose hanger and evacuated.

9. The offshore oil and gas field large-scale fracturing method according to claim 8, characterized in that: In order to ensure that the fracturing operation of the mobile fracturing device and the drilling and completion operation of the drilling rig are carried out alternately without interfering with each other, the wellhead platform is arranged differently in terms of spatial height, specifically: The drilling rig is positioned in the well slot area on the upper deck of the wellhead platform and starts drilling and completion operations; The fracturing manifold and wellhead hanger for fracturing are arranged on the middle deck for fracturing construction; The crane is arranged under the upper deck and is used to fix the fracturing pipeline during fracturing. In order to ensure that fracturing operations are all carried out on the middle deck, a riser must be connected to the Christmas tree. The length of the riser is determined according to the height difference between the middle deck and the Christmas tree operating deck.

10. The offshore oil and gas field large-scale fracturing operation method according to claim 1, characterized in that: The fracturing flowback fluid is treated by using a low-cost on-site environmentally friendly fracturing flowback fluid treatment technology, and the specific steps are: A flowback device is used for flowback, wherein the flowback device includes two modules, a flowback control system and a flowback liquid treatment system, wherein the flowback liquid control system includes a ball catcher, a cyclone desander, a nozzle manifold, a heater, and a three-phase separator; the Christmas tree is connected to the ball catcher and the cyclone desander in sequence through pipelines, and then connected to the nozzle manifold, after the outlet of the nozzle manifold is connected to the three-phase separator through a pipeline, the oil phase outlet of the three-phase separator is connected to the dirty oil tank; the liquid phase outlet of the three-phase separator is connected to the mud pool, and the mud pool is connected to the flowback liquid treatment system; the flowback liquid in the Christmas tree passes through the ball catcher, and then passes through the cyclone desander to remove sand before entering the nozzle manifold, the flowback liquid flows out from the nozzle manifold outlet, is heated by the heater, and then enters the three-phase separator for separation, the separated natural gas is used for combustion or recovery, the dirty oil separated at the initial stage of flowback flows into the dirty oil tank, the separated liquid phase enters the mud pool, and then is pumped into the flowback liquid treatment system; The return liquid treatment system includes an oil-water separator, an oil dehydrator, an advanced oxidizer, a primary flocculator, a secondary flocculator, an oil filter, a precision filter and a microfilter. The water phase outlet of the oil-water separator is connected to the oil dehydrator, the water phase outlet of the oil dehydrator is connected to the waste oil tank, the oil phase outlets of the oil-water separator and the oil dehydrator are respectively connected to the advanced oxidizer, the advanced oxidizer is connected to the primary flocculator, the solid phase outlet of the primary flocculator is connected to the sludge tank, the outlet of the sludge tank is connected to the solid-liquid separator, the solid phase outlet of the solid-liquid separator discharges sludge, and its liquid phase outlet is connected to the The inlet of the first-stage flocculator; the liquid phase outlet of the first-stage flocculator is connected to the second-stage flocculator, the solid phase outlet of the second-stage flocculator is connected to the sludge tank, and the liquid phase outlet of the second-stage flocculator is connected to the oil filter, precision filter and microfilter in sequence and then to the production water system; the return liquid pumped in from the mud pool is separated from oil and water, and the oil in the initial return oil tank is transported back to land for treatment. The polymer in the return liquid after oil and water separation is oxidized by advanced catalysis and degraded into small molecular polymers, and then after adding flocculants, flocculation and sedimentation, and solid-liquid separation, the return water is filtered and enters the platform production water process.

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