阅读说明：本技术 一种深海双层管井底三通道压力控制系统及控制方法 (Deep-sea double-layer pipe well bottom three-channel pressure control system and control method ) 是由 王国荣 苟如意 刘清友 唐洋 周守为 龚彦 李中 钟林 李清平 刘和兴 李炎军 于 2020-06-01 设计创作，主要内容包括：本发明公开一种深海双层管井底三通道压力控制系统及控制方法,包括双层管、套管、钻头、转换接头、外套筒、轴流泵、涡轮马达、液位监测传感器、阀组控制单元、双层管回流管汇、钻井液泵入管汇、钻井泵、钻井液循环罐；所述转换接头连接在双层管的下端上,所述外套筒套设在轴流泵的上半部分上,所述轴流泵、外套筒分别连接在转换接头的下端、中部上,所述轴流泵、涡轮马达、钻头依次连接,所述双层管置于套管内,所述内管、外管、套管为同心管柱。本发明的双层管形成三个钻井液通道,通过改变轴流泵举升性能,实现井底压力自适应控制,有效维持井底钻井液液柱压力的动态平衡。(The invention discloses a deep sea double-layer pipe well bottom three-channel pressure control system and a control method, wherein the system comprises a double-layer pipe, a sleeve, a drill bit, a conversion joint, an outer sleeve, an axial flow pump, a turbine motor, a liquid level monitoring sensor, a valve bank control unit, a double-layer pipe backflow manifold, a drilling fluid pumping manifold, a drilling pump and a drilling fluid circulating tank; the improved axial flow pump is characterized in that the adapter is connected to the lower end of the double-layer pipe, the outer sleeve is sleeved on the upper half portion of the axial flow pump, the axial flow pump and the outer sleeve are respectively connected to the lower end and the middle portion of the adapter, the axial flow pump, the turbine motor and the drill bit are sequentially connected, the double-layer pipe is arranged in the sleeve, and the inner pipe, the outer pipe and the sleeve are concentric pipe columns. The double-layer pipe forms three drilling fluid channels, the self-adaptive control of the bottom pressure of the well is realized by changing the lifting performance of the axial flow pump, and the dynamic balance of the pressure of the drilling fluid column at the bottom of the well is effectively maintained.)

1. A deep sea double-layer pipe well bottom three-channel pressure control system is characterized by comprising a double-layer pipe, a sleeve, a drill bit, a conversion joint, an outer sleeve, an axial flow pump, a turbine motor, a liquid level monitoring sensor, a valve bank control unit, a double-layer pipe backflow manifold, a drilling fluid pumping manifold, a drilling pump and a drilling fluid circulating tank;

the double-layer pipe comprises an outer pipe and an inner pipe arranged in the outer pipe, the adapter joint is connected to the lower end of the double-layer pipe, the outer sleeve is sleeved on the upper half part of the axial flow pump, the axial flow pump and the outer sleeve are respectively connected to the lower end and the middle part of the adapter joint, the axial flow pump, the turbine motor and the drill bit are sequentially connected, the double-layer pipe is arranged in the sleeve, the inner pipe, the outer pipe and the sleeve are concentric pipe columns, the inner cavity of the inner pipe is a first channel, the annular space between the inner pipe and the outer pipe is a second channel, and the annular space between the outer pipe and the sleeve is a;

the drilling pump is communicated with the first channel through a drilling fluid pumping manifold, the drilling fluid circulating tank is communicated with the second channel through a double-layer pipe backflow manifold, the liquid level monitoring sensor is positioned in the third channel, a drilling fluid pumping flow control valve and a drilling fluid pumping flow meter are arranged on the drilling fluid pumping manifold, and an axial flow pump backflow flow control valve and an axial flow pump backflow flow meter are arranged on the double-layer pipe backflow manifold;

the drilling fluid pump is pumped into the flow control valve, the drilling fluid pump is pumped into the flowmeter, the axial-flow pump backward flow control valve, the axial-flow pump backward flow flowmeter, the liquid level monitoring sensor all with valves the control unit electric connection.

2. The deep sea double-layer pipe well bottom three-channel pressure control system as claimed in claim 1, wherein the middle part of the outer surface of the adapter is provided with straight threads, the lower part of the outer surface of the adapter is provided with male threads, and the interior of the adapter is provided with a connecting cavity and a drilling fluid pumping cavity which are communicated in sequence; the inner wall of the connecting cavity is provided with female buckle threads, the conversion joint is also provided with a backflow channel, one end of the backflow channel is communicated with the connecting cavity, the other end of the backflow channel is communicated with the outside of the conversion joint and is positioned between the straight threads and the male buckle threads of the conversion joint, the outer pipe is in threaded connection with the inner wall of the connecting cavity, the second channel of the outer pipe is communicated with the connecting cavity, the inner pipe is in threaded connection with the drilling fluid pumping cavity, and the first channel of the inner pipe is communicated with the drilling fluid pumping cavity; the outer sleeve is in threaded connection with the middle of the outer surface of the adapter, the axial flow pump is in threaded connection with the lower part of the outer surface of the adapter, and the backflow channel is communicated with an annulus between the axial flow pump and the outer sleeve; the axial flow pump is characterized in that a suction inlet and a discharge outlet of the axial flow pump are separated by an outer sleeve, the discharge outlet of the axial flow pump is communicated with an annular space between the axial flow pump and the outer sleeve, and the suction inlet is communicated with the outside of the axial flow pump.

3. The system of claim 2, wherein a riser is sleeved outside the double-layer pipe, and the riser is communicated with the third channel.

4. The control method of the bottom three-channel pressure control system of the deep-sea double-layer pipe is adopted, and is characterized by comprising the following steps:

step S10, respectively installing the casing pipe and the double-layer pipe in the deep sea well;

step S20, filling partition gel for isolating seawater and drilling fluid in an annulus between the sleeve and the double-layer pipe, and installing a liquid level monitoring sensor for monitoring the liquid level of the partition gel in the partition gel;

step S30, the drilling pump starts to work to pump the drilling fluid in the drilling fluid circulation tank into the first channel, and then the drilling fluid pumping flow Q is obtained in real time through the drilling fluid pumping flow meter_in(ii) a Real-time acquisition of axial flow pump reflux flow Q through axial flow pump reflux flowmeter_out(ii) a Acquiring the liquid level H of the drilling fluid in a third channel in real time through a liquid level monitoring sensor;

s40, reasonably matching the drilling fluid pumping flow Q according to the data condition of the drilling fluid level H of the third channel_inAnd axial flow pump return flow Q_outThe lifting performance of the axial flow pump is changed, and the pressure of the drilling fluid column at the bottom of the well is adjusted by changing the lifting performance, so that the pressure at the bottom of the well is equal to the formation pressure;

the method comprises the following specific steps: when the liquid level H of the drilling fluid in the third channel is monitored to be unchanged in real time, the pressure at the bottom of the well is equal to the pressure of the stratum, and the well is normally drilled;

when the liquid level H of the drilling fluid in the third channel is monitored to be reduced in real time, the bottom of the well is lost, and the drilling fluid is lost and enters the stratum; immediately sending a signal to a valve group control unit, wherein the valve group control unit changes the opening of a drilling fluid pumping flow control valve and an axial flow pump backflow flow control valve; pumping drilling fluid into flow rate Q_inAnd axial flow pump return flow Q_outThe difference value between the drilling fluid level and the drilling fluid level is controlled to be larger than zero, and the drilling fluid level H of the third channel is further reduced to be unchanged; at the moment, the bottom hole pressure is reduced to reach new balance with the formation pressure, the pressure regulation achieves the purpose of controlling bottom hole leakage, and the well enters a normal drilling state again;

when the liquid level H of the drilling fluid in the third channel is monitored to be increased in real time, the bottom of the well overflows at the moment, and the stratum fluid invades; immediately sending a signal to a valve group control unit, wherein the valve group control unit changes the opening of a drilling fluid pumping flow control valve and an axial flow pump backflow flow control valve; pumping drilling fluid into flow rate Q_inAnd axial flow pump return flow Q_outThe difference between the drilling fluid levels is controlled to be smaller than zero, and the drilling fluid level H of the third channel is further increased to be unchanged; at the moment, the bottom hole pressure is increased to reach new balance with the formation pressure, the pressure regulation achieves the purpose of controlling bottom hole overflow, and the well enters a normal drilling state again.

5. The deep-sea double-layer pipe well bottom three-channel pressure control system as claimed in claim 4, wherein the drilling fluid in the first channel in the step S30 is pumped into the cavity from the double-layer pipe through the drilling fluid pump of the adapter joint and sequentially enters the axial flow pump and the turbine motor, and the drilling fluid is ejected from the drill bit after driving the turbine motor to rotate; and meanwhile, the turbine motor drives the axial flow pump to work, drilling fluid in the third channel is sucked in from the suction inlet and is discharged into an annular space between the axial flow pump and the outer sleeve from the discharge outlet, and the drilling fluid in the annular space enters the double-layer pipe backflow manifold through the second channel and finally flows back into the drilling fluid circulation tank.

6. The system as claimed in claim 4, wherein the step S40 is performed by using the following three methodsFormula pumping drilling fluid into flow Q_inAnd axial flow pump return flow Q_outThe difference between the drilling fluid pumping flow rates is controlled to be more than zero ①_inIncreasing the return flow Q of an axial flow pump_outConstant ② drilling fluid pumping flow rate Q_inConstant, axial flow pump return flow Q_outReduced ③ drilling fluid pumping inflow Q_inIncreasing the return flow Q of an axial flow pump_outAnd decreases.

7. The system as claimed in claim 4, wherein the drilling fluid is pumped into the flow rate Q in step S40 by three ways_inAnd axial flow pump return flow Q_outThe difference between the drilling fluid pumping flow rates is controlled to be less than zero ①_inConstant, axial flow pump return flow Q_out② increased drilling fluid pumping flow rate Q_inReduced, axial flow pump return flow Q_outConstant ③ drilling fluid pumping flow rate Q_inReduced, axial flow pump return flow Q_outAnd is increased.

Technical Field

The invention relates to a deep-sea double-layer pipe well bottom three-channel pressure control system and a control method, and belongs to the technical field of deep-water oil and gas drilling engineering.

Background

The exploitation of oil and gas resources is developed towards the exploitation direction of deep strata, low permeability, ocean oil and gas and unconventional oil and gas, China is actively expanding the deep water field in south sea, but deep sea drilling exploitation faces a plurality of problems, most prominently, the problem of narrow drilling safety density window is solved, and the interval of stratum pressure and fracture pressure is narrow due to loose deposition and seawater columns in the deep sea bottom. And if the drilling safety density window range is exceeded, drilling accidents such as leakage, overflow, well collapse, drill sticking and the like can occur. How to stabilize the bottom hole pressure within a safe drilling pressure range is an important control method of the bottom hole pressure. The pressure value at the bottom of a well is reduced by adopting a double-gradient drilling technology at present, the whole well section can be divided into two pressure gradients by the double-gradient drilling, the seawater pressure is above a mud line, and the stratum pressure is below the mud line. Common methods in dual gradient drilling technology are: the double-gradient drilling technology of a subsea pump and the double-gradient drilling technology of filling low-density fluid into a marine riser.

The sea-bottom pump double-gradient drilling technology is characterized in that a marine riser is filled with seawater, drilling fluid is directly returned to a drilling platform by using a sea-bottom pump or a bypass return pipeline, and two density systems of a seawater section and a drilling fluid section are formed in the whole drilling annulus. However, the subsea pump needs to be equipped with subsea solid-liquid separation equipment, the subsea pump has poor reliability, and rock debris pollutes the seabed environment, so that the field application of the subsea pump dual-gradient drilling technology is limited.

The double gradient drilling technology for injecting low density medium into the riser includes injecting gas, hollow ball or low density fluid into the drilling fluid to lower the pressure of the sea water column and the pressure loss of the drilling fluid, so that the density of the drilling fluid in the riser is equal to that of sea water and two drilling fluid density systems are formed in the drilling annulus. However, the injection amount of the low-density fluid is not easy to control, so that slug flow is easy to cause, and the control precision of the density of the drilling fluid is poor. The injection point and the injection device of the low-density medium have complex structures, poor reliability and high economic cost.

Therefore, in order to improve the precision of the dual-gradient drilling technology on the pressure control of the shaft, the self-adaptive adjusting function is enhanced. There is a need for an apparatus for efficiently regulating the bottom hole pressure directly from the bottom hole without adding large pumping equipment, fluid injection devices, and debris separation devices. The method can regulate and control the pressure in time according to the change of the bottom hole pressure, and provides a powerful guarantee for the safe, efficient and economic development of deep-sea oil and gas.

Disclosure of Invention

The invention mainly overcomes the defects in the prior art and provides a deep-sea double-layer pipe well bottom three-channel pressure control system and a control method.

The technical scheme provided by the invention for solving the technical problems is as follows: a deep sea double-layer pipe well bottom three-channel pressure control system comprises a double-layer pipe, a sleeve, a drill bit, a conversion joint, an outer sleeve, an axial flow pump, a turbine motor, a liquid level monitoring sensor, a valve group control unit, a double-layer pipe backflow manifold, a drilling fluid pumping manifold, a drilling pump and a drilling fluid circulating tank;

the double-layer pipe comprises an outer pipe and an inner pipe arranged in the outer pipe, the adapter joint is connected to the lower end of the double-layer pipe, the outer sleeve is sleeved on the upper half part of the axial flow pump, the axial flow pump and the outer sleeve are respectively connected to the lower end and the middle part of the adapter joint, the axial flow pump, the turbine motor and the drill bit are sequentially connected, the double-layer pipe is arranged in the sleeve, the inner pipe, the outer pipe and the sleeve are concentric pipe columns, the inner cavity of the inner pipe is a first channel, the annular space between the inner pipe and the outer pipe is a second channel, and the annular space between the outer pipe and the sleeve is a;

the drilling pump is communicated with the first channel through a drilling fluid pumping manifold, the drilling fluid circulating tank is communicated with the second channel through a double-layer pipe backflow manifold, the liquid level monitoring sensor is positioned in the third channel, a drilling fluid pumping flow control valve and a drilling fluid pumping flow meter are arranged on the drilling fluid pumping manifold, and an axial flow pump backflow flow control valve and an axial flow pump backflow flow meter are arranged on the double-layer pipe backflow manifold;

the drilling fluid pump is pumped into the flow control valve, the drilling fluid pump is pumped into the flowmeter, the axial-flow pump backward flow control valve, the axial-flow pump backward flow flowmeter, the liquid level monitoring sensor all with valves the control unit electric connection.

The technical scheme is that the middle part of the outer surface of the adapter is provided with straight threads, the lower part of the outer surface of the adapter is provided with male buckle threads, and the interior of the adapter is provided with a connecting cavity and a drilling fluid pumping cavity which are sequentially communicated; the inner wall of the connecting cavity is provided with female buckle threads, the conversion joint is also provided with a backflow channel, one end of the backflow channel is communicated with the connecting cavity, the other end of the backflow channel is communicated with the outside of the conversion joint and is positioned between the straight threads and the male buckle threads of the conversion joint, the outer pipe is in threaded connection with the inner wall of the connecting cavity, the second channel of the outer pipe is communicated with the connecting cavity, the inner pipe is in threaded connection with the drilling fluid pumping cavity, and the first channel of the inner pipe is communicated with the drilling fluid pumping cavity; the outer sleeve is in threaded connection with the middle of the outer surface of the adapter, the axial flow pump is in threaded connection with the lower part of the outer surface of the adapter, and the backflow channel is communicated with an annulus between the axial flow pump and the outer sleeve; the axial flow pump is characterized in that a suction inlet and a discharge outlet of the axial flow pump are separated by an outer sleeve, the discharge outlet of the axial flow pump is communicated with an annular space between the axial flow pump and the outer sleeve, and the suction inlet is communicated with the outside of the axial flow pump.

According to a further technical scheme, a riser is sleeved outside the double-layer pipe and communicated with the third channel.

A control method of a deep-sea double-layer pipe bottom hole three-channel pressure control system comprises the following steps:

step S10, respectively installing the casing pipe and the double-layer pipe in the deep sea well;

step S20, filling partition gel for isolating seawater and drilling fluid in an annulus between the sleeve and the double-layer pipe, and installing a liquid level monitoring sensor for monitoring the liquid level of the partition gel in the partition gel;

step S30, the drilling pump starts to work to pump the drilling fluid in the drilling fluid circulation tank into the first channel, and then the drilling fluid pumping flow Q is obtained in real time through the drilling fluid pumping flow meter_in(ii) a Real-time acquisition of axial flow pump reflux flow Q through axial flow pump reflux flowmeter_out(ii) a Acquiring the liquid level H of the drilling fluid in a third channel in real time through a liquid level monitoring sensor;

s40, reasonably matching the drilling fluid pumping flow Q according to the data condition of the drilling fluid level H of the third channel_inAnd axial flow pump return flow Q_outThe lifting performance of the axial flow pump is changed, and the pressure of the drilling fluid column at the bottom of the well is adjusted by changing the lifting performance, so that the pressure at the bottom of the well is equal to the formation pressure;

the method comprises the following specific steps: when the liquid level H of the drilling fluid in the third channel is monitored to be unchanged in real time, the pressure at the bottom of the well is equal to the pressure of the stratum, and the well is normally drilled;

when the liquid level H of the drilling fluid in the third channel is monitored to be reduced in real time, the bottom of the well is lost, and the drilling fluid is lost and enters the stratum; immediately sending a signal to a valve group control unit, wherein the valve group control unit changes the opening of a drilling fluid pumping flow control valve and an axial flow pump backflow flow control valve; pumping drilling fluid into flow rate Q_inAnd axial flow pump return flow Q_outThe difference value between the drilling fluid level and the drilling fluid level is controlled to be larger than zero, and the drilling fluid level H of the third channel is further reduced to be unchanged; at this time, the bottom hole pressure is reduced to the groundThe layer pressure reaches new balance, the pressure regulation and control achieve the purpose of controlling bottom hole leakage, and the normal drilling state is entered again;

when the liquid level H of the drilling fluid in the third channel is monitored to be increased in real time, the bottom of the well overflows at the moment, and the stratum fluid invades; immediately sending a signal to a valve group control unit, wherein the valve group control unit changes the opening of a drilling fluid pumping flow control valve and an axial flow pump backflow flow control valve; pumping drilling fluid into flow rate Q_inAnd axial flow pump return flow Q_outThe difference between the drilling fluid levels is controlled to be smaller than zero, and the drilling fluid level H of the third channel is further increased to be unchanged; at the moment, the bottom hole pressure is increased to reach new balance with the formation pressure, the pressure regulation achieves the purpose of controlling bottom hole overflow, and the well enters a normal drilling state again.

The further technical scheme is that the drilling fluid in the first channel in the step S30 is pumped into the cavity from the double-layer pipe through the drilling fluid pump of the adapter joint and sequentially enters the axial-flow pump and the turbine motor, and the drilling fluid is ejected out of the drill bit after driving the turbine motor to rotate; and meanwhile, the turbine motor drives the axial flow pump to work, drilling fluid in the third channel is sucked in from the suction inlet and is discharged into an annular space between the axial flow pump and the outer sleeve from the discharge outlet, and the drilling fluid in the annular space enters the double-layer pipe backflow manifold through the second channel and finally flows back into the drilling fluid circulation tank.

The further technical scheme is that in the step S40, the drilling fluid is pumped into the flow rate Q in the following three ways_inAnd axial flow pump return flow Q_outThe difference between the drilling fluid pumping flow rates is controlled to be more than zero ①_inIncreasing the return flow Q of an axial flow pump_outConstant ② drilling fluid pumping flow rate Q_inConstant, axial flow pump return flow Q_outReduced ③ drilling fluid pumping inflow Q_inIncreasing the return flow Q of an axial flow pump_outAnd decreases.

The further technical scheme is that in the step S40, the drilling fluid is pumped into the flow rate Q in the following three ways_inAnd axial flow pump return flow Q_outThe difference between the drilling fluid pumping flow rates is controlled to be less than zero ①_inConstant, axial flow pump return flow Q_outEnlarged ②Drilling fluid pumping inflow rate Q_inReduced, axial flow pump return flow Q_outConstant ③ drilling fluid pumping flow rate Q_inReduced, axial flow pump return flow Q_outAnd is increased.

The invention has the following beneficial effects:

1. the double-layer pipe forms three drilling fluid channels, the self-adaptive control of the bottom pressure of the well is realized by changing the performance of the axial flow pump, and the dynamic balance of the pressure of the drilling fluid column at the bottom of the well is effectively maintained;

2. the liquid level of the drilling fluid is accurately monitored, the bottom hole pressure control precision of the dual-gradient drilling is improved, the bottom hole pressure is ensured to be within a safe density window, and safe, economic and efficient drilling is facilitated;

3. the system has simple structure, convenient control and low operation cost.

Drawings

FIG. 1 is a schematic structural diagram of a deep-sea double-layer pipe bottom hole three-channel pressure control system and a control method;

FIG. 2 is a schematic structural view of a double-layer pipe of a deep sea double-layer pipe;

FIG. 3 is a schematic diagram of a bottom three-channel structure of a deep sea double-layer pipe;

FIG. 4 is a schematic structural view of a deep sea double-pipe downhole axial flow pump connected with a double-pipe and a drill bit;

FIG. 5 is a control block diagram of three-channel downhole pressure control of a deep-sea double-layer pipe;

FIG. 6 is a schematic of bottom hole pressure control to account for bottom hole leakoff in accordance with the present invention;

FIG. 7 is a schematic of bottom hole pressure control for bottom hole flooding in accordance with the present invention;

FIG. 8 is a schematic structural view of an adapter;

fig. 9 is a structural schematic diagram of a left side view of the double tube.

Shown in the figure: 101. a double pipe, 103, a drilling fluid pumping flow control valve, 104, a drilling fluid pumping flow meter, 105, an axial flow pump return flow control valve, 106, an axial flow pump return flow meter, 107, a fluid level monitoring sensor, 108, a valve bank control unit, 109, a double pipe return manifold, 110, a drilling fluid pumping manifold, 111, a drilling pump, 112, a drilling fluid circulation tank, 113, sea level, 114, mud line, 115, casing, 116, drilling fluid, 117, seawater, 118, a barrier gel, 119, a drill bit, 120, a suction inlet, 121, a discharge outlet, 1011, an outer pipe box thread, 1012, an outer pipe pin thread, 1013, an inner pipe, 1014, an outer pipe, 1015, a first passage, 1016, a second passage, 1017, a third passage, 1018, a water blocking pipe, 1021, a conversion joint, 1022, an outer sleeve, 1023, a turbine motor, 1024, an axial flow pump, 1025, box thread, 1026, 1027, box thread, 1028. male thread, 1029 straight thread.

Detailed Description

The present invention will be further described with reference to the following examples and the accompanying drawings.

As shown in fig. 1, the three-channel downhole pressure control system of the deep-sea double-layer pipe comprises a double-layer pipe 101, a conversion joint 1021, a casing 115, a drill bit 119, an outer sleeve 1022, an axial flow pump 1024, a turbine motor 1023, a liquid level monitoring sensor 107, a valve group control unit 108, a double-layer pipe return manifold 109, a drilling fluid pumping manifold 110, a drilling pump 111 and a drilling fluid circulation tank 112;

as shown in fig. 2 and 9, the double-layer pipe 101 comprises an outer pipe 1014 and an inner pipe 1013 installed in the outer pipe 1014, wherein the upper end of the inner cavity of the outer pipe 1014 is provided with an outer pipe female thread 1011, the lower end of the outer surface is provided with an outer pipe male thread 1012, and the inner pipe 1013 and the outer pipe 1014 are concentric pipe columns;

as shown in fig. 1, the double-walled pipe 101 is placed in the casing 115, the inner cavity of the inner tube 1013 is a first passage 1015, the annulus between the inner tube 1013 and the outer tube 1014 is a second passage 1016, the annulus between the outer tube 1014 and the casing 115 is a third passage 1017, and the third passage 1017 is communicated with the riser;

as shown in fig. 8, a straight thread 1029 is arranged in the middle of the outer surface of the adaptor 1021, a male thread 1028 is arranged on the lower part of the outer surface of the adaptor 1021, and a connection cavity and a drilling fluid pumping cavity which are sequentially communicated are arranged in the adaptor; the inner wall of the connecting cavity is provided with female thread 1027, the conversion joint 1021 is also provided with a return passage, one end of the return passage is communicated with the connecting cavity, and the other end of the return passage is communicated with the outside of the conversion joint and is positioned between straight thread 1029 and male thread 1028 of the conversion joint 1021;

as shown in fig. 4, the outer tube 1014 is screwed to the inner wall of the junction chamber, the second passage 1016 thereof communicates with the junction chamber, the inner tube 1013 is screwed to the drilling fluid pumping chamber, and the first passage 1015 thereof communicates with the drilling fluid pumping chamber; the outer sleeve 1022 is in threaded connection with the middle of the outer surface of the adapter 1021, the axial pump 1024 is in threaded connection with the lower part of the outer surface of the adapter 1021, and the axial pump 1024, the turbine motor 1023 and the drill bit 119 are in threaded connection in sequence;

the backflow channel is communicated with an annulus between the axial flow pump 1024 and the outer sleeve 1022; the suction port 120 and the discharge port 121 of the axial flow pump 1024 are separated by an outer sleeve 1022, the discharge port 121 of the axial flow pump is communicated with the annular space between the axial flow pump 1024 and the outer sleeve 1022, and the suction port 120 is communicated with the outside of the axial flow pump 1024;

the drilling pump 111 is communicated with a first channel 1015 through a drilling fluid pumping manifold 110, the drilling fluid circulation tank 112 is communicated with a second channel 1016 through a double-layer pipe backflow manifold 109, the liquid level monitoring sensor is positioned in a third channel 1017, the drilling fluid pumping manifold 110 is provided with a drilling fluid pumping flow control valve 103 and a drilling fluid pumping flow meter 104, and the double-layer pipe backflow manifold 109 is provided with an axial flow pump backflow flow control valve 105 and an axial flow pump backflow flow meter 106;

the drilling fluid pumping flow control valve 103, the drilling fluid pumping flow meter 104, the axial flow pump backflow flow control valve 105, the axial flow pump backflow flow meter 106 and the liquid level monitoring sensor 107 are electrically connected with the valve group control unit 108.

As shown in fig. 1 to 4, in practical application, the third passage 1017 is filled with a blocking gel 118 for isolating seawater 117 from drilling fluid 116, and a level monitoring sensor 107 for monitoring the level of the blocking gel 118 is installed in the blocking gel 118.

When the drilling fluid circulation type drilling machine starts to work, the drilling pump 111 pumps the drilling fluid 116 in the drilling fluid circulation tank 112 into the first channel 1015, as shown in fig. 4, an arrow in the figure shows the flowing process of the drilling fluid, the drilling fluid in the first channel 1015 enters the axial flow pump 1024 and the turbine motor 1023 from the double-layer pipe 101 through the center of the conversion joint 1021, and the drilling fluid drives the turbine motor 1023 to rotate and then is ejected from the drill bit 119; meanwhile, the turbine motor 1023 drives the axial flow pump 1024 to work, the drilling fluid in the third channel 1017 enters the axial flow pump 1024 from the suction port 120 of the axial flow pump 1024, is discharged from the discharge port 121, and enters the second channel 1016 from the outer sleeve 1022 through the conversion joint 1021. At this point the first passage 1015 and the second passage 1016 are filled with drilling fluid and the third passage 1017 is filled with drilling fluid 116, seawater 117 and the blocking gel 118.

As shown in fig. 1 and 2, the drilling fluid pumping flow control valve 103 can control the pumping flow Q of the drilling fluid into the inner pipe 1013 of the double-layer pipe 101 through the opening degree of the control valve_in(ii) a The drilling fluid is pumped into the flow meter 104, so that the volume of the drilling fluid entering the inner pipe 1013 of the double-layer pipe 101 in unit time can be monitored in real time; the axial flow pump backflow flow control valve 105 can control the return flow Q of the drilling fluid in the outer pipe 1014 of the double-layer pipe 101 through the opening degree of the control valve_out(ii) a The axial-flow pump reflux flowmeter 106 can monitor the volume of the drilling fluid returned from the outer pipe 1014 of the double-layer pipe 101 in unit time in real time;

as shown in fig. 1 and fig. 3, the liquid level monitoring sensor 107 can obtain the liquid level of the drilling fluid in the annulus between the double-layer pipe 101 and the casing 115 in real time and transmit the liquid level value to the valve group control unit 108 in real time, the liquid level monitoring sensor 107 is in a colloidal partition gel 118, and the partition gel 118 separates the seawater 117 from the drilling fluid 116 in the third channel 1017; the valve group control unit 108 can control the drilling fluid to be pumped into the flow control valve 103 and the axial flow pump backflow flow control valve 105 in real time according to the drilling fluid level signal;

as shown in fig. 1 and 2, the borehole pump 111 is connected to the inner tube 1013 of the double-walled pipe 101 by a drilling fluid pumping manifold 110 to form a drilling fluid pumping channel; the drilling fluid circulation tank 112 is connected with the outer pipe 1014 of the double-layer pipe 101 by a double-layer pipe return manifold 109 to form a return channel of the drilling fluid.

The control method of the deep-sea double-layer pipe bottom three-channel pressure control system comprises the following steps:

step S10, respectively installing the casing pipe 115 and the double-layer pipe 101 in the deep sea well;

step S20, filling partition gel 118 for isolating seawater 117 and drilling fluid 116 in an annulus between the casing pipe 115 and the double-layer pipe 101, and installing a liquid level monitoring sensor 107 for monitoring the liquid level of the partition gel 118;

step S30, the drilling pump 111 starts to work to pump the drilling fluid in the drilling fluid circulation tank 112 into the first channel 1015, and then the drilling fluid pumping flow Q is obtained in real time through the drilling fluid pumping flow meter_in(ii) a Real-time acquisition of axial flow pump reflux flow Q through axial flow pump reflux flowmeter_out(ii) a Acquiring the liquid level H of the drilling fluid in a third channel in real time through a liquid level monitoring sensor;

step S40, based on the drilling fluid level signal, the valve group control unit 108 controls the drilling fluid pumping flow control valve 103 and the axial flow pump backflow flow control valve 104, and the drilling fluid pumping flow Q is achieved by changing the opening degree of the valves_inAnd axial flow pump return flow Q_outThe regulation of (1), the flow change of the drilling fluid pumping manifold 110 is monitored in real time by the drilling fluid pumping flow meter 105, the flow change of the double-layer pipe return manifold 109 is monitored in real time by the axial flow pump return flow meter 106, and signals of the drilling fluid pumping flow meter 105 and the axial flow pump return flow meter 106 are fed back to the valve group control unit 108;

drilling fluid is pumped in through a first channel 1015, and the drilling fluid is pumped into a flow Q_inThe lift performance of the axial flow pump 102 can be changed when the pumping flow rate Q is measured_inWhen the rotational speed and torque of the turbine motor 1023 of the axial flow pump 102 increase, the rotational speed, the pump-out pressure and the pump-out flow of the axial flow pump 1024 increase, and when the pump-in flow Q increases_inWhen the rotation speed and the torque of the turbine motor 1023 are reduced, the rotation speed, the pump-out pressure and the pump-out flow rate of the axial flow pump 1024 are reduced;

drilling fluid is pumped through the second passage 1016 and the axial flow pump returns a flow rate Q_outCan change the lifting performance of the axial flow pump 1024 when the flow rate Q is returned_outWhen the flow rate is increased, the pumping pressure and the pumping head of the axial flow pump 1024 are decreased, and when the flow rate is returned Q_outWhen the pumping pressure and the pumping head of the axial-flow pump 1024 are reduced, the pumping pressure and the pumping head of the axial-flow pump are increased;

according to the drilling working condition, the pumping flow Q of the drilling fluid is reasonably matched_inAnd axial flow pump return flow Q_outThe lifting performance of the axial-flow pump 1024 is changed, and the change of the lifting performance can effectively adjust the liquid column pressure of the drilling fluid at the bottom of the well, namely adjust the liquid column pressure of the third channel 1017.

As shown in fig. 4, 5, 6 and 7, the drilling conditions are divided into three types: the first method comprises the following steps: when the well is normally drilled, the pressure at the bottom of the well and the formation pressure are in dynamic balance;

and the second method comprises the following steps: when the bottom hole pressure is less than the formation pressure, flooding occurs at the bottom hole and formation fluid invades.

And the third is that: when the bottom hole pressure is higher than the stratum pressure, the bottom hole is lost, and the drilling fluid is lost to enter the stratum.

When the ground fluid is invaded or the drilling fluid leaks, the liquid level of the drilling fluid in the third channel 1017 changes, the liquid level monitoring sensor 107 obtains the liquid level of the drilling fluid in the third channel 1017 in real time and sends a signal to the valve bank control unit 108, the valve bank control unit 108 changes the opening degrees of the drilling fluid pumping flow control valve 103 and the axial flow pump backflow flow control valve 105, and the drilling fluid pumping flow meter 104 and the axial flow pump backflow flow meter 105 respectively monitor Q_inAnd Q_outAnd fed back to the valve stack control unit 108 in real time. Q_inAnd Q_outThe reasonable matching of the axial flow pump 1024 can achieve a change in the lifting performance of the axial flow pump 1024. When the bottom hole pressure and the formation pressure reach a new balance point, the liquid level of the drilling fluid in the third channel 1017 does not change any more, the valve group control unit 108 stops adjusting the opening of the control valve, the axial flow pump 1024 maintains stable lifting performance, and the bottom hole equivalent density is ensured to be always within the range of a safe density window in the normal drilling process.

As shown in fig. 1, 3, 4 and 6, during normal drilling, the bottom hole pressure is equal to the formation pressure, and is determined by the seawater liquid column L and the drilling liquid column H in the third passage 1017. When the bottom hole pressure is higher than the stratum pressure, the bottom hole is lost, and the drilling fluid is lost and enters the stratum. The drilling fluid liquid level of the third channel 1017 is reduced from H in figure 6a to H1 in figure 6b, the seawater liquid column is increased from L to L1, the liquid level monitoring sensor 107 obtains that the drilling fluid liquid level of the third channel 1017 is reduced to H1 in real time, signals are sent to the valve bank control unit 108, the valve bank control unit 108 changes the opening degrees of the drilling fluid pumping flow control valve 103 and the axial flow pump backflow flow control valve 105, and the drilling fluid pumping flow meter 104 and the axial flow pump backflow flow meter 106 respectively monitor Q_inAnd Q_outAnd fed back to the valve stack control unit 108 in real time. At this time Q_inAnd Q_outThere may be three matching modes, ① Q_inIncrease, Q_outInvariable ② Q_inInvariable, Q_outDecrease ③ Q_inIncrease, Q_outDecrease; when Q is_inAnd Q_outDifference value Δ Q of>When the pressure of the drilling fluid in the third channel 1017 is indirectly reduced from the H1 in the second channel 1016 to the H2 in the FIG. 6c, the pressure of the drilling fluid in the third channel 1017 is reduced from the drilling fluid in the third channel H2 due to the fact that H in the FIG. 6b is increased to H1 in the FIG. 6c, the bottom hole pressure is determined by the seawater liquid column L2 and the drilling fluid column H2 in the third channel 1017, and as the seawater density is smaller than the drilling fluid density, the drilling fluid column is reduced from H1 to H2 due to the fact that the well depth is not changed, the bottom hole pressure is reduced, the seawater liquid column is increased from L1 to L2, and when the bottom hole pressure is reduced and the formation pressure reaches a new balance, the pressure regulation achieves the purpose of controlling leakage loss at the bottom hole.

As shown in fig. 1, 3, 4 and 7, during normal drilling, the bottom hole pressure is equal to the formation pressure, and the bottom hole pressure is determined by the seawater liquid column L and the drilling liquid column H in the third channel. When the bottom hole pressure is less than the formation pressure, flooding occurs at the bottom hole and formation fluid invades. The drilling fluid liquid level of the third channel 1017 is increased from H in the graph 7a to H3 in the graph 7b, the seawater liquid column is reduced from L to L3, the liquid level monitoring sensor 107 obtains that the drilling fluid liquid level of the third channel 1017 is increased to H3 in real time, signals are sent to the valve bank control unit 108, and the valve bank control unit 108 changes the drilling fluid pumping into the flow control valve 103 and the backflow flow of the axial flow pumpThe opening degree of the flow control valve 105, the Q of the drilling fluid pumping flow meter 104 and the Q of the axial flow pump backflow flow meter 106 are respectively monitored_inAnd Q_outAnd fed back to the valve stack control unit 108 in real time. At this time Q_inAnd Q_outThere may be three matching modes, Q_inInvariable, Q_outIncreasing; q_inDecrease, Q_outThe change is not changed; q_inDecrease, Q_outIncreasing; when Q is_inAnd Q_outDifference value Δ Q of<At 0, the suction capacity of the axial-flow pump 1024 is weakened, the outlet pressure is reduced, the lift of the axial-flow pump 1024 is reduced, the liquid column of the drilling fluid lifted in the second passage 1016 is reduced, the H in fig. 7b is reduced to H2 in fig. 7c, the liquid level of the drilling fluid in the third passage 1017 is indirectly reduced from H3 in fig. 7b to H4 in fig. 7c, the liquid level of the drilling fluid is increased to H4, the liquid column pressure of the third passage 1017 is increased, the bottom hole pressure is determined by the seawater liquid column L4 and the drilling fluid column H4 in the third passage 1017, the drilling fluid column is increased from H3 to H4 due to the fact that the seawater density is smaller than the density of the drilling fluid, the well depth is not changed, the drilling fluid column is increased from L3 to L4, the bottom hole pressure is increased to achieve new balance with the formation pressure, and the purpose of controlling bottom hole overflow is. And entering the normal drilling state again.

Although the present invention has been described with reference to the above embodiments, it should be understood that the present invention is not limited to the above embodiments, and those skilled in the art can make various changes and modifications without departing from the scope of the present invention.