1. A method of wellbore flow control based on a dual coiled tubing dual gradient drilling system comprising: the deepwater drilling platform is arranged on the surface of the seawater layer; the double-layer continuous pipe is formed by sleeving a bent inner pipe and a bent outer pipe, the upper end of the double-layer continuous pipe is connected with the deepwater drilling platform, and the lower end of the double-layer continuous pipe penetrates through a seawater layer and a shallow mud layer and extends into a hydrate layer; the surface layer conduit is arranged in the shallow mud layer and sleeved outside the double-layer continuous pipe; the underground lifting pump is arranged at the lower end of the double-layer continuous pipe; the runner adapter is connected with the lower end of the double-layer continuous pipe; a downhole tool assembly connected to the flow passage crossover sub; a drill bit coupled to the downhole tool assembly; the method for controlling the flow of the well shaft is characterized by comprising the following steps of:

1) the drilling fluid enters the underground lifting pump from the annular space of the double-layer continuous pipe through the drilling pump of the deepwater drilling platform, enters the inner pipe of the double-layer continuous pipe through the flow passage conversion joint, enters the well bottom through the drill bit water hole after passing through the inner pipe of the underground tool combination, and forms pressure balance in the process of entering the well bottom; the motor of the downhole tool combination is driven by drilling fluid water power to convert hydraulic energy into mechanical energy to provide power for the rotation of the downhole lifting pump and the drill bit;

2) the drilling fluid enters an annular space of the downhole tool combination from the return hole, enters an inner pipe of the double-layer coiled tubing through the flow passage conversion joint, returns to the platform through the downhole lifting pump, and forms pressure balance in the return process.

2. The wellbore flow control method of claim 1, wherein the pressure balance relationship during pumping of the drilling fluid from the platform to the bottom hole in step 1) is as follows:

p_b＝p_sp+ρgh-Vp_a-Vp_tp-Vp_bit (1)

in the formula, p_bBottom hole pressure; p is a radical of_spIs the riser pressure; rho is the drilling fluid density; h is the borehole vertical depth; vp_aThe annular pressure loss of the double-layer pipe is avoided; vp_tpInternal cavity pressure loss for downhole tool assembly; vp_bitThe drill bit is pressed and consumed.

3. The wellbore flow control method of claim 1, wherein the pressure balance relationship during the drilling fluid flowing from the bottom of the well to the platform in step 2) is as follows:

p_b＝p_s+ρgh-Vp_p-Vp_ta-Vp_pump (2)

in the formula, p_bBottom hole pressure; p is a radical of_sIs the wellhead pressure; rho is the drilling fluid density; h is the borehole vertical depth; vp_pThe pressure loss in the double-layer pipe is realized; vp_taAnnular pressure loss for downhole tool assembly; vp_pumpThe pressure energy provided for the underground lifting pump.

4. The wellbore flow control method of claim 1, wherein in step 2), the bottom hole equivalent circulating density is:

wherein rho is the bottom hole equivalent circulating density; p is a radical of_sIs the wellhead pressure; rho is the drilling fluid density; h is the borehole vertical depth; vp_pThe pressure loss in the double-layer pipe is realized; vp_taAnnular pressure loss for downhole tool assembly; vp_pumpThe pressure energy provided for the underground lifting pump.

5. The wellbore flow control method of claim 1, wherein the drilling process of the double-layer coiled tubing dual gradient drilling system is divided into two stages: firstly, drilling to a target well depth in a well drilling mode, then switching to a well cleaning mode, dragging a pipe column to and fro in a reservoir section to clean a well shaft and a hydrate in a near-wellbore area, and returning to a deepwater drilling platform through an underground lifting pump and a double-layer continuous pipe.

6. The wellbore flow control method of claim 5, wherein the operational flow of the wellbore drilling mode and the wellbore cleaning mode is as follows:

(1) borehole drilling mode: pumping drilling fluid to the underground from an annular space of the double-layer coiled tubing at sea surface, entering an inner tube of the underground tool combination through the flow passage conversion joint, driving an underground motor through hydrodynamic force of the drilling fluid, entering a formation annular space through a drill bit water hole, entering the annular space of the underground tool combination from the return hole, entering the inner tube of the double-layer coiled tubing through the flow passage conversion joint, and returning to the ground through the underground lifting pump;

(2) a borehole cleaning mode: the method comprises the steps of pressing and switching a flow channel of the underground tool through the ground, opening a water hole for communicating the underground tool with the formation annulus, opening a well hole cleaning mode of the double-layer coiled tubing double-gradient drilling system, cleaning mineral particles gathered in the annulus at the bottom of the well by pulling out and putting down the double-layer coiled tubing, and avoiding circulation of drilling fluid in the annulus between the well hole and the double-layer coiled tubing.

Background

The marine natural gas hydrate in China has abundant resources, most of the marine natural gas hydrate exists in a seabed surface layer and a shallow layer argillaceous silt deposit layer, has no compact cover layer, has symbiotic property with oil gas, has the problems of buried depth, weak cementation, drainage and extraction, flow blockage, environmental risk prevention and control and the like, and a safe and economic drilling method is the key for exploration and development of the deep-water shallow hydrate.

Due to the fact that the pressure of an overlying rock layer is low, a shallow stratum is loose, a window between pore pressure and fracture pressure is narrow due to the fact that a seawater section is formed, a single drilling fluid density is adopted in conventional deep water drilling, complex conditions such as serious leakage and the like are prone to occurring in the hydrate drilling process, drilling operation risks and cost are increased, even well hole abandonment and environmental disasters can be caused, and the requirements for exploration and development cannot be met based on the existing conventional oil gas drilling and mining theory.

The solid fluidization method is a new method for exploration and development of deep water shallow hydrates, a hydrate reservoir is broken into fine particles through bottom hole jet flow, fluidized solid-phase particles containing the hydrates are returned to a sea surface platform along a shaft along with drilling fluid, and finally natural gas is obtained through separation. Although the method solves the problems of sand production and the like of the non-diagenetic hydrate in the deep water shallow layer, the trial production time, the yield and the like have great difference with the economic development threshold. The problems of stratum looseness, low leakage pressure and the like in deep water shallow parts are bottlenecks which restrict exploration and development of marine natural gas hydrates, and a new drilling method is urgently needed to solve the problems.

Disclosure of Invention

In view of the above problems, an object of the present invention is to provide a wellbore flow control method based on a dual-layer coiled tubing dual-gradient drilling system, which can improve the operation efficiency, reduce the occurrence of downhole complications, ensure the operation safety, and reduce the operation cost.

In order to achieve the purpose, the invention adopts the following technical scheme:

the invention relates to a wellbore flow control method based on a double-layer continuous pipe double-gradient drilling system, which comprises the following steps: the deepwater drilling platform is arranged on the surface of the seawater layer; the double-layer continuous pipe is formed by sleeving a bent inner pipe and a bent outer pipe, the upper end of the double-layer continuous pipe is connected with the deepwater drilling platform, and the lower end of the double-layer continuous pipe penetrates through a seawater layer and a shallow mud layer and extends into a hydrate layer; the surface layer conduit is arranged in the shallow mud layer and sleeved outside the double-layer continuous pipe; the underground lifting pump is arranged at the lower end of the double-layer continuous pipe; the runner adapter is connected with the lower end of the double-layer continuous pipe; a downhole tool assembly connected to the flow passage crossover sub; a drill bit coupled to the downhole tool assembly; the wellbore flow control method comprises the following steps:

1) the drilling fluid enters the underground lifting pump from the annular space of the double-layer continuous pipe through the drilling pump of the deepwater drilling platform, enters the inner pipe of the double-layer continuous pipe through the flow passage conversion joint, enters the well bottom through the drill bit water hole after passing through the inner pipe of the underground tool combination, and forms pressure balance in the process of entering the well bottom; the motor of the downhole tool combination is driven by drilling fluid water power to convert hydraulic energy into mechanical energy to provide power for the rotation of the downhole lifting pump and the drill bit;

2) the drilling fluid enters an annular space of the downhole tool combination from the return hole, enters an inner pipe of the double-layer coiled tubing through the flow passage conversion joint, returns to the platform through the downhole lifting pump, and forms pressure balance in the return process.

In the method for controlling wellbore flow, preferably, the pressure balance relation during the pumping of the drilling fluid from the platform to the bottom of the well in step 1) is as follows:

p_b＝p_sp+ρgh-Vp_a-Vp_tp-Vp_bit (1)

in the formula, p_bBottom hole pressure; p is a radical of_spIs the riser pressure; rho is the drilling fluid density; h is the borehole vertical depth; vp_aThe annular pressure loss of the double-layer pipe is avoided; vp_tpInternal cavity pressure loss for downhole tool assembly; vp_bitThe drill bit is pressed and consumed.

In the wellbore flow control method, preferably, the pressure balance relation in the process of flowing the drilling fluid from the bottom to the platform in the step 2) is as follows:

p_b＝p_s+ρgh-Vp_p-Vp_ta-Vp_pump (2)

in the formula, p_bBottom hole pressure; p is a radical of_sIs the wellhead pressure; rho is the drilling fluid density; h is the borehole vertical depth; vp_pThe pressure loss in the double-layer pipe is realized; vp_taAnnular pressure loss for downhole tool assembly; vp_pumpThe pressure energy provided for the underground lifting pump.

The wellbore flow control method preferably comprises, in the step 2), the bottom hole equivalent circulating density:

wherein rho is the bottom hole equivalent circulating density; p is a radical of_sIs the wellhead pressure; rho is the drilling fluid density; h is the borehole vertical depth; vp_pThe pressure loss in the double-layer pipe is realized; vp_taAnnular pressure loss for downhole tool assembly; vp_pumpThe pressure energy provided for the underground lifting pump.

The wellbore flow control method preferably comprises the following two steps: firstly, drilling to a target well depth in a well drilling mode, then switching to a well cleaning mode, dragging a pipe column to and fro in a reservoir section to clean a well shaft and a hydrate in a near-wellbore area, and returning to a deepwater drilling platform through an underground lifting pump and a double-layer continuous pipe.

The wellbore flow control method preferably comprises the following operation flows of a wellbore drilling mode and a wellbore cleaning mode:

(1) borehole drilling mode: pumping drilling fluid to the underground from an annular space of the double-layer coiled tubing at sea surface, entering an inner tube of the underground tool combination through the flow passage conversion joint, driving an underground motor through hydrodynamic force of the drilling fluid, entering a formation annular space through a drill bit water hole, entering the annular space of the underground tool combination from the return hole, entering the inner tube of the double-layer coiled tubing through the flow passage conversion joint, and returning to the ground through the underground lifting pump;

(2) a borehole cleaning mode: the method comprises the steps of pressing and switching a flow channel of the underground tool through the ground, opening a water hole for communicating the underground tool with the formation annulus, opening a well hole cleaning mode of the double-layer coiled tubing double-gradient drilling system, cleaning mineral particles gathered in the annulus at the bottom of the well by pulling out and putting down the double-layer coiled tubing, and avoiding circulation of drilling fluid in the annulus between the well hole and the double-layer coiled tubing.

Due to the adoption of the technical scheme, the invention has the following advantages:

1. the double-layer continuous pipe is adopted for drilling operation, a circulation loop of drilling fluid can be established without lowering a marine riser, and a drilling column is connected or detached without stopping a pump and interrupting circulation in the process of tripping the drilling string, so that the stability of bottom hole pressure is favorably kept, and the rock carrying efficiency is favorably improved.

2. The pressure of drilling fluid in the annulus of the wellbore in the stratum is reduced by the power provided by the underground lifting pump, so that the pressure profile of a liquid column in the annulus of the wellbore in the stratum is effectively matched with the pore pressure and the fracture pressure window of the stratum, and the contradiction between the deep water shallow layer loosening and the low leakage pressure is relieved.

In a word, the double-layer coiled tubing double-gradient drilling can improve the operation efficiency, reduce the occurrence of underground complex conditions, ensure the operation safety and reduce the operation cost.

Drawings

FIG. 1 is a schematic structural view of a dual-coiled tubing dual-gradient drilling system according to the present invention;

FIG. 2 is a graph comparing pressure distribution in a dual-layer coiled tubing dual-gradient drilling wellbore of the present invention with conventional drilling;

FIG. 3 is a schematic representation of the combined flow of downhole tools in a wellbore drilling mode in accordance with the present invention;

FIG. 4 is a schematic representation of the downhole tool combination flow in the wellbore cleanout mode of the present invention.

The reference numerals in the figures are as follows:

1-a deepwater drilling platform; 2-double-layer continuous pipe; 3-surface layer catheter; 4-underground lifting pump; 5-flow channel conversion joint; 6-downhole tool combination; 7-drill bit.

Detailed Description

The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings so that the objects, features and advantages of the invention can be more clearly understood. It should be understood that the embodiments shown in the drawings are not intended to limit the scope of the present invention, but are merely intended to illustrate the spirit of the technical solution of the present invention.

As shown in fig. 1, the present invention relates to a double-layer coiled tubing dual gradient drilling system, comprising: the deepwater drilling platform 1 is arranged on the surface of the seawater layer; the double-layer continuous pipe 2 is formed by sleeving a bent inner pipe and a bent outer pipe, the upper end of the double-layer continuous pipe 2 is connected with the deepwater drilling platform 1, and the lower end of the double-layer continuous pipe penetrates through a seawater layer and a shallow mud layer and extends into a hydrate layer; the surface layer conduit 3 is arranged in the shallow mud layer and is sleeved outside the double-layer continuous pipe 2; the underground lifting pump 4 is arranged at the lower end of the double-layer continuous pipe 2; the runner adapter 5 is connected with the lower end of the double-layer continuous pipe 2; the downhole tool combination 6 is connected with the flow passage conversion joint 5; and a drill bit 7 connected with the downhole tool assembly 6.

The invention relates to a shaft flow control method based on a double-layer continuous pipe double-gradient drilling system, which comprises the following steps:

1) the drilling fluid enters an underground lifting pump from the annular space of a double-layer continuous pipe through a drilling pump of a deepwater drilling platform, enters an inner pipe of the double-layer continuous pipe through a flow passage conversion joint, enters the bottom of a well through a drill bit water hole after passing through the inner pipe of an underground tool combination, and forms pressure balance in the process of entering the bottom of the well; the motor of the downhole tool combination is driven by drilling fluid water power to convert hydraulic energy into mechanical energy to provide power for the rotation of the downhole lifting pump and the drill bit;

the pressure balance relation during the pumping of the drilling fluid from the platform to the bottom hole is as follows:

p_b＝p_sp+ρgh-Vp_a-Vp_tp-Vp_bit (1)

in the formula, p_bBottom hole pressure; p is a radical of_spIs the riser pressure; rho is the drilling fluid density; h is the borehole vertical depth; vp_aThe annular pressure loss of the double-layer pipe is avoided; vp_tpInternal cavity pressure loss for downhole tool assembly; vp_bitThe drill bit is pressed and consumed.

2) The drilling fluid enters an annular space of the downhole tool combination from the return hole, enters an inner pipe of the double-layer coiled tubing through the flow passage conversion joint, returns to the platform through the downhole lifting pump, and forms pressure balance in the return process.

The pressure balance relation of the drilling fluid in the process of flowing from the bottom to the platform is as follows:

p_b＝p_s+ρgh-Vp_p-Vp_ta-Vp_pump (2)

in the formula, p_bBottom hole pressure; p is a radical of_sIs the wellhead pressure; rho is the drilling fluid density; h is the borehole vertical depth; vp_pThe pressure loss in the double-layer pipe is realized; vp_taAnnular pressure loss for downhole tool assembly; vp_pumpThe pressure energy provided for the underground lifting pump.

The bottom hole equivalent circulating density is:

wherein rho is the bottom hole equivalent circulating density; p is a radical of_sIs the wellhead pressure; rho is the drilling fluid density; h is the borehole vertical depth; vp_pThe pressure loss in the double-layer pipe is realized; vp_taAnnular pressure loss for downhole tool assembly; vp_pumpThe pressure energy provided for the underground lifting pump.

In the double-layer continuous pipe double-gradient drilling circulation process, the pressure required by the drilling fluid to return to the bottom of the platform is reduced through the pressure energy provided by the underground lifting pump, so that the equivalent circulation density of the bottom of the well is effectively reduced, the bottom pressure of the well is within a stratum safety density window, the double-gradient effect is achieved, and the problem of leakage of deep-water loose shallow hydrate drilling can be effectively solved.

The pressure distribution of the double-layer continuous pipe double-gradient drilling shaft is shown in figure 2, the larger the pressure energy provided by the lifting pump is, the larger the reduction amplitude of the bottom hole pressure is, and the lower the bottom hole equivalent circulation density is. The power of the underground lifting pump is provided by the underground motor, and the output power of the underground motor can be increased by increasing the discharge capacity of the drilling fluid, so that the power provided by the underground lifting pump for returning the drilling fluid is increased. Meanwhile, the on-way pressure loss of the drilling fluid returning to the platform is increased along with the increase of the displacement. Therefore, hydraulic parameters need to be optimized by combining parameters such as well structure, drilling tool size and the like, and a basis is provided for controlling bottom hole pressure.

The double-layer continuous pipe double-gradient drilling process comprises two stages, firstly, drilling to a target well depth in a drilling mode, then switching to a cleaning mode, dragging a pipe column to and fro in a reservoir stratum section to clean a shaft and a hydrate in a near wellbore area, and returning to a platform through a lifting system. The operation flows of the two working modes are as follows:

(1) borehole drilling mode: pumping drilling fluid from the annular space of the double-layer coiled tubing to the underground at sea surface, entering the inner tube of the downhole tool string combination through the flow passage conversion joint, driving the downhole motor through the hydrodynamic force of the drilling fluid, entering the formation annular space through the drill bit water hole, entering the annular space of the downhole tool string combination from the return hole, entering the inner tube of the double-layer coiled tubing through the flow passage conversion joint, and returning to the ground through the downhole lifting pump, wherein the flow process in the downhole tool combination is shown in fig. 3.

(2) A borehole cleaning mode: the flow channel of the downhole tool is switched by pressing the ground, a water hole communicated between the downhole tool and the formation annulus is opened, the well hole cleaning mode of the double-layer coiled tubing double-gradient drilling system is started, the mineral particles gathered in the annulus at the bottom of the well are cleaned by pulling out and putting down the double-layer coiled tubing, no drilling fluid circulates in the annulus between the well hole and the double-layer coiled tubing, and the flow process in the downhole tool combination is shown in figure 4.

In the operation process, the free switching between the two modes of surface pumping can be implemented according to the operation requirement through the pressure monitoring of the shaft and the cleaning condition of the shaft until the operation task is completed, the double-layer pipe column is taken out, and the underground tool combination is recovered.

Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.