Subsea Pump Arrangement for Borehole Pressure Control
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Solution Overview
Problem
Deep water drilling operations face challenges in controlling borehole fluid pressure due to constrained pressure margins between pore and fracture pressures, especially when drilling fluids pick up cuttings and debris, and in dual gradient and riserless drilling configurations where maintaining accurate pressure control is difficult.
Innovation Solution
A subsea pump arrangement is used to generate a fluid pressure in the drilling fluid that is less than or equal to the hydrostatic pressure on the seawater side of a sealing means, comprising a positive displacement pump driven by seawater and a centrifugal pump to control the pressure upstream of the pump, allowing for precise control of borehole pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If drilling fluid density is increased to maintain overbalanced drilling conditions, then borehole pressure control is improved, but the risk of exceeding fracture pressure and causing formation damage increases
Solution Approach 1:
The system dynamically adjusts the density of drilling fluid in the annulus by controlling the flow rate through the drill pipe. By varying the circulation rate, the ECD changes, allowing the system to maintain optimal borehole pressure that prevents both influx and formation fracturing, adapting in real-time to changing drilling conditions
Solution Approach 2:
The system uses pressure sensors to continuously monitor borehole pressure and annulus pressure, feeding this information back to the control system. Based on this feedback, the controller adjusts the drilling fluid density and flow rate to maintain pressure within the safe window between pore pressure and fracture pressure, preventing both well kicks and formation damage
2Productivity
If drilling fluid is circulated at high rate to carry cuttings, then borehole cleaning is improved, but equivalent circulating density increases and constrains pressure margins
Solution Approach 1:
The system segments the drilling fluid circulation into two separate paths: high-velocity flow through the drill pipe for effective cuttings transport, and controlled low-velocity flow in the annulus to minimize ECD. This segmentation allows independent optimization of both borehole cleaning and pressure control
Solution Approach 2:
The system changes the flow rate parameter dynamically - maintaining high flow rates through the drill pipe for cuttings removal while controlling annulus flow rate to keep ECD within acceptable limits. The control system adjusts these parameters in real-time to balance cleaning efficiency with pressure margin constraints
3Adaptability or versatility
If dual gradient drilling is implemented to expand drilling length, then pressure control flexibility is improved, but device complexity increases
Solution Approach 1:
The control system serves multiple functions: it regulates drilling fluid density, controls flow rates, monitors pressure conditions, and adjusts circulation parameters to achieve both overbalanced drilling and optimized cuttings removal. This multi-functionality reduces the need for separate specialized equipment for each function
Solution Approach 2:
The system uses a controlled flow of drilling fluid through the drill pipe as an intermediary mechanism to achieve dual gradient effects. By regulating the flow rate through the pipe, the system creates the desired pressure gradient in the annulus without requiring complex mechanical segmentation or multiple fluid systems
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enables effective control of borehole pressure, expanding the drilling length within safe pressure margins and reducing stresses on drilling equipment, particularly in deep water environments, by creating a dual gradient effect that helps maintain overbalanced drilling conditions.
Implementation Method 1
generate a fluid pressure in the drilling fluid at a location upstream of the pump arrangement, the generated pressure being less than or equal to the hydrostatic pressure of the fluid on the second side of the sealing means
Implementation Method 2
sealing means arranged to sealingly abut an outer surface of the drill pipe to separate the drilling fluid in the borehole on a first side of the sealing means from a fluid on a second side of the sealing means
Implementation Method 3
a subsea pump arrangement arranged to be located under a sea surface, the pump arrangement arranged to receive therein a flow of the drilling fluid from the borehole
Data Source
AI summary
There is described a technique for drilling and controlling the fluid pressure of a borehole (2, 102) during drilling of the borehole. In embodiments of the invention, drill pipe (5) may be arranged in said borehole, the pipe being configured to provide drilling fluid in the borehole. Sealing means (14, 18, 114, 118) may be provided and arranged to sealingly abut an outer surface of the drill pipe to separate said drilling fluid in the borehole on a first side of the sealing means from a column of fluid on a second side of the sealing means. Furthermore, a subsea pump arrangement (12, 112) may be arranged under a sea surface where it receives a flow of said drilling fluid from the borehole. The pump arrangement can operate to pump drilling fluid out of the pump arrangement, and generate a fluid pressure in said drilling fluid at a location upstream of the pump arrangement, said generated pressure being less than or equal to the hydrostatic pressure of said column of fluid on said second side of the sealing means.