Concentric Drillstring Subsea Pump Pressure Control
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Solution Overview
Problem
In deep-water offshore drilling, the reduced differential between pore and fracture pressures requires more frequent installation of short casing joints, increasing drilling time and cost due to the need to isolate wellbore pressure sections.
Innovation Solution
A well system and method utilizing a concentric drillstring and subsea pump to manage fluid pressure by circulating drilling fluid and a hydrostatic fluid with greater density than the drilling fluid, controlling the height of the hydrostatic fluid column in the wellbore to maintain optimal pressure conditions, thereby reducing the need for frequent casing installations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If drilling fluid weight is increased to prevent formation fluid influx, then wellbore pressure control is improved, but fracture pressure of the formation is exceeded causing formation damage
Solution Approach 1:
The system dynamically adjusts the density parameter of the drilling fluid by injecting hydrostatic fluid (greater density) into the wellbore to increase hydrostatic pressure control capability. This allows maintaining wellbore pressure above pore pressure to prevent formation fluid influx while staying below fracture pressure to avoid formation damage, resolving the contradiction through parameter optimization.
Solution Approach 2:
Hydrostatic fluid serves as an intermediary substance injected into the wellbore to provide additional hydrostatic pressure. This intermediary fluid enables precise pressure control between the pore pressure threshold (to prevent influx) and fracture pressure threshold (to avoid formation damage), allowing the drilling fluid to maintain optimal pressure without directly causing formation fracture.
2Reliability
If more frequent casing joints are installed to isolate pressure sections, then wellbore pressure isolation is improved, but drilling time and operational cost increase
Solution Approach 1:
The system replaces the mechanical approach of using frequent casing joints for pressure isolation with a fluid dynamic approach using hydrostatic pressure control. By injecting hydrostatic fluid to maintain optimal wellbore pressure, the system eliminates the need for frequent mechanical isolation barriers, thereby reducing drilling time and operational complexity while maintaining pressure control reliability.
Solution Approach 2:
By changing the pressure control mechanism from mechanical isolation (casing joints) to hydrostatic pressure control (fluid density adjustment), the system achieves the same pressure isolation reliability with fewer interruptions to drilling operations, directly reducing time loss and operational cost.
3Reliability
If drilling fluid density is increased to maintain hydrostatic pressure, then wellbore pressure control is improved, but the differential between pore and fracture pressures is reduced
Solution Approach 1:
The system uses dynamic injection of hydrostatic fluid to adjust wellbore pressure in real-time based on drilling depth and formation conditions. This dynamic control allows maintaining optimal pressure differential margin between pore and fracture pressures while achieving reliable hydrostatic pressure control, adapting to changing conditions without fixed fluid density.
Solution Approach 2:
Hydrostatic fluid acts as an intermediary that provides flexible pressure control without requiring the drilling fluid itself to have excessively high density. This intermediary approach maintains a healthy pressure differential margin while achieving the necessary hydrostatic pressure control through the injected hydrostatic fluid column.
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 approach allows for extended drilling intervals without fracturing the formation, reducing the number of casing joints needed and lowering operational costs by maintaining optimal fluid pressure within the wellbore, thus enhancing drilling efficiency and reducing the time required to reach target depths.
Implementation Method 1
a subsea pump in fluid communication with the wellbore, wherein the subsea pump is configured to manage fluid pressure in the wellbore by controlling a height of a column of hydrostatic fluid disposed in the wellbore
Implementation Method 2
a concentric drillstring extending from the vessel into a subterranean wellbore disposed beneath a mudline, wherein the concentric drillstring is configured to circulate a drilling fluid from the drilling vessel into the wellbore along a first passage, and to circulate the drilling fluid from the wellbore to the drilling vessel along a second passage
Implementation Method 3
a rotating control device (RCD) positioned along the marine riser and configured to seal against an outer surface of the concentric drillstring while permitting relative rotation between the drillstring and the marine riser
Data Source
AI summary
A well system includes a drilling vessel, a concentric drillstring extending from the vessel into a subterranean wellbore disposed beneath a mudline, wherein the concentric drillstring is configured to circulate a drilling fluid from the drilling vessel into the wellbore along a first passage, and to circulate the drilling fluid from the wellbore to the drilling vessel along a second passage, and a subsea pump in fluid communication with the wellbore, wherein the subsea pump is configured to manage fluid pressure in the wellbore by controlling a height of a column of hydrostatic fluid disposed in the wellbore.