Offshore Downhole Telemetry via Subsea Floor Cable
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Solution Overview
Problem
Conventional bi-directional electromagnetic (EM) telemetry systems face challenges in offshore drilling due to difficulties in deploying counter electrodes in varying water depths and the presence of subsea infrastructure, limiting data transmission rates and accessibility.
Innovation Solution
An offshore EM telemetry system that includes a subsea telemetry cable with electrodes positioned on the sea floor, coupled to an umbilical cable extending to a surface communication unit, allowing for real-time bidirectional communication between the bottomhole assembly and the surface, using capacitive coupling and wireless links to overcome deployment and infrastructure limitations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a surface-deployed counter electrode is used in conventional EM telemetry systems, then bidirectional communication can be achieved, but deployment becomes extremely difficult in offshore environments with varying water depths and subsea infrastructure
Solution Approach 1:
The patent introduces a subsea cable with electrodes as an intermediary component deployed on the sea floor, which mediates between the downhole BHA and the surface control system. This subsea cable serves as a fixed infrastructure that eliminates the need to deploy counter electrodes through water column, thereby resolving the deployment difficulty while maintaining adaptability across various water depths.
Solution Approach 2:
The patent transitions the counter electrode deployment from a vertical dimension (through water column from surface) to a horizontal dimension (on sea floor). By placing electrodes on the sea floor rather than deploying them vertically through water, the system avoids the complexities of varying water depths and subsea infrastructure obstacles.
2Reliability
If direct electrical coupling to the wellhead is used, then reliable signal transmission is achieved, but the system becomes vulnerable to electrode degradation and environmental changes
Solution Approach 1:
The patent extracts the electrodes from direct contact with the wellhead environment and places them on the sea floor. This separation removes the electrodes from harmful environmental factors such as wellhead corrosion, high temperatures, and pressure fluctuations, thereby reducing electrode degradation while maintaining reliable signal transmission through the subsea cable infrastructure.
Solution Approach 2:
The patent employs capacitive coupling as a protective mechanism that cushions the signal transmission against environmental variations and electrode degradation. The capacitive coupling allows signal transmission while providing electrical isolation, thereby protecting the system from harmful factors before they can cause damage.
3Duration of action of moving object
If EM telemetry operates at frequencies between 1 and 15 Hz, then continuous operation during all drilling activities is enabled, but data transmission rates remain limited to 3-12 bps
Solution Approach 1:
The patent implements a multi-channel communication system where multiple electrodes on the subsea cable can simultaneously transmit and receive signals. This universal infrastructure supports both continuous operation during all drilling activities and higher data transmission rates by utilizing multiple communication channels in parallel, thereby resolving the contradiction between continuous operation and data rate limitations.
4Adaptability or versatility
If subsea infrastructure (BOP, riser, pipelines) is present, then offshore drilling operations are enabled, but direct access to wellhead and cable placement are precluded
Solution Approach 1:
The patent places the communication infrastructure on the sea floor rather than requiring access to the wellhead area. This dimensional change allows the subsea cable with electrodes to be deployed in the horizontal plane on the sea floor, avoiding obstacles in the vertical wellhead area such as BOP, riser, and pipelines, while still enabling offshore drilling operations.
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
Enables higher data rates and continuous operation in any water depth, eliminating the need for direct electrical coupling to the wellhead, reducing electrode degradation, and providing a non-contact design that is resilient to environmental changes, thus surpassing the limitations of conventional systems.
Implementation Method 1
A telemetry transmitter positioned in the bottomhole assembly transmits a telemetry signal to the subsea telemetry cable on the sea floor
Implementation Method 2
A subsea telemetry cable positioned on a sea floor having a plurality of electrodes positioned therein, wherein the telemetry transmitter is adapted to transmit a telemetry signal from the bottomhole assembly to the subsea telemetry cable
Data Source
AI summary
An offshore measured or logging-while drilling electromagnetic telemetry system includes a bottomhole assembly having a transmitter to communicate one or more electromagnetic telemetry signals. A subsea telemetry cable is positioned on a sea floor to receive the telemetry signals. The subsea telemetry cable is coupled to an umbilical cable extending to a surface communication unit positioned at the sea surface. Signals received by the subsea telemetry cable are transmitted to the surface communication unit for further processing.