Requirements, Constraints and Advantages of Fiber Optic Sensor Arrays for Permanent Offshore Applications
Authors: Houston Mark H. 
Published: October 2008

Evolving technical and economic requirements in reservoir monitoring are driving the introduction of permanent reservoir seismic systems. A step function increase in seismic resolution in the inter-well space at the reservoir level requires improvements in seismic acquisition that are beyond evolutionary changes to standard data acquisition systems commonly in use today. Seabed and borehole receivers and sources will acquire seismic data with greatly improved reliability and resolution. However, cost and a viable business model for all E&P stakeholders are formidable barriers to widespread investment in permanent systems. Fiber optic sensor systems offer several advantages in performance and cost over conventional systems for permanent receiver arrays.

Introduction

A convergence of population demographics, economic pressure and technology waves is driving the upstream Exploration & Production sector of our industry to a Net- Centric vision of asset management. Our industry must rely on technology to boost performance through higher oil and gas recovery, improved efficiencies, improved productivity and lower costs in a climate of volatile oil prices, a background of weakened investor confidence, and a continual downsizing of the E&P personnel base.

The Electric Oil Field or Digital Oil Field is a vision for the future that will have a profound impact on how we do business in the upstream sector. The Digital Oil Field will have the same transformational impact on our business as the concept of Network-Centric Warfare has had on the US military's ability to dominate todays battlefield. Using technologies developed during the 1970's and 1980's, the US military has introduced a command and control structure that converts every vehicle and platform in the battle theater into a detector and sensor source. Fiber-optic networks, broadband satellite and cellular links bring information into central nodes in real time. Military knowledge managers, as the focal points within this command structure, direct plug-and-play teams to deliver on-point action responses.1. 2.

Real-time asset management capabilities will require development of new hardware, software and decision process structures:Hardware for comprehensive real-time data acquisition, downhole Intelligent Well controls and command-control connectivity;Software to integrate enormous quantities and disparate types of data; andBusiness processes to enact timely decision management of the assets. In this paper, we will examine the rationale for permanent seismic systems and briefly discuss some of the business drivers. An outline of requirements, constraints and barriers to more widespread installation of offshore permanent seismic receiver arrays forms a backdrop to the presentation of several alternative scenarios for a permanent deep-water monitoring system. WAG?cost estimates for traditional acquisition technology illustrate the magnitude of investment required for these offshore monitoring systems. Fiber-optic based sensor/telemetry systems offer several advantages for permanent seismic monitoring systems.

Rationale for Permanently Installed Seismic Systems

Why do we need permanently installed seismic arrays? Why can't we do the same reservoir monitoring tasks with retrievable systems that can be installed and used as needed?

In truth, we can achieve equivalent 3-D results with a retrievable seismic array as with a permanently installed array, but not equivalently reliable 4-D results.