Cable development for distributed geophysical sensing with a field trial in surface seismic

Abstract

Fibre-optic distributed sensing has the potential to revolutionize well and reservoir surveillance in the oil and gas industry. Benefits include the passive nature of optical fibre sensors, the potential for cost-effective installations, combined with the possibility of densely distributed measurements along the entire length of the fibre. Amongst a range of fibre-optic sensing technologies, Distributed Acoustic Sensing has the potential to provide a low cost alternative for conventional seismic technologies. To widen the geophysical application scope further, the fibre-optic sensing cable should be made more sensitive to incoming seismic waves that arrive at the cable perpendicular ("broadside") to its axial direction. We introduce the development of such cable concepts, and present results of a successful cable deployment in a surface seismic field trial. Efforts continue to realize cost-effective directionally-sensitive cables for geophysical use, for deployment down-hole and on surface. FIBRE-OPTIC SENSING IN THE OIL&GAS INDUSTRYThe passive nature and inherent long-term reliability of optical fibres, combined with the ability to string numerous individual sensing elements together in a single fibre, makes fibre-optic distributed sensing technology ideally suited for down-hole sensing along a full well path. A variety of fibre-optic sensors developed in the aerospace and defence industries are finding their way into the oil and gas industry, enabling measurement of quantities such as temperature, pressure, chemicals, strain and acoustics along the entire length of the fibre. As multiple fibres, each providing a specific distributed measurement, can be bundled in a single down-hole-deployable cable, the industry is encountering a unique opportunity for robust well and reservoir surveillance based on an abundance of measurements continuous in time and along the fibre's length 1 .In the oil and gas industry, seismic datasets provide a crucial source of information about the subsurface. The use of seismic surveys for finding new reservoirs with producible accumulations of hydrocarbons is widespread. More recently, seismic acquisition repeated during the productive lifetime of a field is becoming more common. This allows monitoring changes in the subsurface as a result of hydrocarbon production, and can help in optimising well integrity, subsurface models and production. Traditionally, electrical geophones have been used in onshore seismic surveys, either deployed on the surface or in a well-bore. Fibre-optic sensing technology provides an opportunity to replace these geophones by fibre-optic cables, offering the potential of reducing cost substantially while increasing the spatial sensor resolution dramatically.This paper focuses on the use of Distributed Acoustic Sensing for geophysical use. We will explain how the construction of fibre-optic cables confines the directional sensitivity, and we will present the development and testing of improved sensing cables.

Interaction of helically wound fibre‐optic cables with plane seismic waves

“…The concept of a cable with helically wound fibres (helically wound cable or HWC) has been recently proposed and tested in the field. The results were partially reported by den Boer et al (2013), Hornman et al (2013), Lumens et al (2013), and Mateeva et al (2014). In this paper we explain the theory of a helically wound fibre-optic cable in more detail.…”

Distributed acoustic sensing for reservoir monitoring with vertical seismic profiling

“…This is not a ma-jor limitation for P waves in a classical VSP geometry (near-vertical well, near-horizontal layering) but it gets restrictive for strongly deviated wells and for S waves in vertical wells. To overcome this limitation, broadsidesensitive cables are being developed , Lumens et al, 2013. A brief summary is given in the next section.…”

Distributed acoustic fibre optic sensors for condition monitoring of pipelines

“…Promising tests with a pipe that was helically enwinded by the optical sensor have lately been carried out showing a very high sensitivity of the system. Combinations of different directionalities of sensor fibres may enable detection of specific propagation modes of sound waves as has recently been shown for seismic waves [9]. Another focus of the project will be the analysis of acoustic signatures from different realistic damage cases, which will be simulated by bending tests and field trials.…”