Technology Update: Distributed Fiber-Optic Technologies Drive New Intervention Applications

Abstract

Technology Update Downhole data acquisition by fiberoptic technology, particularly distributed fiber-optic (DFO) sensing, has gained rapid acceptance. Compared with conventional data acquisition, DFO provides a much better understanding of well and reservoir behavior. Reflecting this trend is the increasing number of well completions equipped with permanent fibers. However, many fibers have been installed only above the production packer and thus are unable to monitor the dynamic changes in the reservoir. During the past several years, Ziebel has developed well intervention technologies for obtaining DFO data from wells without permanent fibers, wells in which fiber installations end above the production packer, and wells in which installed fiber systems have failed. The company offers two methods of collecting this data. They are as follows: The Z-System consists of a composite carbon rod, 15 mm in diameter, containing multiple fiber-optic cables. The rod is safely injected into producing or injecting wells. It is semi-stiff and can achieve a long reach into horizontal wells in an installation similar to conveyance by a light coiled-tubing (CT) string without the need for a well tractor. The new gravity-deployed Z-Line is a composite carbon line, 4.8 mm in diameter, that is designed to be run on wireline units. Its DFO sensing capability is equally effective in all well sections from vertical to highly deviated. However, its extremely high strength-to-weight ratio, coupled with its low friction coefficient to steel and extra stiffness compared with wireline, enhances its reach into highly deviated sections (Fig. 1). So far, the data obtained by these two technologies have been used largely for water and polymer injection allocation, optimizing production, or for monitoring well integrity. Looking ahead, the company plans to expand the use of these technologies to monitor sand production and downhole injection processes in real time to assess stimulation efficiency. Improving the interpretation of DFO data remains a major focus. Identifying Sand Ingress Zones Existing techniques for detecting produced sand are primarily limited to surface detection by acoustic sensors. While sufficiently accurate and timely to warn of a developing problem downhole, these methods are unable to determine the depth from which the sand originates, an essential factor for planning remedial treatment.