Clarion system calls for new approach to downhole seismic in reservoir management

Seismic technology traditionally has played a role in exploration, rather than production, of hydrocarbons. Weatherford, one of the big oil services companies, believes that its new optical seismic sensing system is changing the way the industry applies the technology. After four years of development and field testing, its permanent, in-well Clarion system is now being commercially deployed on a worldwide basis and integrated with other permanent optical sensing products and in-well flow controls for production optimization and reservoir management. Tad Bostick, vice president of business development for Weatherford's Intelligent Completions group, describes the background to the development. In the late 1970s and early 1980s, the industry began to recognize the potential of in-well seismic methods for improving exploration success, reducing drilling costs, controlling uncertainties and improving productivity. These years witnessed an explosive growth of interest in, and use of, vertical seismic profiling (VSP). The conventional seismic check shot survey was transformed to VSP when more well positions were occupied and the entire wavefield sampled by downhole geophones was processed. The acquired seismic signature of the earth was used for independently checking and correlating the surface seismic response. Placement of subsurface sensors, direct measurement of velocities and time versus depth, and the ability to link between the different scales of the various data, enabled comprehensive calibration of surface seismic with well information. Offsetting the source from the receiver (offset vertical seismic profiling, or OVSP) provided higher-resolution structural and stratigraphic images than did surface seismic profiling, despite a spatially limited investigation; but singlelevel tools were costly in terms of rig time, and rudimentary processing restricted widespread adoption of OVSP technology. The popularity of surveys using multi-source positions at surface with fewer well stations, together with the introduction of multilevel three-component (3C) tools, renewed interest in borehole seismic techniques in the late 1980s. In the following decade, the focus of research turned to further integration of surface seismic data, core data, and well logs. Borehole seismic profiling was the natural link; but the geophysical data extracted from this technique were not reliable enough, and acquisition costs were prohibitive. Unfortunately, the price of oil dropped at this time and oil companies restructured to meet increased pressure on nearterm financial targets, significantly curtailing further research. However, the perseverance of a few and some advances in acquisition and processing techniques ultimately made possible the provision of cost-effective borehole seismic data of the required quality. The most significant technical breakthrough was the introduction of more reliable, higher-capacity, multilevel 3C tools, which allowed rapid, simultaneous data acquisition from many levels. Better understanding of seismic wave theory yielded comprehensive 3C processing, resulting in more complete P- and S-wave images. Newer seismic techniques, such as hydraulic fracture mapping and micro-seismic monitoring, were also emerging as viable. By the end of the 1990s, improved desktop processing capability allowed rapid interpretation of borehole seismic data using optimized 3C processing sequences. Three-dimensional (3D) VSP became feasible and is now being vigorously pursued. The borehole seismic image was transformed again into even more useful volumetric information. The next step in the evolution of the technology is permanent sensing. Development of smaller, more rugged, fit-forpurpose optical sensors and state-of-the-art optical multichannel instrumentation has enabled the implementation of reliable seismic arrays for long-term deployment within the tight constraints found in well-bores.