Optical Sensor System for Low Cost Fracture Monitoring

Hydraulic fracturing of oil and gas reservoirs has proven to be extremely productive but also expensive, uncertain, and carrying environmental risks. Part of the problem is the difficulty of mapping fracture networks while they form and as they evolve over the lifetime of the well, preventing a thorough understanding of the reservoir dynamics. Major issues include unproductive frac stages, migration of well or frac fluids into the environment, and costly interventions for unexpected problems. High quality downhole measurements of microseismic signals are proven to help survey reservoirs, study fracture dynamics, and monitor well conditions. However, existing electronic tools appropriate for downhole measurements have high costs and limited survivability in the harsh environments (particularly high temperatures) of modern unconventional wells, with a form factor which is complex to deploy and often incompatible with well configurations where hydraulic fracturing is being used. Our Solution We propose to produce a very small (1” diameter) rugged optical microseismic toolstring which dramatically simplifies deployments and reduces their cost. A passive fiber optic sensor design allows for long-term survival at elevated temperatures (up to 250 C). This encourages observations and surveys to continue long after stimulation, to observe long term dynamics as the fracture network evolves and the reservoir depletes, and to help understand the dynamics of re-stimulation on old wells. It will also improve long-term models of fractured well dynamics to improve future operations. We have already demonstrated sensitivities of order 100 nano-g per root Hertz in a harsh environment optical seismic sensor. In this work, we will miniaturize the sensors and support structures, increase the bandwidth to frequencies up to 1600 Hz, and develop a tool string that can be manufactured at low cost and used in simplified deployment scenarios, such as permanent installation behind casings, rapid deployment and retrieval from common well configurations, or integration with existing well hardware. Commercial Applications and Other Benefits This technology will reduce costs of hydraulic fracturing in several ways: Improved subsurface modeling will reduce the number of failed frac stages and dry wells. Data obtained during and after fracturing improve real-time decisions to maximize production. Identify environmental or safety concerns early, avoiding hazards to operators and the public. Help quantify the total resources available to a well and increase the recovered fraction. Key words Fiber, microseismic, seismic, downhole, optical, hydraulic fracturing, high temperature C