Development of a Distributed Optical Sensor Array for Improved Subsurface Characterization and Monitoring

Today 80% of the produced oil and gas from unconventional oil and gas reservoirs is from 20% of the hydro fracturing operations. Although geophone based micro-seismic monitoring has improved the hydraulic fracturing process, conventional micro-seismic monitoring alone is not sufficient to optimize the process. In order to improve the hydraulic fracturing process new instruments must be developed in order to record new types and larger volumes of seismic data. Cost-effective solutions are required so that society can understand the entire industry wide fracturing and water disposal process through wide spread use of effective sensors that will provide improved characterization and monitoring. Electronic solutions usually have low pressure and thermal limits, which lead to limited applications. Electronic geophones are not capable of measuring and mapping most of the low magnitude signals that are being produced by the hydraulic fracturing process. Furthermore, the electronic systems deployed today are effectively small aperture antennas which limits the accuracy of the location of the mapped events. It has been shown that borehole seismology is technically able to map geologic formations in outstanding detail. It has also been shown that borehole seismology can monitoring fluid and gas injection processes. A single channel interferometric fiber optic seismic sensor will be developed that is capable of being multiplexed into systems containing hundreds of sensors generating a large aperture antenna. This will be created by writing successive Fiber Bragg Gratings (FBGs) into a fiber whereby the fiber between gratings becomes the sensor. This type of Distributed Optical Sensor (DOS) combines the positive attributes of Distributed Acoustic Sensor (DAS) having a large aperture with the positive attribute of interferometric interrogation which is orders of magnitude more sensitive than DAS. The fiber will be pulled through ¼” Inconel tubing to finalize the sensor installation. A single channel interferometric fiber optic interrogator will be designed and prototyped that will validate the design of the sensor. While prototyping the interrogator, Paulsson, Inc. will conduct testing and evaluating the sensors using Paulsson owned interferometric and Coherent Rayleigh scattering interrogators. The sensor will be exposed to simulated environments in a laboratory setting while recording data to validate and optimize the design. Commercial Applications and Other Benefits. There are currently 82,000 wells in the United States that have been fractured, and a backlog of wells awaiting fracture since the price of oil significantly dropped midway through 2014. Once cost-effective solutions are available for monitoring hydraulic fracturing it is likely to be legislated that such monitoring must be performed. The proposed large aperture system will cost effectively monitor and map hydro fracture operations. The low projected sensor cost and the potential sensor sensitivity will make the sensors attractive for permanent deployment in a large number of hydro fracture operations.