Gravel Pack Monitoring With a Strain Sensing Fiber Optic Cable

Achieving and maintaining orehole integrity is a challenge in the successful and sustainable utilization of hydrocarbons, geothermal energy and sites for geological storage. Information about the integrity of casing and cement is mainly available from logs which only produce data at the moment of measurement and require running in hole with logging tools. This study investigates the potential for real-time monitoring of a fiber optic distributed strain sensor, which is permanently installed behind the casing of a geothermal well. Each location of the fiber conveys information about its temperature and mechanical stress state when interacting with a laser pulse, which is sent through the fiber. This article shows field data from a gravel pack installation and compares the results to conventional borehole measurement equipment during the completion of a geothermal well. It was found that the mechanical strain acting on the fiber matches results from conventional downhole logging tools for density measurements. Both downhole cable and casing pipe experience measurable axial compression at locations where wellbore fluid is being replaced by gravel. Moreover, observation of the strain response over the initial hours post completion of the gravel packing reveals an ongoing movement of annular material (sagging and compaction of filtergravel pack).