Looking Deep Beyond the Wellbore: Mid-Field Hydraulic Fracture Diagnostic

Abstract

Abstract Understanding the stimulated reservoir volume and mapping hydraulic fractures away from the wellbore remains one of the biggest challenges in unconventional plays development. Currently available production logging and tracer technologies have shallow depths of investigation—only a few inches beyond the wellbore. Far-field microseismic mapping offers an image of micro-earthquakes that are caused by shear slippage during a hydraulic fracture treatment. Although the location of the associated microseismic events enables spatial mapping of the stimulated rock volume, particularly its orientation and growth characteristics, the microseismic deformation does not provide direct information about hydraulic fracture effectiveness. The latest improvement in deep shear wave imaging processing (DSWI) provides a visual representation of geological features up to 100 feet from the wellbore. DSWI nicely fills the resolution space between conventional near-wellbore diagnostic technology and far-field microseismic mapping. The shear wave azimuthal sensitivity enables estimation of the hydraulic fracture geometry away from the wellbore. It also provides direct visualization of the actual reservoir volume that has been stimulated in the mid-field region with the extension of hundreds feet from the wellbore. This paper presents a case study of the post-hydraulic fracture diagnostic in a shale reservoir using deep shear wave imaging technology. The information derived from the pre- and post-hydraulic fracture imaging enables a better understanding of the stimulation treatment effectiveness and fracture propagation away from the wellbore. This imaging can also be used for the completion optimization of the new drilled wells, as well as for the identification of previously unstimulated zones for re-fracturing. The accuracy and credibility of the DSWI hydraulic fracture diagnostic was confirmed by running a cross-dipole acoustic log in a well with high water cut. Radioactive material present in the produced water caused up to 150 API increase in the gamma ray activity due to precipitation associated with the pressure drop in a hydraulic fracture. The study showed that the lateral intervals with a substantial increase in gamma ray activity matched the hydraulic fracture locations identified by the DSWI process. These case histories highlight the value of the information obtained from the DSWI to enhance the fracture optimization, to improve ultimate recovery, and to reduce overall operational cost.