Imaging Hydraulic-Fracture-Induced Seismic Deformation

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 102801, "Imaging Seismic Deformation Induced by Hydraulic-Fracture Complexity," by S.C. Maxwell, SPE, C.K. Waltman, SPE, N.R. Warpinski, SPE, M.J. Mayerhofer, SPE, and N. Boroumand, Pinnacle Technologies, prepared for the 2006 SPE Annual Technical Conference and Exhibition, San Antonio, Texas, 24– 27 September. Microseismic mapping is used extensively in the Barnett shale to map hydraulic-fracture complexity associated with interactions of the stimulation with pre-existing fractures. Previous studies have indicated a fair correlation between well performance and extent of the seismically active volume. In the full-length paper, the density of the total seismic moment release is used as an indication of the seismic deformation that may correlate to fracture density. Incorporating seismic-moment density with stimulated reservoir volume (SRV) improved correlation with well production. Introduction Microseismic mapping of hydraulic-fracture stimulations has become a common technique used to map fracture growth and geometry. Microseismic images provide details of fracture azimuth, height, length, and complexity resulting from interaction with pre-existing fractures. The resulting images can be used to calibrate numerical simulations of fracture growth, allowing more-confident modeling of other stimulations in the field and identification of the stimulated region that may be drained by the well. Microseismic mapping in the Barnett shale has demonstrated repeatedly extreme fracture complexity resulting from interaction between the injection and a pre-existing fracture network. The Barnett shale has very low intrinsic matrix permeability, and the permeability enhancement associated with the fracture stimulation results in permeable fracture networks sufficient for economic gas recovery. Previous studies have shown a correlation between the SRV, as measured by the volume of the reservoir that emits microseisms during the stimulation, and the production ultimately realized from the well. The correlation is attributed to larger fracture networks being stimulated in wells where a large microseismically active volume of the reservoir has been realized, resulting in more permeable fracture pathways connected to the well and hence a higher potential for gas flow to the well. Recently, many operators in the Barnett shale have attempted horizontal completions, which have enabled large volumes of the reservoir to be stimulated with large fracture networks. Many of these completions use perforated, cemented liners, and the microseismic images allow identification of improved perforation staging to maximize the SRV. Beyond the basic hypocentral locations of the microseisms used to calculate the SRV, additional seismic-signal characteristics allow investigation of the source of the mechanical deformation resulting in the microseisms. In particular, the seismic moment, a robust measure of the strength of an earthquake or microearthquake, can be used to quantify the seismic deformation.