Hybrid Microseismic and Microdeformation Monitoring of a Coal-Seam-Gas Well

Abstract

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 182300, “Hybrid Downhole Microseismic and Microdeformation Monitoring of a Vertical Coal-Seam-Gas Well,” by R. Durant and T. Francis, SPE, Halliburton, and R.L. Braikenridge, SPE, and M. Roy, SPE, AGL Energy, prepared for the 2016 SPE Asia Pacific Oil and Gas Conference and Exhibition, Perth, Australia, 25–27 October. The paper has not been peer reviewed. Providing confidence that hydraulic-fracture geometries are relatively confined to target coal seams and do not grow upward into beneficial groundwater aquifers is a primary concern. A hybrid downhole microseismic and microdeformation array was deployed to monitor fracture stimulation of a vertical coal-seam-gas (CSG) exploration well in the Gloucester Basin in New South Wales, Australia, to provide more-accurate insight into overall fracture height. These technologies complement each other by providing unique, far-field determinations of hydraulic-fracture geometry. Introduction Increasing community and regulatory concern regarding exploration and production of CSG and fracture stimulation has placed extreme constraints on title-holders in New South Wales, to the point of the government rescinding some exploration permits and titleholders nearing a halt to further exploration. The operator is determined to provide evidence that CSG pilot exploration wells and, in particular, fracture stimulation are not affecting beneficial aquifers or interacting with faults. It is important that the operator be able to provide scientific explanations that are understandable and accessible to the community and assist in regulatory approval processes for the industry. The primary goals of the project were to assess any fracture-height growth toward aquifers and possible interaction with surrounding faults. In addition, the operator wanted to determine fracture geometry (i.e., length, height, and azimuth), pay-zone coverage, and relative degree of induced-fracture complexity to aid in the optimization of future completions, well placement, drilling strategies, and fracture designs. Hybrid downhole microseismic and microdeformation monitoring was used on the pilot project to provide independent geophysical measurements of fracture-height growth and increase confidence in the results. Hybridized Downhole Diagnostics The hybrid receiver array used to map this project is a relatively new technology that uses downhole microdeformation tools (tiltmeters) in conjunction with downhole microseismic geophones. The purpose of combining these two technologies, which complement each other, is to improve assessment of fracture-height growth by determining which microseismic events are likely hydraulically connected and to validate and suggest a more-precise analysis of the measured microseismic events.