Assessment of the Mounds Drill Cuttings Injection Disposal Domain

Abstract

Abstract This paper presents an in-depth assessment of the fracture system created during the Mounds Drill Cuttings Injection Project. The project goal was to evaluate the adequacy of multiple injections in creating a "disposal domain". Previous papers have provided overviews of field results without supporting data or model calculations. This paper presents detailed core, log, tracer, and monitoring field data along with stress calculations, and shows that the Mounds disposal domain is more complicated and less-effective than would appear from the overview data. The principal data defining the cuttings-filled fracture system are from cores drilled through the fracture system and imaging logs of fractures in the borehole walls. Supporting data include analyses of cuttings and induced fractures for tracers (radioactive, dye colorants, glass microspheres) injected with the slurry and fracture-diagnostic results from microseismic and tiltmeter arrays. While all field data show an extensive fracture system, core and log data show that only a few fractures have significant cuttings volume and fracture conductivity. The disposal domain created is one where there is a principal, narrow, cuttings-filled, fracture system, along with abundant, minimal-volume, offset, secondary fractures. Stress calculations also show that insufficient cuttings were injected to reorient the stress field and produce a wide range of fracture strikes. Secondary fractures probably formed from limited localized plugging or activation of intersected natural fractures. However, with sufficient additional injection, a wider disposal domain probably would have been created.