CHARACTERIZING FRACTURE DEVELOPMENT IN DIATOMITES WITH SEISMIC MOMENT TENSOR INVERSION ANALYSIS

Multi‑array microseismic monitoring of a hydraulic stimulation in the diatomites by Vinegar et. al. (1992) identified near vertical upward and downward hydraulic fracture growth, approximately N26o E, and a wide process zone related to extensive multi‑fracturing (Mahrer, 1991) surrounding the main fracture. Similar, to the work of Vinegar et. al., data recently recorded on optimally placed mutli‑level multi‑well downhole triaxial geophone arrays offered an opportunity to examine the failure mechanisms, both spatially and temporally, associated with a steaming program in the diatomites. To potentially characterize fracture growth and failure complexity, Seismic Moment Tensor Inversion (SMTI) analysis and source mechanism k‑T type plots were carried out for events with good focal sphere coverage. The k‑T type plots provided a measure of the relative fracture complexity, versus simple fault‑slip type failures, and the components of failure, i.e., crack opening or closure (with directionality), and shearing (double couple). Additionally, the temporal and spatial positioning of fracture complexity relative to the start and position of the injection, is used to examine initiation/reactivation of fractures, breakout into formation, progression of fracture from the treatment well, and fracture infill behind the fracture front. Based on these studies, further consideration is given to developing a model of fracture development in the diatomites.