Microseismic and 3D Seismic Anisotropy Fracture Mapping – A North America Tight Gas Case History

A tight gas case history from the North America Rocky Mountains shows the capability of borehole microseismic and 3D seismic anisotropy to delineate fracture systems induced in a clastic reservoir by hydraulic fracturing of a horizontal well. Dual monitoring of the horizontal well completion indicates improvements in fracture mapping by compressing hypocenters of the microseisms to more linear features that are corroborated by production logging flowmeter. Fracture half-lengths and vertical heights of fractures are indicated for reservoir modelling. Advanced processing of the microseismic 3-component geophone first motions indicates fracture azimuth and dips from a moment tensor inversion and suggests a conjugate set of orthogonal fractures in the reservoir. 3D seismic anisotropy results, using a fast and slow velocity direction calculated from the data, suggest inherent microfractures present in the rock prior to completion. Surface fault mapping in the field supports fractures mapped by both the microseismic and the 3D seismic anisotropy. Multiple regression analysis of drilling, completion and 3D seismic anisotropy parameters versus initial production for 30, 90 and 180 days results show independent contributions to production. A predictive production model based on the multiple regression analysis allows for future well planning and completions to optimise well performance.