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Integrated Analysis of Borehole Microseismic, Completion and Production Data to Characterize Reservoir Depletion and Determine Infill Well Spacing in Tight Sands

Abstract

BP America performed a borehole microseismic monitoring of a ten stage cased hole hydraulic fracturing operation in the Cleveland formation, Anadarko basin. The Upper Pennsylvanian Cleveland sands have been extensively drilled and exploited with vertical wells over the past several decades. Though these sands are of low porosity (3-15 p.u) and permeability (4-400uD) and hydraulic fracturing provided a renewed interest in this formation. Over the years, depletion not only changes the reservoir fluid state but also would affect the horizontal stress magnitudes. To understand the effect of nearby vertical well depletion and changed stress regime on hydraulic fractures, we designed a microseismic monitoring experiment on an infill horizontal well. Majority of the ~3700 ft lateral was drilled and stayed in a clean rock (< 70 GAPI), with minimal variation in rock quality among the various stages. Two offset producers, one on each side of a well bore were shut in and turned into monitoring wells (~60 geophones), along with downhole pressure gauges capped by a bridge plug. A hybrid system of slickwater and crosslink gels was pumped at ~80 bpm along with a biodegradable diverter agent to enhance fracture propagation. From the microseismic event distribution, maximum horizontal stress direction was observed to be SSE-NNW which is in agreement with previous breakout and borehole image log studies in this area. Experimental results showed that the depletion had a profound effect on fracturing fluid distribution and fracture half-lengths. In four stages where the fracture plane was in line with the offset well depletion, lower number of events was recorded compared to the stages at virgin reservoir pressure. Also, a fracture reorientation was observed in three stages where the fracture was preferentially drawn to the low pressure area. Chemical fluid tracer data and treatment plots supported the observations made from the microseismic events. This experiment provided a unique opportunity to observe and delineate depletion from existing producers, thereby providing us with guidelines for future infill drilling.