Characterization of an Induced Hydraulic Fracture Completion in a Naturally Fractured Antrim Shale Reservoir

Abstract

In 1993, Shell began a cooperative evaluation with the Gas Research Institute to study factors controlling gas production from the naturally fractured Devonian shale Antrim formation in Montmorency Co., Michigan. The presence of multiple intersecting sets of natural fractures is the primary control on well deliverability and the Antrim must be fracture stimulated to be economical. However, due to the shallow depths (500- 2000 ft) and naturally fractured nature of the Antrim, fracture geometry is complex, and the determination of the optimal fracture treatment or completion methodology is not straightforward. To evaluate the effectiveness of fracture treatments in the Antrim, Shell conducted pressure transient modeling, microseismic tomography surveys for imaging created fracture dimensions (length, height, and dip), and the cutting of multiple coreholes to core the created hydraulic fractures. The integrated results suggest that fracture growth in the Antrim is very complex. A series of sub-vertical fractures were created that were parallel to the maximum principle stress and defined a zone of fracturing at least 50 feet wide. The fractures grew asymmetrically in height above the top perforation and appeared to follow a tortuous path along joint-set directions. Two coreholes drilled at 35-degree angles from vertical encountered 8 propped hydraulic fractures. Several of the cored propped fractures had varying azimuths suggesting that pre-existing natural fractures, which trend primarily NE/SW and NW/SE, were propped during the fracture treatment. P. 177

How Natural Fractures Could Affect Hydraulic-Fracture Geometry

“…Fisher et al (2002) interpreted other Barnett microseismic data as revealing hydraulic fractures propagating as multiple segments of different orientations influenced by preexisting fractures. In addition, core investigations have confirmed that hydraulic fractures can be diverted along and prop pre-existing natural fractures (Lancaster et al 1992;Hopkins et al 1998).…”

A Validation Assessment of Microseismic Monitoring

“…Fractures were also cored in an Antrim shale experiment (Hopkins et al 1998), and multiple fractures were observed in the highly naturally fractured Antrim shale. It was difficult to determine which fractures were associated with the hydraulic fracture, except for those that clearly showed some evidence of proppant (eight fractures in two cores).…”

“…A core-through or drill-through of a hydraulic fracture (Warpinski et al 1993;Fast et al 1994;Branagan et al 1996b;Hopkins et al 1998;Moschovidis et al 2000) is probably the most ground-truth validation test possible outside of a direct mineback. The observation of the fracture(s) in a core or in image logs provides direct evidence of the presence of the fracture and the level of complexity at that point.…”