Impacts of Heterogeneous Fluvial Environments on Hydraulic Fracture Propagation in Tight Gas Reservoirs

After more than 60 years of hydraulic fracturing, many aspects of fracture growth are still not completely understood. One such aspect is how the depositional environment affects hydraulic fracture growth, particularly in complex fluvial reservoirs.

Our study uses a fully 3D geologic model based on a 160-acre 3D outcrop area in the lower Mesaverde Group near Rangely, CO. A 155-ft thick stratigraphic interval encompasses a series of non-amalgamated crevasse channels and associated splays overlain by a point-bar complex of a meandering fluvial system. Each body has a distinct geometry and internal facies architecture and is separated by varying proportions of floodplain/overbank deposits consisting of coal/carbonaceous shale and siltstone. Sandstone splay and point-bar bodies were populated with facies deterministically, whereas background facies (floodplain/overbank association) were simulated using SIS with measured section facies data serving as hard conditioning “well” data. Petrophysical properties and reservoir conditions in the model are based on subsurface data from a nearby analogous producing field. Rock properties, including Poisson’s ratio and Young’s modulus, were correlated to facies from core via wireline logs and then populated within the 3D geologic model based on statistical distributions for each of five facies.

Hydraulic fracturing cases show that the geology associated with any given modeling scenario had a strong effect on hydraulic fracture growth. The typical layer-cake model based on well logs showed distinctly different hydraulic fracture propagation results when compared with the architecturally complex deterministic model. Using 1D wellbore data to predict lateral architecture provided unrealistic results. This had a cascading effect on proppant concentration, conductivity, and ultimately production. In addition, modeling showed no sign of fracture containment due to the presence of thin discontinuous coal and carbonaceous shale facies. However, more widespread non-reservoir facies (siltstone) limited fracture propagation in all directions. Modeling also suggested that perforation location within the sandstone bodies is critical to the successful placement and coverage of hydraulic fractures.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California