Abnormal Treating Pressures in Massive Hydraulic Fracturing Treatments

Abnormal treating pressures were observed during massive hydraulic fracturing (MHF) treatments in the Mesa Verde formation of the Piceance basin, CO. Data from three widely separated wells and in several zones per well showed a pressure increase during MHF treatments that the authors call ''pressure growth.'' This pressure growth was at least semipermanent. The elevated instantaneous shut-in pressures (ISIP's) did not return to initial values over periods of several days. The magnitude of this pressure growth is highly variable. When its value is less than about 2,300 psi (15.9 MPa), the MHF treatments are usually completed and results are obtained that are within normal expectations. When its value exceeds 2,300 psi (15.9 MPa), sandout occurs and the fracture length estimated from production data is much less than that calculated with crack propagation models. Temperature logs indicate little or only modest vertical extension of the fractures above the perforations. These data, along with sandouts, point to a large increase in fracture width in response to pressure growth. One possible cause of pressure growth is fracture branching. A multiplicity of branches could produce a plastic-like effect. Laboratory measurements have ruled out plasticity as the cause. The stress/strain behavior of the rock ismore » similar to that of rocks where no pressure growth occurs. Pressure growth seems to depend on both pumping rate and fluid viscosity. Thus, there is some hope for its mitigation through treatment design. Also, pressure growth appears to correlate negatively with pay-zone quality. This suggests that the phenomenon can be exploited as a fluid-diversion technique.« less