Abstract
Limitations on the pressure of injected fluids are necessary to preclude the initiation or extension of fractures. For formations within 2,000 ft (600 m) of the surface, the least principal stress which is exceeded during fracturing is often the overburden pressure. Density logs from 17 wells in the study area were integrated to evaluate the overburden pressure gradient of the Arbuckle Formation in northeastern Oklahoma. The regional gradient of 1.08 to 1.14 psi/ft (24.4 to 25.8 kPa/m) depth appears reasonable when compared with published data for the overlying Pennsylvanian sands. Under Oklahoma Rule 818, the maximum total pressure gradient for Class I industrial waste disposal wells shall not exceed sixty-five percent of the established overburden pressure gradient. In accordance with this Rule, injection pressure gradients less than 0.70 to 0.74 psi/ft (15.9 to 16.8 kPa/m) are permissible in the Arbuckle Group of Northeast Oklahoma. Information obtained while fracturing and acidizing the formation to improve injectivity, confirms the absence of fracturing at the allowable injection pressure gradients.
