The basis of Amoco's fracturing design philosophy has changed significantly since 1978 with a resulting marked increase in treatment efficiency and effectiveness. This change has resulted from a coordinated development of field research programs and analytical studies of the fracturing process. An important integrating part of these investigations was the development of a basis for interpreting the fluid-pressure response during and after a treatment and the resultant implications for subsequent treatment design. Principally, this work shows that excessive pressure due to fluid flow in the fracture can cause problems such as excessive height growth and screen-outs which reduce the potential fracture penetration. A primary design change was to limit the pressure through control of the fluid viscosity.
This paper reviews the procedures for analyzing, modeling and interpreting fracturing pressure, the benefits and examples of pressure controlled designs, and the bases for special considerations in fluid, proppant, and pumping schedules to successfully execute controlled pressure designs.
During 1978 Amoco initiated a coordinated program of field data collection and analysis to improve the understanding of the mechanics of the hydraulic fracturing process. Much of this understanding had not changed since the early 1960's and was being severely tested by ever larger and more expensive treatments. A series of papers at the annual meeting of SPE in 1979 presented results from this program dealing with fracture height determination, fracture confinement by in situ stresses, application of fracture azimuth measurements, and the interpretation of fracturing pressures during and after a treatment. At the 1981 annual meeting another group of papers was presented related to massive hydraulic fracturing (MHF) in the East Texas Cotton Valley and the Mesa Verde of Southwestern Wyoming, and the design of precise length treatments for a pilot flood in the Salt Creek Field of Wyoming.