In recent years, the state-of-the-art concerning massive hydraulic fracturing has progressed substantially in low permeability, highly geopressured reservoirs typical of many deep wells in South Texas. Specifically, introduction of closure pressure theory and development of a high strength proppant to compensate for the effects of fracture closure have opened new avenues in fracture design. However, the relatively high cost of the superior proppant necessitates prudent evaluation to determine if the use of the proppant is appropriate and will eventuate the intended results.
An intensive evaluation of applicability of the proppant has been completed for the McAllen Ranch (Vicksburg) Field. Review of historic fracture stimulation techniques and subsequent reservoir performance attributable to fracture effectiveness established a definite need for re-evaluation of stimulation methodology in the McAllen Ranch (Vicksburg) Field in South Texas. The subject of massive hydraulic fracture stimulation of the extremely low permeability reservoirs in the McAllen Ranch Field has evolved as a critical topic in terms of selection and placement of fracture proppant. In reference to proppant placement, considerable attention has been directed to the volume and distribution of proppant within the fracture system.
Selection of proppant has been greatly enchanced by the availability of a proppant of adequate compressive strength to offset the apparent effects of collapse and crushing of conventional proppants. Considerable research focused on the deep, tight, Vicksburg completions in South Texas has led to recommendation and use of sintered bauxite as a propping agent in recent stimulations.
In addition to comparative production data, success of the methodology has been measured primarily through employment of detailed pressure analysis. Pressure data acquired prior to stimulation provides valuable estimates of reservoir parameters necessary in fracture analysis. Pressure information obtained after fracturing is assessed to supply estimates of reservoir parameters in the absence of prefrac data, evaluate existing sand-propped fractures, determine potential for restimulation using bauxite proppant, and to monitor and evaluate original stimulations utilizing the high strength proppant. Numerous problems concerning reservoir heterogenity, treatment intervals, and probable pressure-permeability relationships combine to complicate analysis of designed fractures. Preliminary results of the current methodology point to initial success of a significant magnitude.
Author(s): R.L. Tucker, Forest Oil Corp.
Paper Number: SPE 7925