Practical Pressure Analysis In Evaluation Of Proppant Selection For The Low-Permeability, Highly Geopressured Reservoirs Of The McAllen Ranch (Vicksburg) Field
Authors: Tucker R.L. 
Published: December 2007

PRACTICAL PRESSURE ANALYSIS IN EVALUATION OF PROPPANT PRACTICAL PRESSURE ANALYSIS IN EVALUATION OF PROPPANT SELECTION FOR THE LOW-PERMEABILITY, HIGHLY GEOPRESSURED RESERVOIRS OF THE McALLEN RANCH (VICKSBURG) FIELD

In recent years, the state-of-the-art concerning massive hydraulic fracturing has progressed substantially in low permeability, 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 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 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, parameters in the absence of prefrac data, evaluate existing sandpropped 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.

Introduction

The McAllen Ranch (Vicksburg) Field located in Hidalgo County of South Texas is operated by Shell Oil Company, Forest Oil Corporation, Sun Gas, and Tenneco Oil. The field is comprised of several reservoirs varying in depth from approximately 10,000' to 15,000'. The reservoirs are typically highly geopressured with pressure gradients ranging from .85 psi/ft. to .93 psi/ft. Zones of specific interest in terms of proppant selection are the deeper reservoirs operated by Forest and Shell with completion intervals between 12,000' to 13,500'. Such zones are generally characterized by extremely low formation permeability requiring massive hydraulic stimulation for commercial production. Individual reservoirs exhibit production. Individual reservoirs exhibit considerable discontinuity due to multiple sand lenses, unconformities, and some faulting.

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