A New Fracturing Technique for Dean Sand
Authors: Pugh T.D. , McDaniel B.W. , Seglem R.L. 
Published: December 2007

An innovation in fracturing the Dean sand of the Spraberry trend of West Texas is presented. The development of the new technique is described from the ideal suggestions and engineering aspects through the practical application. Results are reviewed and practical observations are correlated with theory.

Introduction

The Dean sand in the Midland Basin was stimulated by fracturing, using the same design parameters applied to members of the Spraberry-Dean sandstone lithology. The main considerations for a successful treatment were extended flush production and cost reduction. A new technique was applied to the Dean sand that was superior in both categories. This new method pumped alternate volumes of viscous sand-laden and thin spacer fluids to create a fracture system that was propped by "pillars" of sand, creating void channels through which oil was produced. produced. Geology and Reservoir Review

The Dean sand is a Permian-Wolfcamp deposition. It is separated from the Wolfcamp by an identifiable shale marker. The separation from the Lower Spraberry is streaked with limestone and brown calcareous shale. The sand is generally medium to fine grained, has a gray-white to brown color, and contains some acid-soluble material and streaks of shale. The clays generally do not swell in fresh water. However, migration of released fines must be considered. Vertical fractures exist in all productive sections. A typical mineralogical analysis, as productive sections. A typical mineralogical analysis, as indicated by X-ray diffraction, is given in Table 1. The Spraberry and Dean sandstones (Fig. 1) are considered to be a lithological unit, rather than a time unit. Based on treating and production data, the Wolfcamp siltstone may be considered part of this unit. Spraberry-Dean sandstone underlies most of the Midland Basin. The westward anticline of the Spraberry trend forms one of the world&apos;s largest areal producing units. From the top of the Upper Spraberry to the bottom of the Dean it is 1,200 to 2,000 ft. Depositions of less than 1,200 ft have been unproductive generally. Production has been from sand stringers containing vertical fractures that are separated by shaly gray to brown limestone and streaks of brown calcareous shale. Upper Spraberry and Lower Spraberry usually are identified. Other identifications also have been made. Spraberry sandstones are of Permian-Leonard origin. According to Elkins, porosities average about 8 percent, although up to 13 porosities average about 8 percent, although up to 13 percent has been found. Sand permeability ranges from percent has been found. Sand permeability ranges from 0.001 to 1 md. All productive zones contain vertical fractures of varying width, with an average of 0.0002 in., and are spaced from a few inches to several feet. The production through these fractures has been a definite production through these fractures has been a definite feature of the Spraberry-Dean. Elkins also states that while production has been through these fractures, the fractures contain only a little of the oil in place. Although the adjoining shales also are fractured, little of the producible oil is contained in the fractured shale. producible oil is contained in the fractured shale. Production from Permian sandstones in the Spraberry trend usually followed a definite pattern. The separate zones were commingled and natural production was not tested. Even drillstem testing was rare because of inconclusive results. After stimulation, a high flush-production rate normally was observed. Early reports indicated rates of 1,000 BOPD.

JPT

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