Reservoir Management of the Blackjack Creek Field
Authors: Burwell R.B. , Hadlow R.E. 
Published: December 2007

The major steps taken to assure successful reservoir management of the Blackjack Creekfield are summarized. A team effort between geologists and engineers was used to solve specific problems. The need for reservoir description data and early evaluations is discussed.

Introduction

The Blackjack Creek field was discovered in Jan. 1972 with the drilling of Exxon's St. Regis 13-3 well. Key reservoir management decisions required early in the development planning stage were concerned with well spacing, treating-plant size, additional recovery potential, and unitization strategy. The importance and need potential, and unitization strategy. The importance and need for extensive reservoir description data were recognized early in the life of the field and a comprehensive plan was developed to acquire these data. The data obtained were major factors in determining well spacing and plant size. A reservoir simulator model was constructed to predict field performance under primary operations and predict field performance under primary operations and to define the additional recovery potential under a water-injection/pressure-maintenance program. With 20-million-bbl incentive for additional recovery defined by the model, unitization efforts were carried out successfully and the field was unitized before the initiation of production. Production history has matched closely production. Production history has matched closely predicted performance that verifies the accuracy of the early predicted performance that verifies the accuracy of the early evaluation.

Geological Data

As shown in Fig. 1, the Blackjack Creek field is located in the Florida Panhandle about 20 miles north of Pensacola. Its discovery represented an important extension Pensacola. Its discovery represented an important extension of the Smackover formation in the Jurassic trend in this area. Other important discoveries in this trend include Jay-Little Escambia Creek, Flomaton, and Big Escambia Creek fields. More recent discoveries include the Chunchula and Hatters Pond fields north of Mobile.

The Smackover formation in this area occurs at a depth of about 15,700 ft. Dolomites and limestones comprising this formation have a cumulative gross thickness in excess of 400 ft. Core data show that the high-quality productive section of the Smackover is confined to the productive section of the Smackover is confined to the upper, regressive, hardened, pelletal grainstone facies. Only this section of the Smackover was subject to early dolomitization and leaching that preserved and augmented the primary porosity. Porosity development in this facies reaches a maximum thickness of 90 ft at the crest of the structure with pronounced thinning toward the flanks. The lower transgressive algal mat and lime mud deposits retained no effective porosity.

Fig. 2 is a structural map of the top of the Smackover porosity. Structurally, the field is a simple porosity. Structurally, the field is a simple northwest-southeast trending anticline with about 180 ft of closure. The flanks of the field dip gently to the west about 1 1/2 degrees, but steepen to about 4 degrees on the east as the field rolls into the Foshee fault, a major geological feature in this area. There is no evidence of faulting within the productive limits of the field. The oil-water contact was determined to be at - 15,746 ft subsea based on three penetrations. This oil-water contact defines a productive area of about 4,600 acres.

Fig. 3 shows cross-sections illustrating the excellent continuity of the porous reservoir facies (dark-brown dolomite) across the field. These lines of Sections A-A' and B-B' are superimposed on the structure map (Fig. 2). Since the central portion of the structure is underlain by dense, impermeable limestone, water encroachment into the reservoir will occur only around the flanks.

JPT

P. 1235