This paper describes the successful application of the frac-and-pack completion technique to a low-permeability oil-bearing formation in coastal Zaire, West Africa. Using various completion methods since initial field development in the early 1970s, operators have recovered less than 1 % of the estimated oil in place from this formation to-date. Encouraging results from a two-well pilot project initiated in late 1994, led to a decision to work over an additional four wells for frac-and-pack completions in 1995 as part of the pilot project.
This work centers around the Turonian formation, which is a soft, low-permeability siltstone formation. The friable nature of this formation combined with a low median sand-grain size (20 to 40 microns) has led to formation sand and fines production in some wells. Past attempts to stimulate the Turonian through matrix acidizing have been unsuccessful, and completions of the reservoir with both open- and cased-hole gravel packs have shown uneconomical production rates.
The first two frac-and-pack treatments of the pilot project, one in cased hole and one in a 15-in. underreamed open hole, were pumped through a short weight-down gravel pack assembly that allows for monitoring a live annulus during the job and accurate measurement of net fracturing pressures. The four additional frac-and-pack completions were performed with a similar downhole assembly.
This paper highlights the main aspects of this project, including the reservoir description, completion equipment, fluid and proppant selection, design and analyses of the fracture treatments, and optimization of the treatments as the project progressed. A summary of well performance following the frac- and-pack completions is also presented.