Economic Justification for Fracturing Moderate to High Permeability Formations in Sand Control Environments

Abstract

This paper discusses case histories of more than seventy completions requiring sand control. Approximately half of these wells were gravel packed (both slurry and water packs) between 1990 and 1995 while the remaining completions were fracture stimulated (frac-packs) from 1992 through 1995. The case histories include: geopressured oil reservoirs of moderate permeability, normal pressured high perm oil and gas formations, partially depleted high perm gas sands, and shallow dry gas formations. Results of bottom hole pressure transient analyses are included that compare skin values and completion efficiencies of both gravel packed and frac-packed completions. Production plots and decline curves are presented depicting accelerated as well as improved reserve recovery with the frac-packed completions. The associated costs of frac-packing is discussed along with a net present value analysis justifying these costs. Introduction The popularity of fracture stimulation combined with sand control as a completion technique has intensified in recent years. Due to the pronounced success of frac packing, this technique has become the preferred completion method in sand control environments with several operating companies. However, there has been some debate within the industry concerning the feasibility of this technique in moderate to high permeability formations. This paper reviews the results of one operator's experiences in a variety of applications, including both oil and gas reservoirs with permeability ranges of 3 to 4000 md and bottom hole pressure gradients of 0.17 to 0.84 psi/ft. The skin values of 35 frac-pack completions are compared to those observed in 29 gravel packs employing similar completion techniques with the exception of the sand control method. The relationship of skin damage to flow efficiency is also discussed. Several case histories confirm the theoretical calculations, comparing original gravel pack completions that sanded up to their subsequent frac-pack workovers in the same perforated interval. The rate acceleration and improved recovery of these direct comparisons is presented as well as the rig time and costs of the two different techniques. A comparison of productivity index (PI) and the improvement of PI observed over time in frac-packs is summarized. Finally, the economic impact of these improvements is evaluated relative to the increased cost of the frac-pack technique. Skin Damage The most obvious economic justification for frac-pack completions is improved completion efficiency (lower skin) and the resultant higher flow rates. P. 201

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