Review of Sand Consolidation Experience in South Louisiana

Abstract

Abstract Sand consolidation is a key completion tool of economic importance in the unconsolidated oil sands of South Louisiana. A proven consolidation technique uses a phenolic resin with sufficient non-reactive components to insure permeability. Humble Oil and Refining Co., developer of the plastic, has used the material in over 500 treatments with 75 per cent over-all success. Unsuccessful jobs are usually corrected by subsequent treatments. The phenolic plastic is compatible with all completion tools and techniques which use nonplugging fluids in the wellbore. The usual method of placement is through 1-in tubing which has been run through 2 3/8-in. OD tubing in conventional completions, or inside 2 7/8-to 3 1/2-in. OD pipe of tubingless completions. Treatments have been successfully applied directly through 2 7/8-in. OD tubing by using wiper plugs to separate the required fluids. Introduction Sand intruding into a wellbore has long been a problem associated with oil and gas production. The problem is more acute in the loose unconsolidated formations in the Gulf Coast areas of Texas and Louisiana. Formations requiring sand control in South Louisiana, primarily offshore, occur at depths shallower than 8,000 ft. Operators usually report increasing difficulty as the sands occur closer to the surface and as the percentage of fines in the sand increases. There are several explanations of sand production. The most prevalent theory attributes sand production to friction and resultant pressure drop as well fluids pass through the small pores of the sand body. When the pressure drop is high and cementing material between sand grains is weak or absent, the individual sand grains are dislodged and carried into the wellbore. Another explanation suggests that water present when sand grains were first deposited is chemically different from the water contained in the aquifer. Water production can actually dissolve a portion of the cementing material between sand grains. Another concept suggests that formations compact as pressure declines, and the changing load tends to shift sand grains and shear cementing material present. Many methods have been proposed for the control of sand production in the past. Plastics have been used for a number of years. Plastic treatments were designed to bind the loose sand grains and/or an artificial filler material into a strong matrix so that the surrounding wellbore area would remain permeable to oil and gas. Many of the original plastic or plastic-associated treatments required the use of a workover rig which added significantly to cost. Workover rigs were usually needed to drill out excess plastic or plasticized material left inside the wellbore after the plastic had set. Such a requirement is particularly costly when performing remedial sand control measures offshore. Plastic Consolidation About 20 years ago, Humble developed a technique utilizing phenol-formaldehyde resin for consolidating sands in wellbores while retaining good well productivity. The resin, when injected into a producing sand member, eliminated sand production by strengthening the formation in the vicinity of the borehole. A successful resin treatment was a significant improvement over the customary use of screens and gravel packing for sand control. Success ratio, however, was not high because well completion methods at that time did not include maintaining a solids-free fluid in the well prior to the treatment. With fluids containing solids, it is unlikely that the plastic would be injected into all perforations and be free of foreign material. In more recent years, perforating techniques have been studied and the many advantages of clean completion fluids have been recognized. In addition, increased development in high cost areas has required a lasting sand control technique which could be applied through tubing. The technique developed by Humble for sand consolidation uses a plastic solution having about 75 per cent non-reactive ingredients. The polymerized plastic adheres to the sand grain to form a strong bond while the non-reactive ingredients insure that permeability is retained throughout the consolidated interval. Additional chemical elements in the process and the design of the physical treatment are directed toward that basic result. The following characteristics were established as desirable and were designed into the plastic solution. 1. The resin should not precipitate until enough time has elapsed to allow proper placement in the wellbore. JPT P. 545ˆ