Marginal tight wells challenge sand control economics

Total E&P Indonesia operates dozens of shallow wells that produce steady gas flow from unconsolidated, tight sands in the Mahakam Delta. The company maintains a zero-sand production policy because its surface facilities in the Mahakam Delta are not designed to handle sand. If wells produce sand, they are choked back. Ultimately overall field productivity is impaired.

Historically, the company has treated wells in the area with resin-based sand consolidation additives to fix sand and fines in place. Resin systems are ideally used in high-permeability reservoirs (500 mD and above) because of their high viscosity at downhole circulating temperatures. Injection may be difficult or impossible for tighter sands. In addition, resins will typically reduce permeability by 50%; this level of impairment is significant in low-permeability reservoirs and impedes production.

To maintain production goals, Total started to develop marginal reservoirs that produce for only 2 to 4 months. The short lifetime dictates cost-effective, efficient well treatments—precluding the resin-based systems even if they are technically appropriate for the tight formations.

Chemical system promotes sand agglomeration

Schlumberger proposed using SandAid technology, a patented chemical solution that significantly improves sand management and enhances production. The chemical process increases the attraction between particles (zeta potential) without imposing damage, thereby trapping formation sand and fines to maximize sand-free flow rates and increase production. It is suited for use across a wide range of permeabilities (1 to 10,000 mD), which made it ideal for the lower-permeability reservoir of the Mahakam Delta wells.

Several lab tests, including X-ray diffraction, sand agglomeration, and sand retention tests, were performed to obtain the optimal formulation of the SandAid technology. Because of the high clay content in the sand body, a shale inhibitor was added to the formulation to mitigate against clay swelling or migration.

The final formulation developed viscosity of only 1 cP at 70 degF [21 degC], improving pumpability in the tight sands. Engineers also selected a surfactant package to clean the grain surfaces and facilitate the adsorption of the SandAid technology.

Sand-free gas production exceeds expectations

To ensure clean, precise delivery in the well's short interval (<10 ft [<3 m]), the treatments were delivered through coiled tubing from the Delta Biru multipurpose barge. A packer was set to maximize fluid entering the perforation. After an injectivity test with 5% KCl brine, the main treatment sequence was performed: surfactant preflush, SandAid technology, and surfactant overflush. This sequence was repeated until 3 pore volumes had been delivered at 3 ft [0.9 m] of penetration. All fluids were mixed in real time using the liquid additive unit on the barge. The operation was completed with no service quality or HSE issues.

After the treatment, the well was shut in for 6 hours to optimize cleanup. After cleanup, the well produced 3.5 MMcf/d of sand-free gas, exceeding the customer's expectation by 75%. In addition, the treatment reduced the workover cost by 37% compared with a conventional resin-based consolidation treatment.