Propellant-Assisted Perforating—An Alternative Stimulation Solution in Heavily Karstified Carbonate Reservoirs

Abstract

Summary Two gas fields offshore Sarawak, Malaysia, are characterized by heavily karstified carbonate reservoirs. These reservoirs are typified by significant porosity and permeability heterogeneities such that large fluid-loss zones are commonly encountered while drilling the reservoir section. The drilling strategy for the subsea development wells called for the use of a solid drill-in liner as a contingency should major losses be encountered while drilling the reservoir section. This strategy stands opposed to using a predrilled liner. The use of a drill-in liner, however, necessitates perforating. Typically, completions in such reservoirs are acid stimulated to maximize productivity. Complete stimulation of the reservoir section is very difficult to achieve using acid-diversion techniques in a karstic environment because of the large variability in the permeability. Propellant-assisted perforating was considered because it achieves effective stimulation diversion, equally across the entire perforated interval. Modeling work indicated that fracture lengths of 5 ft or longer would propagate from each perforation tunnel. Such large propagation lengths greatly increased the probability of connecting the completion directly to karstic features in the reservoir, to provide enhanced inflow performance. Another significant benefit was that perforation and stimulation would take place in a single operation, thereby reducing the health, safety, and environment (HSE) risk associated with handling acid, while saving rig time. Two successful field trials, totaling three wells, will be presented in detail to illustrate this application for propellant-assisted perforating. The data presented include prejob planning, execution, and post-job inflow-performance analysis. The result was three world-class, low-drawdown wells, each capable of delivering 200 MMscf/ D, providing well capacity that met or exceeded expectations. Applying the propellant-assisted perforating technique in three subsea wells in heavily karstified carbonate reservoirs has proved that this technique can offer a highly effective stimulation method across the entire perforated interval in such an environment. Additionally, its usage eliminates the need for conventional, separate acid stimulation, saving rig time and costs while reducing HSE risks.