Stimulation Challenges and Solutions in Complex Carbonate Reservoirs

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper details the challenges of stimulation in one of the fields in North Oman. The field is a mature, heavily faulted and fractured carbonate reservoir on water flood where acid stimulation carries an inherently high risk of inducing several fold increases in water production. Acid placement challenges are immense as the fracture networks impart massive permeability contrasts and are most often the principal conduits for "premature" injection water breakthrough. We present field data of acid stimulation treatments on cased hole, oil producers as well as open-hole horizontal injectors using a novel self-diverting acid system. This fluid has been recently applied in other reservoirs but to date, none of these applications have held the same magnitude of challenges and barriers to successful implementation of stimulation treatments. We present numerous field studies which identify self-diverting acid systems as a key solution, together with best practices in candidate selection (through reservoir logging evaluation) and coiled tubing placement methodology, in providing consistent improvement in net hydrocarbon well productivity and enhanced injection profile for reservoir management. In addition we present results of a new surfactant based self-diverting system and compare the results to conventional polymer based treatments in this field. The results are indicative of a further improvement in success ratio of acidizing treatments. Similar methodology and fluid systems are applicable in other complex fractured reservoirs where acid placement and minimizing water production present the principal challenges. Moreover, as reservoir management becomes an ever-increasing concern, we present a treatment methodology to enhance productivity, reduce water cut and optimise reservoir sweep, all of which reduce the overall lifting costs.

Stimulation in Asia Pacific Region—Challenges and Opportunities

“…Mature technologies that have been applied within Shell and elsewhere globally [11][12][13][14][15][16] were proposed as expected. They all have proven track record of success.…”

“…They all have proven track record of success. In terms of acid systems, they vary from self-diverting surfactant acid system [10][11][12] to insitu crosslinked gelled acid system [14][15][16] . From engineering point of view, the key factor of success in pumping any of the proposed acid systems is to effectively diverse the acid to cover the whole section of the well and have enough pressure to drive the acid into the formation to generate wormholes.…”