Fracture Design, Execution, and Evaluation in Retrograde Condensate Reservoirs: Case History of the Angsi Field, Offshore Malaysia

摘要

This paper details the evolution of hydraulic fracture design,execution, and evaluation in the Angsi field, OffshoreMalaysia. The primary target for propped hydraulic fracturingtreatments is a 660 ft thick series of stacked fluvial sandstonesat an average depth of 8500 ft-TVD, designated the K-sands.The K-sands are high temperature (320oF), over-pressuredretrograde gas condensate reservoirs ranging from 10 to 90 ftnet thickness and 0.1 to 3 mD. Multi-staged propped hydraulicfracture treatments are required to improve well deliverabilityand to mitigate the detrimental effects of condensate dropouton well performance.The initial treatment screened out very early in the job.Fortunately, extensive diagnostic data were gathered toevaluate the treatment – including temperature and radioactivetracer logs, mini-fracs with real-time BHP and BHT, memorygauges that provided accurate BHP data for the proppedtreatment, and comprehensive fluid QC and rheology (Fann 50on the platform). The integration of the diagnostic data withfracture modeling and engineering analyses indicated that thescreen-out was caused by a combination of complex fracturegrowth and low fluid viscosity. The Angsi treatment strategywas subsequently changed to mitigate and control theproblems associated with complex fracture growth, whichincluded increasing fluid viscosity, using proppant slugs, andoptimizing the perforation placement. The changes intreatment strategy implemented after the initial early screenoutresulted in the successful placement of 38 of thesubsequent 41 treatments (93% success). Success is defined asplacing 90% or more of the designed proppant volume.Fracturing operations were significantly improved with theintroduction of “live annulas” fracturing after the initial well,resulting in cost savings of at least U.S. $10 million in the firstyear. Live annulus fracturing also provided “real-time” BHP measurement that resulted in better treatment control andevaluation. Treatment designs were continuously improvedthroughout the program, increasing both fracture length andconductivity and improving K-sand interval coverage. Thesuccess of the first phase of the fracturing program resulted ingas production of over 190 MMCFD initial capacity and 8,200BCPD.