Abstract
This paper details the evolution of hydraulic fracture design, execution, and evaluation in the Angsi field, Offshore Malaysia. The primary target for propped hydraulic fracturing treatments is a 660 ft thick series of stacked fluvial sandstones at an average depth of 8500 ft-TVD, designated the K-sands. The K-sands are high temperature (320ºF), over-pressured retrograde gas condensate reservoirs ranging from 10 to 90 ft net thickness and 0.1 to 3 mD. Multi-staged propped hydraulic fracture treatments are required to improve well deliverability and to mitigate the detrimental effects of condensate dropout on well performance.
The initial treatment screened out very early in the job. Fortunately, extensive diagnostic data were gathered to evaluate the treatment – including temperature and radioactive tracer logs, mini-fracs with real-time BHP and BHT, memory gauges that provided accurate BHP data for the propped treatment, and comprehensive fluid QC and rheology (Fann 50 on the platform). The integration of the diagnostic data with fracture modeling and engineering analyses indicated that the screen-out was caused by a combination of complex fracture growth and low fluid viscosity. The Angsi treatment strategy was subsequently changed to mitigate and control the problems associated with complex fracture growth, which included increasing fluid viscosity, using proppant slugs, and optimizing the perforation placement. The changes in treatment strategy implemented after the initial early screen-out resulted in the successful placement of 38 of the subsequent 41 treatments (93% success). Success is defined as placing 90% or more of the designed proppant volume.
Fracturing operations were significantly improved with the introduction of "live annulas" fracturing after the initial well, resulting in cost savings of at least U.S. $10 million in the first year. Live annulus fracturing also provided "real-time" BHP measurement that resulted in better treatment control and evaluation. Treatment designs were continuously improved throughout the program, increasing both fracture length and conductivity and improving K-sand interval coverage. The success of the first phase of the fracturing program resulted in gas production of over 190 MMCFD initial capacity and 8,200 BCPD.
