Angsi K–Sand Production Performance: A Case History of Hydraulically Fractured Retrograde Gas Condensate Reservoir

Abstract

Angsi K-sand is the first tight gas reservoir development in Malaysia, developed in 2002 to meet an increasing domestic gas demand. K-sand is high temperature (320 oF), multi-layered over pressured retrograde gas condensate reservoirs ranging from 10–90ft net thickness and permeability of 0.1 - 3.0 mD. It was developed through multi-staged propped hydraulic fracturing to improve well deliverability and to mitigate productivity impairment due to condensate dropout near the wellbore. In general, initial gas production from these wells exceeded expectation with condensate level significantly higher than initially anticipated in the development plan. However, several wells exhibited relatively faster and steeper production decline with indications of productivity loss related to the liquid drop out in the vicinity of the wellbore. Scale problem and proppant flow back were also observed at surface during clean-up of production facilities. There are many challenges in managing this complex reservoir and 'unconventional' well performance in an area with a history of conventional gas well operation only. The main challenge is to develop operating strategies in producing these wells at sufficient rate and recovery to meet the short term gas commitment and provides sufficient return on the projects economics. The strategies adopted are flexible enough to face the decision making required by this type of reservoir under anticipated production operations. Additionally, these strategies are the key in identifying opportunities, defining uncertainties and developing specific plans to gather information to allow fast response. Based on actual performance and surveillance data, various changes to the original plan are being implemented. Active reservoir surveillance planning and execution were carried out to provide a better understanding of well behavior and the effect of strategies to the well performance. This paper summarizes the reservoir management challenges, techniques and technologies applied to monitor and evaluate the reservoir performance and operating strategies. Introduction The Angsi Field is the largest integrated oil and gas development in Malaysia and in the region. It is located 170 km off the East Coast of Terengganu in Peninsular Malaysia. The location is shown in Figure 1. Angsi is a joint venture between PETRONAS Carigali Sdn. Bhd (PCSB) and ExxonMobil Exploration and Production Malaysia Inc. (EMEPMI). Angsi is operated by PCSB as a Production Sharing Contractor (PSC) to Petroliam Nasional Bhd. (PETRONAS), the Malaysian National Oil Company. The current development is only concentrated in four areas; Main, West, North and South, each with a separate wellhead platform in water depths of 70 m. The development is shown in Figure 2 and Figure 3. The field is a major contributor to the gas and oil production for PCSB Peninsular Malaysia Operations (PMO). The current gas production is about 350 MMscf/d which contributes 50% PCSB-PMO's production. The Angsi field is an asymmetrical anticline elongated in a north-west to south-east direction. It is part of the Angsi- Besar-Duyong regional structure trend. The Angsi development targets stacked sandstone reservoirs at depths ranging from 6,000 to 9,000 feet. Stratigraphically, hydrocarbons are found in the Group I, J and K sandstones of Lower Oligocene to Middle Miocene age. Volumetrically, the major gas bearing reservoirs are the I-1, I-85, I-100 and K-Sands while the I-35 and I-68 sandstones form the major oil bearing reservoirs. Figure 4 shows the cross section of the K-Sand.

Innovative Process for Formation Damage Removal in Sandstone Reservoir Based on Real-Time Downhole Monitoring: A Malaysia Case History

“…Accumulation of condensate near the wellbore will reduce gas saturation, and consequently gas effective permeability. In order to delay formation of condensate banking, K reservoir wells were hydraulically fractured right before the well completion (Othman et al, 2008). On the other hand, after few years of production, several carbonate scale buildup issues were also recorded among the K reservoir wells.…”