Valuable lessons have been learned from the development of eight retrograde gas-production wells located in offshore Vietnam operated by the Korean National Oil Company. The intent of this paper is to share these lessons by presenting the concepts considered for well design, the selection process for the completion equipment and techniques, the preplanning for the installations, and the experiences encountered during the actual installations.
The completion challenges included isolation of water production below the casing shoe and controlling condensate banking, sand production, and co-mingling multiple production zones in the long openhole sections.
A different type of completion that involved an expandable liner hanger (ELH) with an external-sleeve inflatable packer collar (ESIPC) was chosen and installation and cementing were accomplished in a single trip. The ESIPC was deployed just below the water-producing zone, and cement was pumped up the annulus from the ESIPC to where the expandable liner hanger (ELH) was set above it. This would prevent water from entering the wellbore while enabling optimum production. To prove the concept, a stack-up test was done at surface before actual deployment on location to ensure that the cement wiper plugs would pass through the expandable-liner-hanger ball seat and that the concept would perform as intended.
Swellable packers were selected from the various proven openhole isolation devices available to the industry to provide the zonal isolation required in the multi-zone intervals.
This was the first openhole completion in Southeast Asia in a high-temperature, commingled gas environment in which isolation would be contained solely by swellable packers.
The Rong Doi (RD) and Rong Doi Tay (RDT) gas fields are offshore in approximately 85m of water. They are approximately 300 km southeast of Vung Tau, Vietnam (Fig 1). This high-temperature reservoir (300ºF) is within the Mid-Miocene Dua formation from 3050 to 3900 m true vertical depth sub sea (TVDSS).
The formation is an anticline with a four-way dip closure, split by three NNW-SSE sealing faults, and overlain by the Thong formation. Data from three offset wells; i.e., RD 1X drilled in 1994, RDT 1RX drilled in 1996, and RD 2X drilled in 1997, were available.