Integrated Downhole Isolation Valve and Managed Pressure Drilling To Facilitate Development of Sour Fractured-Limestone Gas Reservoir in East Java, Indonesia

Abstract

AbstractDrilling operations for the development of a sour gas reservoir (up to 7,000 ppm H2S and 20-25% CO2) in the Kujung fractured-limestone formation in East Java, Indonesia are prone to kick-loss cycles. Well control incidents have been experienced on two previous wells drilled in the area. Most of the drilling budget was spent on cement and lost circulation materials to mitigate circulation losses and the resulting kicks. The skin factors of the said wells are therefore understandably high.In planning subsequent wells, underbalanced drilling was ruled out due to the sour nature of the reservoir, and managed pressure drilling (MPD), which involves drilling at near-balanced pressure, was selected. To further ensure the minimization if not elimination of the release of sour reservoir fluids at surface, MPD methods were integrated with the utilization of a downhole isolation valve (DIV). The implementation of the DIV + MPD system in recent drilling operations has allowed drilling operations to reach the target depth. The operation gradually shifted from conventional to MPD methods, based on the level of circulation losses encountered, thereby minimizing the amount of reservoir fluid released at surface and keeping skin factors low while penetrating deeper into the fracture limestone reservoir. The absolute open flow potential (AOFP) for the newly drilled well is considerably higher than offset wells. The DIV was able to keep sour reservoir fluids from reaching surface during MPD operations, undergoing as much as 47 open/close cycles during drilling, tripping, fishing and well test operations, all of which were performed while experiencing total loss of circulation.The details of the DIV + MPD system utilized will be presented in this paper, together with an assessment of how these results impact the development of sour fractured-limestone gas reservoirs in the area.