Nowadays many exploration and production companies have high interest in producing deep, high pressure gas reservoirs that contain sour gas. Carbonates in East Java, Indonesia faced challenges related to workover and completion operations that are prone to kick-loss cycles based on the drilling experiences.The presence of hydrogen sulfide (H 2 S) and carbon dioxide (CO 2 ) in the formation made the completion operation dangerous and difficult to be carried out in the field where is adjacent to a populated area, thereby increasing the requirement and need to prevent the release of sour gases during completion operations.

Downhole Isolation Valve (DIV) technology has been used for numerous reasons to improve the efficiency of drilling and completion operations all over the world. The technology, which basically involves the installation of a valve system for isolation within the casing string above the reservoir to be drilled, was used in East Java, Indonesia to assist in the drilling and completion phases of the development of a sour gas reservoir that is very prone to severe circulation losses. The fractured and/or vugular nature of the geological formation involved, the Kujung formation, is frequently if not consistently responsible for kick -loss cycles and well control incidents. In fact, well control incidents were experienced on two previous wells drilled using conventional methods in the area and large amounts of cement and lost circulation materials were used to mitigate severe and total circulation losses, which consequently reduced the productivity of the wells. The main reason for the utilization of a DIV was to isolate and prevent sour formation gas from reaching the surface, should severe circulation losses and subsequent well kicks occur. The DIV was also meant to produce improvements in reservoir productivity as well as in drilling and completion efficiency, as roughly measured through the time required for tripping and for dealing with well control incidents.Three wells were drilled and recently completed in the area with the DIV installed. All of the wells experienced severe circulation losses and utilized the DIV as part of a managed pressure drilling (MPD) system that allowed drilling to continue and reach target depth. After drilling and well testing operations were concluded, all the wells were temporarily plugged without curing and cementing the loss zones, to preserve productivity. After almost a year in suspension, the completion systems for two of these wells were recently installed in the presence of severe circulation losses and attempts were made to utilize the DIV system to optimize completion operations. As the DIV used was designed mainly to facilitate drilling and immediate completion of wells, its performance during a subsequent completion run, after an extended period of time in suspension and after having been previously exposed to harsh drilling and sour gas environments, will be of interest.The details of the DIV system utilized and the performance of the DIV system during the drilling and subsequent completion phases of the wells that have been constructed will be presented in this paper. Data and results will also be provided and discussed as to how the DIV system enhanced and improved operational efficiency and well productivity, thereby assisting greatly in the accelerated development of the sour carbonate gas reservoir.

The development of a sour gas reservoir (7000 ppm H2S and 20–25% CO2) in the Kujung fractured-limestone formation in the Gundih Field, Java, Indonesia faced challenges related to drilling operations that are prone to kick - loss cycles. Well control incidents were experienced on previous wells drilled in the area and large amounts of cement and lost circulation materials were used to mitigate severe and total circulation losses, which consequently reduced the productivity of the wells. To further add to the complexity of the situation that the sour gas development project faced, the field's location is adjacent to a populated area, thereby increasing the requirement and need to prevent the release of sour gases during drilling operations. This condition ruled out the use of underbalanced drilling (UBD) to address circulation losses as bringing sour reservoir fluids to surface, even at a controlled condition, carried too much of a risk. In the process of finding a solution to these issues, the operator has identified that safety is the primary issue for the development of Gundih field, closely followed by the ability to drill these wells and maintaining reservoir performance. The solution developed involved the use of pressurized mud cap drilling (PMCD) techniques (along with a guaranteed and sufficient supply of sacrificial fluid, mostly water) and the installation of a downhole isolation valve (DIV), to isolate and prevent sour gas from the formation from reaching the surface, should severe losses and subsequent kicks be encountered. The PMCD+DIV system has allowed recent drilling operations to properly address the situation where severe, total and immediate circulation losses are encountered, thereby concurrently minimizing reservoir damage and the amount of sour reservoir fluid released at surface while penetrating deeper into the fracture limestone reservoir. In one instance, the DIV was able to keep sour reservoir fluids from reaching surface during PMCD 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 PMCD+DIV system utilized will be presented in this paper, together with an assessment of how the system enhanced and improved the handling of health, safety and environment (HSE) issues during the drilling process, thereby assisting greatly in the accelerated development of the sour fractured-limestone gas reservoir in Gundih Field.

Drilling 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.