Downhole Isolation Valve Performance in Drilling and Subsequent Completion Operations

Abstract

Abstract 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. Introduction Exploratory wells drilled previously and conventionally in a field in East Java, Indonesia experienced significant problems with well control events. Much of the drilling budget was spent on cement and lost-circulation material (LCM) in efforts to mitigate circulation losses and the resulting kicks. One of the exploration wells reached target depth in about 230 days versus the planned 80 days, while on the second well bullheading and well control operations were performed continuously for more than 20 days, including 19 cement plugs, before drilling operations could continue. The many problems encountered included poor rig performance, shale sloughing, stuck pipe and severe losses in drilling the Kujung carbonate formation. Severe losses of as much as 600 bbl/hr were experienced on these wells along with subsequent kicks.