Thru-Tubing Zonal Isolation and Water Shut-Off Utilizing Coiled Tubing in the Java Sea: Operational Challenge & Treatment Strategy

Abstract

Almost all the wells in the Offshore North West Java (ONWJ) field penetratemulti-layer reservoirs. To accommodate reservoir management issues, most ofthese wells were therefore completed in multiple packer completions (dual orsingle string with multiple packer). As the field is getting mature, more wellsare becoming wet and consequently more wells are dying due to waterencroachment. Therefore, remedial actions to revive dead wells play animportant role to maximize the revenue. To address this issue, thru-tubingcement squeeze and polymer squeeze using coiled tubing have proved to beefficient methods to reduce water production by isolating watered out zones inthe ONWJ field. However, the operation of this job can be more complicated when done inmultiple packer completion or in dual completion cases, especially when thetubing has leaks in order to avoid the cement or polymer from penetrating otherplaces or productive zones. In several cases, the condition of old tubing thathas experienced deformation (buckling/ collapse) has made the task even morechallenging. Therefore, treatment strategies must be designed carefully forsuccessful cement/polymer placements into the target zone without affectingproduction from the other string or zones. From 1999 to 2003, a total of 36 thru-tubing zonal isolation & watershut-off jobs utilizing coiled tubing were done with a high degree of success, although in many cases the tubing had leaks and mechanical problems. Severalmethods were used and modified to ensure proper cement or polymer placement.Through the use of the innovative "cement packer" technique and inflatablepacker, the jobs were accomplished successfully. The coiled tubing has provento be an effective solution to deal with well conditions in the ONWJ field. This paper will also discuss three case histories, with each caserepresenting different operational challenges. Field History The Offshore North West Java Production Sharing Contract (ONWJ PSC) area islocated off of the North Coast of Java Island in Indonesia. The firstexploration well was drilled in 1,967 and production first started in 1971.Throughout its 30 years of production history, 13 flow stations, 150 productionplatforms, 700 wells with 1,013 production strings have been built in a seadepth of up to 40 meters. Currently, the field produces around 38,000 BOPD with300 MMCFD of gas. The continuous decline of crude production is a challenge tothe company's goal of being a low cost offshore operator. Initially, the ONWJ fields produced dry oil and gas. Now, the field producesas much as 50% water cut. Many gas and oil wells have been shut-in due to waterout problems. This condition has challenged the company to find better ways inmanaging downhole water production and maximizing oil and gas production.Therefore, shutting-off the watered out zones and finding more by-passedreserves are the primary targets in this mature field. To achieve them, thecoiled tubing is used and has been proven as one of cost effective solution todeal with challenging well conditions in the ONWJ field. Zonal Isolation and Water Shut-off Operations The very nature of the oil & gas industry leads to the unwantedproduction of water that can seriously affect the profitability of the wells.Some of the methods and practices currently in use today to help eliminate thisproblem include, but are not limited to: placement of cement across the zone, plugging back the zone with the aid of mechanical isolation devices, pullingthe completion and performing a complete work-over. In the ONWJ field, due to the well architecture (multiple packers withsliding sleeve doors), most of watered out zones can be easily isolated just byclosing the sliding sleeve or setting a tubing plug. However in some cases dueto multi zone production, location of the zone, and the mechanical conditionsof the well, more advanced and complicated technology is necessarilyrequired. In 1995, coiled tubing began to be utilized for thru-tubing zonal isolationand water shut-off operation in the ONWJ field. However, more aggressive coiledtubing operations for this type of job started in early 1999. During the periodbetween 1999–2003, a total of 36 jobs were done with a high degree of success, consisting of 16 cement packers, 12 cement squeezes, 3 cement plugs, 3 polymersqueezes, 1 polymer water shut-off, and 1 mechanical water shut-off.