Well Control in Carbonate Zone – Total Loss and Kick in Gas Reservoir

Abstract

Abstract North Senoro Gas Field is located onshore at Sulawesi Island, operated by JOB PERTAMINA – Medco E&P Tomori Sulawesi. The aim of North Senoro Project Development is to produce gas from limestone reservoir (Mentawa reef) which has unique characteristic formation that total loss hazard wasn't found at the adjacent well. One of effort to solve the problems is bullheading. In this paper, it will explain how bullheading might become a sufficient method for controling pressure during stripping operation while curing loss circulation problem. Well control situation in sandstone and carbonate formation has different characteristic. In carbonate, well control issue is mostly come by total loss which caused the mud hydrostatic pressure was less in the wellbore. Curing loss circulation was the first major to control pressure on the well. Also on sandstone formation, has more compact if hasn't fault or fracture on there. The well control issue happened in 8-1/2? hole section; the situation occurred when suddenly got total loss in the bore hole. It was followed by the increasing number of background gas from the cutting. Shut in well, got record of SICP is 1700 psi and SIDP is 0 psi. The operations continued with circulate gas out through choke simultaneously with original mud and LCM to try plugged the loss zone and filled up the hole. The result was same with no indication of curing the loss problem. Decided to circulate on the two side, through annulus and inside drill string, while circulate mud and LCM through drill pipe got plugged. The engineer team made some analysis then created few scenarios, such as severing BHA, perforate drill pipe to make communication with annulus, continued pumping mud and LCM via annulus (bullheading), or stripping operation. With all assumptions and condition, the stripping operation while bullheading became the best choice to POOH BHA and running OE to cure loss circulation with BDOP/BDOC, then continue with circulate out gas/kick. Finally, with 2 spot BDOC and the last BDOC was modified using LCM to mitigate micro fracture in cement, loss circulation solved then following circulate out gas by driller method. For total loss and kick issue, the important thing that we have to assure is pressure gradient and availability of water and LCM material. Setting casing shoe at the high rating pressure will give us much possibility to select the way of curing loss circulation and kick. RIH OE pipe and spot BDOP & BDOC through OE pipe became success story to curing the loss for next well. Finally, the safety for crew, environment and production target is achieved with this option at North Senoro Gas Field.