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

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.

Paleokarst features in the Aptian carbonates of the Barra Velha Formation, Santos Basin, Brazil

“…However, there is a need for careful considerations when dealing with these karst and fracture zones, as they may pose significant hazards to well development in situations of loss of mud, risking failure of well completions which could lead to serious complications or even total loss of the assets. Asides drilling complications, karst and fracture zones typically called thief zones are difficult to map on seismic due to their sub-seismic scale in most situations and issues associated with their capture on NMR measurements (Kumar et al 2012, Mahry et al 2016, Sallee et al 2019, Maksimov et al 2021.…”

Prediction and Early Detection of Karsts—An Overview of Methods and Technologies for Safer Drilling in Carbonates

“…Encountering karsts while drilling can cause critical safety incidents. Depending on the size of the encountered karst, losses of drilling fluid can be uncontrollable, resulting in rapid gas migration to the surface and causing a loss of well control [3]. In the case of well-communicated fractures and caverns, which are common in some regions, losses can be treated without success for several weeks with the subsequent plugging and abandoning of the wells [4].…”

“…In the western offshore fields of India, drilling and completion problems due to mud loss have been reported for a number of wells [7]. In the North Senoro Gas Field of the Philippines, well control issues in carbonates and total mud losses have been followed by gas kicks [3]. In Eastern Siberia, Russia, catastrophic mud losses reaching several thousand cubic meters have occurred while drilling in carbonates and resulting in gas kicks [8].…”