Handling and analysis of downhole troubles during sealed coring in Well INJ-02B in Limau Oilfield of Indonesia

Well INJ-02B was the first cored well in Limau Oilfield of Indonesia. The design well depth was 1 500 m and the coring section was 90 m. Compared with electric logs, it was found that the upper part of the coring section had collapsed and shrunk, leading to failure of running coring tools. Very soft formation was encountered during coring drilling, so the core strength was not enough to form a rock, hence blocking the core. Meanwhile, the ROP in soft formation was fast, so it is impossible to determine on surface if the core was blocked or not, hence leading to core grinding. Field analysis shows that roller bit should be run to ream the hole in irregular hole intervals to ensure regular and consistent hole size, When the bit was lowered to the bottom, large blocks of cuttings were broken by the rotary table at high RPM. At the same time, high-viscosity drilling fluid was pumped down to carry the large cuttings out of the hole to ensure hole cleaning. Then through analyzing the coring drilling time, the core-forming rate was improved using such drilling parameters as low WOB, low rpm and low displacement which were suitable for loose formations, so as to reduce the risk of core blocking and core grinding. The above measures were taken in a timely manner, so the overall core recovery rate of this well was up to 90.37%. This technique is applicable to sealed coring in collapsed wells and soft formations in Limau Oilfield of Indonesia.