Relief Well Breakthrough at Problem Well 2/4-14 In the North Sea

Abstract

Abstract After being out of control for a year, an underground blowout in well 2/4-14 in the North sea was successfully killed through a relief well. This paper covers mainly the breakthrough phase. A theory for relief well break-through is also presented along with the field case. Introduction The underground blowout in Saga Petroleums problem well 2/4-14 took nearly a year to get under control. This paper will mainly cover the final phase of the well paper will mainly cover the final phase of the well control operation, where a relief well was drilled into 2/4-14 and the underground blowout was stopped. A rock mechanics theory for relief well breakthrough was developed. The later well killing operation behaved in close agreement with the new theory. This paper presents the theory as well as the field experience gained during the killing of the problem well. Failure mechanisms are identified and the critical distances between the boreholes to establish communications are addressed. To our knowledge, this is the first paper giving a theory for relief well breakthrough. Therefore, the theory and field results presented will improve the understanding or relief well drilling. Relief well breakthrough can be handled safely by implementing proper field procedures, as demonstrated in well 2/4-14. These include rock mechanics considerations such as: fracturing and collapse of boreholes and understanding of borehole breakthrough. In particular, it is shown that breakthrough occurs as the blowing well collapse towards the relief well. FIELD CASE Well 2/4-14 was drilled on an upper Jurassic prospect in production license no. 146, which covers the northern production license no. 146, which covers the northern part of Block 2/4. The license area is situated in the part of Block 2/4. The license area is situated in the southern part of the North Sea, approximately 300 km southwest of Stavenger. The location map is shown in Figure 1. The operation of the well started with the semisubmersible drilling rig Treasure Saga in October 1988. No particular problems were experienced until the 9-5/8 particular problems were experienced until the 9-5/8 in. casing was run and cemented in the lower part of the upper Cretaceus chalk section at 4437 mRKB. A leakoff test (LOT) yielded 2.128 SG, and drilling of the 8-1/23 in. section continued. Pore pressure signals from the well were sparse until the base Cretaceous unconformity was penetrated at 4702 mRKB. Increasing gas readings indicated a rather rapid pore pressure increase, and the mudweight was increased corresponding to 2.08 SG. A drilling break was experienced at 4708.5 mRKB, and drilling continued to 4713 mRKB where a negative flow check was performed. Circulating bottoms up gave gas-cut mud (68% gas), fine-grained sand, and the well was shut in and observed for 30 minutes. No pressure increase was observed, and the mud weight was increased to 2.10 SG. The well was circulated until the gas readings were less than 1%, and drilling continued to 4714 m where return was lost. Then return was attempted regained at different rates without success. The well was stable when the pump was shut down. A total of 470 bbls was lost prior to pumping a 100 bbls LCM pill in place. The mud weight was cut back to 2.09 SG, and place. The mud weight was cut back to 2.09 SG, and the hole was circulated clean, and the well was stable. The interval was evaluated to be a thin sand string in the upper Jurassic Mandal formation.