Key techniques for drilling ultra-deep pre-salt highly-deviated wells in Kelasu tectonic belt

The Kelasu tectonic belt presents complex geological conditions in deep formations, leading to premature completion of multiple wells due to encountering fault zones during drilling. To enhance drilling success rates, a strategy employing highly-deviated wells to bypass certain fault zones and to mitigate drilling complexities was proposed. Considering the regional geological characteristics, the technical challenges faced in drilling ultra-deep pre-salt highly-deviated wells, including uncertainties in casing shoe sealing points, difficulties in wellbore trajectory design and control, challenges in precise positioning at the salt bottom, and significant friction encountered during casing running in highly-deviated sections in salt layers, were analyzed. Based on rheological experiments on salt rock creep in the Kelasu tectonic belt, the original seven-section vertical wellbore design was optimized into a five-section design for pre-salt highly-deviated well structure. The directional drilling method in salt formations using a “rotary steering + concentric reamer” bottom hole assembly (BHA) was explored, a new combination of “conventional pipe stick techniques + GLASS forward-viewing technology” for salt bottom pipe stick was tested, and key technical measures for safe casing running in highly-deviated salt formations were analyzed and formulated, leading to the development of a set of crucial drilling techniques tailored for ultra-deep pre-salt highly-deviated wells suitable for the Kelasu tectonic belt. Field applications in six wells including Well Keshen A and Well Keshen B demonstrate that this technology can effectively address the technical challenges encountered in drilling ultra-deep pre-salt highly-deviated wells in the Kelasu tectonic belt, which may achieve a drilling success rate of 100%, meeting the exploration and development demands.