Integrated strategy delivers secure and fast drilling in deep CO 2-rich gas reservoir in volcanic formation

The great exploration discovery of natural gas resources in volcanic formations has uncovered a prospective prologue for tremendous development activity in deep Songliao Basin, China, which inherently contains a high CO 2 concentration of about 14%-30%. The CO 2-rich environment combining with the poor drillability of volcanic rocks has made operators confronting with challenges in drilling and completion operations, such as anti-corrosion against pipe string and set cement, optimization of casing program and bit type, ROP improvement, and cost effective UBD and multi-lateral drilling methods. An integrated strategy was successfully proposed and deployed to address drilling related problems. Firstly, based on the analysis of wellbore stability and anti-corrosive mechanism under different downhole condition, the casing program and anti-corrosive scheme for production casing material were optimized for vertical well and horizontal well, respectively. Secondly, a new CO 2 corrosion resistant cement slurry was developed using a new anti-corrosive material F11F and other anti-channeling HT agents. Thirdly, with respect to detailed study on CO 2 invasion affection, reservoir sensitivity, scale building prediction and wellbore multi-phase flow mechanism, appropriate UBD drilling fluid and bottom underpressure value were determined. Then, the specific bit design method and gas drilling technology were jointly applied to enhance ROP in deep volcanic formations. Finally, matching technologies for horizontal and multi-lateral well operations were systematically modified considering the PDM (positive displacement motor) tool and geosteering method. Favorable achievements have been obtained during years of continuous optimization of drilling scheme. The integrated strategy allows more secure and faster drilling in deep volcanic formations, and offers a tight foundation to maintain profitable production in Songliao Basin. This paper will highlight the technical development in the CO 2-rich area, and present helpful case histories and recommendations. Copyright 2011, Society of Petroleum Engineers.