Cementing Liner String through Salt Formation in Well Dabei-X by Precise Pressure Control

Abstract

Well Dabei-X is an exploratory well drilled in the Keshen block, an area located in the Kelasu structure, Kuche depression, Tarim Basin. The fifth interval of the well, which was to be cased with φ177.8 mm+φ182 mm liner strings, penetrated creeping pure rock salt and had coexistence of high- and low-pressure zones. Long open hole, narrow annulus, deep running of liner strings and narrow safe drilling window (only 0.03 g/cm3) were very likely to result in downhole troubles such as coexistence of blowout and mud losses in different depths or alternate occurrence of mud losses and well kicks. To avoid and solve these potential downhole problems, precise control of wellhead pressure was tried during cementing job. By precisely controlling pressure at the wellhead, the occurrence of well kick and well leaking can be avoided. During cementing, the wellhead pressure was precisely controlled in normal injection of cement slurry, and the cement slurry was further reversely squeezed into the annular space. Measures related to the safety of well cementing, such as anti-channeling, prevention of well kick and well leaking, were all put in practice to ensure the success of the cementing job. CBL/VDL logs proved that the bonding in the overlapping section and the open hole section was qualified. Quality of the cementing of the 200 m above the upper casing shoe was excellent. Low density drilling fluid can be safely used in the next interval because of the successful cementing job of the fifth interval. Techniques used in the cementing operation have provided experiences for cementing wells with narrow drilling windows and wells in the Keshen block with similar downhole problems.