Difficulties in Cementing Salt Formation in Well Keshen-Y: Analyses and Technical Measures

The fourth interval of the well Keshen-Y penetrated several salt zones, mud loss zones and high pressure formation water zones. High creeping tendency of salt may cause resistance to casing running. A narrow safe drilling window of only 0.03 g/cm³ in a hole section where high pressure formation water and mud loss zone coexist may cause mud loss and overflow. In well cementing operation, low leak-off pressure and eccentricity of casing string result in poor displacement of mud and hence difficulties in cementing the high pressure water zones. Several measures have been developed to address these problems. First, based on the analyses of the geological and engineering conditions, it was decided to ream the salt sections and to perform wiper trip with a simulation string. The well cementing techniques were reviewed based on the evaluation of leak-off pressure and overflow pressure, and a "normal injection reverse squeezing plus timely pressurizing" cementing program was established. Using software simulation, the placement of centralizer and the rheology of spacer were optimized, and high flow rate and multiple displacement were used to increase the displacing efficiency. Field application of these technical measures showed that the casing string were run smoothly to the designed depth. No lost circulation and overflow have ever occurred during normal injection cementing. High flow rate was obtained and the top of cement was controllable during reverse squeezing cementing. Channeling test at the bell nipple at negative pressure was certified, indicating that the water zones were successfully cemented.