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Cementing Services
Upper-Section Cementing with Stage Collar

BACKGROUND

Onshore vertical well of 4,727m TD with cement interval (900-4486m) at Sichuan Shale Gas. In order to protect the main gas reservoir between 4500m and 4700m from the contamination of the cement slurry and meet the needs of the later multi-stage fracking, the casing tally with stage cementing collar & external casing packer is adopted for the production casing cementing. Cement the upper section above the stage collar and leave lower section open hole. 

CHALLENGES

  • Long cementing interval with high differential temperature: 900m/104degF and 3,586m/180degF
  • High slurry density (Cement slurry@19.2ppg, spacer @17.5ppg)
  • Stage-collar with swell packers was utilized, leaving the interval below stage-collar uncemented
  • Displacement fluid: OBM
  • Cement/displacement fluid compatibility: 1m3 cement slurry followed closing plug to separate cement and OBM

SOLUTIONS

  • Multi-FIT Cement System with elastoplastic additive for flexibility and fiber additive for gas migration prevention and losses added to cement.
  • Weighted oil-removal spacer was utilized ahead of cement and 4m3 (25bbls) over-flush of spacer was utilized behind cement and ahead of displacement.
  • Cement basket was placed below the stage cementer to minimize cement contamination to uncemented section.

RESULTS

Cementing job was successfully accomplished with no losses during operation and plug bumped as desired. This cementing application is the first ever successful case on southwest China unconventional gas wells.