Vertechs, a primary service provider for cementing in this IOC shale gas project, successfully spotted a reservoir cement plug and achieved a seal of the formation with a single plug over 1000 m.
The subject well is an abandonment after four years of production where 8 intervals were perforated and 4 of them were successfully fractured.
In abandonment cementing, a key factor is the Top of Cement (TOC) placement for isolation. In this case the TOC range has a difficult target window at ±200 m of length or equivalent to 1.0 m³ of cement. This means planning of the formulation, mixing the slurry and pumping requires great precision to execute correctly.
Critical factors included: 1) Potential losses into perforated and fractured intervals. If losses are serious enough then TOC will be deeper than design. 2) In a perforated and fractured gas well, gas migration is possible during and after cementing. If gas migration occurs during displacing or WOC, the TOC could be shallower than design. The whole cement plug design length is around 1000 m placed across a perforated section of about 700 m. 3) In this well a section of casing was deformed with a Hold up Depth (HUD) 100 m above TD, meaning the plug must be placed successfully across this restriction.
Targeted at the unique challenges for this well, Vertechs designed and provided an especially-stable cement slurry system with a customized formulation to seal the ultra-long perforated section. The mixing and pumping operational procedures were optimized to ensure the minimal pressure fluctuation during execution. This demanding operation proved the stability of Vertechs Multi-Fit cement slurry and excellent teamwork during the operation showed the design criteria was strictly followed.
When the cement top was tagged, the result showed the TOC was within the design limit and a subsequent inflow test verifies adequate isolation. The versatile Multi-Fit cement plug recipe, supervised by the Vertechs cementing team, delivered the barrier required between the reservoir and well bore to abandon this well. This cementing result exceeded the client’s expectation and continues Vertechs 4+ year track record of delivering exceptional results in a very complex environment for Sichuan shale gas wells.