Reducing drilling risk on Culzean using WAVI-VSP
Rachel Jones, John Banks, Howard Simpson, Nick Randall and Antoine Paré
Journal name: First Break
Issue: Vol 37, No 10, October 2019 pp. 49 - 54
Info: Article, PDF ( 1.55Mb )
The Culzean field is an ultra-High Pressure, High Temperature (uHPHT) gas-condensate field located in block 22/25a of the UK sector, Central North Sea (Figure 1). The primary reservoir is Triassic and combined with a secondary reservoir in the Jurassic (Figure 2). Total recoverable resources are estimated to be between 250 and 300 MMBOE. From both the exploration and appraisal phases it has been demonstrated that placement of the production liner, at 13,500 ft (~4100 m), within the Lower Cretaceous Valhall formation (and ideally the Tuxen Limestone member) is a critical component of a successful well, and thus development project delivery. Failure to achieve an optimum setting depth for the production liner would have resulted in either the production liner set too shallow or drilling into the reservoir section with insufficient mud weight. Both scenarios have significant detrimental project implications. If the section TD had been too shallow, then the cementing of the production liner might have been compromised. Additionally, this would have resulted in a lower than expected leak off test (LOT) in the subsequent hole section and would have required the setting of a drilling liner. Drilling too deep into the section would have resulted in a number of negative impacts. Initially reservoir pressure would have been encountered with insufficient mud weight, resulting in a potential well control incident, once under control it would have necessitated the setting of a drilling liner.