Chayvo Field, Sakhalin Island, Russia: Identification of a Significant Oil Leg from 3-D Seismic and Execution of a World Class Extended Reach Drilling Program

Apotria, Ted¹, Randall Mathis¹, Rick J. Powell², Bridget Venner² (1) ExxonMobil Development Company, Houston, TX (2) ExxonMobil Development Company,

In 1997, the ExxonMobil-operated Sakhalin I Consortium acquired a 3-D seismic survey over Chayvo Field, located off Sakhalin Island. Chayvo was previously thought to contain primarily gas given the results of 5 exploration wells. Interpretation of 3-D seismic revealed amplitude anomalies which conformed to structural spill downdip of gas accumulations seen in the crestal wells, indicating the potential for very large, previously unrecognized oil rims. An appraisal well was drilled in 2000 and penetrated several large oil legs postulated from the 3-D seismic. Associated sequence stratigraphic studies resulted in a significant oil project.

Development drilling at the field began in 2003, with the first phase comprising a series of extended reach wells drilled from an onshore location reaching offshore 9 to 11 kilometers to the western limb of the Chayvo anticline. These wells are technically complex and very expensive, but can be attractive considering offshore platform costs in a remote, environmentally sensitive location characterized by seismic activity and icebergs.

In 2002, a multi-disciplinary team was assembled to address these challenges. 3-D seismic visualization played a key role in planning the well paths. The primary geological concern was the accuracy with which the horizontal wellbores could be placed within the oil column as reservoir simulation indicated the need to be within 10 m of a specified vertical depth to optimize production performance. Ongoing ERD drilling has proven to be successful with actual reservoir depths coming within a few meters of prognosed depths at well reaches of 9-11 kilometers.