The Well Trajectory Impact on Hydrocarbon Discovery in Fractured Basement Reservoirs - A Case Study from CuuLong Basin, Vietnam

Li, Bingjian¹; Embong, Wan Z.²
¹Schlumberger, Ho Chi Minh City, Viet Nam.
²Petronas Carigali, Ho Chi Minh, Viet Nam.

The Mesozoic granite basement in the CuuLong Basin of southern offshore Vietnam experienced a few major tectonic deformations which resulted in development of multiple fracture and fault systems within. The potential productivity for each fracture set can vary significantly. Therefore recognition of the main potential productive fracture set(s) in any given field for optimizing well trajectory plays a critical role in delivering a productive well and then impacting both exploration and development success.

In this case study, there were three exploration wells drilled to the basement in the selected field in the past without commercial oil discovery. The existing wells include one vertical and one highly deviated in the southern part of the field and one highly deviated in the northern part. Hydrocarbon shows were detected in all wells. Prior to a new exploration well proposal in 2011, the acquired borehole images and Dipole Sonic Imagers from existing wells were studied along with dynamic data. As a result, a group of NNW-SSE sub-vertical fractures was interpreted as the dominant potential productive fracture set in the studied wells. Outcrop data from the nearby coastal area provides very useful information to better understand the fracture systems structurally. A conceptual fracture model was built for the studied field by integrating all data available. On the basis of the fracture study results, an optimal well trajectory recommendation was made to the new well. The new well, located based on 3-D seismic attributes, was drilled in the southern part of the field between the two existing wells with NE-SW well azimuth and high deviation. A successful commercial oil discovery was finally made in the field. The case study shows that the right well trajectory with maximized penetration of the defined potential productive fractures made a positive impact to the new well success. The experience learned from the case study has application to the future exploration and development in fractured basement reservoirs.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012