A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering in Offshore Technology and Management, School of Engineering and Technology

Thesis (M.Eng.) - Asian Institute of Technology, 2008

Pattani Basin is located in the Gulf of Thailand. Exploration of Pattani Basin by The Company was started in 1973. Production wells were drill into high temperature zone which affect mud selection and stability of additive. This zone is consisted of claystone, sandstone and slightly present of coal. For a soft and unconsolidated formation, it is important to maintain wellbore stability. Shale always is concerned in claystone well type. Typical drilling fluids which well known are used for drilling in many locations. Frequently, there is necessary to improve performance of drilling fluid to fulfill a drilling objective or prevent potential hazard. Three wells were selected from different field in Pattani Basin. This study requires formation data, drilling report, mud report, and mud log. The formation data and mud log were processed in this study. Properties of drilling fluid and additive were study from Mud report. The drilling fluid properties obtain by mud testing which can describe condition in well bore. The mud test result was analyzed and adjusts properties to deal with changed condition. Most time in the process of drilling well, one or more of properties precedence over the other. Likewise one additive is mainly improves one property but side affect to other properties. Comparison effect of temperature in these three wells was processed and shows how it affects to mud properties especially rheological. Methods used for mud selection based on formation condition are described with recommendation to be used for future resemble operation