Cement Evaluation in the Gulf of Thailand

Abstract

ABSTRACT Union Oil Company of Thailand, a subsidiary of Unocal Corporation, has developed major natural gas and condensate reserves in the Gulf of Thailand, approximately 130 miles south of Bangkok. Union, as operator on behalf of its co-ventures Southeast Asia Petroleum Exploration Company and Mitsui Oil Exploration Company Limited, has developed four offshore fields which are currently capable of producing 450 million cubic feet of gas and 20,000 barrels of condensate per day. Natural gas from these fields supply 30 percent of Thailand's energy requirements. The Gulf of Thailand provides a challenging environment for primary cementing and cement evaluation. Most wells are directionally drilled, deviated up to 60°, with an average total depth of 10,500', and have a bottom hole temperature of 320° F or greater. Oil base mud is used routinely for drilling, and requires consideration when planning the cementing operation. Evaluation of the cementing operation is critical, as zones to be perforated are always in close proximity to water, either as gas water contacts or permeable water sands. In order to obtain a good evaluation of cement quality and distribution, the Cement Evaluation Tool (CET) has been used on over 30 wells to complement and improve the information obtained from the conventional Cement Bond Log (CBL). This paper shows examples of both CBL and CET on several wells in the Gulf of Thailand. Recently, the CET and CBL have been recorded simultaneously on one trip in the well, enabling a special presentation which displays the data on one film. These practical examples show how gas migration and channelling can be identified, in addition to the effects of casing centralization. The accuracy and resolution of the CET acoustic caliper for use in casing inspection is shown. Examples show the importance of the total circumferential cement distribution data provided by the CET in determination of zone isolation. The lack of microannulus effect on the CET is presented, along with recommendations on how to obtain good quality log data.