Mitigation of Slim Open Hole Wireline Logging Risk Under High Overbalance Conditions

The oil and gas fields offshore Malaysia-Thailand border are well known for the presence of high pressure and high temperature reservoir characteristics. The hot environment favours the use of hostile wireline logging tools over logging while drilling tools for some measurements. High overbalance conditions are sometimes a necessary requirement to safely drill particular formations but bring with them operational challenges. For wireline logging a critical hazard is that of becoming differentially stuck, especially in the case of stationary logs such as pressure measurements, sampling, and coring. A reduction in allowable safe stationary times for these measurements can also compromise the quality of the results. Production wells in this area are generally drilled with slim 6-1/8″ sections through the reservoir. As the borehole becomes smaller the risk of sticking increases as the tool contact area increases and so is a particular concern in slim holes. This often leads to logging being run using costly pipe conveyed methods or the inability to obtain required data altogether. This paper presents case histories of wireline formation pressure testing and sampling in 6-1/8″ sections with high deviation, 3D trajectory boreholes with overbalance pressures of over 2,000 psi. The use of a high-performance roller system to create tool stand-off to mitigate differential sticking as well as eliminate friction is described, along with the use of an engineered hole finder to address hole access concerns. The importance of wireline simulation models to identify risks and test solutions in such conditions is also considered. Slim hole logging and logging under overbalanced conditions are often a source of concern for subsurface, drilling and service company personnel alike. Describing a successful approach to address both is of interest to all involved parties and should provide ideas and confidence to plan cost-effective logging in similar wells.