Due to the long section (between 700 and 1200 meters) of the anhydrite and salt in the upper Jurassic formation on the right bank of the Amu Darya in Turkmenistan, a polymer-sulfonated saturated salt (NaCl) based mud (PSSSM) system was prepared by using laboratory tests to prevent drilling fluid contamination from anhydrite and salt solids. Corresponding technical measures were determined after the laboratory testing and field application. This kind of mud system can effectively prevent down hole problems which will commonly occur in long sections of anhydrite and salt, such as plastic flow of salt and anhydrite, drilling fluids heavy contaminated by the salt and anhydrite, hole washout, pipe sticking, etc.
The PSSSM mud system can safely and effectively overcome the problems associated with these troublesome formations. More than 50 wells were drilled 100% successfully compared with other kind mud systems used in Turkmenistan. The drilling success ratio was only 40% before using this kind of mud system in this locality. A significant amount of experience was gained during the past 3 years which contributed to successful application of this fluid system.
Additionally, a lot of plant derivatives were used as fluids additives in the saturated salt water based mud system, which will satisfy the increasing of environmental concerns. All the plant derivative additives can easily be allowed to biodegrade after the completion of fluids services. Fluids recycling measures were also implemented to lower the cost and environmental impact. Sufficient mud weight (MW), amount of calcium and chloride ion needs to be maintained before and during drilling the anhydrite and salt section.
All the technical measures and conclusions have been retained for reference on future drilling in geologically similar areas. Considerations for improving the environmental impact and better reservoir protection can be made on the basis of these experiences.