Abstract
Extreme climatic conditions in northern Russia can complicate the process of optimizing drilling and reducing the risk of non-productive time (NPT). To prevent these problems, the design process should incorporate new proactive technologies. However, to achieve efficient drilling of any single well, companies often choose only field-proven technologies.
At the Kyrtayel field in Komi Republic, a KCl-polymer mud was typically used when constructing wells with a four-string casing design and an average depth of 3,000 m. While drilling, a significant amount of NPT occurred due to the incompatibility of the traditional KCl-polymer drilling fluid with the Kynovsko-Sargayevsky bedrock formation, located above the roof of the production zone. Drilling fluid incompatibility led to such difficulties as caving formations and related hole reaming, bottomhole assembly (BHA) drag, and loss of circulation due to the clogged annulus.
To solve such problems, an improved drilling fluid selection process was implemented. Extensive tests were conducted on core samples, and global and local experiences from applying high-performance drilling fluids were analyzed. The drilling process analysis was performed on finished wells and the applicable mud systems. Based on the analysis, the company required a drilling fluid that meets the following conditions:
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A water-based fluid to reduce environmental impact and labor costs;
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A significant reduction of NPT and well construction time.
The core analysis showed that the high tendency for wellbore instability is caused by the mixed layers of hydromica. As a result of extensive discussions, it was agreed to study a recently developed, high-performance KCl-based, non-dispersed water-based fluid (HPNDF) in a lab environment.
After the research, an aqueous HPNDF, formulated with an optimized package of shale inhibitors, was approved for field testing.
Field test results showed a significant reduction of NPT corresponding to the sharp improvement in wellbore stability. After several fluid optimizations, the next well was drilled with zero NPT. The HPNDF reduced the caving intensity, improved hole cleaning and allowed for better cement job quality on the intermediate casing. The system was maintained within the required parameters using standard equipment on the rig.
This paper provides lab results, analysis of drilled wells, the formulation and the field test results for the proposed fluid.
