In Block Baka of Tuha Oilfield, China, because of coalseam, the borehole is unstable extremely, complex problems, accidents occured in downhole frequently, prolonged drilling period and reduced drilling rate. For the sake of safe operation with drilling in coalseam encountered, this study analyzed the primary reasons that weak anti-collapse ability and poor inhibitive ability resulted in complexities. Strong inhibitor and anti-caving agent were optimized by experiments. Finally, Aluminum & Amino Drilling Fluid formulation was developed. Aluminum & Amino Drilling Fluid provides many advantages with better rheological performance, less fluid lose and high temperature resistance, in particular, it has strong inhibitive ability and anticollapse ability.

Aluminum & Amino Drilling Fluid was applied from 2000–3527m in well Ke 21-Ping 1 while drilling. 64 layers of coalseam with 136m in total and 30 layers of carbonaceous shale with 49m in total were drilled. The thickness of single coalseam is up to 34m; 2 layers of coalseam with 11m and 58m thickness were encountered in directional interval in well Ke 33-Ping, and no borehole problems and accidents happened. Good results were obtained from the application of the drilling fluid in two wells on site.

In order to drill massive coalseam safely, and to improve the anti-collapse and inhibitors, the drilling fluid was applied to two wells in Block Baka successfully. The strong inhibitor and the efficient anti-caving agent played a positive role in stabilizing borehole in thick coal layers, and reduced complex circumstances effectively.

Therefore, Aluminum & Amino Drilling Fluid can ensure the stability of sidewall in the formation with thick coalseam, and reduce the complexities effectively; it played an important role in improving drilling rate and drilling efficiency, and accumulated a valuable experience for safety drilling in deep and complex formation.

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