During Pulling Out of Hole operations, we observed a thick, black, tar-like material coating the BHA—strongly indicating the presence of asphaltic or bituminous hydrocarbons in the formation. This type of occurrence can point to natural bitumen, biodegraded oil zones, or heavy hydrocarbon residues near oil-water contacts. While visually striking, these materials pose real operational challenges: fouling of downhole tools, reduced solids control efficiency, and the need for immediate cleaning and analysis. It’s a reminder that the subsurface is full of surprises—and how critical it is to integrate geological awareness with operational readiness at every stage of drilling.
This type of occurrence often points to the presence of asphaltic or bituminous layers in the formation. Such substances are typically viscous, tar-like, and may result from biodegraded hydrocarbons, natural bitumen, or even tar sands. They are often found near oil-water contacts or in shallow, heavily altered reservoir sections.
Other possible causes could include hydrocarbon soaking from oil-based mud or the return of formation fluids following lost circulation. In some cases, this kind of sticky buildup might also be linked to plugged or overpressured zones that release heavy hydrocarbons during tripping operations.
Operationally, this raises a few concerns:
-The need to thoroughly clean the BHA and tools before going back in hole
-Potential sensor interference on MWD or LWD tools
-Reduced efficiency in solids control systems
-The importance of sampling the material for lab analysis to confirm its origin
To better understand the nature of this material, correlating with logs, gas readings, and formation tops is essential. Sampling and laboratory analysis (e.g., GC-MS, FTIR) will help determine if it’s naturally occurring bitumen, crude oil, or an artifact of drilling fluids.
This is a great reminder of how dynamic and unpredictable subsurface geology can be—and the importance of staying observant and prepared during every phase of drilling operations.