In Y Field, three wells were temporarily abandoned, which were based on conventional technology while drilling through this sour active HPHT asphalt formation (Kazh). MPD Operation & technology were introduced and finally solved the problem and successfully delivered the said three wells in time.
Conventional MPD was focusing on Constant bottom-hole pressure (CBHP), which is widely used in narrow operation window while drilling. During drilling those three wells, different concept were set to control asphalt invasion and hole stability, which was referred as “dynamic bottom hole pressure difference while drilling” by means of MPD operations.
The paper addressed feasibility studies to adopt MPD in active asphalt formation in Y Field prior to the real operation; “fit-for purpose” MPD operation design & operations while drilling through the first well in Y field; MPD equipment and parameters modifications after acquired experience from the first well; associated necessary knowledge and technologies to successfully drilled through abovementioned asphalt formation, Running Casing, Cement the same were also mentioned inside the paper. In order to completely introduce this different utilization in Y Filed, another case of drilling through formation Kazh (Asphalt formation in Y Field) with MPD under mud cap when hole is in total loss, is also introduced in this paper.
In conclusion, the paper indicated that knowing the character of Kazh formation stood the first position before introduce any new technology. While distribution of asphalt was not clear, a dedicated size of casing to seal off other formations in the original same open hole (e.g.: well F21) is still the option. If none of the above can be obtained, to analyze/investigate invasion speed of asphalt under different assumptions & conditions, utilizing MPD with controlled flow rate to selected asphalt shall be one of the best options, meanwhile, drilling fluid & tools should also be updated to adapt to this option. In case of failure of controlled flowing rate efforts, drilling asphalt with MPD and Mud Cup in order to quickly drill through will be the last solution to asphalt formation in Y field.