The Solving Interpretation of Mn3o4-K Formate Mud Effect on LWD/LWT Measurement: Case Study Of Hpht Gas Field, Offshore Madura Strait, East Java

Abstrak

HCML had drilled several horizontal development gas wells in the high pressure and high temperature (HPHT) field which is located in offshore Madura Strait, East Java. The objective reservoir in this field is Kujung Formation, which has low reservoir heterogeneity and good reservoir properties due to diagenesis process. The manganese tetraoxide-potassium formate (Mn3O4-K formate) mud was used in latest development wells, as one of the first well in Indonesia that use this advanced mud. Its unique physical and chemical mud properties were successfully ensuring borehole stability in drilling process. However, it confirmed large mud effects and showed significant changes of log character based on the latest LWD/LWT data in these development wells
This paper explains the effect of Mn3O4-K formate mud on logging measurements, including borehole and invasion effects. Basically, the properties of Mn3O4-K formate mud are significantly different from the conventional water based mud that was used in previous exploration well. It has high radioactivity, high density, high photoelectric factor, low hydrogen index (HI), extremely conductive mud and strongly invasive into formation especially in high porosity and permeability reservoir. Therefore, formation evaluation showed underestimate result due to this mud effect. The simplistic approach to correct the Mn3O4-K formate mud effect was using log normalization method due to data limitation on these development wells. This method assumed that the reservoir has low heterogeneity and the mud had invaded into formation completely. Thereafter, deterministic approach can achieve the appropriate logging interpretation.
The formation evaluation result of the latest development well had been compared with the previous exploration well which had wire-line log and core data. Other than that, the evaluation of gas deliverability during well cleanup was also applied to validate formation evaluation result. Finally, the application of Mn3O4-K formate mud is encouraged and the challenges of the formation evaluation have been successfully overcome.