Drilling Fluid Optimization at M Fields: How to Deal with the Total Loss in Globigerina Limestone Reservoir

Abstract A vision to become the largest gas producer in East Java – Indonesia, has led Husky-CNOOC Madura Limited (HCML) to increase its gas production by developing high-gas wells at M Fields. In December 2021, HCML commenced the M Fields development drilling campaign. Ten (10) development wells in three (3) fields were drilled and completed by March 2023. During the campaign, HCML used water-based mud (WBM) to drill all sections, including the reservoir section. The reservoir section is thin-highly porous Globigerina (GL) Limestone. This reservoir was characterized by Globigerina foraminifera abundance with excellence which has an average net-to-gross (NTG) of 95%, average porosity of 33-49%, and average permeability of 5-225 mD. Critical challenges were encountered due to limited available data on offset exploration wells leading to uncertainties in the simulation model and drilling design. Total loss circulation occurred while drilling the reservoir section of the first development well leading to the earlier setting of the well target depth (TD). Upon the total loss occurrence, critical actions were taken directly in a relatively short time, including the re-assessment of wellbore stability, reservoir properties, and fluid gradient and then followed up by optimization of the drilling fluid system and properties and application of optimized drilling parameters. This paper presents successful strategic actions to drill reservoir section in M Fields wells after encountering massive total loss circulation in the first field. These actions resulted in a technically feasible, economically viable, and reservoir-friendly system with adjustable mud weight (MW) and an optimized drilling operations plan and procedure. Ultimately, this process helped to drill the subsequent development wells safely and economically to TD leading to a successful M Fields development drilling campaign.