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M Field, the largest waterflood field in Southeast Asia, has been in production since 1952. As of October 2023, it produces 29 MBOPD/4.5 MMBFPD/99.4% Water Cut. Geologically, the reservoirs in M Field were formed in the fluvial to the inner neritic environment in the Central Sumatra Basin. BK Fm, BN Fm, and MN Fm are productive reservoirs in the Sihapas group, with the remaining oil controlled by stratigraphic and facies changes due to high reservoir heterogeneity. Therefore, M Field currently features two reservoir types, high quality reservoir and low quality reservoir, determined by facies types and rock properties.

Majorly from 1948 until 2015, the high quality reservoir was the primary focus for development in M Field, utilizing both Directional and Horizontal Wells. Yet, the water cut in M Field steadily rose to 99.4%. The project team has devised a development strategy focusing on low quality reservoirs. Various indications support that low quality reservoirs will be a future development in this field. For instance, a report from conventional core analysis post-surfactant injection in the Chemical Enhance Oil Recovery (CEOR) area, specifically Well M#1810, revealed remaining oil in fining upward facies after chemical flooding. Additionally, the interpretation of Side Wall Core (SWC) data indicates a promising potential for oil. Swab single data also adds confidence, indicating water cuts below 60%, opposite to the current field water cuts. However, producing low-quality reservoirs in directional or vertical wells only lasts for a short time due to low fluid rates. As a result, the M project team has started developing low quality reservoir layers with Horizontal Wells.

The horizontal pilot execution surpassed expectations, remarkably reducing the water cut from 99.4% to 6% in the initial test of well M#2058. Despite challenges in maturation and execution, the fluid rate achieved was 919 BWPD, and the oil rate remarkably reached 863 BOPD.