Meteoric Water Flushing and Microbial Alteration of Klamono and Linda Oils, Salawati Basin, Eastern Indonesia: Geochemical Constraints, Origin, and Regional Implications
Satyana, A.H.*, Wahyudin, M.**
* JOB Pertamina-Santa Fe Salawati, currently at Pertamina-BPPKA
** Pertamina-EP Irian Maluku Exploration Team
Klamono and Linda Fields provide good examples of oil alteration due to meteoric water flushing and biodegradation. The oils show characteristics of biodegraded oil : low gravity, high sulfur content, high viscosity, low pour point, low saturated hydrocarbon content, removal of the majority of n-paraffins and isoprenoids, and increased δ13carbon isotope ratio of saturates. Based on the molecular geochemistry (GC/GC-MS) data, the oils are moderately biodegraded (level 3 to 4 at Hunt, 1996’s scale).
Regional evaluation answers the question on the origin of the biodegradation. The Miocene Kais carbonates forming the reservoir of the Klamono Field was outcropped to the east at the Ayamaru Platform. Meteoric water has entered this area, flowed downdip westwards to the Klamono Field, and altered the oils through microbial alteration. The shallow depth of the Klamono reservoir enhanced the biodegradation.
The Linda Field is in different mechanism of biodegradation. The field is located frontal to a major surface normal fault called the Cendrawasih Fault. A splay of the Cendrawasih Fault faulted the Linda Field. The faults are considered to have acted as conduits for meteoric water to reach faulted Kais reservoir of the Linda Field and altered the oil through microbial alteration. Other oils located along the Cendrawasih Fault are biodegraded and thus support this consideration. Based on the above two mechanisms, the regional distribution of biodegraded and non-biodegraded oils within the Salawati Basin can be expected. The methods of this study can be applied elsewhere.
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