Electrofacies Modeling in Volcanic-Naturally Fractured Reservoir : The Jatibarang Field Case Study

Syamsu Yudha¹, Arief P. Handoyo², Bambang Widjanarko¹, Emmy Suparka³, and Dardji Noeradi^3
1Pertamina EP Region Jawa, Cirebon, Indonesia
²Pertamina Ep Region Jawa, Cirebon, Indonesia
³Institute of Technology, Bandung (ITB), Bandung, Indonesia

A classical problem in characterization of volcanic-naturally fractured reservoir of the Jatibarang field is on its high heterogeneity and the existence of fractures. Electrofacies modeling has been conducted to characterize the reservoir. This model is built based on log expression on volcanic interval which then compiled with lithologic data from core. Artificial Neural Network method has been used to develop electrofacies model on uncored interval in four key wells. Facies variation in those key wells was then propagated to other wells in the field over the volcanic interval.
The modeling showed that reservoir can de divided into five electrofacies, i.e. lithic tuff, crystal tuff, vitric tuff, igneous rock, and sandstone facies. Vitric-and crystal tuff facies has been identified as the most prolific facies of oil production among the five-facies.
Porosity in vitric and crystal tuff facies was developed by fracture porosity and pore spaces that preserved after dissolution processes of unstable mineral in the rocks. Combination of such porosities formed permeability with the best storage capacity. Lithic tuff facies has also undergone dissolution processes of unstable mineral, but probable ineffective fracturing on this facies did not create a better permeability in compare to that of both vitric- as well as crystal tuff facies. Igneous rock facies shows less fractured due to its high resistance to deformation. To such facies, fractures did not significantly contribute permeability because they did not intensely develop.

AAPG Search and Discovery Article #90072 © 2007 AAPG and AAPG European Region Conference, Athens, Greece