Abstract

In order to improve identification of low resistivity pay in the Attaka field, Magnetic Resonance Image Logging (MRIL) was acquired over selected intervals in five wells. The introduction of this new technology was intended to directly measure irreducible water saturation, effective porosity, moveable fluids and permeability.

There are two types of low resistivity pay in the Attaka field : (1) due to large amounts of irreducible water and (2) due to shoulder or thin bed effects. The low resistivity pay was recognized during the development starting in the mid 1980's and since then has made a major contribution to production. Over the years various methods were used to enhance log analysis with mixed success. Extensive RFT testing and field experience remained as the most reliable methods to recognize these reserves.

MRIL logging was introduced to improve the identification of low resistivity pay by directly providing a clay volume indicator, which is especially applicable to intervals with a high content of volcanic rock fragments.

The MRIL results from limited wells and intervals are being applied over the entire field using statistical methods. One immediate benefit is improving estimation of permeability and the understanding of the contribution of each layer to the initial production. Other benefits will come from the contribution to ongoing projects involving detailed 3-D geological modeling aimed at improving recovery by infill drilling and enhanced recovery. MRIL results and interpretations are compared to other logs and core data. Its value and limitations are discussed as well as the impact on future development of low resistivity pay.