Well Productivity Prediction for Laminated Reservoirs Using Borehole Electrical Image Logs.

Abstract

Abstract Due to increasing costs in hydrocarbon exploration, formation evaluation needs to be efficient in order to avoid excessive expenditures. Proper reservoir characterization in thinly laminated reservoirs is a key to successful field development. These thinly laminated reservoirs are complex due to their vertical heterogeneity. As a result, there is low resistivity contrast between water and hydrocarbon bearing zones when standard resistivity logs are used. Thus, it is crucial to deploy a high resolution formation evaluation in order to capture reservoir pay and detect hydrocarbon zones. This paper aims to demonstrate a methodology of using borehole electrical image log to determine effective permeability. The paper is the first attempt to develop a numerical technique to build a correlation between synthetic resistivity derived from borehole electrical image tool with other dynamic permeability measurements such as dual packer formation tester. A single well predictive model was used in the process to generate a high resolution numerical radial model from high resolution log data. Since the 1980's, micro electrical imaging tools have mainly been used for sedimentological and structural interpretation, qualitative interpretation for sand quality, and also for the sand count. However, from the systematic integration of borehole electrical image, NMR, pressure transient from an Interval Pressure Transient Test (IPTT) in the thinly bedded reservoirs, it is possible to use electrical image log variations for permeability estimations. This study therefore aims to develop the methodology for actual field data to predict well productivity. Introduction Laminated formations pose two major evaluation challenges for reservoir engineers:- 1st is the classic low resistivity pay problem as seen in vertical wells. Layers of clay, silt and fine-grained sand distributed within a hydrocarbon bearing sand will significantly reduce the apparent resistivity measurement. This low resistivity results in wrong fluid identification and therefore this zone might be overlooked. 2nd is the high angle well evaluation problem. The same laminated formation, when measured by an induction tool at moderate - high relative dip, will exhibit an increase in apparent resistivity beyond that measured in the vertical well. Again, the inaccurate calculation of water saturation and hydrocarbon volume may cause the error in reservoir estimation.