An Assisted Method for Depositional Facies Mapping and Reservoir Connectivity Evaluation Based on Converted Pressure

Abstract

Formation test pressure is one of the most important and invaluable surveillance data to understand reservoir dynamic behavior, but usually pressure of different wells are not tested at the same time which limit its function. This paper proposed a simplified material balance equation to convert all tested pressure to the same date, then use converted pressure to assist depositional facies mapping and reservoir connectivity evaluation. Take M1 reservoir for example, all pressure data are converted to the same artificial test date with a simplified material balance equation. The material balance equation is simplified under certain assumptions, which is similar to that of volumetric undersaturated oil reservoirs. Then wells were classified into different groups for each zone according to their converted depletion pressure change behavior, and depositional facies and reservoir lateral connectivity of different groups of wells are analyzed with clear understanding and obvious characteristics. M1 reservoir is a multi-layered sandstone reservoir under primary depletion currently, which have 18 wells conducted formation test from 2010 to 2011. It is found that pressure analysis of these wells have no obvious characteristic. But after all pressures converted to the same date with well production constrained, depletion pressure change has clear trend. Then for each zone, wells were classified into different groups according to pressure change behavior, which indicates pressure depletion is similar in the same group while much different from that of other groups. Converted pressure data were analyzed in detail for each zone and used for depositional facies mapping and reservoir connectivity evaluation. Most are consistent between pressure depletion behavior and geological understanding, but some also have contradictions which helps to revise depositional facies. For reservoir connectivity, similar results of depositional facies are drawn. This paper offers a case study of converting pressure to the same date based on simplified material balance equation, and how to use converted pressure for depositional facies mapping and reservoir connectivity evaluation study are also detailed presented.