Abstract

This paper presents a cost effective, quantitative methodology that has been successfully demonstrated to provide improved reservoir characterization and prediction of permeability, production and injection behavior during primary and enhanced recovery operations. The method is based on identifying intervals' of unique pore geometry (rock type). This approach applies high level image analysis techniques of core material to quantitatively identify various pore geometries. When combined with more traditional petrophysical measurements on conventional core samples, various pore geometries (rock types) can be recognized from conventional wireline logs in non-cored wells or intervals. This allows the calculation of rock type and a superior estimation of permeability and saturation. Based on geological input, the reservoirs can then be divided into hydrodynamically continuous layers (flow units) and grid blocks for simulation.

An overview of the results obtained in a complex carbonate and a sandstone reservoir are presented. When combined with production data, the improved characterization and predictability of performance obtained using this unique technique has provided a means of targeting the highest quality development drilling locations, improving pattern design, rapidly recognizing conformance and formation damage problems, identifying bypassed pay intervals, and improving assessments of present and future value.

Introduction

This paper presents a technique for improved prediction of permeability and flow unit distribution in two different types of reservoirs. The studies focus on the use and integration of pore geometrical data and wireline log data to predict permeability and define hydraulic flow units in complex reservoirs. The two studies referenced in this paper are funded by the US Department of Energy as part of the Class II and Class III Oil Programs for shallow shelf carbonate (SSC) reservoirs and slope/basin clastic (SBC) reservoirs. One objective of the program is to demonstrate advanced reservoir characterization tools that will result in a significant increase of reserves.

SHALLOW SHELF CARBONATE RESERVOIR
Background

SSC reservoirs in the USA originally contained > 68 BBO (about one-seventh of all the oil discovered in the Lower 48 States). Recovery efficiency is low; some 20 BBO have been produced and current technology may only yield an additional 4 BBO.1 The problem of low recovery efficiency in SSC reservoirs is not restricted to the USA - it is a worldwide phenomenon. SSC reservoirs share a number of common characteristics, including:

  1. A high degree of areal and vertical heterogeneity, relatively low porosity and relatively low permeability

  2. Reservoir compartmentalization, resulting in poor vertical and lateral continuity of the reservoir flow units and poor sweep efficiency

  3. Poor balancing of rates of injection and production, and early water breakthrough in certain areas of the reservoir. This indicates poor pressure and fluid communication and limited re-pressuring

  4. Porosity and saturation as determined from analysis of wireline logs do not accurately reflect reservoir quality and performance

  5. Many injection and production wells are not optimally completed with regard to placement of perforations, and the stimulation treatment can be inadequate for optimal production and injection practices

The North Robertson Clearfork Unit exhibits all of these characteristics.

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