Applying Downhole Fluid Analysis and Wireline-Formation-Testing Techniques in Reservoir Management and Well Completion—Case Studies

Abstract

Abstract The Gharif and Al Khlata Formations form significant reservoirs in north-central Oman. The reservoirs are multilayered, heterogeneous and highly variable in terms of geometry, connectivity, permeability and fluid properties. Newly drilled wells often show differential pressure depletion between layers, which helps assess lateral and vertical reservoir continuity. However such complexity and reservoir heterogeneity means that conventional pressure-depth plot and pressure gradient analysis of wireline pressure data is not easy, and identification of in-situ fluid density changes can be difficult. A significant part of formation evaluation within these reservoirs has required the application of downhole fluid analysis (DFA) and fluid identification using a pumpout wireline formation tester. The primary objectives being to obtain a measurement of formation pressures, identification of the formation fluids, capture fluid samples and determination of fluid mobility. Such information is important input for both reservoir management purposes and in optimizing the well completion strategy. We discuss testing techniques using a modular wireline formation tester equipped with a dual packer and/or probe modules, and latest generation optical fluid analyzers. The tests usually comprise of extended pumpout, drawdown and buildup periods, during which oil-based mud filtrate contamination, and fluid composition are monitored in-situ in real time. The techniques applied include in-situ characterization of reservoir fluid type and composition, gasoil-ratio (GOR), and the use and application of fluorescence measurements. In this contribution we compare and demonstrate the utilization of data from wireline downhole formation fluid analysis and formation tests, and also their practical application in reservoir management.. The field examples described are from wells mainly drilled with oil-based mud. We present some case studies and discuss how the results from tests conducted in different flow units in individual wells, and arealy across the field in multiple wells, have been used in reservoir management and well completion.