Standard Operating Procedure for Analysis of Oil Rim Occurrence & Viability in Gas-Down-To Reservoirs

Abstract

Abstract Nigeria has over 180 Tscf of gas resource volumes to support its export and domestic gas demand. Significant quantity of these resource volumes are associated with reservoirs encountered in down dip oilrim with varying oilrim thicknesses or in Gas-Down-To (GDT) situation requiring appraisal and justification prior to gas development which may lead to restriction on gas readiness. Unlocking these gas volumes is key to maintaining gas supply and meeting contractual obligations. Therefore, this paper presents a Standard Operating Procedure (SOP) which provides a structured approach and workflow for analyzing and managing the uncertainty of potential oilrim below known GDT reservoirs and evaluating the technical producibility and viability of the oilrim reservoirs. It also discusses the different methods currently being used in the industry, applications and boundary conditions in estimating hydrocarbon fill below know GDT and highlights results of blind test analysis carried out for five wells drilled in the Niger Delta. The application of this SOP provides a quick assessment guide to aid timely decision on gas field development without necessarily drilling an appraisal well thereby saving huge cost especially in this era of low oil price and funding challenges. The SOP adopts an integrated approach and involves the use of available geoscience and engineering data to estimate fluid contact below known GDT. It takes into account the environment of deposition, reservoir depth, historical knowledge and production data to estimate contact and oilrm viability. Minimum data required for each analysis is detailed in the SOP workflow and methodology outlined for ease of adaptation. These methods are reliable techniques and should not be used in isolation but to compliment the other. Results from blind test analysis for five wells selected for this study demonstrates a potential savings of $60 MMUSD from drilling a minimum of two appraisals wells and enabled a timely decision to be taken for the development of the gas reservoirs leading to maximimzation of cash flow and NPV.