AN OFFSHORE GABON INTEGRATED RESERVOIR EVALUATION APPROACH USING WIRELINE NMR AND PUMPOUT FORMATION TESTER

摘要

Oil, gas, and condensate are produced in offshoreGabon where conventional formation evaluationtechniques are often inadequate. Clay volume,water saturation, and reservoir quality are highlyvariable and unpredictable based on onlyconventional logs. Nuclear magnetic resonance(NMR) T_2 analysis is used to quantify clay volumeand reservoir quality, and 2D NMR is used toestablish fluid type. Fluid type analysis is a keyformation evaluation facet because reservoircompartmentalization is prevalent, resulting inunanticipated fluid column profiles, including freewater on top of oil and oil on top of gas. AlthoughNMR fluid type analysis enhances fluid columnprofiling, the method is affected by mud filtrateinvasion because of limited NMR depth ofinvestigation, which compromises the validity ofthe technique in some cases.A new formation evaluation approach evolvedfrom NMR fluid typing whereby pressure testingand pump-out fluid sampling are used to confirmand normalize NMR predictions. In addition,pressure testing is used to determine formationpressure and mobility before initiating samplingoperations. If mobility is high enough to moveformation fluids, a pump-out operation is initiatedto monitor the degree of filtrate contamination andto determine fluid type before initiating samplecollection. This integrated workflow combinesconventional log and NMR with pressure testingand fluid sampling analysis to confirm fluid typeand reservoir quality interpretation.Another key aspect of this integrated approach isthe simulation of the pumping time required toreduce filtrate contamination to an acceptable levelto determine fluid type and collect PVT-qualityfluid samples. These simulations are used as a prejobplanning guideline and are compared to actualcleanup times to refine future in-field predictions.This paper presents a multiple well case studyencompassing conventional log, NMR, and apressure testing and sampling integrated workflowfor determining fluid type and reservoir quality.This new approach provides an overall improvedunderstanding of offshore Gabon reservoircomplexity.