The oil and gas potential of the pre-salt carbonatesof Brazil and West Africa has been the focus ofsignificant recent exploration interest. The primaryoil targets within the Kwanza basin of West Africaare complex pre-salt carbonate reservoirs. Indiscovery wells, hydrocarbon fluid identification,porosity characterization, and permeability arenecessary for robust resource estimates and asinput data for a strategy to determine intervals fordrill stem tests.The challenges to formation evaluation, includinghydrocarbon identification, are multifold.Complex distributions of pore geometries andreservoir quality are present in the formations.Light-medium native oil identification iscomplicated by oil-based mud filtrate invasion.The accurate determination of fluid volumes andpermeability in this challenging environmentrequires a solution with a higher level of reservoirunderstanding.A suite of advanced logging sensors, in addition toconventional measurements, are used to acquire asignificant body of data for analysis, comparison,and calibration to laboratory fluid and coremeasurements. The gradient and samples obtainedfrom formation testing are crucial in determiningthe thickness, quality, and connectivity of thehydrocarbon zone and, in turn, the commercialfeasibility of the well. In the pre-salt play, whererig costs can exceed 1 million USD per day, theability to focus data collection on zones that willyield good formation tests is of significant value tothe asset operator.This paper outlines a method of faciesclassification based on nuclear magnetic resonance(NMR) data. This method, when combined withother log data, has shown encouraging results interms of identifying facies which have a highprobability of yielding tight tests. These intervalsmay be avoided to improve the overall efficiencyof the pressure and sampling program. The methodpresented uses an integrated workflow, developedby the operator and service company, and enablesa significant savings in rig time and, subsequently,overall formation evaluation cost while stillacquiring critical information.
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