The well within the context of this paper is carbonate formation in East Java basin deposited in late Oligocene to early Miocene. It is divided to 3 reservoir targets and potentially has different flow units, which believe predominantly due to secondary porosity. The well testing in exploration well drilled on the carbonate reservoir has commingled mixed between oil and water. Further appraisal well was necessary to be drilled to evaluate hydrocarbon saturation. The studied well was designed by combining the development and appraisal objective, therefore the deviation of the well was significantly high angle well.

The conventional water saturation from resistivity based Archie did not give conclusive result because of fresh water environment and low contrast resistivity features. Utilizing nuclear magnetic resonance (NMR) log has been used for decades on carbonate evaluation through T2 (transversal relaxation time), and T1 (longitudinal relaxation time) for determination of pore type/system and differentiation of irreducible water from free fluid volume with applying fix pre-determined T2 cut-off.

NMR log acquired while drilling gives the continuous T2 distribution which can be utilized to derive the poro-fluid facies on the porosity system from the measured actual T2distribution. The new technique based on statistical "factor analysis" search the peak response from each T2 distribution in depth level. Each changing on the T2 peak distribution on every depth will be recognized as actual cut off the T2 distribution and it will represent the poro-fluid facies constituents inside the T2 distribution. This paper will discuss the application the technique applied to the LWD NMR for determining poro-fluid facies analysis on the carbonate reservoir. The ultimate purpose is to identify the free fluid type presence on the porous rock. It will also discuss the advantages of this technique applied to the NMR acquired while drilling and use synthetic based mud to minimize the invasion and the ambiguity of filtrate invasion that may effect the free fluid determination on the rock.

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