Wettability becomes a crucial parameter in understanding the reservoir rock behavior due to its effect on characterizing the distribution of fluid saturation, estimation of primary oil recovery, and certainly to determine the IOR/EOR application plans. However, many practitioners in core laboratory analysis use inappropriate fluids (synthetic oil) in measuring special core analysis (SCAL), while the detail compositions of fluid in reservoir condition can strongly influence the wettability value. As the consequences, the results of measurement give unmatched to the real reservoir condition. This paper dedicates a case in carbonate reservoir to estimate in-situ reservoir wettability and capillary pressure by using wireline pressure test data and conventional log while the core data analysis are un-trusted to be implemented.
Two well cases are used in this study from a carbonate reservoir field located in the North East Java Basin area. Relative permeability, capillary pressure, and electrical property obtained from the core measurement of TB reservoir shows that the wettability of TB Reservoir is water wet. The interpretation of in-situ wettability using reservoir pressure test data suggests that the wettability of rock is weakly oil wet. This study also re-construct the capillary pressure which is appropriate with in-situ wettability.
Regarding to this case, an integrated analysis of conventional log and wireline formation testing data are strongly needed. At first, Free Water Level (FWL) and Oil Water Contact (OWC) are determined by integrating formation pressure test, flow test, and well log data (especially for resistivity log) which can also be used to define the reservoir wettability. Then, the vertical water saturation is interpreted by simple Archie's equation with a and m parameters are obtained from Pickett Plot and n is generated from Al-Hilali's method and Krygowski and Cluff's method. By plotting and interpreting formation pressure data versus depth and vertical fluid saturation from electrical log respectively, a new capillary pressure curve model and wettability are established.