Case Study of Petrophysical Evaluation Utilizing Well Logs Data with Optimization of Reservoir Cut-off Parameters

Abstract

Petrophysical evaluation of well log data is essential for the exploration and evaluation of hydrocarbon-bearing formations. Moreover, there are no standard criteria to implement cut-offs on petrophysical properties as a direction for economic decisions. In the present work, a petrophysical evaluation of well logging data from four wells in a mature oil field is performed to identify formation quality as a potential for hosting mature hydrocarbons reservoirs. Full consideration of cut-off values was taken into account. The cut-offs were estimated from well-recognized petrophysical relationships for permeability as a function of porosity, water saturation, and shale content. Results verification and calibration were also made based on laboratory measurements of petrophysical properties obtained from available core plugs in order to minimize uncertainty. Lithology analysis and characteristics revealed that the target formation is mainly sand and shale sequences. Results from well logs were in agreement with results obtained from core data. Formation effective porosity varies from 16 to 26% in all wells. A wide range of variations is observed in water saturation ranging from 28 to 57% and permeability ranging from 20 to 3300 mD. This is in good agreement with other measurements and well log analysis that show the mature formation remains to be a good hydrocarbon reservoir with significant potential.

Experimental Measurements to Study Correlations between Porosity, Absolute Permeability, and Capillary Pressure

“…Whereas threshold capillary pressure may be very small for vuggy limestone consisting of large pores as well as for sandstones in which some particles are microporous such as clay or chert particles, and also for fractured rocks. Cut-off is another criterion that limits values of particular parameters such as porosity and permeability [26]. Reservoir quality is greatly affected by reservoir grain sizes as the reservoir quality increases with porosity and permeability increase.…”