Taking Petrophysics to New Horizons – Far Field Saturation and Lithology in Clastic Reservoirs

Abstract

AbstractConventional logging-while-drilling tools acquire measurements close to the wellbore. Recent development of deep and ultra-deep resistivity technology has enabled measurements more than 100 ft from the wellbore. Far-field petrophysics in simple carbonate lithology is possible since saturation is dependent on resistivity and porosity. Hence, combining deep and ultra-deep resistivity measurements with data from offset wells can provide reasonable saturation mapping. However, in clastics the evaluation is more complicated since resistivity is more dependent on lithology.In most cases, the main challenge in carbonates is permeability identification. Far-field carbonate petrophysics can be derived from mapped resistivity utilizing deep or ultra-deep resistivity and offset logs. Evaluation of far-field petrophysics away from the wellbore in clastics is more complicated as it requires lithology identification to be incorporated into the petrophysical model. A workflow has been developed integrating near-wellbore measurements with ultra-deep resistivity and anisotropy derived from 3D inversion. The workflow provides a qualitative indication of the lithology, allowing saturation in porous sand to be derived based on inverted resistivity.An innovative workflow has been developed based on the available data and combining multiple sources of data from near wellbore, offset logs to inverted resistivity data. 3D inversion plays a critical role in this workflow as it provides a lithology indication far away from the wellbore, differentiating between shale and sand. The identification of shale members at a distance also provides critical information for models of reservoir connectivity and potential barriers to water influx. The combination of far-field petrophysics with lithology gives better evaluation on a reservoir scale for critical decisions in terms of completion and reservoir performance.The new workflow has been successfully tested on several wells and different reservoirs. The workflow has been used for far field petrophysics and saturation mapping based on real-time logging-while-drilling (LWD) data and offset data analysis combining shallow and deep measurements with the 3D inversion from ultra-deep resistivity. There are several benefits from this innovative workflow, including optimizing well placement, improving understanding of fluid distribution, and optimizing completions design and reservoir management strategies.