Abstract
Abstract Chlorite bearing sandstones usually give low resistivity signals, and are thus erroneously identified as non pay zones, even if they exhibit good preserved porosities at depth. The purpose of the paper is to provide petrophysical and mineralogical laboratory measurements, that help improving the log interpretation in these sandstones. The main results, obtained on a selection of reservoir cores, for sandstones having an amount of chlorite between 3 and 11 wt-%, are (1) the cementation index and saturation exponent (m and n) have values lower than the common 2 values, n frequently around 1.5. These low values have been carefully checked in order to avoid experimental artefacts. (2) Cationic Exchange Capacities (CEC) and Specific Surface Area (SSA) have low values, as expected from the clay structure. (3) the distribution of pore throats is bi or tri-modal, with a large contribution of microporosity. The interpretation suggested by these results is that the amounts and distribution of microporosity associated to pore lining clay is the key of the chlorite sandstones electrical behavior. The values of CEC or SSA are too low to fully explain the low values of saturation index n. Use of these low values in log interpretation has the effect of increasing the evaluation of oil in place. Advantages of a multi-disciplinary approach for better evaluation of such complex argillaceous sandstone reservoirs is highlighted.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call