CHARACTERIZING PORE SIZE DISTRIBUTIONS OF WELL-CUTTINGS UTILIZING WATER INTRUSION POROSIMETRY

Understanding porosity and pore size distribution of reservoir facies is essential in assessing the producibility of petroleum deposits. Currently, measuring porosity requires gas pycnometry and/or mercury porosimetry; both of which occur after wellbore installation. However, due to heterogeneity of target formations, such methods may result in non-optimal well emplacement. As the exploration of tight, extended, unconventional shale plays continue to evolve, a porosity measurement method may be able to increase the success of wellbore placement. The Iowa Pore Index (IPI) test is a water intrusion porosimetry method that measures macro- and micro-pore volume in crushed rock samples. Although initially devised to evaluate pore size distributions within pebble-sized crushed sedimentary rock, this method can be advantageous for understanding the petrophysics of reservoir rock during drilling by analyzing cuttings through an inexpensive, non-destructive manner.

First, we generated IPI measurements from cuttings taken from Kansas petroleum wells. The fine nature of cuttings resulted in faster water intrusion that is observed with the pebbles usually analyzed by IPI. Second, to account for this faster intrusion, we modified the IPI; water intrusion at 35 psi (240 kPa) is measured after 1 and 15 minutes, by measuring the water intruded over shorter time intervals (0.1-2.0 seconds), as well as recording intrusion at up to 100 psi (689 kPa). With this method, 21 carbonate samples were compared to “traditional” IPI measurements, resulting in more accurate pore volumes. Results were compared with traditional petrophysical (e.g., helium and mercury porosimetry) and petrographic techniques. Cumulative intrusion plotted for the first two minutes of testing accurately discriminated lithology. Plotting incremental intrusion amongst various pressures suggests that the transition from macro- to micro-pore intrusion is source-specific and differs based on individual rock properties (i.e., pore sizes and types). With individualized IPI calculations, porosities better represent individual lithologies. This method may provide wellsite geologists with real-time estimations of pore sizes in shale and other tight rocks that can be used to better plan wellbore emplacement within a heterogeneous target zone.