NMR MEASUREMENT OF POROSITY AND DENSITY FROM DRILL CUTTING OF UNCONVENTIONAL TIGHT RESERVOIRS

Abstract

Petrophysical data, essential for reservoir description and modeling, are obtained by expensive laboratory core measurements and/or well-log measurements. Due to the high cost, these tests are typically only carried out for a limited number of wells in the exploration phase. In contrast, drill cuttings are available for all the wells and thus can provide reservoir data throughout all the phases of the field development. A nuclear magnetic resonance (NMR) based method was developed to accurately determine petrophysical properties including porosity, bulk density, and matrix density from drill cuttings of unconventional tight reservoirs. NMR technology allows for the separation of liquid signals from within and between the shale cutting particles and when used in combination with Archimedes-based mass measurements provides accurate porosity and density data for both vertical and horizontal wells. The results from the NMR cutting analysis were in good agreement with other accepted lab measurement techniques having reproducibility well within 5%. We show the measured porosity and density from the cuttings changes significantly along a tested horizontal well, which is a strong indication of horizontal heterogeneity of the reservoir. The results may be used to guide selection of certain stages for hydraulic fracturing. This method can be easily adapted at the wellsite to evaluate reservoir heterogeneity and select zones with large porosity for optimized fracturing. Obtaining accurate petrophysical data from drill cuttings can provide quasi-real-time data for quick formation assessment for the wellsite engineers and cut costs by reducing or eliminating some expensive and inadequate formation evaluation tools.