Digital Rock Physics Assessment of Reservoir Quality from Ditch Cuttings Using SEM-Derived Porosity Analysis of D1 Sandstones in the Inneh Field, Niger Delta, Nigeria

Abstract

Conventional core analysis remains the most reliable basis for calibrating reservoir properties, yet full-core acquisition is commonly restricted by cost, operational risk and limited interval coverage, particularly in offshore fields. This study restructures and advances a Digital Rock Physics approach for evaluating reservoir quality from ditch cuttings obtained from the D1 reservoir interval of the “Inneh” Field, offshore southeastern Niger Delta, Nigeria. The work applies scanning electron microscopy, 2D image segmentation, and pore-area-based porosity estimation to representative ditch cutting samples from “Inneh”-1, “Inneh”-7 and “Inneh”-10. The central objective is to test whether ditch cuttings, when processed through a controlled SEM-based workflow, can provide reservoir-quality information consistent with conventional log-derived porosity. The analyzed samples show quartz-rich sandstone fabrics with partially fractured grains, open intergranular pores, secondary pore features and locally infilled pore spaces. Image analysis yielded SEM-derived porosity values of 34.8%, 34.9% and 37.5% for “Inneh”-1, “Inneh”-7 and “Inneh”-10, respectively, compared with log-derived porosity values of 32.0%, 37.0% and 36.0%. The absolute differences range from 1.5 to 2.8 percentage points, with a mean absolute error of 2.13 percentage points, a root mean square error of 2.20 percentage points and a mean absolute percentage error of 6.20%. Although the small sample size limits statistical correlation, the close absolute agreement supports the use of SEM-derived porosity as a screening and validation tool where conventional cores are unavailable. The study demonstrates that ditch cuttings retain meaningful pore-scale information and can supplement formation evaluation workflows in clastic reservoirs. The applied workflow provides a practical, cost-conscious route for integrating readily available drilling materials into preliminary reservoir characterization, while recognizing the need for larger sample populations, core calibration, and three-dimensional imaging before pore connectivity or field-scale reservoir behavior can be evaluated for full field-scale validation.