Data-Analysis Approach Aids Reservoir-Quality Prediction of Microporous Carbonates

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper IPTC 19972, “Improving Reservoir-Quality Prediction of Microporous Carbonates Using a Multiscale Geophysical Data-Analysis Approach,” by Ahmad Ramdani, SPE, Viswasanthi Chandra, and Thomas Finkbeiner, SPE, King Abdullah University of Science and Technology. The paper has not been peer reviewed. Copyright 2021 International Petroleum Technology Conference. Reproduced by permission. Understanding the effect of microporosity on reservoir quality and predicting the spatial distribution of microporosity at the reservoir scale accurately is required to improve the recovery of remaining hydrocarbons from reservoirs. Using an integrated data-analysis approach applied to multiscale geological and geophysical data sets from micrometer-scale scanning-electron-microscope (SEM) imagery to decameter-scale seismic data, the authors predict the distribution of microporosity at the reservoir gridblock scale. The proposed methodology is applied in the complete paper to the Arab-D reservoir equivalent outcrop data from the Upper Jubaila formation in Saudi Arabia. Methodology This methodology is tested at an 800-m-long roadcut along the Riyadh-Mecca Highway in Saudi Arabia, stratigraphically equivalent to the Upper Jubaila Formation in the subsurface (Fig. 1). A 35-m-long core was drilled from the top of the same roadcut (dubbed the DQ-1 well), from which 106 cylindrical horizontal core plugs were obtained, drilled with an average spacing of 30 cm. This outcrop location was chosen because the pore volume in this interval is characterized by porosity with pore-diameter distribution of less than 10 µm. This outcrop provides an excellent analog to study microporosity-dominated carbonate rocks irrespective of their diagenetic origin. Moreover, the Upper Jubaila formation is a part of the Arab-D reservoir in the subsurface, which has been acclaimed as the most prolific oil reservoir in the world. Because this study used outcropped rocks, the authors acknowledge that differences in petrophysical properties with the subsurface rock formations will exist. Therefore, the study is not intended as a one-to-one analog for the Arab-D reservoir. Instead, the aim is to establish a general methodology that links micrometer-scale morphology of microcrystals that hosts microporosity with macroscale petrophysical properties and seismic attributes. Details of the methodology of seismic data acquisition and petrographic and petrophysical analysis are provided in the complete paper.