Abstract

The primary goal of this paper is to investigate the caprock sealing capacity to assess the feasibility of CO2 injection in major hydrocarbon fields of Oklahoma Panhandle. This study was done by selecting 49 representative core samples from caprock formations in three counties (Cimarron, Texas, Beaver) of Oklahoma Panhandle. Core samples were collected from various formations (e.g. Cherokee, Keys, Morrowan) at different depths. Available sources of information are MICP (Mercury Injection Capillary Pressure) and SEM (Scanning Electron Microscopy) for all 49 samples. SEM images were used to study the distribution of minerals and texture of the core samples. Moreover, EDS (Energy Dispersive X-Ray Spectrometer), specific surface area, and TOC (Total Organic Carbon) tests were available for 30 samples. Pore-throat-size distribution, sorting, and grain size were determined using MICP and Sedigraph measurements.

Through studying the sealing capacity, we tried to identify the major factors controlling sealing capacity of the caprock and their respective contributions. Better understanding of the factors controlling the sealing quality of the caprock will advance our knowledge regarding the sealing capacity of the shales, anhydrate, and carbonates.

Among available 49 core slabs, shales and carbonates with interbedded layers of shales showed relatively higher threshold capillary pressure. Based on these observations, shale formations could be considered as a promising caprock in terms of preventing carbon dioxide leaking into above formations. We believe that certain characteristics of the shales e.g. low permeability, fine pore size, high specific surface area, and strong physical chemical interaction (surface tension) between wetting phase and mineral surface makes shales a decent caprock for both CO2 sequestration and hydrocarbon reservoirs.

We hypothesized that the sealing capacity of the caprock could be controlled by textural and/or compositional properties. Using multi-variable data analysis techniques we tried to assess the effects of each group of properties on maximum hydrocarbon height that can be hold by the caprock. We conclude that bulk density, quartz content, and specific surface area showed positive correlation with sealing capacity of the caprock. In contrast, mean pore radius and porosity were the most distinctive parameters with negative correlation with sealing capacity.

Keywords: carbon dioxide sequestration, sealing capacity, mercury injection porosimetry, principal component analysis