Alan Butcher

3D porosity and mineralogy characterization in tight gas sandstones

Tight gas reservoirs exhibit storage and flow characteristics that are intimately tied to depositional and diagenetic processes. As a result, exploitation of these resources requires a comprehensive reservoir description and characterization program to identify properties which control production. In particular, tight gas reservoirs have significant primary and secondary porosity and pore connectivity dominated by clays and slot-like pores. This makes them particularly susceptible to the effects of overburden stress and variable water saturation. This paper describes an integrated approach to describe a tight gas sandstone at the pore scale in 3D. In particular, the primary and secondary porosity of a tight gas sandstone are identified and quantified in three dimensions using 3D X-ray micro-CT imaging and visualization of core material at the pore scale. 3D images allow one to map in detail the pore and grain structure and interconnectivity of primary and secondary porosity. Once the tomographic images ar...

High-Resolution Petrographical and Chemical Scanning of Karoo Sedimentary Rocks Near Dolerite Sill Contacts Reveals Metamorphic Effects on Shale Porosity

Host rock alterations related to high heat flow associated with igneous intrusions play an important role in changing the reservoir characteristics of oil and gas bearing shales. Such effects are common in the Permian black shale formations of the Karoo Basin that were intruded by basin-wide dolerites in the Early Jurassic (~182 Ma). Distinct changes in mineralogy and cracking of organic matter associated with high heat and fluid flow affect the porosity and permeability of host rocks. Analysis of drill core samples of the Karoo black shales close to upper and lower contacts of the dolerite sills indicates increased quartz content, decrease in hydrous minerals, and formation of metamorphic chiastolite. Most importantly, a notable decrease in the porosity is also observed in these samples.