Use of X-Ray CT to Measure Pore Volume Compressibility of Shaybah Carbonates

Abstract

The Lower Cretaceous Shu'aiba formation (Shaybah field) in southeastern Saudi Arabia is a heterogeneous carbonate formation with various facies because of diagenetic alteration of the original rock fabric. Preliminary laboratory rock-mechanics studies indicated that the Shu'aiba carbonates are mechanically weak, with the majority of the rocks tested yielding very low strength values (less than 3,000 psi) when compared to samples from other carbonate reservoirs (Salamy and Finkbeiner 2002). On the basis of laboratory-derived rock-strength data from triaxial tests, the formation appears to behave in a plastic manner that strengthens the wellbore. To understand the stress behavior of the Shaybah rocks better, a set of pore volume compressibility tests was conducted in which the changes taking place within the samples were observed and quantified using an X-ray computerized-tomography (CT) scanner. A new technique involving dual-energy CT scanning was used to obtain the pore volume compressibility values, which were compared against the conventional triaxial-cell-generated data and published results by Harari et al. (1995) on cores taken from the same reservoir. Although the magnitude of the pore volume compressibility was the same between different setups, visual data showed some interesting behavior of the Shaybah cores including movement of grains in an irreversible manner even for a relatively low imposed effective stress of 2,000 psi. Some of the advantages of the new CT-based analysis technique include the generation of multiple pore volume compressibility curves from the same plug (a band of data, each at a different slice location), the "visualization" of the changes, the possibility of using either hydrostatic or triaxial cells to make the test more case-specific, and the possibility of measuring permeability under different stress conditions before, during, and after the test.

High-resolution X-ray computed tomography in geosciences: A review of the current technology and applications

“…a full strain map). The implementation of triaxial test cells in a micro-CT scanner (Charalampidou et al, 2011;Geraud et al, 1998;Hall et al, 2010;Lenoir et al, 2004;Otani et al, 2010;Raynaud et al, 2010;Siddiqui et al, 2010;Viggiani et al, 2004;Watanabe et al, 2009) can help to understand the stress-and timedependent deformation of porous structures (Figure 7). The magnitude of the rotation of individual grains during triaxial compression tests, plotted for the vertical slices through the middle of the scanned specimen is shown in Figure 7a.…”

Application of micro-CT to deep-marine outcrop data: towards a new tool to better assess primary sedimentary structures and processes at their origin

“…Since then, micro-CT techniques have been widely applied in Earth Sciences, especially in (i) 3D pore characterization (McCoy et al, 2006;Polacci et al, 2010) such as for reservoir characterization (Coenen et al, 2004;Sok et al, 2010;Tiwari et al, 2013;Kim et al, 2016;Schmitt et al, 2016;Lei et al, 2019;Su et al, 2022) and soil analysis (Sleutel et al, 2008;Munkholm et al, 2012;Singh et al, 2021); (ii) 3D grain analysis (Carlson, 2006;Jerram et al, 2009;Cnudde et al, 2011) particularly for minerals with metallurgical significance (Kyle and Ketcham, 2015;Ghorbani et al, 2011;Evans et al, 2015); (iii) structural processes (Otani et al, 2010;Siddiqui et al, 2010;Wildenschild and Sheppard, 2013), especially in fracture analysis (Bertels et al, 2001;Kumari et al, 2018;Yang et al, 2020). Without disregarding, the clastic sedimentology community also shows a growing interest in using micro-CT, particularly to highlight microfacies in sediment cores (Bendle et al, 2015;Van Daele et al, 2016;Wils et al, 2021;Sabatier et al, 2022).…”