Effect of Reservoir Structural Rhythm on Carbon Capture and Sequestration (CCS) Performance

Abstract

In addition to the evolution of green and nano energy, sequestration of CO₂ is also an evolving method to control the global CO₂ footprint and greenhouse effect. Carbon Capture and Sequestration (CCS) is an established technique to capture carbon from anthropogenic sources, such as power and chemical plants, and then inject the same in subsurface rock micropores, to permanently store the CO₂. Besides its environmental credentials, CCS also offers economic opportunities in Gas Enhanced Oil Recovery and Methane displacement in coalbed reservoirs. CCS process incorporates various geological, geometrical and engineering understandings of porous media and fluid dynamics. Previous investigators have identified low permeability rock as a better site for CCS. However, little is known of the propagation and effectiveness of CCS in reservoirs that have multiple layers of sedimentation, vis-à-vis well topology and density, flow direction, storage site, and power optimisation. In reality, these layers altogether form a structural rhythm and gradient. In this study, we investigated the structural rhythms and gradients that optimise CCS by using two objective functions (Darcy and interstitial flowrates) and 15 structural criteria (such as pore size, porosity, tortuosity, and aspect ratio). An experimental method has been applied. Five analogous reservoir porous core samples with varying structural parameters have been tested. The results indicate that CCS optimisation is responsive to structural parameters. The rhythm analysis from this study suggests that the CCS gas flow requires a compound rhythm that has a positive porosity and negative pore gradients. That is, the CCS injection wells should be placed in the reservoir area with relatively low porosity (3%) and large pore size (6000nm), while the storage site should be at a relatively high porosity (20%) and smaller pore size (200nm). This study can be directly applied to CCS practice, such that, given a layered reservoir, engineers can predict the well placement or topology that would optimize some of the essential performance objectives of CCS.