Title : The mechanisms and effects of CO2 brine rock interaction during supercritical CO2 fracturing for shale reservoirs
Abstract:
The development of hydraulic fracturing and horizontal drilling techniques has promoted the exploitation of shale gas/oil resources. Supercritical carbon dioxide (SC-CO2), with its special physical properties, has shown potential to enhance shale gas/oil recovery replacing water as the stimulation fluid. This presentation reports on the current status of shale gas/oil recovery, the potential role of SC-CO2 as a working fluid for shale gas recovery, and CO2 geological sequestration in shale reservoirs. SC-CO2 has a better rock-breaking capability than water, which is useful when drilling through shale formations. SC-CO2 fracturing creates rougher and more complex fracture networks than hydraulic fracturing, leading to higher permeabilities. Some of the injected CO2 for shale gas recovery could also be safely sequestered in shale reservoirs, thereby lowering carbon emissions and accessing CO2 tax credits. However, shale–CO2 or shale–water/brine–CO2 interactions during & after shale gas/oil recovery and sequestration can affect reservoir properties. The implied shale–CO2 imbibition process from available data generally persists for several years, far more than the several days assumed for most laboratory tests. A more detailed understanding is required for SC-CO2 injection on the efficiency of shale gas/oil recovery and the cost and environmental concerns of this technology. This will support the development of safe sequestration methods, supported by suitable laboratory and field tests, especially those focusing on geochemical, petrophysical, geomechanical and hydraulic properties.
