Synchrotron Microtomography of Vugs and Microfractures Formation within Sediments due to Fines Migration via Multiphase Flow

Summary Ensuring safety and stability of reservoir formations is critical, yet fines migration due to multiphase flow, can destabilize sediments within the formation. Gas moving through microscopic pores toward a production well, along with sweeping motion of the gas-water interface, can mobilize fine clays within the sediment pores. Such migration causes pore-throats to narrow then clog with fines, leading to reservoir pressure build-up within pores, which dislocates sand grains in unconsolidated porous media, causing the formation of vugs or fractures. To predict such catastrophic changes to the porous media, in-situ pore-scale observations within sediments are necessary. Therefore, 3D scanning using fast synchrotron microcomputed tomography experiments of unconsolidated sandy sediments was utilized. Kaolinite and Montmorillonite clay was used to prepare six mixtures of sand and clay powders, three for each clay type with clay content of 2%, 4%, and 6% (of sand weight). Samples underwent multiphase flow and were scanned at Argonne National Laboratory. Formation of fractures in sandy sediments due to fines migration was observed at a clay content of 6% kaolinite. For the same content using montmorillonite vugs formed. Gas pathways were connected through microfractures, but disconnected within vugs. Throughout all samples, fines migration resulted in sediments compression and consolidation.