Influence of Flow Pathway Geometry on Barite Scale Deposition in Marcellus Shale during Hydraulic Fracturing

摘要

Barite scaling is a common problem in the shale gas industry. Barite precipitation due to rock-fluid interactions has been studied intensively in static and flow-through experiments, but the impact of flow pathway geometry on barite scaling remains a question. The complex fracture passages can lead to local concentrated geochemical interactions, resulting in spatially variable scaling distribution. In this study, designed patterns with channels and holes were milled in two Marcellus shale cores to represent the main flow pathways, where the slow flow travels from the inlet to the outlet, and near-stagnant zones, where the fluid is trapped. Hydraulic fracturing fluid, created using synthetic water and Monongahela River water as base fluid, was injected at 0.02 mL/min into the cores at 66 degrees C, a core pressure of 12.4 MPa (1800 psi), and a confining pressure of 13.8 MPa (2000 psi) for 28 days. For the core with both channels and holes, barite coatings formed in the channels and the holes, with thicker barite accumulations occurring on the non-patterned half of the core adjacent to the holes on the milled half. For the core with only holes, proppants were added to prop up the main flow pathways. Barite formed on the propped fracture surface. The proppants in the holes were covered with and glued together by barite. Such barite-proppant conglomerates were not found in the main propped fracture. These barite-proppant conglomerates may block transport pathways as well as the barite coatings.