Experimental Quantification of Slickwater Proppant Transport in Subsidiary Hydraulic Fractures

Abstract

Hydraulic fractures created by slickwater fluids are commonly known for generating fracture network complexity, which presents a challenge for the associated proppant transport. The difficulty of proppant transport in subsidiary fractures is attributed to the velocity inside them and slickwater's low viscosity. Subsidiary fractures are believed to have lower propped area relative to the primary fracture; however, this is not quantified and its effect on proppant grain distribution is not established. This paper presents laboratory measurements of such slickwater-created propped areas in subsidiary fractures and describes the dune development mechanisms and the associated effects on grain sorting. Experiments were conducted using a 30/70 mesh brown sand and a specially designed slot flow apparatus that has a multi-fracture network of three secondary and two tertiary fractures, in addition to the main slot. The secondary fractures were attached at 90° angles from the primary fracture and separated at equal distances. The study results show that slickwater transports large amounts of proppant into secondary fractures, reflected by the large developed dunes areas of 40.8% of the total fracture area. Fractures closer to the slurry entry point show higher propped area than ones further away. For tertiary fractures, they developed only 4.5% of the total network propped area, indicating poor slickwater proppant transport inside them. Distinct proppant transport mechanisms were identified for the subsidiary fractures with different dune heights. This finding indicates grain size sorting and different proppant size distribution in the fracture network. This paper presents for the first time an experimentally quantified propped area distribution by slickwater in a complex fracture network. It reveals new insights about slickwater proppant transportability into subsidiary fractures and establishes a new understanding of proppant transport mechanisms and grain size distributions in subsidiary fractures, which can have a considerable impact on hydraulic fracture conductivity estimation and, hence, productivity enhancement.