Comprehensive experimental study of proppant transport in an inclined fracture

Abstract

The application of slickwater fracturing technology along with horizontal drilling has revolutionized oil and gas energy industry. Solid particles, i.e. proppant, are mixed with slickwater and injected into the formation to keep fractures opened after fracturing. Many researchers have studied the proppant transport and distribution in vertical fractures. However, in unconventional reservoirs with multiple bedding layers and preexisting natural fractures, hydraulically induced fractures with inclined angles are often generated. Thus, proppant transport in various angles of fracture geometry is necessary to study further. In this study, multiple case studies including fracture inclination angle, proppant size, and injection point location were performed to experimentally quantify proppant delivery mechanism in an inclined fracture. Laboratory parameters were scaled down from field conditions to successfully capture proppant transport mechanism without any significant boundary effect. Sand slurry was pumped into a fracture channel and proppant placement was recorded at various conditions. The effect of individual parameter was scientifically analyzed at predetermined condition to quantify the proppant transport trend within an inclined fracture.Friction due to wall roughness and different effective vertical gravitational forces completely change proppant transport behaviors in inclined plane. Frictional force acts stronger, as the fracture plane angle becomes closer to the horizontal plane. Strong wall friction effect creates a thin suspension area rather than settling and forming compact dune. Some proppants are invested for the suspension zone instead of dune area. This leads to greater proppant coverage area, yet smaller dune area. Suspended zone is the most differentiating feature compared to vertical fractures. There is almost no suspended zone observed in the vertical fractures, yet suspended zone is well observed and prevalent in inclined fractures. Fine mesh sized proppants travel farther due to low settling velocity. It therefore forms a well distributed sand pack. Fine particles are heavily influenced by the flow, therefore it follows the streamline of the incoming flow. They also experience strong wall friction. Thus suspension zone and total coverage area increase with smaller proppant size. In addition, the difference between having a single inlet point at various depth compared to having several opened inlet points provides an insight while operating in field environment. The inlet location determines the shape of the sandpack, especially near the wellbore. Lower injection point pushes the sandpack farther, yet this poses a potential wellbore closure or collapse.