Abstract
Slick-water can effectively reduce the flow drag of fracturing fluid. Many studies have focused on the drag reduction performance of slick-water in wellbore and perforation, but there has been little research on drag reduction characteristics in fracture flow. In this paper, a new visualization experiment system is used to simulate real fracture. The fracture surface is produced through actual triaxial hydraulic fracturing and is copied by a three-dimensional printer using resin material to maintain its shape feature. In comparing the experimental results, it was found that the main factors affecting drag reduction in a fracture are the relative molecular weight and the added concentration. Unlike the flow rule of the drag reducer in a pipeline, when the concentration is greater than 0.10%, a negative DR effect begins to appear. The influence of molecular weight is related to the flow stage; the increasing of molecular weight causes a reduction in DR effect when the flow rate is 0.24 m/s. However, the flow rate exceeds 0.5 m/s; drag reducers with higher molecular weight demonstrate better drag reduction performance. The drag reduction mechanism analysis in fractures was obtained from visualization observations, and the flow characteristics of fluid were characterized by using tracking particles. Drag reduction effect occurs mainly on the surface of the fractures in contrast to near the centre of the flow channel. This research can provide a reference for the experimental study on drag reduction in fractures and is of great significance to the optimization and improvement of drag reducing agent.
Highlights
Slick-water fracturing is a systemic method that increases production by injecting several million gallons of water into a formation to create a fracture network [1,2,3,4]
Pipeline flow tests were used as a reference to explore the drag reduction characteristic in fracture flow
If the flow rate further increases, the drag reduction rate will decrease. When it comes to fracture flow, the flow rate has a similar influence on the drag reduction rate
Summary
Slick-water fracturing is a systemic method that increases production by injecting several million gallons of water into a formation to create a fracture network [1,2,3,4]. Slick-water is commonly used in large-scale volume fracturing for its low flow drag, which is an advantage in creating more fractures and complex fracture networks to maximise the initial production rate, as consistently observed in the field [5,6,7]. Accurate estimation of fracturing flow drag is critical to fracturing design, and drag reduction performance is one of the most important technical indicator of slick-water fracturing fluid. A small amount of additives can produce a significant pressure drop in turbulent flow, known as the drag reduction effect (DR effect) [8, 9]. Previous drag reduction mechanism research has focused mostly on Geofluids wellbore flow drag. As a decisive factor in fracturing design, fracture flow drag requires research of flow patterns and drag reduction characteristics [18,19,20]. Research on the pipeline flow has provided us with a foundation, the flow patterns and characteristics in the fractures need further thorough research
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