New Comprehensive Large Tortuous Slot Flow Testing for Unconventional Fracturing
Authors: Singh Amit , Liu Xinghui , Jiehao Wang , Rijken Peggy , Stribling Michelle , Wildt Pat , Anschutz Don 
Published: October 2020

Unconventional completions have experienced many different trends within the last decade. Many of the changes are based on learnings using conventional fracture mechanisms and studies. Previous studies evaluated the impact of various parameters on proppant transport by pumping a premixed proppant laden slurry into an open, homogenous slot to visually monitor proppant distribution. Basic flow characteristics can be captured with this type of traditional tests; however, it misses significant factors of unconventional fracture mechanisms including tortuosity, variable width, leak-off, and the ability for in-situ analysis of the materials after being pumped. This paper discusses the need and development of new equipment with innovative features, and several revolutionary laboratory techniques that were specifically applied to further understand proppant and fluid behavior in unconventional reservoirs.

Unconventional fracture characteristics learnings from industry's advanced field studies were included while defining the features of new comprehensive test equipment to represent the unconventional fracture mechanisms. This ultimately led to the construction of a large, sectional, 10'x20’ slot flow wall. The twenty-five sections of the wall were modified to accommodate a wide variety of testing regimes and flow patterns. Additionally, the pumping equipment delivering the proppant laden slurry was upgraded to adhere to today's completion designs. Through the use of large fluid tanks, proppant hoppers, a mixing blender tub, pump and flow loop, shear history, and multiple types of proppant and fluid were integrated into the test procedures to better replicate current pump schedules. Flow meters, pressure transducers, a densitometer, and linear variable differential transformers were installed to monitor the movement of the material and structure throughout the test. After testing, the patent-pending equipment is designed for disassembly for detailed analysis on the proppant and fluid. Equipment can also be modified on a smaller scale to create a winged fracture, transverse fracture and a tilted fracture, all of which are necessary when analyzing fracture and proppant transport behavior in an unconventional reservoir.

The new, comprehensive, large and tortuous slot flow equipment allowed the creation of a customized tortuous path for the proppant and fluid for twenty feet before exiting the structure into separate effluent tanks. The slot has an original width of 0.5 inches but can be tailored to establish varying slot widths and/or complete obstructions using panel inserts. With multiple inlet points, fracture growth can be documented with a total of one hundred side panel leak-off ports and eight additional leak-off ports along the top. To maximize learnings from each test, innovative test practices were applied such as, dying the frac sand of different mesh size groups to visualize the segregation of the proppant while pumping, and mounting 10-15 cameras throughout the structure to document slurry behavior through the acrylic panes. Data analyzed included, but was not limited to, a sieve analysis, proppant concentration, fluid viscosity, and proppant conductivity testing on the samples. The testing demonstrated a significant impact on proppant transport, dune generation, and dune structure after shut-in through a tortuous path with varying fracture width and leak-off ports as compared to standard slot flow test.

This paper introduces novel, comprehensive, large, and tortuous slot flow testing equipment with features to represent the unconventional fracture behavior. Advanced equipment capabilities, test procedures and data collection methodology allow the industry to optimize the selection and deployment of various fracturing materials and treatment designs for unconventional well production enhancement.