DEM-CFD Modeling of Proppant Pillar Deformation and Stability during the Fracturing Fluid Flowback

Haiyan Zhu,John D Mclennan,Wei Huang,Fengshou Zhang,Bo Huang,Jiadong Shen,Liaoyuan Zhang

doi:10.1155/2018/3535817

Abstract

In this study, proppant pillar deformation and stability during the fracturing fluid flowback of channel fracturing was simulated with DEM-CFD- (discrete element method-computational fluid dynamics-) coupling method. Fibers were modeled by implementing the bonded particle model for contacts between particles. In the hydraulic fracture-closing period, the height of the proppant pillar decreases gradually and the diameter increases as the closing stress increases. In the fracturing fluid flowback period, proppant particles could be driven away from the pillar by the fluid flow and cause the instability of the proppant pillar. The proppant flowback could occur easily with large proppant pillar height or a large fluid pressure gradient. Both the pillar height and the pillar diameter to spacing ratio are key parameters for the design of channel fracturing. Increasing the fiber-bonding strength could enhance the stability of the proppant pillar.

Highlights

Channel fracturing is a relatively new stimulation technique first proposed by Gillard et al in 2010 [1]
The major difference between channel fracturing and conventional fracturing lies in the pattern of proppant placement
An investigation based on the results of more than 1000 times channel fracturing found that more than 99.9% of the channel-fracturing jobs fully completed the proppant placement and by average channel fracturing could save 43% of the proppant compared with the conventional technique implemented in adjacent wells [3, 4]

Summary

Introduction

Channel fracturing is a relatively new stimulation technique first proposed by Gillard et al in 2010 [1]. The above studies have pointed out that effects such as fluid viscosity, fluid pressure gradient, and closing stress are crucial to the proppant flowback for the conventional proppant placement scheme They laid an important foundation for the research of proppant flowback with channel fracturing. Yan et al [22] developed an analytical model to represent the physical deformation of channel-fracturing fractures, and the DarcyBrinkman equation was applied to simulate the flow in pillars and fluid channels. Deng et al [23] adopted the discrete element method to study interactions between shale and proppant Effects of factors such as shale modulus and proppant size on fracture aperture were numerically modelled and learned. The effects of pressure gradient, fluid viscosity, pillar height, pillar diameter to spacing ratio, and bonding strength of fibers are investigated, and the amount of flowback proppant and the spreading area of proppant are studied. This work could provide a potential guideline and theoretical background for the design of channel fracturing and the optimization of field fracturing operation

Theoretical Background and Numerical Model Setup

Discussions

Findings

Conclusions