Million node fracture: size matters?

A Lavrov

doi:10.1007/s13202-021-01296-x

Abstract

Transmissivity of self-affine fractures was computed numerically as a function of the grid size. One-million-node fractures (1024 × 1024 nodes) with fractal dimensions of 2.2–2.6 were cut into successively smaller fractures (“generations”), and transmissivities computed. The number of fractures in each generation was increased by a factor of 4. Considerable scatter in transmissivity was observed for smaller grid sizes. Average transmissivity of the fractures in the generation decreased with the grid size, without approaching any asymptotic value, which indicates no representative elementary volume (REV). This happened despite the average mean aperture being the same in each generation. The results indicate that it is not possible to estimate the transmissivity of a large fracture by cutting it into smaller fractures, running flow simulations on those and averaging the results. The decrease in transmissivity with the grid size was found to be due to an increase in the flow tortuosity.

Highlights

Fractures play an important role in controlling hydraulic and transport properties of fractured rocks
The objective of our study is to investigate whether fracture transmissivity converges to a certain value with the grid size
Hydraulic aperture averaged over 4 g simulations in each generation, g, was found to decrease with the grid size (Fig. 5)

Summary

Introduction

Fractures play an important role in controlling hydraulic and transport properties of fractured rocks. In some types of hydrocarbon reservoirs, they can largely control the reservoir flow (Aguilera 1980; Li et al 2021). Understanding flow, transport and fluid displacement in natural fractures is crucial for optimization of production from such reservoirs. Understanding fracture flow and fracture permeability is important for optimization of drilling operations and drilling fluid design since fracture properties often control mud losses (Majidi et al 2010). Fractures control groundwater flow and contaminant transport in certain types of aquifers (Maldaner et al 2021). Experimental studies of fluid flow in fractures should, ideally, be conducted in situ.

Objectives

Methods

Results

Discussion

Conclusion