Streaming potential modeling in fractured rock: Insights into the identification of hydraulically active fractures

TL;DR

This paper introduces an efficient numerical method for modeling streaming potentials in fractured rocks, enabling better interpretation of self-potential data for identifying hydraulically active fractures and understanding fracture-matrix interactions.

Contribution

The paper presents a novel two-dimensional discrete-dual-porosity modeling approach tailored for complex fracture networks in fractured rock.

Findings

Accounting for matrix fluid flow is crucial for accurate SP modeling.

SP sensitivity is linked to fracture-matrix fluid interactions.

Hydraulically conductive fractures produce strong SP signals.

Abstract

Numerous field experiments suggest that the self-potential (SP) geophysical method may allow for the detection of hydraulically active fractures and provide information about fracture properties. However, a lack of suitable numerical tools for modeling streaming potentials in fractured media prevents quantitative interpretation and limits our understanding of how the SP method can be used in this regard. To address this issue, we present a highly efficient two-dimensional discrete-dual-porosity approach for solving the fluid flow and associated self-potential problems in fractured rock. Our approach is specifically designed for complex fracture networks that cannot be investigated using standard numerical methods. We then simulate SP signals associated with pumping conditions for a number of examples to show that (i) accounting for matrix fluid flow is essential for accurate SP modeling and (ii) the sensitivity of SP to hydraulically active fractures is intimately linked with fracture-matrix fluid interactions. This implies that fractures associated with strong SP amplitudes are likely to be hydraulically conductive, attracting fluid flow from the surrounding matrix.