Leakage Pathways in Diatomite Formation: A Study of Overburden Dynamics and Fracture Network in Hydrocarbon Fields
Authors: Hajiabadi M. R. , Nick H. M. 
Published: August 2024

ABSTRACT:
Formations in the overburden of hydrocarbon fields may have flow potential and may need to be plugged during future plug and abandonment operations in the North Sea. In this context, fractured formations with weak mechanical properties are, among others, of primary concern due to the potential alteration of their flow properties caused by deformation above depleted and compacting reservoirs. Diatomite formations present in the overburden of hydrocarbon fields in the Danish North Sea are one of the main formations that may need to be plugged. Diatomite formations have a unique structure, which is characterized by high compressible rock, low density, high porosity, and low permeability. The focus in the past research has been on methods to increase production from diatomite formations by hydraulic fracturing. This study investigates the effect of underlying reservoir's deformation on fracture apertures in diatomite formation. The flow potential has been studied in a production plan through the diatomite formation. A fracture model has been proposed to consider empirical formulations of Barton-Bandis in ABAQUS. Using a conceptual model, it shows that variations in the deformation of the underlying reservoir significantly influence the permeability of fractured overburden formation, such as diatomite.

1. INTRODUCTION
Diatomite formations in the overburden of hydrocarbon fields in the Danish North Sea are one of the main formations that may have flow potential and may need to be plugged during plug and abandonment (P&A) operations. Diatomite formations have a unique structural and chemical stability, which is characterized by soft texture, high adsorption, low density, and high porosity (Crawford et al., 2016). Because of its high porosity and microstructure, diatomite belongs to high compressible soft rock with low compression modulus and high plastic deformation. Therefore, diatomite has a weak ability to resist deformation.
Furthermore, diatomite deposits have very low permeability and are typically fractured. The focus in the past research has been on methods to increase production from Diatomite formations (Dietrich & Scott, 2007; Blanco-Martín et al., 2016). It is still unknown whether subsurface deformation of an underlying reservoir during hydrocarbon production can affect the flow potential of such fractured weak formations. This study mainly aims to answer this question. Moreover, we explore the mechanisms controlling the possible changes of flow potential of diatomite overlying producing field. For this purpose, it is necessary to consider empirical formulation of fractures in aperture prediction model. Many researchers have used well-known Barton-Bandis formulation in their models (Min et al., 2004; Bisdom et al., 2017; Lei et al., 2021). In this study, we first propose a method to take into account these sets of empirical formulation in ABAQUS. Then, the effect of reservoir deformation and production on flow potential of diatomite is investigated using a conceptual model.