Seal bypass systems

TLDR

Seal bypass systems (SBS) are geological features that allow fluids to circumvent sealing sequences, potentially invalidating predictions based solely on bulk rock flow properties. The study introduces an interpretational framework and defines SBS as seismically resolvable features that enable cross‑stratal fluid migration. Using 3‑D seismic data, the authors illustrate SBS across different seal types, classify them into fault‑, intrusion‑, and pipe‑related groups, and provide evidence of focused vertical or subvertical fluid flow. The examples demonstrate focused vertical/subvertical fluid flow and show that fault, intrusion, and pipe SBS behave differently, with distinct flux‑dimension scaling and varying short‑ and long‑term impacts on seal integrity.

Abstract

We present an interpretational framework for the analysis of a diverse set of geological structures that breach sealing sequences and allow fluids to flow vertically or subvertically across the seal. In so doing, they act as seal bypass systems (SBS). We define SBS as seismically resolvable geological features embedded within sealing sequences that promote cross-stratal fluid migration and allow fluids to bypass the pore network. If such bypass systems exist within a given seal sequence, then predictions of sealing capacity based exclusively on the flow properties (capillary entry pressure and hydraulic conductivity) of the bulk rock can potentially be negated by the capacity of the bypass system to breach the grain and pore network. We present a range of examples of SBS affecting contrasting types of sealing sequences using three-dimensional (3-D) seismic data. These examples show direct evidence of highly focused vertical or subvertical fluid flow from subsurface reservoirs up through the seal sequence, with leakage internally at higher levels or to the surface as seeps.We classify SBS into three main groups based on seismic interpretational criteria: (1) fault related, (2) intrusion related, and (3) pipe related. We show how each group exhibits different modes of behavior with different scaling relationships between flux and dimensions and different short- and long-term impacts on seal behavior.