Modeling Natural and Well‑Related Seepage in the Norwegian North Sea

During the offshore petroleum production era, thousands of wells were drilled, many in regions characterized by active natural gas seepage. Observations show gas emissions near plugged and abandoned wells, raising key questions about well integrity and the origin of detected seepage. It remains unclear whether such seepage is induced by compromised wells, would occur naturally in the absence of wells, or reflects contributions from deeper reservoirs versus shallow gas accumulations.

In this study, we investigate these questions using fully coupled fluid‑flow and geomechanical modeling. Our simulations incorporate realistic deformation behavior of soft sediments, pressure‑dependent permeability, and two‑phase fluid flow. The study focuses on the  Norwegian channel and its western bank in the northern North Sea, which hosts the Heincke and Sentinel natural seep systems. Geological and geophysical data collected during a recent research cruise were integrated into a detailed subsurface model.

We simulate natural fluid migration without wells and compare it with scenarios including a hypothetical well-related seep. The results demonstrate that the presence of a well perturbs natural flow pathways, modifies seepage patterns, and alters both the timing and magnitude of seepage. We quantify seepage rates for natural and well‑influenced scenarios and identify zones where migrating fluids are most likely to reach the seafloor. The modeling further reveals that seepage is inherently intermittent, with rates varying over time due to coupled hydro‑mechanical processes.