The Value of Outcrops in Understanding the Complexities of Sand Intrusion Reservoirs: Learnings From the Volund Field

Abstract

The outcrops of the Panoche and Tumey Giant Injection Complexes in California have been instrumental in refining the interpretation of the sandstone intrusion reservoirs in the Volund Field, Norway. Insights from the outcrops enhanced the subsurface team's confidence and understanding of reservoir presence and connectivity during field production. This led to more accurate estimates of hydrocarbon reserves. Learnings from the Volund Field show that historical reservoir models underestimate net reservoir volume and reservoir connectivity. Outcrop data reveal step-like geometry in some intrusions, which potentially explains the lack of seismic resolution of sandstone intrusions in some areas of the field. Failure to recognise this leads to misinterpretation of parts of the field as non-reservoir. In some intervals, well logs interpreted as non-reservoir mudstone-rich units are actually mudstone-clast breccia, which, because of good connectivity within the sandstone matrix, can comprise significant reservoir volumes. The rationale for including sandstone intrusions as reservoirs, although unresolved by seismic or borehole log data in static models, is validated by reference to outcrop data and from recent drilling in the adjacent Kobra Field. Observations of outcrop analogues enhance the interpretation of subsurface data, and the knowledge acquired from outcrops helped justify the drilling of more production wells in areas where reservoir presence and quality were difficult to predict, but almost nearly doubled the hydrocarbon reserves.