AAPG Annual Convention and Exhibition

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Gunflint Field: Effective Field Development in a Challenging Subsalt Environment

Abstract

The Gunflint Field is located in southern Mississippian Canyon blocks MC 948 and MC 992, in approximately 6,100 feet of water. Hydrocarbons are located in Middle to Lower Middle Miocene deepwater sandstones within a four-way structural high. This presentation will focus on the depositional environments and architecture of the reservoirs, and the workflow for effective field development within a seismically complex subsalt environment. Gunflint lies beneath two salt bodies (diapir and salt sheet), and was discovered in August 2008. Seven reservoirs encountered a variety of hydrocarbons, ranging from oils to dry gas. Three reservoirs out of the seven will be discussed in this presentation: A, B, and C, respectively, from shallow to deep. All of these reservoirs are seismically challenged, with a tuning thickness of approximately 300 ft. Therefore, interpretations of environment of deposition and reservoir architecture rely heavily on accurate geologic models, as interpreted from conventional core, conventional logs and image logs. Finally, outcrop analogs bridge the gap between what is interpreted from the limited, one dimensional view of well logs, to correlating and inferring potential connectivity between the wellbores and beyond. Interpretations are based on facies assemblages observed in core, log responses, vertical stacking patterns from logs, and lateral variations between wells. The A and B reservoirs are interpreted as the channel-lobe transition zone, mainly within weakly-confined channels that give way to more lobe-like packages. Core and image logs indicate that Reservoir B is more compensationally stacked, whereas reservoir A appears more layered. A similar integrated data approach indicates that reservoir C is a compensationally stacked lobe system, with distinctive heterolithic boundaries between depositional elements. The implications of these varying reservoir architectures on vertical and lateral connectivity were critical in the field development plan. We propose that this workflow, which employs data acquired from the field, literature, and nearby field analogs, addresses the critical aspects of reservoir architecture models for Gunflint development. Gunflint commenced production in July 2016 from the A, B and C reservoirs, and is anticipated to reach a minimum gross production of 20,000 boe/d. Early production supports the interpretation presented herein, with future reassessment of geologic models to be performed as production continues.