AAPG Geoscience Technology Workshop

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Leviathan Field: The Big Picture

Abstract

Leviathan Gas Field was discovered in late 2010, the largest in a string of exploration successes for Noble and its partners in the region. Early appraisal work at Leviathan included two fully evaluated appraisal wells at a spacing of approximately 10 kilometers, and a production test in the discovery well. 3-D seismic interpretation, and the data gathered during drilling of these wells proved the broad extent and high quality of the reservoir units and a consistent gas-water contact throughout. During more recent drilling campaigns, the partnership finalized appraisal of the reservoir with two more wells and completed the initial Leviathan production wells. Production test data from all wells indicates very high potential flow rates from the reservoir sand section. 3-D seismic mapping indicates an extent of approximately 325 square kilometers at the top Lower Miocene reservoir level. Leviathan is a structural trap with approximately 300 meters of closure at its crest. Extensive sets of whole core and sidewall core were taken during the appraisal stage at Leviathan. These rock samples along with comprehensive suites of wireline data indicate extensive, very high-quality reservoir rock across the field. The reservoir interval at Leviathan consists of four sand units with relatively thin intervening shales. Deposition of these clastics occurred in basin floor to lower slope turbidite settings during Early Miocene time. These “Tamar Sands” are named from a nearby field, where earlier wells discovered and helped delineated the sands. Reservoir pressure data from wireline and production testing shows very good connectedness of the sand prior to production. A set of relatively minor faults within the field area apparently serves to connect the sands across the shale intervals. This has resulted in excellent alignment of pressure data along single gas and water gradient lines. The Field Development Plan for Leviathan was approved in 2016. An integral early part of the Plan has been an optimized drilling program featuring wells that are drilled and evaluated for full appraisal then sidetracked for completion and production with open hole gravel packs. The development plan, notionally, includes completion of high-rate, long-life gas production wells. Learnings from early production in the field and from nearby analogs will be used to high-grade the actual development program beyond the initial phase. From initial discovery, the partnership was confident of the technical viability of a development at Leviathan. Appraisal drilling and the four initial well completions were finished during 2018 and production of first Leviathan gas is now expected near year-end 2019.