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Evaluating the Thermal History of the Los Angeles Basin Through 3-D Basin and Petroleum System Modeling

Abstract

The Los Angeles Basin presents a valuable opportunity for 3D basin and petroleum system modeling due to its impressively high hydrocarbon productivity relative to sediment volume, high source rock TOC, and the geochemical diversity of the produced oils. A 3D Earth model of the Los Angeles Basin was constructed from basement to ground surface to examine the various factors impacting heat flow through the basin's history. The basement surface is defined by the SCEC Community Velocity Model supplemented by well penetrations on the basin flanks. Overlying sedimentary strata are mapped from well logs, to include top Pico, Repetto and Monterey (Puente) formations, as well as several chronostratigraphic surfaces, including top Miocene, Oligocene, Eocene and Paleocene. The Miocene Puente Formation is additionally subdivided into several subunits, including the organic-rich Nodular Shale source rock unit. The chief aim of this model is to better understand the impacts of the basin's complex geologic history, resulting in a number of often conflicting thermal effects, which overlap through geologic time, on the thermics of the basin. The relative impacts and magnitudes of the various thermal effects are explored from a basin modeling perspective through scenario testing and comparison with calibration data and mapped source rock maturity trends, buttressed by new custom bulk kinetics of the nodular shale phosphatic source rock. We examine the following successive tectonic episodes having conflicting thermal effects: a) pre-basinal subduction of the Farallon plate through the Paleogene resulting in early depression of isotherms b) subsequent subduction of the East Pacific Ridge and transition to a transform plate boundary, associated with volcanism, schist upwelling and increased heat flow; and c) rapid subsidence of the basin initiated in the middle to late Miocene, producing in turn a cooling effect through the thermal blanketing effects of deposited sediments and the lateral heat loss through steep basin margins. This new model of the Los Angeles Basin will provide for a more comprehensive understanding of this basin's unique petroleum system.