Subduction zones and their hydrocarbon systems

Abstract

Subduction zones are common tectonic features central to large-scale crustal and elemental cycling, and they are accompanied by basins often with thick sedimentary fill and structures suitable for hydrocarbon preservation. However, significant hydrocarbon production occurs in only a handful of subduction zone locations. Here we explore our current understanding of the controls on hydrocarbon systems associated with subduction zones, in terms of the strongly variable conditions inherent to this tectonic setting that either favor or limit petroleum production, and in the context of three case studies (Cook Inlet and Sacramento basins, USA; Talara basin, Peru). This review concentrates on continental rather than intra-oceanic subduction settings due to limited basin preservation and hydrocarbon prospectivity in the latter. Overall, the primary limitations on hydrocarbon potential in forearc and/or trenchslope basins are time-to-maturation (low geothermal gradients), reservoir quality, source-rock presence and quality, structural complexity, and depth to reservoir. The latter two conditions may explain why offshore exploration has been limited near subduction zones, even where onshore production is robust and/or hydrocarbon seeps are common. Prospectivity may increase with enhanced seismic imaging and offshore infrastructure in some locations, and with the economic development of unconventional resources such as gas hydrates in accretionary prisms or deep shale gas in forearc basins. In any case, the presence of hydrocarbon systems in subduction zones, whether prospective or not, is an important part of the cycling of carbon and other elements at active convergent margins.

Thermal structure and source rock maturity of the North Peruvian forearc system: Insights from a subduction-sedimentation integrated petroleum system modeling

“…The long lateral migration hypothesis from the Tumbes depocenter to the Talara fields (Fildani et al, 2005) The model results are more consistent with the presence of local source rocks in the Talara Basin. The observation of two maturation pulses in the model results fits the interpretation of two migration pulses from geochemical analysis (Higley, 2004a;Hessler and Sharman, 2018; and references therein). At the location of the modeled section, the Talara Formation shales reach the oil generation window in the deeper parts of the Talara Fernández et al, 2005), this source rock is mature and has generated hydrocarbon.…”

“…The density of Tumbes and Talara oils varies from 18 to 48 °API. Geochemical analyses indicate they present different degrees of biodegradation, but were all originated from a same type of source rock, with probably at least two migration pulses (Higley, 2004a;Hessler and Sharman, 2018; and references therein). The Cretaceous source rocks of the Muerto and Redondo Formations (deep marine black shales with type II, II/III kerogen; Figure 3.4 and Figure 3.5) have sufficient organic matter content (1-4.5% TOC) and thermal maturity to be considered active source rocks in the Talara Basin, where they are present (Fernández et al, 2005;Table 3.1).…”

“…Alternative explanations for the Oleanane presence in the Talara oils are the acknowledgment of a younger, Upper Cretaceous, age for the Muerto Formation (Fernández et al, 2005) or the occurrence of locally potential Tertiary source rocks (Higley, 2004a and references therein). The available TOC measurements and pyrolysis data indicate also a locally fair source rock potential for Eocene Talara shales (Fernández et al, 2005;Figure 3 The migration mechanism is also still debated (Hessler and Sharman, 2018). The hypothesis of hydrocarbon generation from the Oligocene-Miocene source rock in the offshore Tumbes depocenter (Fildani et al, 2005) requires a long migration towards the onshore Talara Basin before the segmentation of the two basins.…”

“…Understanding the thermal history of forearc basin systems is a challenge to better evaluate oil and gas exploration potential in subduction zones. Forearc systems are generally considered as regions with low petroleum potential due to high structural and stratigraphic complexities, polyphase tectonic histories, and depressed thermal regime (Hessler and Sharman, 2018).…”

“…However, the producing Talara Basin, part of the North Peruvian forearc zone, is one of the striking exceptions to this generally held idea, as are the Cook Inlet Basin along the Alaska-Aleutian forearc zone or the Sacramento Basin along the Cascadia subduction zone of the USA (Moberly et al, 1982;Carozzi and Palomino, 1993;Higley, 2004a,b;Fildani et al, 2005;Harun et al, 2014;Hessler and Sharman, 2018). Significant hydrocarbon production occurs in these basins (Hessler and Sharman, 2018). To better understand the thermal history of the forearc regions and the dynamics of their petroleum systems, we focused on the thermal modeling of the North Peruvian forearc system across the Tumbes-Talara-Lancones basins system (Figure 3.1).…”