Seismic evidence of gas hydrates, multiple BSRs and fluid flow offshore Tumbes Basin, Peru

Abstract

International audienceIdentification of a previously undocumented hydrate system in the Tumbes Basin, localized off the north Peruvian margin at latitude of 3°20′—4°10′S, allows us to better understand gas hydrates of convergent margins, and complement the 36 hydrate sites already identified around the Pacific Ocean. Using a combined 2D–3D seismic dataset, we present a detailed analysis of seismic amplitude anomalies related to the presence of gas hydrates and/or free gas in sediments. Our observations identify the occurrence of a widespread bottom simulating reflector (BSR), under which we observed, at several sites, the succession of one or two BSR-type reflections of variable amplitude, and vertical acoustic discontinuities associated with fluid flow and gas chimneys. We conclude that the uppermost BSR marks the current base of the hydrate stability field, for a gas composition comprised between 96% methane and 4% of ethane, propane and pure methane. Three hypotheses are developed to explain the nature of the multiple BSRs. They may refer to the base of hydrates of different gas composition, a remnant of an older BSR in the process of dispersion/dissociation or a diagenetically induced permeability barrier formed when the active BSR existed stably at that level for an extended period. The multiple BSRs have been interpreted as three events of steady state in the pressure and temperature conditions. They might be produced by climatic episodes since the last glaciation associated with tectonic activity, essentially tectonic subsidence, one of the main parameters that control the evolution of the Tumbes Basin

Deciphering the Late Cretaceous‐Cenozoic Structural Evolution of the North Peruvian Forearc System

“…The Tumbes depocenter also shows NE‐trending extension including NE and SW dipping listric normal faults (Auguy et al, ; Fernández et al, ) (Figure b). Strike‐slip behavior may have also occurred along the Banco Peru fault zone.…”

“…The offshore structural architecture is dominated by the broad structural high of the Banco Peru located between the Tumbes depocenter and the trench axis (Figure b). Along strike, this structure extends from the onshore Talara depocenter to the Gulf of Guayaquil (e.g., Auguy et al, ; Calvès et al, ; Collot et al, ) (Figure ). The structural interpretation of seismic profiles VMX09‐23 and RIB93‐01 of section B (Figure ) suggests that this major structure was generated by imbrication of three or more thrust sheets made of off‐scrapped sediments (distal equivalents of the Eocene, Oligocene, and Miocene strata observed onshore) including oceanic mafic bodies (intrusives and volcanic) (Fernández et al, ; Shepherd & Moberly, ).…”

“…It is a tectonically active system related to the post‐Jurassic geodynamics of the Nazca (Farallon) and South American convergence plate system (Jaillard et al, ). The North Peruvian forearc system displays a complex structural architecture with a southeastern onshore domain including basement highs, such as the Amotape High and subsurface Carpitas‐Zorritos High, and a northwestern offshore domain characterized by a shallow‐water (120 m below sea level (bsl)) flat‐topped high so‐called Banco Peru (Auguy et al, ; Calvès et al, ; Fernández et al, ), located ~50 km seaward from the coastline (Figure b). These NE trending structural highs delimit four major depocenters of Cretaceous and Cenozoic siliciclatic strata (Lancones, Talara, Tumbes, and Trench‐Slope forearc depocenters) reaching locally more than 9 km in thickness (Figure b).…”

Gas-In-Place Estimate for Potential Gas Hydrate Concentrated Zone in the Kumano Basin, Nankai Trough Forearc, Japan

“…GH is widely distributed across forearc basins like Kumano because subduction zone compressional tectonics produce fracture and fault networks that can act as fluid migration pathways enabling the delivery of gas-charged fluids from depth into the hydrate stability zone [16][17][18][19]. These fluids are often rich in chemical compounds including methane and potentially other higher C2+ hydrocarbons such as ethane and propane [17,20].…”

Fore‐arc seafloor unconformities and geology: Insight from 3‐D seismic geomorphology analysis, Peru

“…Within the studied area we have identified sediment remobilization features, such as pockmarks [van Rensbergen et al, 2003]. These are spatially related to vertical discontinuities that are at the apex of faults of various types and in some areas with the occurrence of potential gas hydrates as marked by bottomsimulating reflectors (BSR) ( Figures 5 and 6) [Auguy et al, 2017]. Shallow subsurface hydrological and hydrate systems within fore-arc basins offshore Peru have been identified [e.g., Kukowski and Pecher, 1999;von Huene and Pecher, 1999].…”