Model-Based Identification of the Base of the Gas Hydrate Stability Zone in Multichannel Reflection Seismic Data, Offshore Costa Rica

Abstract

Along the pacific margin offshore Costa Rica the Bottom Simulating Reflector (BSR) shows a patchy occurrence in 2-D seismic reflection profiles. The reason for this can be either lack of free gas beneath parts of the gas hydrate stability zone (GHSZ) or poor seismic imaging. We compare far to near offset stacked common midpoint sections to reduce imaging ambiguity utilizing the amplitude variation with offset effect and thus successfully distinguish BSRs from regular sediment reflections. In combination with 1-D modeling of the base of the GHSZ we disqualify or qualify reflections in the predicted depth range as BSR. Additionally we calculate the heat flow and compare it with an analytical solution to detect thermal anomalies, for example, at the frontal prism. The higher confidence in BSR depths based on the far offset stacks and heat flow calculations allows further analyses on gas hydrate concentration estimates and tectonic evolution of the margin.

Natural gas hydrates in the Rio Grande Cone (Brazil): A new province in the western South Atlantic

“…The identification of such provinces is accomplished by using geophysical indications, geochemical evidence and/or direct recovery and sampling. The most widely used geophysical indication is the presence of bottom simulating reflectors (BSR) in seismic records (Shipley et al, 1979;Katzman et al, 1994;Gehrmann et al, 2009). Geochemical parameters, such as the variation in interstitial fluid salinity associated to hydrate dissociation or formation, are also employed (Ussler et al, 2001;Coffin et al, 2007).…”

Bayesian inversion of marine controlled source electromagnetic data offshore Vancouver Island, Canada

“…A BSR is observed on the middle slope (blue dashed line) as far landward as Site U1329, but cannot be observed further upslope. The base of the GHSZ is calculated from the observed BSR depths and extrapolated landward of U1329 following Gehrmann et al (2009).…”

Gas-hydrate stability thickness map along the Indian continental margin

“…This map is useful in modeling a discontinuous BSR by interpolation, provided the geothermal gradient and sea-bottom temperature are known. This procedure works well within short distances but is not appropriate in the case of thermal anomalies and greater distances (Gehrmann et al, 2009).…”