Archive for category: IRESS2018

The Quest for Permeability

Tobias Hoeink

Baker Hughes, a GE company

The only economical way to extract hydrocarbons from low-permeability shale reservoirs is to increase reservoir contact. Horizontal drilling, multi-stage completion, and hydraulic fracturing have proven key technologies in this respect. Yet, there is more to consider when engineering for optimal recovery on the quest for permeability. Many reservoirs are blessed with networks of natural fractures that are thought to act as hydrocarbon highways and contribute significantly to production. Focusing on fractured reservoirs, we will review how fractures across many length-scales contribute to permeability improvements that make unconventional reservoirs economically viable. We will discuss recent technology advances in fracture modeling, fracture network analysis techniques, and case studies that highlight the influence of fractures on stimulation and on the importance of integrated technology application for successful production.

Carbon Cycling, from Volcanoes to Source Rocks, a sedimentary perspective

Daniel Minisini, Shell

The deep Earth processes (e.g., tectonism, magmatism, volcanism) control the first order shape of the continental margins, the surface Earth processes (e.g., climate, erosion, sediment supply) reshape them through the redistribution of sediment. The interaction between the deep and the surface Earth processes impacts, among other things, the stratigraphic record and the carbon cycle. This contribution shows the interaction between volcanism, whose products drive long-term inputs of carbon dioxide and represent nutrients for marine organisms, and sedimentation, whose deposits include mudstones rich in organic carbon derived from the blooms of marine organisms, hence representing carbon sinks. The mudstones rich in organic carbon represents also a fundamental element of the petroleum system (together with migration, reservoir, trap, seal). Furthermore, since the “Unconventional Revolution” helped geologists to see the petroleum system with different eyes, the buried mudstone rich in organic carbon is considered now a stand-alone petroleum system that includes all the aforementioned elements. A rich and multidisciplinary dataset at different scales will show the connection of volcaniclastic material and organic matter, with cases from the Mesozoic in South and North America, and from the Holocene in the Mediterranean Sea. We will see how these rocks formed, what was their environment of deposition, and how we can produce energy from them. This simplified exposition of basic concepts important to the hydrocarbon exploration aims to bring together the mindsets of Industry and Academia, juxtaposing complex disciplines that rarely interact. I hope this form of interaction around the “carbon cycle” allows address in new ways some of the key questions we are tackling nowadays in hydrocarbon exploration: e.g., which are the predisposing factors and the triggers that allow the thickest and highest concentration of organic matter? How can we estimate quantities of hydrocarbon in these organic-rich mudstones? How do fluids migrate in pores just slightly larger than molecules? How do we optimize the production of hydrocarbons?

Gas hydrates in sandy reservoirs interpreted from velocity pull up: Are Mississippi-fan turbidites diffusively charged?

Andrew Madof, Chevron

Gas hydrates are recognized as an emerging energy resource and submarine geohazard; they are also thought to be a modulating mechanism on the global organic carbon budget and on past climate change. Although identified primarily from reflectivity changes at the base of the stability zone, gas hydrates located above this boundary are regularly difficult to interpret. Here, I introduce a non-reflectivity travel-time based method to detect gas hydrates in sandy reservoirs. The technique uses seismic travel-time deficits below high-velocity deposits in the stability zone to identify gas hydrate accumulations, and magnitudes of velocity pull up (VPU) to quantify in-situ saturation. The approach has been applied to a portion of the central Gulf of Mexico and has uncovered continuous high-velocity accumulations contained within sandy turbidites of the Quaternary Mississippi fan. Deposits extend more than 175 km southeast, and are interpreted to be vast and previously unidentified gas hydrates locally reaching saturations >70%. Based on reflection character and a marked lack of faulting, accumulations are inferred to have been sourced by short-migration diffusion of gas, making them one of the only known interpreted seismic examples of a non-focused-flow gas hydrate system. Further application of the VPU method can be used to provide insight into gas-migration mechanisms, and to catalogue worldwide distributions of gas hydrates in sandy reservoirs.

Volcanic CO₂ flux into the atmosphere

Marie Edmonds (Cambridge University)

Volcanoes are a primary mechanism for the transfer of carbon from the interior of Earth (mantle and crust) to the surface environment. Over Earth history, volcanic outgassing has played a central role in setting the atmospheric concentration of CO₂. Quantifying the magnitude of the volcanic CO₂ flux in the present day is a significant challenge. Over the past 10 years important advances have been made in instrumentation to measure and monitor volcanic CO₂, and recently the very first observations of volcanic CO₂ from space were published. The magnitude of the volcanic CO₂ flux into the atmosphere in the present day can now be estimated, although significant uncertainties remain. The data reveal that the volcanic CO₂ flux is a small fraction (of the order of 1%) of the estimated anthropogenic flux of CO₂ into the atmosphere. Long term datasets at individual volcanoes reveal that the CO₂ flux may be highly variable with time. There are a few volcanoes and volcanic regions that dominate the volcanic CO₂ flux, including large continental volcanic centres such as Yellowstone (USA) and Mount Etna (Italy).  The isotopic composition of the carbon tells us about carbon provenance: arc volcanoes outgas carbon that is isotopically heavier than typical mantle values and is derived partly from the subducting slab, and partly from the assimilation of limestones in the crust. Over geological time, it is likely that the relative importance of continental volcanoes would have waxed and waned, with implications for both the atmospheric concentration of CO₂ and the isotopic composition of Earth’s surface reservoir.