Noble Gases in Deepwater Oils of the U.S. Gulf of Mexico

Abstract

Hydrocarbon migration and emplacement processes remain underconstrained despite the vast potential economic value associated with oil and gas. Noble gases provide information about hydrocarbon generation, fluid migration pathways, reservoir conditions, and the relative volumes of oil versus water in the subsurface. Produced gas He‐Ne‐Ar‐Kr‐Xe data from two distinct oil fields in the Gulf of Mexico (Genesis and Hoover‐Diana) are used to calibrate a model that takes into account both water‐oil solubility exchange and subsequent gas cap formation. Reconstructed noble gas signatures in oils reflect simple (two‐phase) oil‐water exchange imparted during migration from the source rock to the trap, which are subsequently modified by gas cap formation at current reservoir conditions. Calculated, oil to water volume ratios ( normalVnormalonormalVnormalw) in Tertiary‐sourced oils from the Hoover‐Diana system are 2–3 times greater on average than those in the Jurassic sourced oils from the Genesis reservoirs. Higher normalVnormalonormalVnormalw in Hoover‐Diana versus Genesis can be interpreted in two ways: either (1) the Hoover reservoir interval has 2–3 times more oil than any of the individual Genesis reservoirs, which is consistent with independent estimates of oil in place for the respective reservoirs, or (2) Genesis oils have experienced longer migration pathways than Hoover‐Diana oils and thus have interacted with more water. The ability to determine a robust normalVnormalonormalVnormalw, despite gas cap formation and possible gas cap loss, is extremely powerful. For example, when volumetric hydrocarbon ratios are combined with independent estimates of hydrocarbon migration distance and/or formation fluid volumes, this technique has the potential to differentiate between large and small oil accumulations.

Identifying thermogenic and microbial methane in deep water Gulf of Mexico Reservoirs

“…The field lies on the eastern flank of a salt-cored ridge that defines the western margin of the Popeye-Genesis minibasin. The Genesis field produces oil with solution gas from stacked Pliocene through Pleistocene deep-water reservoirs (Sweet, 2007;Barry et al, 2018) with perforation depths of 3000-4200m. The range of reservoir temperatures is 63-82 o C. The Genesis oils are sourced from the Upper Jurassic interval, most likely the Tithonian marl comprising dominantly marine organic matter (Hood, 2002).The oils are hosted in stratigraphic traps that pinch out against a salt diapir.…”

A Novel Method for the Extraction, Purification, and Characterization of Noble Gases in Produced Fluids

“…Noble gas analyses were conducted in the Noble Laboratory at the University of Oxford, UK, where the analysis of gas phase samples is well established using a custom‐built high vacuum gas purification system to purify and separate noble gas species before measurement (e.g., Barry et al, , ; Barry, Kulongoski, et al, ; Barry, Lawson, et al, ; Byrne et al, , ). Samples containing significant liquid volumes cannot be analyzed in this way, as the liquids are not adequately removed using conventional cryogenic or gettering techniques, are adsorbed easily to the inside of the stainless‐steel system and are difficult to remove even using ultra‐high vacuum turbomolecular and diaphragm pump combinations.…”

“…In systems with long hydrocarbon production histories, it is valuable to determine the pristine signature (before EOR) and how the system has evolved geochemically with production; injected fluids play a significant role on this evolution. Noble gases represent powerful geochemical tracers, as they are chemically inert and therefore act conservatively in geologically dynamic systems (e.g., Ballentine et al, 1991Ballentine et al, , 1996Ballentine et al, , 2002Barry, Kulongoski, et al, 2018;Barry, Lawson, et al, 2018;Bosch & Mazor, 1988;Darrah et al, 2015;Gilfillan et al, 2008Gilfillan et al, , 2014Holland & Gilfillan, 2013;Pinti & Marty, 1995). Noble gases are most readily determined in systems dominated by a single phase (e.g., gas or groundwater); however, within a hydrocarbon system they can reside in multiple phases (i.e., oil, water and gas) and thus may be present in each component.…”

“…Previous studies have successfully used noble gas isotopes and abundances to quantify water-oil-gas interactions in both conventional and unconventional hydrocarbon systems and those effected by EOR techniques (Ballentine et al, 1991(Ballentine et al, , 1996(Ballentine et al, , 2002Barry et al, 2016Barry et al, , 2017Barry, Kulongoski, et al, 2018;Barry, Lawson, et al, 2018;Byrne et al, 2018aByrne et al, , 2018bDarrah et al, 2014Darrah et al, , 2015Györe et al, 2017Györe et al, , 2015Prinzhofer, 2013). These studies have primarily focused on natural gas systems, although some have specifically investigated oil systems (e.g., Ballentine et al, 1996;Györe et al, 2017), unconventional systems (e.g., Byrne et al, 2018b;Zhou et al, 2005) and multi-component systems (Barry, Lawson, et al, 2018). The use of noble gases as tracers in oil-dominated systems is not yet well established due to the multiphase nature of these samples meaning they are not amenable to the normal high-vacuum noble gas purification procedures for natural gases.…”

“…As a result, the focus of previous studies has been primarily on gas phase hydrocarbon samples, which are exsolved from oil as they decompress during production (Figure S1 in the supporting information; Ballentine et al, ; Prinzhofer, ). Recent studies reconstructed the noble gas composition of the oil phase from casing gas measurements using broad assumptions about gas solubility in oil (e.g., Barry, Kulongoski, et al, ; Barry, Lawson, et al, ). However, production practices are often not amenable to collecting casing gas samples, and therefore produced fluids must be used to geochemically characterize the hydrocarbon reservoir.…”