Abstract
Gas geochemistry, a fundamental element of oil geosciences, has been utilized for evaluating source rocks possibility of shale gas as well as in conventional exploration like a guide for figuring out potential productive formations. However, in contemporary occasions, new concepts of gas geochemistry happen to be used in delineating the potency of caprocks. Caprock is a crucial component of a oil system, the volumes of rocks overlaying reservoirs have the effect of the configuration which the buildup sits and fosters essential upkeep. Within this study headspace gas offered the objective of delineating leakage and figuring out migration pathways, mechanism and discriminating gas types within the formations overlaying the reservoirs.
Keywords
Gas geochemistry Caprocks Leakage Thermogenic gas Thermogenic signature
Introduction
Gas geochemistry – a brand new comer within the number of geochemistry has demonstrated vital in delineating caprock leakage employing headspace gas. Before the present occasions, headspace gas data were used to identify by pass–pays, interpretation of maturity, source and gas correlations [1], assess the maturity and productive capacity of corresponding formations and often as indicators of oil accumulations [2]. Together, direct hydrocarbon indicators (DHIs) for example oil stains, oil shows and seeps, were also accustomed to evaluate the existence of accumulations. Evolving studies on caprock has introduced to deal with using gas clouds within the crest of fields in seismic sections and basically the use of headspace gas to discern the possibility leakage mechanism and migration pathways of leaked oil in oil caprocks. The motorists with this study includes the truth that formerly, headspace gas data were utilised for exploration purposes, lately searching for an easy, reliable but versatile strategy is in need of assistance for preliminary look at caprock leakage before using robust methods for example mercury injection capillary pressure analysis. Next depleted hydrocarbon reservoirs are predicted as carbon sinks in carbon sequestration studies the power for that caprock to have to wait thermogenic wet gas could give a look in to the caprock integrity regarding CO2 sequestration. The hypothesis which this research rest is the fact that, the appearance of thermogenic hydrocarbon (as reflected in headspace gas data) in immature caprock formation overlying oil reservoirs, infers leakage from the caprock or migration from the hydrocarbon in the reservoir in to the caprocks. Biogenic and thermogenic gases comprises the gas [3], biogenic gas consists mainly of methane from immature organic matter and lignite that is isotopically very light, while thermogenic gas is produced by kerogen or oil during funeral, with heavier carbon isotope values [2]. Thermogenic wet gas describes ethane, lp and butane components (C2-C4) from the thermogenic gas and it is normally expressed as %wetness ((C2-C4)/C1- C4) × 100). Within this study, the existence of thermogenic hydrocarbons in immature caprock sections overlying oil reservoir is made using thermogenic gas-depth profile (TGD) in corroboration with thermogenic signature-depth profile (TSD) and also the vitrinite reflectance from the formations and a few key conventional mix plots. The log view profiles were modelled with Techlog 2007.3 as the descriptive lithology from the formations were modelled using Genesis 4.8.
Methodology
This research belongs to a broader study regional leakage look at its northern border Ocean. Data with this study were sourced from well completion reports, evaluation reports, composite logs and general information folios on 50 wells in 41 oil fields within the United kingdom and Norwegian Sectors from the North Ocean (Figure 1). Data types contain headspace gas compositional and isotopic data pore pressure data expressed as EMW (Equivalent dirt weight), organic matter maturation data and general geological information for example reservoir fluid types. Data were acquired in the Norwegian Oil Directorate, Public domain along with a study set of hydrocarbon seepage by BP. The headspace data which contain various gas compositions i.e. methane, ethane, lp and butane were presented as log plots of thermogenic wet gas-depth plots and thermogenic signature (iC4/nC4 ratio)-depth plot. The plots were corroborated using the descriptive lithology and vitrinite reflectance data to decipher depths for biogenic and thermogenic gases. Depths where the thermogenic signature is more than 1. were construed as contain biogenic, immature and biodegraded gaseous hydrocarbons. The thermogenic–biogenic gas boundary reaches values that the iC4/nC4 ratio doesn’t exceed 1.. The consistence from the thermogenic signature in the reservoir sand body with the reservoir-caprock interface in to the overlaying formations signifies migration of hydrocarbons in the reservoir in to the formations above inferring leakage.
Resourse: https://omicsonline.org/open-access/
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