Noble gases solubility models of hydrocarbon charge mechanism in the Sleipner Vest gas field
Noble gases solubility models of hydrocarbon charge mechanism in the Sleipner Vest gas field
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DOI：
10.1016/j.gca.2016.08.021
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发表时间：
2016-12-01
影响因子：
5
通讯作者：
Ballentine, C. J.
中科院分区：
文献类型：
--
作者：
Barry, P. H.;Lawson, M.;Ballentine, C. J.
惰性气体具有化学惰性，可溶于地壳流体。它们主要通过与地层水的交换进入油气藏，可用于评估运移途径和机制，以及储层储存条件。特别有趣的是地下水在油气运移中的作用，这反映在油气-水体积比中。本文介绍了挪威北海Sleipner Vest油田的成分、稳定同位素、稀有气体同位素和丰度数据。Sleipner Vest气体是由干酪根的一次裂解和石油的热裂解产生的。天然气从南部进入Sleipner Vest，随后向东迁移，填充并溢出到Sleipner Ost油田。气体主要由碳氢化合物（83-93%）、二氧化碳（5.4-15.3%）和N-2（0.6-0.9%）以及微量惰性气体组成。氦同位素（He-3/He-4）主要是放射性成因，范围为0.065 ~ 0.116 RA；报告相对于空气(RA = 1.4 x 10(-6)；Clarke et al., 1976；Sano et ., 1988)，显示主要（bbb98 %）的地壳贡献，与Ne （Ne-20/Ne-22从9.70到9.91；Ne-21/Ne-22从0.0290到0.0344）和Ar同位素（Ar-40/Ar-36从315到489）一致。空气衍生的稀有气体同位素（Ne-20, Ar-36, Kr-84, Xe-132）通过与空气饱和水（ASW）直接交换引入烃系统。气源惰性气体的分布受相分配过程的控制；由于它们在流体中的溶解度低，因此它们优先分解为气相（即甲烷）。因此，碳氢化合物相和地层水之间的交换程度——之前已经与大气平衡——可以通过研究空气衍生的惰性气体来确定。我们利用元素比来解决过程（即开放与封闭系统）和浓度来量化烃水交换的程度（即体积气水比）。这些数据在几个概念模型的框架内进行了讨论：(i)总气溶出模型，该模型假设所有惰性气体都已从水相中剥离出来，从而定义了与碳氢相相互作用的最小水体积；（ii）平衡模型，该模型假设P、T储层地下水与油气相及矿化度的平衡；以及（iii）使用浓度和元素比的开放和封闭系统气体汽提模型。通过将这些模型应用于Sleipner的Ne-Ar数据，我们估计体积气水比V-g/V-w在0.02到0.07之间，低于标准的地质气水估计值（类似于0.24），该估计值是通过将天然气就地估计值与地下水孔隙度估计值相结合得出的。Sleipner Vest数据可以通过开放系统模型进行最佳近似，该模型在迁移过程中预测的地下水相互作用比地质估计多一个数量级，表明存在动态含水层系统和/或含水迁移路径。在开放系统中，气体损失的程度可以估计在8到10个储层之间，这些储层已经通过系统并丢失（即填充和泄漏）。(C) 2016 Elsevier Ltd.版权所有。
Noble gases are chemically inert and variably soluble in crustal fluids. They are primarily introduced into hydrocarbon reservoirs through exchange with formation waters, and can be used to assess migration pathways and mechanisms, as well as reservoir storage conditions. Of particular interest is the role groundwater plays in hydrocarbon transport, which is reflected in hydrocarbon-water volume ratios. Here, we present compositional, stable isotope and noble gas isotope and abundance data from the Sleipner Vest field, in the Norwegian North Sea. Sleipner Vest gases are generated from primary cracking of kerogen and the thermal cracking of oil. Gas was emplaced into the Sleipner Vest from the south and subsequently migrated to the east, filling and spilling into the Sleipner Ost fields. Gases principally consist of hydrocarbons (83-93%), CO2 (5.4-15.3%) and N-2 (0.6-0.9%), as well as trace concentrations of noble gases. Helium isotopes (He-3/He-4) are predominantly radiogenic and range from 0.065 to 0.116 RA; reported relative to air (RA = 1.4 x 10(-6); Clarke et al., 1976; Sano et al., 1988), showing predominantly (> 98%) crustal contributions, consistent with Ne (Ne-20/Ne-22 from 9.70 to 9.91; Ne-21/Ne-22 from 0.0290 to 0.0344) and Ar isotopes (Ar-40/Ar-36 from 315 to 489). Air-derived noble gas isotopes (Ne-20, Ar-36, Kr-84, Xe-132) are introduced into the hydrocarbon system by direct exchange with air-saturated water (ASW). The distribution of air-derived noble gas species are controlled by phase partitioning processes; in that they preferentially partition into the gas (i.e., methane) phase, due to their low solubilities in fluids. Therefore, the extent of exchange between hydrocarbon phases and formation waters - that have previously equilibrated with the atmosphere - can be determined by investigating air-derived noble gas species. We utilize both elemental ratios to address process (i.e., open vs. closed system) and concentrations to quantify the extent of hydrocarbon-water exchange (i.e., volumetric gas-water ratios). These data are discussed within the framework of several conceptual models: (i) total gas-stripping model, which assumes all noble gases have been stripped from the water phase, thus defining the minimum volume of water to have interacted with the hydrocarbon phase; (ii) equilibrium model, which assumes equilibration between groundwater and hydrocarbon phase at reservoir P, T and salinity; and (iii) open and closed system gas-stripping models, using concentrations and elemental ratios. By applying these models to Ne-Ar data from Sleipner, we estimate volumetric gas-water ratios V-g/V-w between 0.02 and 0.07, which are lower than standard geologic gas-water estimates of similar to 0.24, estimated by combining gas-in-place estimates with groundwater porosity estimates. Sleipner Vest data can be best approximated by an open system model, which predicts more than an order of magnitude more groundwater interaction during migration than geologic estimates, indicating a dynamic aquifer system and/or a hydrous migration pathway. In an open system, the extent of gas loss can be estimated to be between 8 and 10 reservoir volumes, which have passed through the system and been lost (i.e., filled and spilled). (C) 2016 Elsevier Ltd. All rights reserved.