路易斯安那州西北部上侏罗世海恩斯维尔页岩中与层理平行的方解石 "牛肉 "层的起源

IF 2.7 3区 地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY
AAPG Bulletin Pub Date : 2024-02-01 DOI:10.1306/01192321189
L. Taras Bryndzia, Calum I. Macaulay, Alexander P. Litvinchuk, Brian D. Monteleone
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引用次数: 0

摘要

在整个海恩斯维尔地层过成熟页岩中,保持纤维状 "牛肉 "纹理的层状平行方解石层(BPCL)十分常见。方解石层与主页岩的交接处含有石膏花岗岩后的放射状无水石膏假象,这表明方解石层起源于原生蒸发或早期埋藏。在某些地方,方解石层含有残余的重晶石或无水石膏,与其主方解石在结晶学上保持一致,这表明方解石是通过取代纤维状硫酸盐前驱相而形成的。因此,页岩和碳氢化合物系统的氧化还原状态变成了还原状态,这一点可以从无处不在的 H2S 中看出来。无水石膏和重晶石在 H2S 的存在下不稳定,会被热化学硫酸盐还原所消耗。在埋藏高峰期,液态碳氢化合物裂解为 CH4 气体和残余的固态火沥青,通常占据纤维状方解石层的中间缝合带。我们利用微激光拉曼光谱直接测量了 BPCL 中 CH4 气体包裹体的密度,从而估算出了海恩斯维尔页岩中参加热化学硫酸盐还原的原位 CH4 压力。纤维状方解石中保留的平均流体压力梯度约为 0.87 ± 0.03 psi/ft(±1σ;n = 4),大大高于静水压力,但低于覆盖层和页岩裂缝梯度。我们没有发现任何证据表明流体压力超过了岩石压力,也没有发现纤维状方解石在扩张的脉系中从其边缘向BPCL的中心生长。方解石对原生层状无水石膏和重晶石的置换保留了前驱硫酸盐矿物的原始方向,换句话说,它们的纤维状牛肉纹理是一种继承特征。方解石取代硫酸盐导致固体体积损失约 20 至 30%。由于体积损失和覆土应力导致地层坍塌,最小水平应力与垫层平行。焦沥青层由于拉伸破坏而被压缩和分解。晚期方解石和解离的焦沥青随后都沿着最小水平应力的方向(即与垫层平行)生长。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Origin of bedding-parallel calcite “beef” layers in the Upper Jurassic Haynesville shale, northwestern Louisiana
Bedding-parallel calcite layers (BPCLs) preserving a fibrous “beef” texture are common throughout the overmature Haynesville Formation shale. Their interfaces with the host shale contain radiating splays of anhydrite pseudomorphs after gypsum rosettes, suggesting either a primary evaporitic or an early burial origin. In places, the calcite layers contain remnant barite or anhydrite in crystallographic alignment with its host calcite, indicating that the calcite formed by replacing a fibrous sulfate precursor phase.During burial and heating, maturation of source rock organic matter resulted in the expulsion of hydrocarbons (oil and gas). Consequently, the redox state of the shale and hydrocarbon system became reducing, as indicated by the ubiquitous presence of H2S. Both anhydrite and barite are unstable in the presence of H2S and were consumed by thermochemical sulfate reduction. At peak burial, liquid hydrocarbons cracked to CH4 gas and remnant solid pyrobitumen, which typically occupies the median suture zone of the fibrous calcite layers. It was along this median suture that calcite replacement of anhydrite and barite was initiated, proceeding to replace sulfate minerals from the center of the layer out toward the shale contact.We estimated the in situ CH4 pressure attending thermochemical sulfate reduction in the Haynesville shale by using microlaser Raman spectroscopy to directly measure the density of CH4 gas inclusions in BPCLs. Average fluid pressure gradients preserved within the fibrous calcite are approximately 0.87 ± 0.03 psi/ft (±1σ; n = 4), considerably above hydrostatic but below both overburden and shale fracture gradients. We found no evidence to suggest that fluid pressures exceeded lithostatic or that fibrous calcite grew in dilated vein systems from their margins toward the center of the BPCLs.The replacement of primary bedded anhydrite and barite by calcite preserves the original orientation of the precursor sulfate minerals—in other words, their fibrous beef texture is an inherited feature. The replacement of sulfate by calcite results in a solid volume loss of approximately 20 to 30 vol. %. Collapse of the layers due to loss of volume and overburden stress results in the minimum horizontal stress being parallel to bedding. Pyrobitumen layers were compressed and disaggregated due to tensile failure. Both late-stage calcite and disaggregated pyrobitumen subsequently grew in the direction of minimum horizontal stress (i.e., parallel to bedding).
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来源期刊
AAPG Bulletin
AAPG Bulletin 工程技术-地球科学综合
CiteScore
6.60
自引率
11.40%
发文量
73
审稿时长
4.8 months
期刊介绍: While the 21st-century AAPG Bulletin has undergone some changes since 1917, enlarging to 8 ½ x 11” size to incorporate more material and being published digitally as well as in print, it continues to adhere to the primary purpose of the organization, which is to advance the science of geology especially as it relates to petroleum, natural gas, other subsurface fluids, and mineral resources. Delivered digitally or in print monthly to each AAPG Member as a part of membership dues, the AAPG Bulletin is one of the most respected, peer-reviewed technical journals in existence, with recent issues containing papers focused on such topics as the Middle East, channel detection, China, permeability, subseismic fault prediction, the U.S., and Africa.
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