Middle and Upper Devonian gas shales of the Appalachian Basin host a sequence of mode I cracks from early veins to late unmineralized joints. These fractures develop during a cycle of burial and exhumation starting with horizontal veins, then vertical veins, then vertical joints, and ending with pancake joints. Veins are most common in the cross-fold orientation in gas shale of the deep hinterland, whereas joints are common in the shallow foreland fringe. Of particular interest for the recovery of natural gas are joints striking northeast to east-northeast in shallow core and outcrops of Appalachian gas shales, particularly in the underpressured, southwestern part of the basin. Northeast to east-northeast fractures are sparse in the deeper, northeastern part of the basin where the Marcellus gas shale is highly overpressured. The common occurrence of unmineralized joints in shallow gas shales is best explained with a stress–pressure–depth model for the evolution of pore pressure in the Appalachian Basin. Our model shows that by Skempton’s poroelastic relaxation, gas-charged porosity can drive natural hydraulic fractures during exhumation. In the shallow foreland fringe of the Appalachian Basin, exhumation was sufficient to favor the propagation of east-northeast–striking neotectonic joints in the contemporary tectonic stress field. These joints appear mainly at shallow depths where they facilitate leakage to form an underpressured gas column trapped by groundwater (i.e., Big Sandy gas field, Kentucky). Exhumation was insufficient for Skempton’s poroelastic relaxation to favor propagation of east-northeast joints in the deep, central part of the basin where capillary forces maintain overpressured gas shale.

中文翻译：

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Skempton的孔隙弹性松弛：解释阿巴拉契亚盆地黑页岩中孔隙压力和与掘出相关的裂缝的分布的机制

阿巴拉契亚盆地中上泥盆统天然气页岩具有从早期矿脉到晚期未矿化节理的I型裂缝序列。这些骨折发生在埋葬和回火的周期中，首先是水平静脉，然后是垂直静脉，然后是垂直关节，最后是煎饼关节。在腹地深部的页岩中，褶皱在横褶方向上最常见，而在前陆浅部的边缘则常见。对于天然气的回收特别感兴趣的是在浅层岩心和阿巴拉契亚气页岩的露头，从东北向东北走向的节理，特别是在该盆地西南部欠压的地区。在马塞勒斯气页岩压力过大的盆地深部，东北部，东北至东北向的裂缝稀疏。用阿巴拉契亚盆地孔隙压力演化的应力-压力-深度模型可以最好地解释浅层页岩中未矿化节理的普遍发生。我们的模型表明，通过Skempton的孔隙弹性松弛，带气孔可以驱逐尸体，从而驱使自然的水力压裂。在阿巴拉契亚盆地的浅前陆边缘，掘尸活动足以促进东向东北走向的新构造缝在当代构造应力场中的传播。这些接头主要出现在较浅的深度处，在这些深度处它们易于渗漏，形成被地下水困住的负压气柱（即肯塔基州的大桑迪气田）。掘尸不足以使Skempton的孔隙弹性松弛不足以促进深部东西向关节的繁殖，