Mechanical properties of Michigan Basin’s gypsum before and after saturation

The stability analysis of an abandoned underground gypsum mine requires the determination of the mine pillar’s strength.This is especially important for flooded abandoned mines where the gypsum pillars become saturated and are subjected to dissolution after flooding.Further,mine pillars are subjected to blast vibrations that generate some level of macro- and micro-fracturing.Testing samples of gypsum must,therefore,simulate these conditions as close as possible.In this research,the strength of gypsum is investigated in an as-received saturated condition using uniaxial compressive strength (UCS),Brazilian tensile strength (BTS) and point load index (PLI) tests.The scale effect was investigated and new correlations were derived to describe the effect of sample size on both UCS and BTS under dry and saturated conditions.Effects of blasting on these parameters were observed and the importance of choosing the proper samples was discussed.Finally,correlations were derived for both compressive and tensile strengths under dry and saturated conditions from the PLI test results,which are commonly used as a simple substitute for the indirect determination of UCS and BTS.

High concentration retene and methylretene in Silurian carbonate of Michigan Basin

Retene and methylretene have been identified by gas chromatography-mass spec-trometry in aromatic hydrocarbon fractions of Silurian carbonate extracts of the Michigan Basin. Retene identified in pre-Devonian carbonates indicates that the compound not only is the biomarker of higher plants but also derived from alga or bacterium. The geochemical significance of methylretene has been discussed.

高变质煤区的煤层气可采性

高变质煤中煤层气的勘探开发是一个极具探索性的新领域。重新认识和正确评价高变质煤煤层气的可采性是突破这一领域的关键。对美国密执安盆地安特里姆页岩气的地质背景、成因、赋存和产出机理、气产能地质控制因素及其成功开发经验进行的全面分析表明，以吸附状态存在于无内生裂隙储集层中的天然气，能够仅凭借密度较高、延伸较长、走向多变且开后性较好的外生裂隙而大量产出。我国东部具备形成外生裂缝系统的构造动力条件，能够充分改善高变质煤煤层气的可采性，东部地区高变质煤分布区煤层气的可采性应明显好于安特里姆页岩气的可采性，因而具有良好的勘探开发前景。

美国密歇根盆地安特里姆页岩气区带成藏特征

安特里姆页岩广泛覆盖在北美古大陆的中下泥盆统之上,其中,生物成因的天然气富集于埋深浅、欠压实、富含有机质的页岩储集层内,气体多被有机质和黏土吸附。诺伍德段和拉钦段有机质含量最高,为区带内最主要的页岩气勘探层。对密歇根盆地的安特里姆页岩气区带的烃源岩及其厚度、物性特征、矿物含量以及裂缝系统和成藏作用进行了探讨,并对区带的勘探潜力进行了评价。该区安特里姆页岩经历较深的埋深后又被抬升遭受大气淡水淋滤,在适宜的条件下生成生物气并成藏。安特里姆页岩气成藏特征的研究将会对中国页岩气勘探有所裨益。

密执根盆地的热弹性模拟

沉积盆地的沉降过程受沉积物载荷的控制,但热也起着相当重要的作用。本文系用一种热弹性分层模型,考虑载荷及温度的共同影响,并计入了二者之间的弱耦合作用,讨论盆地的沉降过程。用这种热弹性分层模型模拟计算了密执根(Michigan)盆地在古生代的沉降曲线。密执根盆地是北美大陆上一近圆形的大盆地,具巨厚层沉积物,构造作用简单,属于稳定的克拉通内部盆地。计算结果与实际资料能较好地吻合,并且指出了有关热事件是升温或者降温的性质。