A guide to petrophysical models for shale gas reservoirs based on sensitivity analysis of key variables

基于在美国的成功，页岩气被视为对英国政府和工业界具有吸引力的提议。评估资源的一个关键不确定因素是天然气储量，现有的大量岩石物理方法或模型往好了说是令人困惑的，往坏了说是误导的。该催化剂提案旨在解决这一问题，并为行业、政府和社会提供穿越岩石物理迷宫的指南。它通过开发实质性的JIP，满足了NERC的要求，使我们在页岩气方面的行业合作得以发展和扩展，并直接落入主题：非常规碳氢化合物。页岩气指的是细粒地层，其中有机质已经成熟，主要产出天然气，但这些天然气没有迁移到很远的地方。烃源岩实际上就是储层，尽管储层的地质和岩石物理性质变化很大。页岩气通常以两种不同的气体成分为特征：自由气体能够移动并占据孔隙，而吸附气体则固定在有机表面上，并通过压力保持在原位；这两个占据相邻的体量，将两个分开以避免重复计算是重要的一步。在过去的5年里，我们对页岩气岩石物理学的理解发生了重大变化，部分原因是我们自己的研究，部分原因是已发表文献的重大发展。通过开发和应用岩石物理模型来计算天然气储量，对于页岩气有许多不同的方法。我们建议以我们在页岩气岩石物理方面的工作为基础，根据我们对Haynesville页岩的分析、已发表的数据、同行评审的论文和行业经验，开发出这些岩石物理模型的指南。我们将确定模型中的关键变量，并探索模型对地质和岩石物理参数强加变化的敏感性。我们还将对是否存在控制或决定页岩气储层岩石物理特征的潜在地质特征进行初步调查。对于英国来说，这是一个关键时刻，提供模型之间差异的清晰度，以及识别适当模型选择的能力是一个迫切的需求。在英国，英国地质调查局（British Geological Survey）最近对石炭纪鲍兰德页岩（Bowland Shale）的估计表明，存在大量天然气，并将天然气量量化为1329万亿立方英尺或37.6立方米，作为中心（P50）数字。然而，英国地质调查局承认，这些估计需要对岩石物理建模做出相当大的假设。拟议的催化剂资金建立在英国在提高我们的理解的关键时刻，而且在学术界和工业界以及整个社会之间提供知识交流的基础上。这项建议将为计算现有的天然气提供明确的指导方针，并将这些指导方针传达给工业界、政府和公众。主要成果将是对页岩气岩石物理模型变化的清晰解释，以及它们的使用指南。这将提高人们对页岩气的普遍理解，而且通过将这些指导方针传达给行业、政府和公众，还可以促进学术界、工业界和社会之间的知识交流。我们的成果将包括同行评议的指南出版物，页岩气岩石物理模型的行业KE研讨会，政府简报文件，以及向社会通报的推广文章。这项初步研究将通过JIP的开发得到进一步发展和加强，以进一步评估页岩气模型，重点是英国的环境。JIP的一个重点将是为岩石物理研究带来大量新的地质研究。

Shale gas is seen as an attractive proposition to UK government and industry based on success in the USA. A key uncertainty in evaluating the resource is the gas in place and a plethora of petrophysical approaches or models exist that are at best confusing and at worst misleading. This catalyst proposal aims to address this and provide industry, government and society with a guide through the petrophysical maze. It addresses the NERC call in enabling the development and extension of our industry collaboration on shale gas through the development of a substantial JIP, and falls directly into the theme: Unconventional Hydrocarbons.Shale gas refers to fine-grained formations where organic matter has matured to produce predominantly gas, but that gas has not migrated any significant distance. The source rock is effectively the reservoir, although the geological, and petrophysical, nature of the reservoir can be incredibly variable. Shale gas is frequently characterized by two distinct gas components: free gas is able to move and occupies the pores, while adsorbed gas is fixed onto organic surfaces and held in place by pressure; these two occupy adjacent volumes and separating out the two to avoid double counting is an important step. Our understanding of shale gas petrophysics has changed significantly in the last 5 years, partly as a result of our own research and partly because of significant developments in the published literature. Calculating the quantity of gas in place is done through the development and application of a petrophysical model and for shale gas there are a number of different approaches. We propose to build on our work on shale gas petrophysics and develop a guide to these petrophysical models based on our own analysis of the Haynesville shale, published data, peer-reviewed papers, and industry experience. We will identify key variables within the models and explore the sensitivity of the models to imposed changes in geological and petrophysical parameters. We will also carry out a preliminary investigation of whether there are underlying geological characteristics that control or determine the petrophysical characteristics of the shale gas play. This is at a critical time for the UK, and providing clarity of the differences between the models, and the ability to identify an appropriate choice of model is an urgent requirement. In the UK, recent estimates by the British Geological Survey for the Carboniferous Bowland Shale suggest very significant amounts of gas exist and quantify the gas at 1329 tcf or 37.6 tcm, as a central (P50) figure. The BGS, however, acknowledge that these estimates necessitated making considerable assumptions concerning the petrophysical modeling. The proposed catalyst funding builds on these developments at a critical time for the UK in improving our understanding but moreover in providing knowledge exchange between academia and industry, and society generally. This proposal will provide clear guidelines for calculating the gas in place and will communicate these to industry, government and public.The main deliverables will be a clear explanation of how petrophysical models for shale gas vary, and guidelines for their use. This will improve the general understanding of shale gas, but moreover provides knowledge exchange between academia and industry, and society generally, through communicating these guidelines to industry, government and public alike. Our outcomes will include a peer-reviewed publication of the guidelines, an industry KE workshop on shale gas petrophysics models, a briefing paper for government, an outreach article to inform society. This initial study will then be developed and strengthened through the development of a JIP to further evaluate shale gas models with emphasis on a UK context. A focus of the JIP will be to bring substantial new geological research to bear on the petrophysical study.