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

基于页岩气在美国的成功，页岩气被视为对英国政府和行业具有吸引力的提议。评估资源的一个关键不确定性是天然气的到位，以及过多的岩石物理方法或模型，往好了说是令人困惑，往坏了说是误导。这项催化剂提案旨在解决这一问题，并为行业、政府和社会提供走出岩石物理迷宫的指南。它回应了NERC的呼吁，即通过开发一个实质性的JIP来促进我们在页岩气方面的行业合作的发展和扩展，并直接涉及到主题：非常规碳氢化合物。页岩气是指细粒地层，其中有机质已经成熟，以生产天然气为主，但这种天然气没有迁移任何显著的距离。源岩实际上就是储集层，尽管储集层的地质和岩石物理性质可能会有令人难以置信的变化。页岩气通常有两种不同的气体成分：游离气能够移动并占据孔隙，而吸附的气体固定在有机表面并通过压力保持在适当的位置；这两种气体占据相邻的体积，将两者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，部分原因是出版的文献取得了重大进展。天然气储量的计算是通过开发和应用岩石物理模型来完成的，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，根据我们自己对海恩斯维尔页岩的分析、发布的数据、同行评审的论文和行业经验，开发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制变化的敏感性。我们还将开展初步调查，以确定是否存在控制或决定页岩气藏岩石物理特征的潜在地质特征。对英国来说，这是一个关键时刻，澄清两种模式之间的差异，以及识别适当模式选择的能力是一项紧迫的要求。在英国，英国地质调查局最近对石炭纪鲍兰页岩的估计表明，存在着非常大量的天然气，并将其量化为1329tcf或37.6tcm，作为一个中心数字(P50)。然而，英国地质调查局承认，这些估计需要对岩石物理模型做出相当大的假设。拟议的催化剂资金建立在这些发展的基础上，对英国来说，在一个关键时刻提高了我们的理解，而且还提供了学术界和工业界以及整个社会之间的知识交流。这项提案将为计算现有天然气提供明确的指导方针，并将这些指导方针传达给行业、政府和公众。主要成果将是明确解释页岩气的岩石物理模型如何变化，以及它们的使用指南。这将提高对页岩气的总体理解，并通过向行业、政府和公众传达这些指导方针，在学术界和工业界以及一般社会之间提供知识交流。我们的成果将包括一份经过同行评议的指南出版物、一次关于页岩气岩石物理模型的行业KE研讨会、一份面向政府的简报文件、一篇向社会提供信息的外联文章。随后，这项初步研究将通过开发联合投资计划加以发展和加强，以进一步评估页岩气模型，重点放在英国的背景下。JIP的一个重点将是为岩石物理研究带来实质性的新的地质研究。

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.