[ENERGY] Rupture properties from microseismic data

低渗透储层，如致密气、页岩气和地热储层，必须通过水力压裂来达到经济的生产水平。水力裂缝引起微地震，微地震的位置和破裂特征由源矩张量（MT）表示，可以监测裂缝的控制，评估压裂体积和设计下一口井。来自此类微地震事件的直纵波矩张量反演（MTI）可能会受到通常用于此类观测的一维井眼地震阵列孔径不足以及事件与传感器之间介质特性不为人所知的双重影响。剪切（S-）波和纵波的使用可以限制MTI，但重要的是要了解P波和S波衰减差异的影响，以及剪切旅行时间和波形对介质各向异性的更大敏感性。使用来自同一裂缝带相似位置的事件簇，并表现出相似的波形特征，通过分析相对的MT解决方案，可以将传播的不确定性降到最低。在求解了局部集群中的MT并假设在类似应力条件下经历类似因果事件的扩展源区域的类似机制之后，就有可能反演源和传感器之间介质的空间特性。对于只有一两个井眼传感器阵列的微地震数据集，这两种方法都很困难。White教授拥有来自冰岛的高质量数据集，涵盖岩浆和地热诱发的事件，这些事件是水力压裂事件的密切代表。这些数据集具有良好的地面地震台网孔径控制和良好的信噪比。岩浆活动与熔体注入堤密切相关。它们还位于地壳的正常韧性区域，通过消除预先存在的开放裂缝的一些影响，使分析比脆弱的浅层地壳更简单。有两类极性相反的事件，它们本身值得进一步研究，但可以很容易地加以区分，并用于测试通过相对MTI更好地理解介质性质的想法。需要对早期合作博士项目开发的现有计算机算法进行一些扩展，这将有利于工业和学术应用。代码和工作流程可以在项目合作伙伴（SCR）开发的1D和3D全弹性建模代码生成的精确3D合成地震图上进行测试，然后再用于高质量的冰岛数据集。然后，该方法将在一个约束良好的行业数据集上进行测试，该数据集包括位于地球表面、浅井和深井中的许多传感器的组合。斯伦贝谢计划与一家石油公司合作获取该研究数据集，并将提供给学生。这将允许对方法的孔径限制进行分析，并探索测量不确定度，介质不确定度以及矩张量的体积和补偿线性矢量偶极子（CLVD）分量的界限之间的权衡。学生将受益于与SCR和大学小组的互动，利用最先进的数据，以及来自这两个机构的建模和反演程序。这将为数据处理和解释流体（岩浆、水力压裂、地热或二氧化碳）与地下裂缝和裂缝的相互作用方式提供强大的协同作用。正如知识转移一节所述，这项研究将具有经济和社会效益，并将进一步加强产学研合作。

Low permeability reservoirs, such as tight gas, shale gas and geothermal reservoirs, must be stimulated by hydraulic fracture to achieve economic levels of production. Hydraulic fractures cause micro-earthquakes whose locations and rupture characteristics, expressed by the source moment tensor (MT), can be monitored for control of the fracture, evaluation of the stimulated volume and design of the next well. Moment tensor inversion (MTI) of direct compressional (P-)waves from such microseismic events can suffer both from lack of aperture of the 1D borehole seismic array usually employed in such observations and from the poorly-known properties of the medium between the event and the sensors. The use of shear (S-)waves as well as P-waves can constrain the MTI, though it is important to understand the effects of differences between P- and S-wave attenuations, and the greater sensitivity of shear travel-times and waveforms to medium anisotropy. The use of clusters of events, from similar locations on the same fracture zone and exhibiting similar waveform characteristics, allows the propagation uncertainty to be minimised by analysing relative MT solutions. Having solved for the MT in a local cluster and assuming similar mechanisms along an extended source region undergoing similar causative events under similar conditions of stress, it may then be possible to invert for the spatial properties of the medium between the sources and the sensors. Both these approaches are difficult with a microseismic dataset from just one or two borehole sensor arrays. Prof. White has high quality datasets from Iceland, covering magmatic- and geothermally-induced events, which are a close proxy for hydraulic fracture events. The datasets have good aperture control from surface seismometer networks and excellent signal to noise ratio. The magmatic events are closely constrained to a melt injection dyke. They are also in a normally ductile region of the crust, which enables simpler analysis than in the brittle shallow crust by removing some of the influence of pre-existing open cracks. There are two populations of events with opposing polarities which are worthy of further investigation in their own right but which can easily be distinguished and used to test the idea of obtaining a better understanding of the medium properties through relative MTI. Some extension of existing computer algorithms, developed in an earlier collaborative PhD project, would be required which would benefit both industry and academic applications. The code and workflow can be tested with accurate, 3D synthetic seismograms generated by 1D and 3D full elastic modelling codes developed by the project partner (SCR )before being used on the high quality Icelandic datasets. The approach would then be tested on a well-constrained industry dataset comprising a combination of many sensors located at the earth's surface, in shallow wells and in deep boreholes. Acquisition of this research dataset is planned by Schlumberger in conjunction with an oil company and would be made available to the student. This would allow the analysis of aperture limitations on the method and exploration of the tradeoff between measurement uncertainty, medium uncertainty and bounds on the volumetric and compensated linear-vector dipole (CLVD) components of the moment tensor. The student would benefit from interaction with both the SCR and university groups, drawing on state-of-the-art data, and modelling and inversion programs from both institutions. This would provide a powerful synergy for new advances both in data processing and in interpretation of the way fluids (be they magmatic, hydrofrac, geothermal or CO2) interact with cracks and fractures in the subsurface. As described in the Knowledge Transfer section, this research would have both economic and societal benefits, and would further strengthen industry-academic collaborations.