[ENERGY] Rupture properties from microseismic data

低渗透气藏，如致密气、页岩气和地热气藏，必须通过水力压裂来增产，才能达到经济的产量水平。水力压裂引起微震，其位置和破裂特征(由震源矩张量(MT)表示)可以被监测，以便控制裂缝、评估激发体积和下一口井的设计。微震直接纵波(P-)的矩张量反演(MTI)会受到这种观测中通常采用的一维钻孔地震阵列缺乏孔径的影响，以及事件和传感器之间介质性质的鲜为人知的影响。横波(S波)和纵波的使用可以限制大地电磁测深，但重要的是要了解P波和S波衰减的差异的影响，以及横波走时和波形对介质各向异性的更大敏感性。使用来自同一断裂带上相似位置且表现出相似波形特征的事件簇，允许通过分析相对MT解决方案来最小化传播不确定性。在解决了局部集群中的MT，并假设沿着在类似应力条件下经历类似起因事件的扩展源区的类似机制之后，就有可能对源和传感器之间的介质的空间特性进行反转。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。怀特教授拥有来自冰岛的高质量数据集，涵盖了岩浆和地热引起的事件，这是水力破裂事件的密切指标。该数据集具有良好的地表地震台网孔径控制和良好的信噪比。岩浆活动与熔融注入岩墙密切相关。它们也位于地壳的正常延展性区域，这使得分析比在脆性浅地壳中更简单，因为消除了一些先前存在的开放裂缝的影响。有两类具有相反极性的事件本身值得进一步研究，但它们很容易被区分开来，并用来检验通过相对MTI更好地理解介质性质的想法。需要对早期合作博士项目中开发的现有计算机算法进行一些扩展，这将使行业和学术应用程序都受益。代码和工作流程可以使用由项目合作伙伴(SCR)开发的1D和3D全弹性建模代码生成的准确的3D合成地震图进行测试，然后在高质量的冰岛数据集上使用。然后，该方法将在受良好约束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。斯伦贝谢与一家石油公司合作计划获取这一研究数据集，并将向学生提供。这将允许分析方法上的孔径限制，并探索测量不确定度、中等不确定度与力矩张量的体积和补偿线性矢量偶极(CLVD)分量的界限之间的权衡。学生将受益于与SCR和大学团体的互动，利用两个机构的最新数据以及建模和反演程序。这将为数据处理和解释流体(无论是岩浆、水压裂、地热还是二氧化碳)与地下裂缝和裂缝相互作用的方式提供强大的协同作用。正如知识转移部分所述，这项研究将具有经济效益和社会效益，并将进一步加强产业界和学术界的合作。

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.