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AAPG European Region, Geothermal Cross Over Technology Workshop, Part II

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Multigeophysical Exploration

Abstract

Exploration for natural resources is based on the use of geophysical Previous HitdataNext Hit and advanced mapping tools. Petroleum exploration and geothermal exploration has many fundamental things in common, and a few important details that are different. In both cases, exploration is carried out within the a play concept. The purpose of geophysical studies in the predrill exploration phase is to contribute to prospect evaluation, and to understand the risk factors defining the play. In petroleum, the risk factors are source rock, reservoir and trap/seal. In geothermal exploration, the corresponding factors are heat source, container and recharge. The most important geophysical technique in petroleum exploration is seismic imaging. This is used to define the geological framework, and to identify reservoirs and closures. Non-seismic Previous HitdataNext Hit is heavily used only when seismic Previous HitmethodsNext Hit fail. Examples are subsalt imaging, and fluid prediction, when CSEM Previous HitdataNext Hit is used together with AVO Previous HitinversionNext Hit to obtain higher confidence (Nordskag et al., 2013). The most useful geophysical parameter for geothermal exploration is resistivity, due to its direct sensitivity to temperature. Seismic information is often obtained only from passive Previous HitmethodsNext Hit. Reflection seismic should probably be used more often, to obtain better structural information. In complex exploration problems, on the regional as well as the prospect scale, it’s beneficial and necessary to systematically utilize all the Previous HitdataNext Hit available, together with general geological knowledge. We have experienced, in both petroleum and geothermal exploration, that the best results are obtained when combining at least one mechanical parameter (P-wave velocity, S-wave velocity, density) and one electromagnetic parameter (resistivity, susceptibility, magnetization). A general procedure for multigeophysical Previous HitinversionNext Hit can be presented as a Bayesian network. We assume that geophysical model parameters are conditionally independent, but depend on common parent parameters of interest. Multigeophysical Previous HitinversionNext Hit can then be performed in two steps: (1) Previous HitInversionNext Hit for model geophysical models given Previous HitdataNext Hit. (2) Previous HitInversionNext Hit for properties given model parameters. The first step is conventional geophysical imaging and Previous HitinversionNext Hit. The second step is typically rock physics Previous HitinversionNext Hit. We do the multigeophysical Previous HitinversionNext Hit in a pragmatic way. Only the second Previous HitinversionNext Hit step is fully statistical. Then we can utilize geophysical models computed with different Previous HitmethodsNext Hit, by various service providers, and produce results with fast turnaround. From the geological models, we may infer the properties of key interest, such as subsurface temperature in geothermal explorationr heat flow for basin Previous HitmodelingNext Hit (Hokstad et al., 2017). Also, geochemical Previous HitdataNext Hit and remote-sensing imagery can be utilized in the Previous HitinversionNext Hit This research was partly funded by the EC Horizon 2020 project DEEPGS.