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Abstract

An important cause of subsidence is the withdrawal of large volumes of natural gas, oil and water from<br>hydrocarbon reservoirs. Every point of depletion in the subsurface causes a subsidence bowl with a<br>radius corresponding to the depth of the depletion point. The depletion of a large volume in the<br>subsurface leads to a subsidence bowl of which the shape and the size are directly related to the<br>subsurface properties and processes. Besides the amount of hydrocarbons produced and the geometry<br>of the reservoir, relevant features include the subsurface elasticity profile, the compaction coefficient<br>and the strength of the aquifer.<br>Surface subsidence measurements (e.g. Interferometric Synthetic Aperture Radar (InSAR), leveling<br>measurements, or GPS) can be used to better quantify the subsurface parameters and processes.<br>Simple inversion approaches do not usually provide a sensible solution due to non-uniqueness of the<br>solution and the sensitivity of the inverse problem to small fluctuations in the data. We have developed<br>a time-integrated inversion scheme for resolving the spatial and temporal reservoir pressure drop from<br>surface subsidence observations. This inversion procedure is unique because it utilizes all the available<br>prior knowledge including the uncertainty and the correlations within it. Elements of this prior<br>knowledge are the geological model, the reservoir model, the sealing properties of faults, and the acquifer activity.<br>We have applied our inversion method to a highly compartmentalized reservoir in the Netherlands<br>where we used the observed surface subsidence (leveling), the geological model, the reservoir model,<br>and the prior knowledge about possibly sealing faults, to obtain insight into undepleted pockets of<br>natural gas in the reservoir. We used prior models which complied with the measured flux and pressure<br>measurements of the production profile. With these data, we were able to better quantify the amount<br>of compaction in the different compartments in the reservoir and the pressure depletion causing it.<br>The approach followed is essentially a two-step approach: the history match is the first step, and the<br>inversion of subsidence measurement the second. The risk of this approach is that not the complete<br>solution space is being searched. We are currently also developing an approach in which the inversion<br>of production data and subsidence measurements are integrated.

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/content/papers/10.3997/2214-4609-pdb.248.095
2010-03-07
2021-10-20
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