地盤沈下・地表水平変位移動マップによる油田ガス田の広がり推定法

Abstract

Normally, the inverse problem to map a reservoir compaction from surface subsidence data is an ill-conditioned system since the subsidence bowl gradually changes its curvature, hence, the boundary of pressure depleted area cannot be clearly identified from subsidence bowl. However, the analysis in this paper shows that the peak of lateral surface movement approximately coincides with the pressure depleted periphery. Therefore, if both subsidence and lateral movement maps are constructed, the approximate shape of the pressure depleted area and the lateral distribution of reservoir compaction can be identified. These two maps may be used without processing as a diagnosis tool to identify the location of sealed fault, extent of reservoir section and non-recovered hydrocarbon section.Imaging the reservoir compaction is further improved if a proper inverse method is applied with the subsidence and surface displacement maps as input data. This paper suggests, for inverse problems with real field conditions where reservoir compaction and elastic moduli are both unknown, to lump multiple layers into a few layers with equivalent anisotropic Young's moduli and to inversely calculate the reservoir compaction and the lumped anisotropic elastic moduli. The resolution and fluctuation of seek parameters are effectively adjusted by the Potter's error covariance off-diagonal elements. The inverted compaction map shows, more clearly than the original surface displacement maps, the location of sealed fault, extent of reservoir section and non-recovered hydrocarbon section even for relatively deep reservoirs.