Estimating tectonic thinning of a layer using core data and pure shear/simple shear faulting models

Tectonic thinning of a layer is estimated here using two different models: (i) a pure shear model with conjugate microfaults, and (ii) a simple shear model in which the microfaults dip in the same direction. These end-member bulk models may be interpolated in terms of a stretching factor. Formulas for use of deviated well data in calculating tectonic thinning are defined. The input to the modelling is data from structural core logging. in data is the number of microfaults and the mean displacement associated with them. The formulas are derived as if the microfaults were regularly spaced and all with the same (mean) displacement and applied to data showing variability. For pure shear this makes no difference, and for simple shear this is an approximation containing the assumption that the local layer (reservoir) has somewhat constant mechanical properties. ype of modelling is useful for hydrocarbon exploration and production for the case where a local layer (reservoir) thickness anomaly at the well position—caused by microfaulting—is suspected. By identifying this, a more correct well-to-seismics layer thickness calibration can be carried out. A case study from the North Sea is presented at the end of the paper.