Contribution of Rock Physics Laboratory Tests and Modelling to Improving Uplift Estimates

Abstract

Most currently applied procedures for uplift estimation rely on assumptions that porosity and seismic / log measured velocity are unaltered by the uplift process. Laboratory experiments have been performed with synthetic sandstones having different degrees of cementation and formed at different stresses. In idealized scenarios, the effects of burial after cementation, followed by uplift, and effects of uplift directly after cementation, have been addressed. The experimental results reveal that large velocity reductions may occur during unloading, in particular directly after cementation, whereas measured strains indicate minor changes in porosity. P-wave anisotropy appears from the laboratory tests as a feasible attribute of uplift. The velocity – stress trends seen during unloading are non-linear, indicating that velocity reductions will be largest when the uplifted strata are relatively shallow. The idealized scenarios may form a basis for development of a rock physics based methodology for uplift and uplifted rock stress estimation, but need to incorporate e.g. effects of diagenesis during burial and uplift.