Geological Mapping of Lower Indus Basin using Geostatistical and Geophysical Techniques

Abstract

For a number of years regional studies are in progress to understand the structural and tectonic features of different stratigraphic units of a basin. Ordinary Kriging, Trend Surface analysis and Universal Kriging techniques are used to analyze and model the topographic variations of sedimentary cover of Lower Indus Basin. The input data used for this process is formation top of 461 wells. Statistical analysis is carried out on the data to estimate variance and standard error between the generalized model surfaces. Surfaces of different formations are generated by using Ordinary Kriging, Trend surface analysis and Universal Kriging techniques. Ordinary Kriging gives more detail in terms of local variations while Universal Kriging provides the regional trend. Trend surface analysis uses polynomial regression of increasing order up to 3. Surfaces of high orders are generated to effectively account the variation in formation tops. But surfaces of high orders cannot be generated due to complex geometry problems. Initially Universal Kriging was selected as final technique on the bases of standard deviation and standard error value, but after some tests it was found that Ordinary Kriging along with a smoothing operator of very high order produces similar results. To compromise between localized and regional trends Ordinary Kriging along with smoothing kernel operator of 21*21 points. The Geostatistical grids are used to assemble a multilayer Digital Sub-Surface Model (DSSM) which can be used to generate columns and subsurface cross-sections within the area at any location within the geographic window. This can be useful in seismic interpretation of adjacent areas, establishing well control over a point and generation of correla