Geomechanical Modelling to Identify Sub-Seismic Faults and Fractures Characteristics Using Elastic Dislocation (ED) Theory: A Case Study from Potwar Foldbelt, Upper Indus Basin (UIB) of Pakistan

Abstract

Abstract The study will address the failure reasons of wells and point out the high-density fracture zones, to drain out the remaining hydrocarbons in the field. A robust 3D geological model was developed based on 3D seismic interpretation. The rock mechanical properties of carbonates were incorporated. The total strain i.e., the background or remote strain (Bulk deformation) and the strain from displacement along the fault surfaces are mapped to each segment/element of the generated fault surfaces. This total strain calculates stresses and the failure for deformation surface. The geomechanical model based on Elastic Dislocation (ED) theory identified strain fields on horizon surface / observation grids and then finally fractures corridor and their characteristics i.e. distribution, orientation. Fault planes generated from interpretation play a major role in the ED method for fracture analysis. The fault surface consists of an array of panels, each contributing to the ED equation calculation. The main outcome is the sub-seismic faults and fractures identification around larger faults on the horizontal observation medium. The identified fractures corridors characteristics, distribution and orientation changes along the strike of the major fault system. In the developed ED model the predicated fractures system are parallel to the major reverse fault direction, but oblique fractures corridor is also observed along the middle segments, aligning with observed variations in structure dip. The crestal portion of the anticline has a higher density of fractures than the rim. The ED modelling fractures results were verified against FMI data of the targeted horizon, which demonstrated that the wells which were drilled in high-density fracture zones (modelled) have produced hydrocarbons and vice versa. There is a correlation between modelled results with image logs and well-testing results (DST's), which increases the reliance on the ED theory's ability to correctly identify small-scale (sub-seismic) fractures, joints and faults system. The Eocene carbonate reservoirs have low primary porosity and permeability. The productivity of these reservoirs is dependent on permeable natural fractures and sub-seismic faults. The identification of these features is a major problem before drilling while, conventional techniques do not provide optimum solutions to their understanding. A case study of compressional tectonic regime in Himalayan fold & thrust belts is presented here, where an integrated approach is applied in the form of geomechanical modelling, which is built on the ED theory provide a reliable base for well planning.