Elastic Dislocation Modeling is an Indirect Tool for Sub-Seismic Natural Fractures Identification for Carbonate Reservoirs in Wildcat, Exploratory, and Development Blocks: A Case Study from the Complex Compressional Tectonic Zone of Pakistan
Authors: Khan Imran , Ali Iftikhar , Malik Muhammad Ameer Nawaz , Akhtar Shamshad , Ahmad Shakeel , Shahzad Khurram , Hussain Khadim , Khan Mahmood , Badshah Aatef 
Published: November 2024

The main aim of this research work was to find out the sub-seismic faults and fracture corridors and their characteristics, including density and orientation, for a potential Paleocene fractured carbonate reservoir. This work will address the sub-seismic faults and fracture sets identification and their impact on the reservoir's potential, regarding maximum hydrocarbon flow and also for well-bore stability, as well as address the reasons behind a well failure in case of fracture dependent reservoirs.

A validated, balanced 3D-structural model was developed using 3Dseismic data interpretation, and it was then converted into an Elastic Dislocation (ED) model (Geomechanical Model) by adding the Geomechanical properties (Young modulus, Poison ratio, Bulk density, etc.) of the carbonate rock. ED theory was used to execute the valid Geomechanical model by forward modeling (Solutions of Okada, 1985, 1992). By mapping the fault geometry and slip distribution in 2D/3D seismic-reflection datasets, the application of the ED theory can forecast the distribution of displacement, strain, and stress in the rock volume surrounding significant deformation impact as faults. Calculations were made to determine the overall strain, which included displacement strain along the fault surface and background or regional strain. This total strain calculates and predicts stress and failure for deformation horizons.

The ED model results predict the sub-seismic faults and fracture corridors and their characteristics (Density, orientation) for carbonate reservoirs. The ED model predicts that wells # 01 and 02 (Producing well) have a fall in high fracture density zone and fracture sets are striking almost NW-SE / WNW-ESE direction apart from some variation, while well#03 (Dry) has less fracture density, and its fracture set strikes in NE-SW / ENE-WSW directions. The Formation Micro image logs (FMI) of three wells correlate with the ED model fracture analysis results. The results for fracture prediction will be more accurate and reliable, if the seismic quality is excellent, best interpreted to develop a valid structural geological model (Restorable/balance) and judicious choice of mechanical properties of carbonate rocks, applying appropriate boundary conditions as per the tectonic regime.

Planning a well to drill out the maximum fracture sets with the correct orientation in a carbonate reservoir is a difficult task. In the fields under study, the Paleocene carbonate reservoirs have poor primary porosity and permeability. These reservoirs’ production is reliant on naturally occurring permeability along sub-seismic faults and fractures. The ED method is an innovation in exploration to predict the occurrence of naturally fractured corridors for better well placement to get maximum hydrocarbon production. This technique of finding sweet spots on fracture carbonate is helpful in wildcat areas, where there is no sub-surface data available for analysis. Also, it helps in the evaluation of dry wells.