Geomechanics‐Constrained Evaluation of Fracture Effectiveness and Activity in Lithologically Heterogeneous Buried Hill Reservoirs: Insights From Stress Modelling and Multi‐Source Data Integration

ABSTRACT

Accurate evaluation of fracture effectiveness and activity in buried‐hill reservoirs remains challenging because fracture development is commonly controlled by multi‐stage tectonic overprinting, lithological heterogeneity, weathering‐related mechanical contrasts and complex present‐day stress fields. These difficulties are, particularly, pronounced in buried‐hill intervals composed of crystalline basement rocks, metamorphic or igneous lithologies and weathered fractured zones, where fracture density alone is insufficient to determine reservoir effectiveness. To address this problem, this study develops a geomechanics‐constrained and interval‐specific workflow for evaluating fracture activity and effectiveness within buried‐hill reservoirs. The proposed approach integrates laboratory‐derived rock mechanical parameters, log‐based dynamic–static elastic parameter calibration, seismic structural interpretation, lithology‐constrained three‐dimensional geomechanical modelling and fracture‐scale stress analysis. The workflow explicitly links buried‐hill lithological subdivision, present‐day stress tensor reconstruction, fracture orientation characterisation and three‐dimensional Mohr stress analysis. Different buried‐hill lithologies and weathering zones are assigned distinct mechanical parameters to better represent the vertical and lateral heterogeneity of the reservoir interval. The numerical stress model is iteratively constrained by measured in situ stress data, wellbore information and structural interpretation to improve mechanical consistency. Fracture activity is quantitatively evaluated by resolving the normal and shear stresses acting on mapped fracture sets under the present‐day stress regime, whereas fracture effectiveness is assessed by jointly considering fracture orientation, stress state, lithological layering and mechanical stratification. Model predictions are further validated using borehole image logs, drilling responses and production performance, allowing effective fracture intervals within the buried hill to be identified more reliably. The results show that effective fractures in buried‐hill reservoirs are primarily controlled by stress–structure–lithology coupling rather than by fracture density alone. Fractures that are critically oriented with respect to the present‐day stress field and hosted in mechanically favourable lithological or weathered intervals exhibit higher activation potential and better agreement with observed fracture development and well productivity. This study provides a more geologically constrained, mechanically consistent and interval‐specific framework for fracture effectiveness evaluation in buried‐hill reservoirs. The proposed workflow improves the linkage among geological interpretation, geomechanical simulation, fracture activity assessment and reservoir performance prediction and, therefore, offers practical guidance for sweet‐spot identification and development optimisation in fractured buried‐hill systems.