Analytical Evaluation of Integrated Formation Damage Diagnosis and Stimulation Design for Naturally Fractured Carbonate Wells in the Anambra Basin, Anambra State

Formation damage in naturally fractured carbonate reservoirs manifests through complex interactions between fracture plugging, matrix acidising, and in situ stress changes that demand an integrated diagnostic and stimulation design approach fundamentally different from conventional matrix acidising protocols. This study analytically evaluates integrated formation damage diagnosis and stimulation design methodologies for naturally fractured carbonate wells in the Anambra Basin, Anambra State, South East Nigeria. Pressure transient data from post-damage build-up tests in four carbonate wells were analysed using specialised fractured reservoir models to decompose the composite skin into matrix damage, fracture conductivity impairment, and geomechanical compaction components. Pressure derivative signatures characteristic of damaged fractures versus damaged matrix were identified and used to classify the dominant damage mechanism in each well. Laboratory acid diversion experiments using foam acid and self-diverting viscoelastic surfactant acid were conducted at reservoir temperatures of 145 to 165 degrees Celsius to evaluate acid distribution efficiency in heterogeneous carbonate samples. Numerical stimulation modelling using Kinetix coupled to the dual-porosity reservoir model quantified projected post-stimulation skin improvement under fracture wash-acid, matrix squeeze-acid, and bullhead acid programs. The fracture wash-acid protocol targeting fractured interval open perforations delivered the greatest skin reduction (from plus 11.2 to minus 2.8) in the laboratory-validated numerical simulation. Keywords: formation damage, naturally fractured carbonate, acid stimulation, Anambra Basin, Anambra State.