Acid stimulation and fracturing in multiple layers formation requires an integrated approach to design and execute an effective stimulation treatment. An extensive campaign of acid stimulation on carbonate formation to increase productivity index in a deep High Pressure High Temperature (HPHT) gas bearing carbonate formation is discussed here. A high degree variation in permeability across long interval, stress barriers between target zones, and completion limitations were main challenges to design an effective stimulation treatment.
The target was to achieve effective acid stimulation for multi-layers carbonate formation with different formation properties and stress barriers. Although all layers had similar initial pressures and gas compositions; but different properties. Comingled flow was planned from the formation, therefore effective stimulation for each layer was recommended to drain effectively and improve recovery.
To assess the best stimulation strategy in early stage of development, complete set of diagnostics conducted across all formations before and after the acid treatment coupled with geomechanical studies on actual core samples. Various stimulation techniques were implemented from Small Matrix Treatments (SMT) with Coiled Tubing, Matrix Acidizing Treatments (MAT), High Rate Matrix Acidizing (HRMA), and Acid Fracturing Treatment (AFT). Thorough study of results as part of learning process was conducted to optimize the important parameters that affect the stimulation efficiency such as perforation strategy, completion design, diverter selection, fracturing design and implementation. The importance of modeling in optimization process, comparison between different treatment types and fluid systems is discussed supported by actual data such as temperature logs, post-treatment flowback analysis, pressure transient analysis and production logging results.