Effective stimulation of thick, layered carbonate reservoirs is required to reach production targets for present and future demand. It is common that the completed intervals intersect several layered reservoirs, commingle multiple zones, and extend hundreds to more than a thousand feet in length. Even with the best petrophysical measurement and interpretation available in the industry, the key formation parameters considered in acid stimulation are still clouded by uncertainty. Several matrix acidizing techniques have been applied to stimulate these types of reservoirs based on the knowledge of petrophysical data. This paper strives to outline some of the key pitfalls that can occur due to the uncertainty in this data. Using reservoir simulations, the long term adverse impact of these pitfalls on both production and overall recovery can be shown.
A new acid diverter, based on degradable fiber and visco-elastic surfactant technologies, has been applied, along with a placement model, to optimize treatment design and to maximize diversion in heterogeneous carbonate reservoirs. The system is robust, diverting from high permeability streaks, fissures and natural fractures with very little diverting effect from the low permeability zones, and therefore generates a more uniform stimulation than conventional fluid systems. This approach has been used to optimize various stimulation campaigns on carbonate fields throughout the Middle East.
Maximizing treatment fluid coverage across the entire intervals can be achieved across thick, even naturally fractured, carbonate intervals using degradable fiber technology within a visco-elastic surfactant fluid. The diversion technique does not overly rely on certainty in petrophysical data, such as permeability and porosity, and can be successful in a variety of potential scenarios.