Dealing with Uncertainty of Reservoir Heterogeneity and Pressure Depletion to Optimize Acid Placement in Thick Carbonate Reservoirs
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For carbonate reservoirs, it is common for completed intervals to intersect several layered reservoirs, commingling multiple zones, and to extend hundreds to more than a thousand feet in length. The long interval presents uncertainty on the key formation parameters considered in acid stimulation even with the best petrophysical measurement and interpretation available in the industry. Stimulation of such intervals can be further complicated by differential depletion between the zones and large differences in hydrostatic pressure during stimulation treatment. 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. Based on degradable fiber and visco-elastic surfactant technologies, a new acid diverter, 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. The diversion technique does not overly rely on the accuracy of petrophysical data, such as permeability and porosity, or reservoir pressure and can be successful in a variety of potential scenarios. 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. Copyright 2013, Society of Petroleum Engineers.
author list (cited authors)
Retnanto, A., Orellana, E., & Ryan, A.