Dynamic Diverter Technology Efficiency in Acid Fracturing Applications

Abstract

Acid fracturing has been an integral part of reservoir development strategies for carbonate reservoirs as mechanical and chemical means of bypassing formation damage enhances productivity. Over the past few years, acid fracturing has significantly increased targeting more carbonate reservoirs. There is a need to fully address the heterogeneous petrophysical and geomechanical properties of target reservoirs, which adversely affects the stimulation efficiency and production if fluids are not properly designed. When injecting stimulation fluids to fracture the reservoir rock, the fluid is prone to traveling along the path of least resistance, and consequently less permeable zones and high stress reservoir rock receive treatments that could be further improved or enhanced. Accordingly, this drives the industry to continuously develop high performance chemical dynamic diverter systems. To ensure an effective and sufficient acid fracturing is achieved when treating long intervals of perforated clusters or openhole horizontal wells. Recent advancements in diversion technology utilize various forms of degradable particles, where they serve to provide a temporary bridge, which is either inside the existing fracture or the perforation entrance. This allows for intentionally forming a low permeability pack, allowing the pressure inside the fracture to increase and redirect the next stage of fluid to the zone having a higher degree of stress that has not yet been covered by the fracture. The objective is to increase the fracture complexity, particularly in vertical wells where there is big variation in geomechanical properties of the formation. To gain a deeper understanding of the performance of these diverters, a simulation study was conducted to analyze and compare the efficiency of particulate diverters used in two pilot wells. Fracture modelling and sensitivity analysis were also performed to understand the effect of diverters on the fracture geometry. To match the actual treatments, modelling validation and control were achieved through utilization of field data such as production logging, temperature surveys and pressure buildup tests. The study determined that the success of the particulate diverter employed for the fracturing application is heavily dependent and governed by the geomechanical properties of the treated zone and the ability of the diverter to overcome the stress difference in the stimulated interval. Optimization of the diverter design and degradation profile is still needed to improve and achieve the best stimulation efficiency.

A High Effective Acid System to Stimulate Sandstone Reservoirs

“…This property can be of particular importance in the stimulation of underpressured reservoirs. Disadvantages of foam diverting include the increase in wellhead pressure due to foam's lower hydrostatichead and potential surface and treating facility problems due to the foaming agent not being used in the correct application or concentration [28][29][30]. In general, the benefits of using foam slugs for diverting include the benefits listed for foamed fluids but at a considerably lower cost and less risk of system upsets during treatment flowback.…”