Development of Water-Swelling Agents with a Function of Programmable Self-Destruction for Well Killing Operations in Oil and Gas Condensate Fields Complicated by Fractures and Abnormally Low Reservoir Pressure

Abstract This work presents a water swelling agent with a function of "programmable" self-destruction for reservoirs complicated by fractures, and investigates the possibility of its application for well-killing operations, where conventional agents are ineffective. At the first stage, the synthesis of water swelling gel particles formulations was carried out, taking into account the selection of crosslinker to achieve "programmable" self-destruction of the formulation after a certain period of time. Then, works were carried out on selection of optimal formulations on the basis of study of swelling coefficient, long-term stability, self-degradation time, rheological parameters and blocking properties under different salinity conditions and compared with current commercial agent. The efficiency of the compositions was determined on the basis of wellbore modeling system under reservoir conditions to analyze the blocking efficiency of gel particles in real time. Synthesis of samples based on different crosslinker monomers, initiators, and modifiers (79 compositions) were carried out, which allowed us to develop a composition with optimal degradation dynamics, capable of being stable for 7 days and further self-degrade at 40 °C and salinity of 3.6 g/L (grams per litter), have a low density and are compatible with reservoir fluids. All samples, have corrosion rates up to 0.1 g/m2·hour (grams per square meter hour) and characterized by a high strength factor for 7 days. After this period, the parameter decreases due to the beginning of degrade. The results of studies of rheological characteristics of blocking compositions indicate that the synthesized samples show high values of static and dynamic shear stress more than 62 Pa (pascal). According to the results of studies, on the HTHP filter press, it can be concluded that the synthesized particles are characterized by sufficiently high blocking properties, capable of creating a fracture aperture 0.2 mm (milimeters) opening and low ability to penetrate, less than 4 ml of liquid has been filtered during experiment. According to the results of filtration studies, the synthesized gel particles can effectively block the model of an idealized fracture, 0.1 mm opening up to pressures of 63 bar, making this system a great potential for well killing operations in reservoirs complicated by fractures. Based on the results of laboratory tests, the developed particles can be recommended for further pilot tests. Generally, the developed water swelling gel particles with "programmable" degradation showed high efficiency of blocking and reduction of well development costs. This allows expanding the application to well killing operations for abnormally low formation pressure reservoirs complicated by natural fractures.