Self-healing efficiency of EVA-modified cement for hydraulic fracturing wells

During hydraulic fracturing, the cement sheath of oil wells experiences a huge pressure and alternating stress, and may crack due to its hard and brittleness. The cracks could lead to the transmission of formation fluids behind the casing and before the formation. A new emerging science on the self-healing cement provides solutions to the problem. In this work, the ethylene-vinyl acetate (EVA) copolymer was used as the self-healing agent to improve the self-healing efficiency of cement for hydraulic fracturing wells, and different methods were considered for evaluating the self-healing efficiency. The experimental results show that mixing EVA into oil well cement significantly decreases the fracture permeability and flow channels by melting flow-out and blocking, and markedly improves the broken bonding strength by mechanical and chemical bonding. The EVA-modified cement has excellent repetitive self-healing properties. When the EVA-modified cement is used, the working temperature should be higher than the softening temperature of EVA. The effect of pressure on self-healing effect is very small, and the self-healing observably increases with the increase in the temperature before 110 °C.