A laboratory study of self-healing hydrophobic association gels used as lost circulation material

Abstract

Polymer gels, composed of preformed particle gels and in-situ gels, have generated broad interest in lost circulation control for decades. However, there are some drawbacks to them. The sealing layer formed by preformed particle gels was easily eroded by cyclic drilling fluid. The size of them needs match that of pores or fractures. In-situ gels, forming the expected pill in the correct location is challenging due to short gelation time, poor resident ability, and gel strength. Due to their unique recovery properties after damage, self-healing gels have been extensively researched and applied in the biomedicine field. Their prospect application in oil and gas drilling and development engineering has been investigated. In this article, we used self-healing hydrophobic association gels prepared in our previous paper to study their performance in lost circulation control, which aimed to integrate advantages of preformed particle gels and in-situ gels and abandon their disadvantages. The chemical structure and thermal stability of self-healing hydrophobic association gels were measured by FTIR and TGA, respectively, indicating good thermal stability. The swelling experiments at different temperatures suggested that they could absorb more water with the rise of temperature. The healing performance of self-healing gel particles at different temperatures and pressures showed that they could heal into a whole gel with good strength at 1–6 MPa and 25–80 ℃. Their healing properties were prone to temperature, followed by healing time. Their plugging performance was tested by a high temperature and pressure filter, meaning that the breakthrough pressure of 3% self-healing gel plugging agent was 3.5 MPa at 80 ℃, using a steel model with a fracture width of 1 mm to imitate fracture formation. The microscopic visualization device saw gel particles' plugging and healing process, indicating that they entered the lost circulation channels, formed a sealing layer like preformed particle gels, and healed into gel pill like in-situ gels. Self-healing gels could provide a new approach to controlling lost circulation and have a promising application prospect.