Development and Application of the Anti-High-Temperature Delayed Crosslinking Polymer as a Gel Plugging Additive for Drilling Fluid

Abstract

With the gradual deepening of the exploration and development of deep and ultra-deep oil and gas resources, the problem of lost circulation in drilling operations is becoming more and more complex. From field experience, conventional plugging materials cannot fully meet the technical requirements of plugging operations in drilling engineering. In this study, a high-temperature- and salt-resistant polymer HDZ−A was synthesized. A high-temperature and delayed crosslinking polymer gel plugging agent can be prepared by adding a certain concentration of a crosslinking agent and a retarder. In this paper, the optimum synthesis conditions of the HDZ−A were determined with orthogonal experiments using viscoelasticity and viscosity as evaluation criteria for newly developed polymers. The molecular structure, temperature resistance, and relative molecular mass of HDZ−A were determined using infrared spectroscopy, nuclear magnetic resonance spectroscopy, and gel permeation chromatography. In addition, the optimal formula of the gel plugging agent was determined using gel strength as the evaluation standard. The results show that the newly developed gel plugging agent has stable performance after high-temperature crosslinking, and can resist high temperatures of 160 °C during formation. Under conditions of 160 °C, the gelation time can reach 4.5 h, and the plugging efficiency can reach more than 97%. Finally, the field test of the newly developed high-temperature-resistant delayed crosslinking polymer gel plugging agent was carried out in the direct exploration well KT-14X in the Ordos Basin. The field test showed that the plugging effect of the HDZ−A gel plugging agent was remarkable.

Synthesis and Performance Study of Self-Degradable Gel Plugging Agents Suitable for Medium- and Low-Temperature Reservoirs

“…The reason for this phenomenon is that when the dosage of the cross-linking agent is low, the density of the system cross-linking agent is small, resulting in difficult cross-linking of the system. With the increase of the cross-linking agent dosage, the cross-linking of the system becomes easier, facilitating the formation of a good three-dimensional network cross-linking structure in the hydrogel system and thereby shortening the gelation time but prolonging the degradation time . It can be seen from the figure that when the cross-linking agent dosage is 0.6%, the gelation time is moderate and has little effect on the degradation time; therefore, the initiator dosage is set at 0.6%.…”

“…At present, the commonly used polymer gel systems are mainly cross-linked polymer gels based on polyacrylamide and modified cross-linked polymer gels based on acrylamide. , Freedman et al have developed a series of degradable hydrogels by combining covalent network degradable cross-linking agents and hydrolyzable ionic cross-linked backbone polymers, and these hydrogels have shown high mechanical properties, adhesion, and degradability in tests up to 16 weeks; Jia et al have studied a new type of high-strength degradable nanocomposite gel, and this system can be gelled within 20–50 min at 75 ∼ 105 °C, boasting excellent shear resistance . However, the existing similar hydrogel plugging agents cannot be easily adopted in medium and low-temperature plugging operations due to problems such as poor breaking performance, nonspontaneous degradation, and reservoir pollution, leading to great difficulty and high risks in on-site constructions. − Quaternary ammonium ester cross-linkers are an important class of cross-linkers for hydrogels, and compared to other common cross-linkers, quaternary ammonium ester cross-linkers applied to hydrogels can achieve low- and medium-temperature self-degradation. − …”