Comprehensive Review of Polymer and Polymer Gel Treatments for Natural Gas-Related Conformance Control

A high temperature-resistant, strong, and self-healing double-network hydrogel for profile control in oil recovery

Hydrogels are widely used in profile control to plug high-permeability zones in oil recovery. In this study, a novel double-network (DN) hydrogel is developed for profile control. The two networks of the prepared hydrogel are polyacrylamide (PAAm) crosslinked by N,N'-Methylenebisacrylamide (MBAA) and konjac glucomannan (KGM) crosslinked by borax (B), respectively. The two networks are interconnected by their interpenetrating structures and hydrogen bonds. Based on the results of a series of evaluation experiments, the AAm/KGM DN hydrogels developed in this study exhibit a strong mechanical strength with their fracture stresses exceeding 0.137 MPa. Meanwhile, the AAm/KGM DN hydrogels can remain thermally stable after being heated at 130 °C for 24 h, indicating the good high-temperature resistance of the new sample. Moreover, the prepared AAm/KGM DN hydrogels present excellent self-healing performance due to the abundant hydrogen bonds in their structures, which helps form stable and long-term plugging in porous media. In addition, the pure PAAm hydrogel and the AAm/KGM DN hydrogel are sheared into two dispersed particle gel (DPG) suspensions to investigate their plugging performances. The results demonstrate that the AAm/KGM DN DPG can effectively plug a high-permeability sandpack with a plugging efficiency of 93.2 %, while the pure AAm DPG can only provide a much lower plugging efficiency of 60.5 %. The AAm/KGM DN hydrogel developed in this study, with its high mechanical strength, high-temperature resistance, and self-healing capability, offers a promising new candidate for profile control in oil recovery.

Use of Self-Generating Foam Gel Composition with Subsequent Injection of Hydrogel to Limit Gas Inflow in Horizontal Wells of Vostochno-Messoyakhskoye Field

Gas inflow control in oil wells is one of the most challenging types of repair and sealing operations, the success rate of which does not exceed, as a rule, 30%. Conventional shutoff methods are often ineffective for this purpose. For instance, cement solutions cannot be injected into wells in the required volumes, while gel screens can only temporarily block the breakthrough zones, as gas easily seeps through the gel, forming new channels for gas inflow. Technology for the two-stage injection of gas-insulating gel systems for gas control in horizontal wells was developed. At the first stage, a self-generating foam gel composition (FGC), consisting of gel-forming and gas-forming compositions, was used. A foam gel structure with enhanced rheological and flow characteristics was formed over a controlled time as a result of the interaction between the gel-forming and gas-forming compounds. A PAM-based hydrogel crosslinked with an organic crosslinker was added to the FGC at the second stage of treatment. The laboratory experiments substantiated the technology of well gas and water shutoff by the sequential injection of self-generating foam gel composition and hydrogel. Field tests confirmed the correctness of the chosen concept. It is very important to clearly identify the sources of gas inflow for the success of this well intervention and take into account the well design, as well as the reservoir geological structure and characteristics. The gas shutoff operation can be properly designed for each well only by comparing all these factors. The validity of the selected technology was tested through a series of laboratory experiments. Successful laboratory tests allowed for the application of the studied technology in a field setting, where the gas shutoff agent was injected into three horizontal wells. As a result of the field application, the gas inflow was successfully isolated in two wells. However, the application of the technology failed in the third well which gave an opportunity to revisit the technology's design and to review the sources of gas inflow. Overall, the achieved success rate of 66% demonstrated the high efficiency of the studied technology and supported its wider application in the field.

Application of Polymer Hydrogels in the Prevention of Postoperative Adhesion: A Review

Postoperative adhesion is a common post-surgery complication formed between the surface of the body cavity, ranging from a layer of connective tissue to a fibrous bridge containing blood vessels and nerve tissue. Despite achieving a lot of progress, the mechanisms of adhesion formation still need to be further studied. In addition, few current treatments are consistently effective in the prevention of postoperative adhesion. Hydrogel is a kind of water-expanding crosslinked hydrophilic polymer network generated by a simple reaction of one or more monomers. Due to the porous structure, hydrogels can load different drugs and control the drug release kinetics. Evidence from existing studies has confirmed the feasibility and superiority of using hydrogels to counter postoperative adhesions, primarily due to their outstanding antifouling ability. In this review, the current research status of hydrogels as anti-adhesion barriers is summarized, the character of hydrogels in the prevention of postoperative adhesion is briefly introduced, and future research directions are discussed.

Injection of Gelling Systems to a Layered Reservoir for Conformance Improvement

The paper describes the introduction and estimation of performance criteria for the gelling agent injection technology based on a general approach to modeling physical and chemical enhanced oil recovery (EOR) methods. The current mathematical models do not include performance criteria for the process of gelling agent injection and do not allow for assessing the level of success of a treatment job in production wells. The paper introduces such criteria for the first time. To simulate the effect on injection wells, the mass conservation laws and the generalized flow law are used, and closing relations for the gelling rate are taken into account. A conformance control coefficient is introduced which characterizes the positive effect of well treatments and injectivity drop which characterizes the negative effect. The performance criteria allow for identifying the wells where the treatment jobs were the most successful. The model verification, based on the comparison of post-treatment injectivity estimated in the developed model, with Rosneft’s field data showed a satisfactory match. The developed correlations can be used as the basis for a surrogate model that allows for avoiding building sector geological and flow simulation models of the treated zone.