| The development of stimulated reservoir volume (SRV) fracturing technology was one of the necessities of the successful commercial development of shale gas. But the massive water consumption due to poor sand carrying ability of slick-water fracturing liquid which widely used in SRV fracturing caused great waste of water resource and a series of ecological and environmental problems. Therefore, its application was affected in China and worldwide. In this paper, by analyzing the root cause of the problem, a solution which was to gain high drag reducing and sand carrying ability simultaneously under the premise of meeting low viscosity requirement of SRV fracturing was proposed. Through the increasing of sand carrying ability, the water consumption of sand carrying by turbulence could be greatly reduced and the total water usage could also be reduced at the same time. Based on the mechanism and research status of structural fluid drag reducing and sand carrying, and also taking field application and costs into consideration, hydrophobically associating water-soluble polymer (HAWSP) was selected to meet the rheological requirement mentioned above. Its possibility of solving the existing problems was proved theoretically and experimentally by researching mechanism and influencing factors of HAWSP aqueous solution drag reducing and sand carrying. And theoretical foundation and experimental basis of its field application were also provided. The main aspects of this research listed below:Testing apparatus was designed to test drag reducing and carrying performance at different temperature and Reynolds number (Re) by studying the testing method of drag-reducing and carrying ability of HAWSP aqueous solution. Characterization and testing method of drag reducing and sand carrying performance was also established. And necessary means of researching the mechanism and influencing factors of HAWSP aqueous solution drag-reducing and sand carrying were provided.The microstructures of HAWSP aqueous solutions in different concentration range and the microstructures of HAWSP aqueous solutions with different molecular structure parameters around critical association concentration (CAC) were observed by ESEM. Based on the microstructure, combined with drag reducing performance, turbulent drag reducing mechanism of HAWSP aqueous solution was studied systematically. The results of experiments showed that:the special molecular structure of HAWSP determined that its aqueous solution had both linear polymer and surfactant drag reducing mechanism, so it could have better drag reducing ability than the widely used drag reducer. And HAWSP with different molecular structure or in different concentration range could show distinguished drag reducing performance. According to the research of related rheological parameters, the special rheological parameter (N1/?2) was found to characterize drag reducing performance of HAWSP after CAC. It also provided a fast and effective method to evaluate drag reducing performance of HAWSP aqueous solution. According to the aim of this research, combined with microstructure and rheological properties, sand carrying and drag reducing performance of HAWSP with low molecular weight and high hydrophobic monomer proportion after CAC was selected to be the main object of this study. The molecular structure of HAWSP with high drag reducing performance after CAC was concluded by investigating effects of molecular weight, hydrophobic monomer proportion and hydrolysis degree on drag reducing characteristics.Also based on the microstructure of HAWSP aqueous solution observed by ESEM, combined with sand carrying performance, sand carrying mechanism of HAWSP aqueous solution was studied systematically. The results of experiments showed that:sand carrying performance of HAWSP aqueous solution was determined by microstructure of solution, sand carrying mechanism was different before and after CAC. According to the research of related rheological parameters, the special rheological parameter (G') was found to characterize sand carrying performance of HAWSP after CAC. It also provided a fast and effective method to evaluate the sand carrying performance of HAWSP aqueous solution. The molecular structure of HAWSP with high sand carrying performance after CAC was concluded by investigating effects of molecular weight, hydrophobic monomer proportion and hydrolysis degree on sand carrying characteristics.Considering both high drag reducing and sand carrying performance, combined with the low apparent viscosity requirement of SRV fracturing, the molecular structure parameters range of HAWSP could be concluded:(1)molecular weight:100×104g/mol?300×104g/mol;(2)hydrophobic monomer proportion:10%?20%;(3)hydrolysis degree:20%-40%.The molecular structure parameters range mentioned above provided guidance of developing and evaluating of HAWSP fracturing liquid product used in SRV fracturing with high drag reducing and sand carrying performance simultaneously. By adjusting molecular structure parameters in the range, three kinds of HAWSP fracturing liquid could be developed:(1)Increase sand carrying performance to some extent, and increase drag reducing performance significantly:compared with imported slick-water fracturing liquid, drag reducing performance raised 11.5%; suspension performance raised 27.8%; carrying performance raised 26.8%.(2)Balance drag reducing and sand carrying performance:compared with imported slick-water fracturing liquid, drag reducing performance raised 4.3%; suspension performance raised 85.2%; carrying performance raised 54.2%.(3)Increase sand carrying performance significantly with drag reducing performance equivalent to imported slick-water fracturing liquid:compared with imported slick-water fracturing liquid, drag reducing performance raised -0.46%; suspension performance raised 168.5%; carrying performance raised 167%.Three kinds of HAWSP fracturing liquid mentioned above provided more possibilities and choices to solve existing major technical problems of slick-water fracturing liquid.Effects of temperature and salinity on drag reducing and sand carrying performance of HAWSP aqueous solution and effects of molecular structure parameters on temperature and salinity resistant ability were also studied. The results of experiments showed that:the requirement of different application environment could be met by adjusting molecular structure parameters of HAWSP. |
PDF Full Text Request