Study Of Aqueous Foam Stabilized By Betaine And The Application In Foam Drilling

As a kind of the typical low-density drilling fluids, aqueous foam is a potentially useful drilling fluid for under-pressured reservoirs and workover fluid. The paper investigates the properties and existing problems of aqueous foam used as drilling fluid. The process of foam drilling is separated into four specific stages, such as the foam generation, foam injection, foam flowback and defoaming process. Specific research methods are utilized to evaluate the performance and the impact of factors to find out the theoretical mechanism of each above specific stage, and the key technical parameters are extracted out.Cocamidopropyl betaine (CAPB) and Dodecyl-2-hydroxy-1-proply sulfobetaine (DSB) are separately used as the major frother. The foam performance and additives on the properties of the bubble are evaluated. As well as the ability of carrying solid and liquid of the drilling fluid is evaluated by a specially self-designed simulating device, and a pre-drainage technique is suggested to be used to increase the drilling efficiency and avoid the damage to the wall of the well coursed by drainage of drilling foam in the well, pH control and heat radiation are used to achieve the foam-based liquid recycling.On the stage of the foam generation, the foaming ability and the nature of foam are studied. Using a variety of experimental methods, the effect of drilling fluid additives, such as polymer and salts, on the foaming ability and foam stability are also determined; comprehensive survey of the bubble in the nature and function of anti-inflation and other circumstances, the drilling foam-based fluid composition is determined.In the process of foam injected into the wells, the main object of our study is the drainage of foam. It has been shown that in the existing site drilling technology, foam is always generated in the way that the high-speed nitrogen air flow through the foam solution across the porous media, in which the effect of mechanical entrainment is significant, and the fresh foam contains a lot of free water. The free liquid in the foam will drain out and accumulate at the bottom of the well, which is not sufficient for carrying cuttings and water and may lead to drilling accidents. The discovery reveals a key impact on the application of foam drilling technology. And a pre-drainage method was proposed to solve these problems.During the process of foam flowback, the flowing capability of foam and the dynamic shear stability and the capacity of carrying water and solid are concernful. The disturbances rotating shear apparent viscosity of foam column is measured to quantify the performance of the aforementioned changes in the foam, which provide a basis to determine the optimal formula.On the defoaming process, the main concern is about the defoaming and the foam-based fluid recycling. In the paper, the foam recycling is achieved by adjusting the pH, while a new technique is raised to improve the defoaming rate using thermal radiation technique. This method can reduce the base fluid loss, and improve efficiency.On the basis of experiments, the properties of the bubble-based drilling fluid are evaluated. The mechanisms of the process of the key technology segments are found, and several new solutions are put forward. This is a great significance to promote the development of foam drilling technology.The innovations in the thesis are as follows:1. The process of foam drilling cycle is divided into four stages, specific research methods are established for each stage, and key parameters are used to quantify the performance of drilling foam.2. Interface formation energy IFE is used to determine the foam formation capability. The area of foam films is considered to evaluate the foamability of surfactants used as drilling foam stabilizer.3. A simulation well shaft setup is designed to simulate the inspection process of the foam in the drilling of the migration cycle, the key functional factors and parameters are determined.4 Molecular simulation methods and experimental methods are combined to determine the drainage mechanism of foam films. A new pre-drainage technique is suggested to increase the foam drilling efficiency.5. A new technique is raised to improve the defoaming rate of the drilling foam efficiently using thermal radiation, by which the foam drilling base fluid loss can be reduced.