Search Results (4)

Reversible emulsion drilling fluids can concentrate the advantages of water-based drilling fluids and oil-based drilling fluids. Most of the existing reversible emulsion drilling fluid systems are surfactant-based emulsifier systems, which have the disadvantage of poor stability. However, the use of modified nanoparticles as emulsifiers can significantly enhance the stability of reversible emulsion drilling fluids, but ordinary nanoparticles have the disadvantages of high cost and easily causing environmental pollution. In order to solve the shortcomings of the existing reversible emulsion drilling fluid system, the modified nanocrystalline cellulose was considered to be used as an emulsifier to prepare reversible emulsion drilling fluid. After research, the modified nanocrystalline cellulose NWX-3 can be used to prepare reversible emulsions, and on this basis, reversible emulsion drilling fluids can be constructed. Compared with the reversible emulsion drilling fluid stabilized by HRW-DMOB (1.3 vol.% emulsifier), the reversible emulsion drilling fluid stabilized by the emulsifier NWX-3 maintained a good reversible phase performance, filter cake removal, and oily drill cuttings treatment performance with less reuse of emulsifier (0.8 vol.%). In terms of temperature resistance (150 °C) and stability (1000 V < W/O emulsion demulsification voltage), it is significantly better than that of the surfactant system (temperature resistance 120 °C, 600 V < W/O emulsion demulsification voltage < 650 V). The damage of reservoir permeability of different types of drilling fluids was compared by physical simulation, and the damage order of core gas permeability was clarified: water-based drilling fluid > reversible emulsion drilling fluid > oil-based drilling fluid. Furthermore, the NMR states of different types of drilling fluids were compared as working fluids, and the main cause of core permeability damage was the retention of intrusive fluids in the core. Full article

The reversible emulsion drilling fluid system combines the advantages of both oil-based and water-based drilling fluids, which can achieve ideal results in different stages of drilling and completion, and the system can be reused to effectively reduce costs. However, the research on reversible emulsions mainly focuses on the development of new reversible emulsifiers, while the specific phase transformation mechanism of reversible emulsion systems is still unclear. In this paper, a stable reversible emulsion was prepared using the reversible emulsifier DMOB as a raw material, and the reversible emulsion performance of the alkali response from the O/W emulsion phase to the W/O emulsion was studied. The microstructure of reversible emulsions was studied by a microscope, a cryogenic transmission electron microscopy, and a laser particle size analyzer. The changes in macroscopic properties of reversible emulsions in the process of alkali conversion were studied by pH, conductivity, demulsification voltage, static stability, viscosity, rheology, and other indicators, and the conversion mechanism of reversible emulsions from O/W emulsion ⟶ bicontinuous structure ⟶ O/W/O emulsion ⟶ W/O emulsion was clarified. The details are as follows: in the first stage, when the amount of NaOH ≤ 0.43 vol.%, the overall particle size of the emulsion decreases first and then increases with the increase in NaOH dosage. In the second stage, when the amount of NaOH was 0.45 vol.%, a double continuous structure was formed inside the emulsion. In the third stage, when the amount of NaOH is 0.48 vol.%, the O/W/O emulsion is formed, and with the increase in stirring time, the internal oil droplets gradually accumulate and are discharged from the water droplets, and finally, the W/O emulsion is formed. In the fourth stage, when the dosage of 0.50 vol.% ≤ NaOH ≤ 5.00 vol.%, the W/O emulsion was formed, and with the increase of NaOH dosage, the structure and compactness between water droplets increased first and then decreased. In the whole process, with the increase in the amount of NaOH solution, the total particle size of the emulsion first decreased and then increased. Full article

Reversible emulsification drilling fluids can achieve conversion between oil-based drilling fluids and water-based drilling fluids at different stages of drilling and completion, combining the advantages of both to achieve the desired drilling and completion effects. The foundation of reversible emulsion drilling fluids lies in reversible emulsions, and the core of a reversible emulsion is the reversible emulsifier. In this study, we prepared a reversible emulsifier, DMOB(N,N-dimethyl-N′-oleic acid-1,4-butanediamine), and investigated the reversible phase inversion process of reversible emulsions, including the changes in the reversible emulsifier (HLB) and its distribution at the oil–water interface (zeta potential). From the perspective of the acid–alkali response mechanism of reversible emulsifiers, we explored the reversible phase inversion mechanism of reversible emulsions and reversible emulsification drilling fluids. It was revealed that the reversible phase inversion of emulsions could be achieved by adjusting the pH of the emulsion system. Then the proportion of ionic surfactants changed in the oil–water interface and subsequently raised/lowered the HLB value of the composite emulsifier at the oil–water interface, leading to reversible phase inversion of the emulsion. The introduction of organic clays into reversible emulsification drilling fluid can affect the reversible conversion performance of the drilling fluids at the oil–water interface. Thus, we also investigated the influence of organic clays on reversible emulsions. It was demonstrated that a dosage of organic clay of ≤2.50 g/100 mL could maintain the reversible phase inversion performance of reversible emulsions. By analyzing the microstructure of the emulsion and the complex oil–water interface, we revealed the mechanism of the influence of organic clay on the reversible emulsion. Organic clay distributed at the oil–water interface not only formed a complex emulsifier with surfactants, but also affected the microstructure of the emulsion, resulting in a difficult acid-induced phase transition, an easy alkali-induced phase transition, and improved overall stability. Full article

In drilling and completion projects, sludge is formed as a byproduct when barite and oil are mixed, and later sticks to the casing. This phenomenon has caused a delay in drilling progress, and increased exploration and development costs. Since nano-emulsions have low interfacial surface tension, wetting, and reversal capabilities, this study used nano-emulsions with a particle size of about 14 nm to prepare a cleaning fluid system. This system enhances stability through the network structure in the fiber-reinforced system, and prepares a set of nano-cleaning fluids with adjustable density for ultra-deep wells. The effective viscosity of the nano-cleaning fluid reaches 11 mPa·s, and the system is stable for up to 8 h. In addition, this research independently developed an indoor evaluation instrument. Based on on-site parameters, the performance of the nano-cleaning fluid was evaluated from multiple angles by heating to 150 °C and pressurizing to 3.0 Mpa to simulate downhole temperature and pressure. The evaluation results show that the viscosity and shear value of the nano-cleaning fluid system is greatly affected by the fiber content, and the cleaning efficiency is greatly affected by the concentration of the nano-emulsion. Curve fitting shows that the average processing efficiency could reach 60–85% within 25 min and the cleaning efficiency has a linear relationship with time. The cleaning efficiency has a linear relationship with time, where R² = 0.98335. The nano-cleaning fluid enables the deconstruction and carrying of the sludge attached to the well wall, which accomplishes the purpose of downhole cleaning. Full article