The application of fiber in the completion fluid can improve the rheological properties of the completion fluid and the plugging quality of the production layer by the completion fluid and reduce the damage of the filtrate to the reservoir formation. However, there are few studies on the influence of fibers on the rheological properties of completion fluids and the flow behavior in pores. In this paper, plant fiber, mineral fiber, and synthetic fiber are discussed. Carbon fiber, bamboo fiber, polypropylene fiber, and polyester fiber are selected as research objects. The dependence of the rheological property of polymer solution on fiber type, fiber concentration, temperature, and shear rate is evaluated. The evaluation is carried out by observing the microscopic state of the fiber through a microscope and a scanning electron microscope, testing the rheological property parameters of the fiber with an OFITE 900 rheological tester, and fitting with the Herschel–Bulkley model. The results show that polypropylene fiber and carbon fiber have the best dispersion in polymer solution. The higher the fiber content, the greater the influence of fiber on the rheological properties of the solution. Compared with the other three fibers, carbon fiber has the greatest influence on the rheological properties of polymer solution. When the temperature is lower than 70 °C, the influence of the fiber on the rheological properties of the solution is not affected by the temperature. When the temperature exceeds 70 °C, the carbon fiber and polypropylene fiber are affected by the temperature, and the viscosity of the polymer solution is increased. The flow behavior of fiber suspensions in pores varies with the flow factor n. Carbon fiber suspensions are most conducive to the transition of polymer solution to plate laminar flow, which can improve the bearing capacity of plugging materials.

The great amount of solid particles contained in a weighting agent is a major cause of the problems in both rheology properties and damage control mechanism of an oil-based drilling fluid (OBM). Therefore, a proper type of weighting agent can be a solution for the application of OBM. In this study, three weighting agents that have been commonly used with OBM, namely, standard barite, submicron barite and superfine manganese ore, are studied. Rheological properties of OBM and the degree of formation damage are assessed with regard to the three weighting agents. The agents are also studied in aspects of particle size, micromorphology, filtration loss and wall-building property, acid dissolution efficiency of mud cake, lubricity and sedimentation stability to analyse the effects of the agents on rheological properties and the degree of damage as well as to figure out the mechanism of rheology control and damage control. For the OBM, there is a mutual effect between rheological stability and the degree of damage. In consideration of the agents' properties, we can enhance the rheological stability of the OBM and control the degree of formation damage by properly selecting particle size, using acid-soluble materials and forming the mud cake with ultra-low permeability that can easily be cleared away.

Clay minerals are an important part of the mud shale reservoir, and their type of content has a great impact on the hydration of the formation. The hydration of clay minerals causes a decrease in drilling fluid performance, an increase in pore pressure, and a decrease in rock strength, leading to wellbore wall collapse. Therefore, it is important to study the influence of clay mineral hydration on well-wall stability. In this paper, we analyze the hydration process of clay minerals qualitatively and quantitatively by simulating the mineral clay fraction and the effect of the change in cations on their hydration and clarify the difference in the hydration of different clay minerals. The results show the following: (1) montmorillonite has the most obvious hydration and swelling effect, while the hydration of illite is mainly based on hydration and dispersion, which easily produce exfoliations and fall off in the stratum; kaolinite has poor hydration performance, while chlorite shows certain hydration but low hydration degree. (2) Cations have a certain inhibitory effect on the hydration of clay minerals, and the degree of hydration inhibition is different for different types. (3) Different clay minerals also differ in the form of state after water exposure, as montmorillonite shows swelling, while illite has no swelling, but its dispersion is stronger.

Deep fractured tight gas reservoirs have attracted more and more attention worldwide, which also promotes the large‐scale application of oil‐based drilling fluids. Due to its poor permeability, deep tight gas reservoirs need to pay more attention to the issue of reservoir protection. However, previous studies have shown that reservoir damage of oil‐based drilling fluid is small, and limited damage studies mainly focus on one aspect of work, and there is not a systematic reservoir protection method of oil‐based drilling fluid for tight gas reservoir. Based on the particularity of fractured tight gas reservoir protection, the thesis clarifies the fracture factors that affect the reservoir protection efficiency and the preferred factors of reservoir protection materials. Considering fully the characteristics of fracture and oil‐based drilling fluid, the design basis and overall design idea of reservoir protection method of oil‐based drilling fluid are established. Considering the four conditions of fracture determination and method selection, difference of Engineering requirements, particle selection, fracture plugging, and plugging removal mechanism, the reservoir protection technology of oil‐based drilling fluid is constructed, and the simulation experiments of reservoir protection technology of oil‐based drilling fluid for fractured tight gas reservoir were carried out; the results provided a reference for reservoir protection of oil‐based drilling fluid.

Offshore oil- and gas-field development is shifting from shallow water to deepwater on a large scale. Deepwater shallow bentonite slurry drilling fluid has a single composition and a simple structure. Therefore, the bentonite slurry drilling fluid has been neglected for the shallow wellbore strengthening ability. Based on the shallow geological characteristics and bentonite hydration mechanism, considering the economy and application effect, the optimization of bentonite slurry drilling fluid from four aspects of viscosity enhancement, adsorption, trapping, and physical plugging to carry out deepwater shallow wellbore strengthening research has been undertaken. For an indoor simulation of bentonite slurry and its drilling slurry-making process using a 2-10% mass concentration of bentonite slurry drilling fluid, laser particle size analysis found an interesting phenomenon different from the traditional understanding: for every 5% increase in particle size accumulation in the range of 0.1-100 μm, the bentonite slurry particle size increases linearly. Based on this interesting phenomenon, the basic performance of drilling fluids with different concentrations of bentonite slurry was evaluated. Experiments were conducted to introduce cationic emulsified asphalt as a deformation filler and to explore a new inexpensive drilling and wellbore strengthening material, AEH-P. The effectiveness of deepwater shallow strengthening was evaluated for AEH-P and cationic emulsified asphalt from both mechanistic and experimental aspects. It is obvious that the wellbore strengthening effect is the result of both particle settling and particle size matching. By exploring the relationship among bentonite slurry hydration dispersion, the charged nature, particle concentration, and the wellbore strengthening effect, a set of low-cost deepwater shallow bentonite slurry drilling fluids with a good wellbore strengthening effect are constructed. The research results provide a method to strengthen the wellbore for the subsequent fast and efficient drilling of deepwater shallow wells, further improving the drilling efficiency.