Exploring deep and ultradeep wells has rapidly become more significant to meet the global demand for oil and gas. The study of rheological and filtration-loss properties is essential to designing drilling muds and determining their performance under operational conditions. Rheological and filtration-loss properties of drilling muds were found to have a negative impact when exposed to elevated temperatures in the wells. In this study, an amphoteric polymer (abbreviated to PEX) was synthesized and characterized using a combination of analyses: FTIR, SEM, ¹³CNMR, and TGA. The synthesized PEX was used as an additive in water-based drilling muds to improve rheological properties and reduce fluid loss at elevated temperatures (180–220 °C). The experimental results demonstrated that inclusion of an optimal concentration of PEX (0.3 wt %) into the drilling mud formulation increased the rheological properties by 62.3% and decreased the filtration loss by 63.5% at an aging temperature of 180 °C. Moreover, PEX was found to perform superbly compared to polyanionic cellulose (PAC-LV) and polyacrylamide (PAM), the widely used drilling mud additives. PEX not only improved the rheological properties and reduced the filtration loss behavior but also bolstered the thermostability of the drilling mud formulation. It was concluded that the rigidity and amphoteric nature of PEX accounted for the exceptional performance and temperature resistance for PEX-drilling mud formulations. Succinctly, PEX exhibits admirable properties in smart drilling mud formulations for drilling operations under high-temperature geothermal conditions. Moreover, in terms of rheological models, the Herschel–Bulkley model adequately described the rheological properties of all the studied drilling mud formulations.

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.

The brittleness and the poor resistance to external load of oil well cement impede the development of oil and gas wells. To overcome these deficiencies, latex powder or rubber and their hybrid combinations were used to modify the oil well cement. The conventional properties, mechanical properties, and scanning electron microscopy (SEM) images of the modified cement were analyzed. In comparison with latex powder‐incorporated cement and rubber‐incorporated cement, a significant improvement of fluid loss, flexural strength, impact strength, and elasticity of the cement slurry was observed when using the hybrid combinations of 3 wt.% latex powder and 2 wt.% rubber, although this synergistic effect was not remarkable on the compressive strength and the thickening time. These evidences arose from the synergism between latex powder and rubber leading to the formation of a three‐dimensional network structure and a flexible structure which subsequently improved the elasticity and toughness of cement stone. The improved elastic matrix has a buffering effect on external impact when the cement stone is subjected to an external load.