Worldwide growing in hydrocarbon demand is driving the oil and gas companies to explore areas with more hostile conditions, such as high-pressure, high-temperature conditions. By increasing the number of projects in these conditions improved technology, material selection and testing procedures are required to overcome the challenges. One of the main reasons, causing the cement systems to fail in these environments, is concentration of stresses inside the wellbore induced by downhole changes of temperature and pressure. Therefore the objective of this work is to develop a high resistant cement system. The stress resistant cement systems in this study are produced by adding silica sands and silica flour to the dry cements. To study the effect of temperature and pressure on strength properties of set cements all samples are cured at elevated temperatures and pressures. Also the effect of curing time on the strength properties are investigated. The results show that the developed cement systems with silica flour show more strength properties, due to its microstructure properties. In these cement systems, the number of cracks and micro fracture are less than the systems with silica sand due to the fine particles size of silica flour. The cracks and fractures inside the failed set cement systems serve as pathways for formation fluids to the surface, and thus reducing the life of the well. Increasing the concentration of silica sand and silica flour will increase the strength properties but at the same time it strongly affects the other properties of cement slurry. So additives have been used to adjust other essential properties of cement systems.

In recent years, thanks to telemetry systems, measurement while drilling and geo-steering technologies, drilling directional and horizontal wells has been improved significantly. But still there are a lot of complications in directional drilling operations. Cutting transportation is a serious challenge in high angle and horizontal wells. High mud flow rate is required to clean cuttings from the wellbore which is not always practically possible. High flow rates can lead to formation fracturing and result in mud loss. In addition, downhole motor's optimal fluid rate range may limit the value of fluid rate. In high-angle and horizontal wells, it is necessary to take into account presence of cutting bed as an inevitable fact and try to conduct all of the operation based on this fact. For example, while drilling horizontal or extended reach wells, it is not recommended to pull the drilling string out before cleaning the wellbore with high mud flow rate. Also, build rate must be calibrated based on cutting bed effect on bending moment and accordingly build rate. In this work, the effect of cutting bed on build rate and deviation from the planned path for horizontal and highly deviated wells has been investigated. In "Rhinoceros" and "ANSYS", downhole elements shape, their characteristics and their interactions with each other have been simulated and analyzed. The simulation is done based on data from a real case in West-Siberian oil-field. Using Finite Element Method jammed cutting around the stabilizer have been modeled and its effect on wellbore deviation from planned path has been investigated. Jammed cutting has been simulated like a gravelly sand soil that increases the accuracy of the simulation. In the previous works, jammed cutting around stabilizer has been modelled as an increase in diameter that in this work, this assumption has been corrected.

No abstract