Abstract
To improve the pay zone exposure and avoid hazardous interbed, the wellbore trajectory is necessary to be adjusted in real-time according to the geosteering data in a long horizontal wellbore, leading to a special wavy trajectory. At present, there are few pieces of research on hole cleaning and pressure management for the wavy wellbore trajectory. Besides, there is no quantitative definition of the trajectory. In this study, a transient solids-transport model with the modified mass flux is employed to assess the risk of hole cleaning and the feasibility of pressure management of the wavy trajectory. As a new quantitative definition, the wavy wellbore trajectory has the wellbore tortuosity with periodic variations. The wavy wellbore is classified as the up-dip wellbore, the down-dip wellbore, and the complex wellbore to evaluate the influences of wellbore trajectory on the cuttings bed height and the annulus pressure compared with the conventionally horizontal and smooth wellbore. A parametric analysis of build-up rate is conducted to assess its fluence on hole cleaning and pressure management. The result indicates that the wavy wellbore displays higher risks of drilling complicacy than the conventional wellbore. The down-dip wellbore has 1.36 times the volume of cuttings bed and 1.49 times the bottom hole pressure of the horizontal wellbore. The bottom hole pressure of the up-dip wellbore is 0.49 times that of the horizontal wellbore. In comparison to a smooth wellbore, the up-dip wellbore contains 43% hazardous sections. The build-up rate has an optimal value on hole cleaning and the larger build-up rate is beneficial to manage pressure. In the simulation of a field instance in West China, excessing drag and torque, wall instability, and lost circulation exist at the same time, of which inducements are predicted by the model very well. The findings serve as a useful guideline to risk prediction and control in drilling the long horizontal wellbore with wavy intervals.
NSTL