Wellbore trajectory impact on equivalent circulating density.
Rafał Wiśniowski, Krzysztof Skrzypaszek, Piotr Kiebzak, Maciej Kański
Vol. 34, no. 1 (2017), s. 181-201, 
Undermentioned article presents how wellbore trajectory changes may impact mud flow pressure losses in wellbore annulus and overall Equivalent Circulating Density (ECD) value. In order to investigate this topic, there were conducted two series of tests. In the first round actual, field data from six previously drilled wells was used to recreate real wellbores conditions in Halliburton Landmark Drilling Software and to calculate ECD values. In order to check and confirm the results accuracy, the outcomes were compared with pressure while drilling (PWD) equipment surveys’ results made during drilling operations. Next it was analyzed how ECD parameter's values change in particular sections of vertical and horizontal wellbores, due to trajectory angle modifications. With aim of expanding scope of the work, the second group of tests was made in Drilling Fluids Laboratory at Faculty of Drilling, Oil and Gas. Using Grace Sagging Tester M8500 Ultra HPHT it was examined how in wellbore conditions (high pressure and temperature) wellbore trajectory angle modifications may impact solids sedimentation process and fluid density changes in the annulus thus ECD value as well. The results indicate that there is a relationship between wellbore trajectory angle changes and ECD value shifts. In addition there are included field tests outcomes prepared by K&M Technology Group which confirm presented assumption.