Analysis of the factors that affect the target depth in deviated wells

Abstract

This thesis presents the analysis of the factors that affect the target depth. Depth measurement is one the most important parameter and most difficult to identify. For the target depth measurement key factors that affecting the drill string that is pressure temperature, axial load, drag and the errors in the surveys is described in the study. For the study a realistic well geometry and drilling string parameters were considered. WELLLPLAN TM software and Microsoft Excel are used for the calculation and graph. In the analysis phase most of the factors that affect the target depth in deviated well are discussed and the emphasis is on the key factors that are the major contributors in wellbore position uncertainty. This study presents two major areas: • The first one is sensitivity study in order to investigate the effect of survey uncertainty on various parameters such as dogleg severity, vertical section, tortuosity and torque. This was done by introducing +/-­‐ 10% error in inclination and azimuth. The result is compared with the reference survey well data. • The second part is to calculate the elongations due to mechanical loading, thermal and hydraulic effects. The analysis was under various drilling operations like “tripping in”, “rotate on bottom”, “tripping out”, “rotate off bottom” and “slide drilling”. The details of the analysis result shown in Chapter §3. Here some of the result is presented as the following: a) +/-­‐10% error affects on the graphs like dogleg severity, vertical section and tortuosity and deviate the wellpath from the reference well data. It also shows the torque will increase and decrease due to effect of the errors. b) Elongation due to pressure effect on the reference geometry is about 10 ft. for tripling in and 12 ft. for tripping out operation. c) Elongation due to temperature on the reference geometry is 8.23 ft. d) Loading effect on the reference geometry is from 5 ft. for sliding drilling and to 8.4 ft. for tripping out. e) Total elongation due to key factors on the reference geometry is 23ft. for sliding drilling, 25.5 ft. for tripping in and rotate on bottom and to 28.6 ft. for tripping out.