No abstract

Torque and drag models estimate downhole forces, torques and moments acting in wellbores and drillstring elements during drilling and completion operations. A comparison was made between soft string and stiff string torque and drag model using conventional survey data. Survey data needed for torque and drag modeling are provided by field surveys. Field survey can be conventional survey or continuous survey. Conventional survey is carried out every 90 to 100ft interval or more and only gives a partial representation of the actual wellpath, micro-doglegs and micro-tortuosities may not be fully captured with this survey. Continuous survey is carried out between 1 to 5ft intervals of the wellbore using high resolution survey tools and captures more the micro-doglegs and micro-tortuosities but more expensive than the conventional survey. Torque and drag simulations were performed using both Soft and Stiff String models for comparison using a novel software package. Data provided includes deviational survey data from conventional survey, drillstring/BHA data, and fluid rheological data. The torque and drag simulation produced results for hook loads and buckling while running-in-hole (RIH) and pulling-out-of-hole (POOH). Results from this study show that prior to buckling, results from soft string and stiff string model are almost identical with minimal differences within the range of 0.8% to 1.6% and these were achieved as open-hole friction factors (CHFF) from 0.1 to 0.25. High buckling risk was detected for OHFF of 0.3. When buckling occurs, the differences in results between the two models become very apparent. This paper showed that in order to use stiff string torque and drag model for a more realistic, representative and more accurate pre-buckling and post-buckling operations in a highly deviated well, a high resolution continuous survey is needed; this will capture more readily, the micro-doglegs and micro-tortuosities in the wellbore paths.

No abstract

Excessive torque and drag, buckling and shear forces on downhole strings and tubulars are often encountered in the drilling of longer reach or deviational wells. Buckling of drillstring and BHA occurs in drillstring mainly due to high compressive forces. A point may be reached where these compressive forces rise and exceed the critical buckling loads leading to buckling of the drillstring/BHA or tubulars. This study focuses on the evaluation of the effect of tool-joint on the buckling of drillstrings for highly deviated wells. Tool-joint in pipes changes the pipes geometry in the wellbore thus affecting its hydraulics, orientation and stress distribution. A notable error will arise when straight pipe (with uniform outside diameter (OD) models are used to model pipes with end couplings and connections (such as tool joints). These errors may impact critical buckling loads, buckling initiation points, and post-buckling analysis of the pipe or BHA, thus affecting the success of drilling and completion operations. Torque and drag simulation and analysis was carried out for drillstring and BHA components in 9 5/8 in casing and 8.5 in open-hole sections to determine buckling loads. Two cases were considered; case 1 investigated the modeling and definition of buckling conditions for single straight body drillstrings and case 2 evaluated the buckling conditions for tool-jointed pipes. The result shows that buckling in tool-jointed pipes follows similar trend to that of straight body pipes with sinusoidal or lateral buckling being initiated first, and gradually progresses to helical buckling on increased axial force transfer. Furthermore, from the comparison of the results from two cases considered, it was observed that the presence tool-joint in the pipes led to a critical buckling load of 5.8% for sinusoidal buckling modes. The paper suggests that higher compressive force is needed to buckle the tool-jointed ends of the drillstring than the straight ends.