How Far Can We Push the Boundary of Horizontal Drilling? A Rivalry Between Wellbore Friction and Drillpipe Buoyant Weight and Stiffness

Abstract

To estimate the maximum attainable reach for a horizontal wellbore one needs to investigate the rivalry between the amount of available driving force and the opposing frictional forces. As we provide more driving force through further slack-off, we are more likely to buckle the string and create large normal contact forces, which result in additional tangential frictional forces opposing the forward motion of the BHA. In other words, all the provided driving force will not be transmitted to the desired point (i.e. drillbit) along the string. The greater the stiffness of the drillpipe, the later it buckles and comes into contact with the wellbore wall to create additional normal forces. However, greater stiffness might come with greater weight, as is the case for Steel Drillpipe (SDP) compared to Titanium Drillpipe (TDP), Aluminum Drillpipe (ADP) and Composite Drillpipe (CDP).In this study a new approach for modeling the coupling between tangential frictional force and normal contact force between wellbore and helically-buckled drillstring is developed. The validity of the model is confirmed with experimental data available in the literature. The axial force transfer capability of drillstrings made of SDP, TDP, ADP and CDP are compared. For a limited amount of compressive force provided at the beginning of the horizontal section, different categories of pipes (in the horizontal section of the well) take on different configurations. In addition, along a drillstring some parts remain straight, while some parts buckle helically or sinusoidally. This makes different drillstrings transfer the same amount of provided load differently. In practice, we are able to supply a limited amount of compressive load close to the critical lock-up load in the vertical/slant section of the wellbore. Moreover, below a minimum weight on bit (WOB) drilling becomes impractical. After simultaneous consideration of different buckling modes along the entire drillstring, it is quantitatively shown under what condition ADP can be considered as a superior option over CDP to be used in the horizontal section; and why ADP and CDP have shown a remarkable increase (almost two to three times larger) in the attainable horizontal reach compared to TDP and SDP. This article helps drilling engineers to design an optimum hybrid drillstring for ultra-extended-reach-wells.

Prediction Model of Mechanical Extending Limits in Horizontal Drilling and Design Methods of Tubular Strings to Improve Limits

“…Therefore, if the effect of friction force on critical helical buckling load is neglected, the horizontal extending limits are underestimated a lot. In Mehrabi and Miska's [18] derivation, the effect of friction force on critical buckling load is considered, so the results for these two models are very close to each other. However, Mehrabi and Miska's [18] have not given the explicit calculation expressions of horizontal extending limits while considering the axial force and torque transfer in vertical and build-up wellbores.…”

“…In Mehrabi and Miska's [18] derivation, the effect of friction force on critical buckling load is considered, so the results for these two models are very close to each other. However, Mehrabi and Miska's [18] have not given the explicit calculation expressions of horizontal extending limits while considering the axial force and torque transfer in vertical and build-up wellbores. In this paper, a case study in which kinds of ground and down-hole constraint factors are comprehensively included is conducted and given in Section 2.5.…”

“…The diameter of the horizontal wellbore is 0.2159 m. The values of other parameters are given in Table 1. Figure 2 shows the horizontal extending limits of SDP for Wu and Juvkam-Wold's [1] and Mehrabi and Miska's [18] models and the proposed model. Wu and Juvkam-Wold [1] have deduced the extending limit of coiled tubing in horizontal well.…”