The Effect of Well Trajectory on Horizontal Well Performance

摘要

Horizontal wells provide extended contact with the reservoir,rnand have unique advantages over vertical wells in manyrnapplications. As nominally horizontal wells get longer andrnfollow more complicated trajectories, wellbore hydrodynamicsrnbecomes an important issue on well performance. In thisrnpaper, we will discuss a problem in horizontal wells - thernelevation change in well trajectory and its effect on wellrnperformance. In general, a horizontal wellbore is neverrnperfectly horizontal. The inclination angle could be a result ofrndrilling control, or sometimes could be designed on purposernfor an extremely anisotropic formation. When verticalrnpermeability is much smaller than horizontal permeability, anrnundulating wellbore may be favorable to overcome the lowrnvertical permeability. Undulation in wellbore trajectory willrnchange the inflow distribution along the wellbore, andrntherefore change the wellbore performance. When two-phasernflow is involved, especially gas-liquid flow, the pressurerndistribution in the wellbore may cause flow problems, such asrntrapping gas because of accumulated liquid at low spots. Wernuse a simple analytical model to examine the flow conditionsrnfor inclined or undulated horizontal wells. The reservoirrninflow is interactively coupled with the wellbore flow, and thernpressure and flow rate distribution are predicted by the model.rnThe model then is used to analyze the development planrnfor the Cosmopolitan field in Alaska. The field has stressdependentrnpermeability, and the vertical permeability is muchrnlower than the horizontal permeability. The results of thernmodel explain the effect of wellbore trajectory on wellrnperformance of horizontal wells, and justify the benefits ofrnundulating wellbores in horizontal well development in thisrnlow vertical permeability reservoir. The study showed thatrnundulating wells in the Cosmopolitan field can help tornimprove well productivity.