PRESSURE DROP CALCULATION FOR AGGREGATE FLOW IN MULTILATERAL WELLS

With the improvement of economic development mode and the exploitation of offshore hydrocarbons, more and more attention is paid on the multilateral wells in the development of hydrocarbon resources. A distinguished feature of multilateral-well development mode is the convergence of branches and major branch. The local resistance loss in the intersection point is named as the aggregate flow pressure drop. Therefore, it is necessary to establish the physical and mathematical flow model for the aggregate flow pressure drop, analyze the magnitude of the local resistance, and thereby offer foundations for the productivity analysis when developing oil and gas with multilateral wells. The physical model for three-branched well was established by means of analogy. The aggregate flow models for the equant tee joint of three braches and for the equant oblique branch were established respectively by the analysis of fluid mechanics. Computation results for the aggregate flow pressure drop show that the local resistance loss is negligible for both the equant tee joint and the equant oblique branch when the total flow rate is less than 1000 m3/d and the diameter of each branch is no less than 76mm, the maximum value of which is about 0.01MPa that is about 0.13 percent of the gravitational pressure drop of a well at the depth of 1000m. Simultaneously, the local resistance loss in the bore hole is only 0.17 percent of the horizontal drawdown pressure of 6MPa. In the light of the in-situ engineering practice, the local resistance loss resulted from the multilateral aggregate flow can be negligent. Meanwhile, it is better to use equant tee joint on the intersection point when the normal Y-branch is adopted on the branch point of three-branched well.