The Research Of Confluence Character And Productivity Prediction Of Multilateral Wells

The research of confluence character and productivity prediction of multilateral wells are one of the most important contents that must be investigated in drilling engineering, production engineering and reservoir engineering for multilateral wells.The research before are contraposed to planar or pseudo-three-dimensional flow field. In this paper, a single-phase 3D steady state confluence character of multilateral wells in the reservoir is studied, it reflects exactly the real space status underground.In this paper, a 3D steady state potential distribution due to horizontal borehole in a unbounded reservoir is derived, and it is proved that its potentiometric surfaces are a bouch of ellipsoids of revolution which focuses are the two ends of the horizontal borehole, based on it the 3D steady state potential distribution of multilateral wells are established. A assuming is presented that a open hole borehole is treated as being composed of a certain number of 3D line sinks with uniform flux boundary, but each of which has different rate, and for perforated completion case a perforation as a 3D line sink with uniform flux boundary and the perforated borehole as being composed of all perforation line sinks on it. The imaging and superposition principles are applied to derive the potential distribution and pressure distribution of one multilateral well in different types of reservoir include bottom water dive, edge water drive, gas cap with bottom water drive and horizontal unbounded reservoir.New formulas of calculating pressure drop along the open hole wellbore and perforated wellbore for single phase liquid flow are derived based on the principle of conservation of mass and momentum theorem. The models exactly reflects the flow character of single phase variable mass fluid flow in horizontal and directly slanting borehole.A model coupling the 3D steady state flow in the reservoir with the flow in the multilateral wellbore is developed and the method for solving the model is presented. The confluence character and productivity prediction model with considering pressure drop along multilateral wellbore are developed using the coupling model and a related software is also developed.A number of calculations for examples using the coupling model were made and several important results included the following were obtained.1. The productivity index per unit length along the wellbore is not constant.2. The total well rate doesn't increase with increasing well length for length exceeding a certain value.3. The IPR curves for multilateral wells producing single-phase oil are curved rather than straight lines due to pressure drop within the wellbore.4. from increasing productivity point, multilateral wells are more suitable for developing reservoir with thin layer.5. The position of the wellbore in the formation influences the productivity.