Liquids Phase Holdup and Separation Characteristics as a Function of Well Inclination and Flowrate

Abstract

Abstract The maturing Middle Eastern oil fields with natural aquifer support or waterinjection can pose a challenging produced water handling and disposal issues.The increased water-oil ratio also presents productivity problems: many wellswill die prematurely due to increased water holdup. The produced watermanagement cost @US$ 0.50—1.00 per barrel involving millions of barrels ofwater (even at a modest WOR of 50% from current 30–35%) will be in billions dueto the high daily oil production rate envisaged. In this paper, we focus onvarious aspects of downhole oil-water separation, which we believe will lessenthe cost significantly. The downhole water separation technology developed andapplied in the western hemisphere cannot be directly applied here because ofthe orders of magnitude higher production rates per well. Lacking a production flow-loop facility in the region with full-scaleproduction equipment, we use an industry-standard commercial computationalfluid dynamics (CFD) simulation tool to investigate inline oil and waterseparation characteristics under downhole conditions. Specifically, weinvestigate the startling sensitivity of well inclination in the 80–100 degreesrange. We show that it is crucial to control the well inclination within atight regime to achieve effective and manageable liquids separation in nearhorizontal wells. We also show that the liquids phase separation in these wellsare sensitive to the gross liquids flow rate. The CFD simulation study reported in this paper will lead to new technologydevelopment that can be used to achieve more effective well completion designin near horizontal wells drilled specifically to obtain downhole oil-waterseparation. The success of such innovative oil-water separation will save manyproducing wells from dying prematurely and save millions of dollars in producedwater handling and disposal. Introduction With the advent of horizontal wells in the early 90's, the question offluids holdup in the deviated and horizontal well sections became importantfrom production well logging point of view (Bamforth et al., 1996; Catala etal., 1996; Theron & Unwin, 1996). Various studies conducted to investigatethe effect of well inclinations on oil-water phase hold up inside the pipestemmed from the concern to determine the accuracy of production tools todetermine fluid entries and relative flow rates.