A Semi-Analytical Model for Extended-Reach Wells with Wellbore Flow Splitting; a Production Optimization Scheme

Abstract

Well design have evolved noticeably during the last decade from the design of conventional vertical wells to extended-reach/multilateral horizontal well design using directional drilling technology. Evolving horizontal well design range from simple horizontal wells with single wellbore to complex multilaterals with multiple sublaterals (fishbone wells). Furthermore, advancements in horizontal well drilling allows horizontal wells to be drilled several thousands of feet long. However, field experience and flow meter surveys on long horizontal drain-holes revealed that the frictional pressure losses in the wellbore is an important factor limiting the effective length of long horizontal wells and consequently hindering the full use of the entire length of the horizontal wells. The frictional pressure losses may be comparable with the drawdown at the producing end of the well rendering a portion of the horizontal drain-hole unproductive. Well completions have also been advancing to cope with the technological advancement in horizontal well drilling and new equipment for monitoring and subsequent selective control have been developed to optimize the productivity of the horizontal wells. The complex architecture of those wells generally makes them more expensive to drill and complete. Therefore, these wells must be planned efficiently. For these reasons we present a viable method to produce these long horizontal wells and laterals from the two ends (heel and toe) by using U-shape wells. The introduction of the U-shaped wells is driven by the need to maximize flow contribution from the entire drain-hole lengths. To confirm the viability of this idea, a rigorous semi-analytical model was developed to study the performance of the U-shape horizontal well under different production scenarios. The model incorporates the impact of wellbore hydraulics into the solution, and the U-shaped wells can be produced from both ends at constant rates to predict the pressures at the two ends. The model was used to calculate the flow profile along the horizontal section under different production scenarios. Furthermore, the model can be used as an optimization tool to maximize the benefits from long horizontal drain-hole as it allows producing the two wings at different flow rates. The U-shape wells can also be optimized to have more uniform flux distribution along the horizontal drain-hole in reservoirs subjected to water drive. The developed model can also be used to evaluate the reservoir parameters in such well architecture by calculating the classical horizontal well performance and reservoir characteristics by measuring wellbore pressure at one or both wings.