Initially, it was believed that a horizontal well should be drilled as long as possible. This was motivated by the advancements in horizontal well drilling, which allows horizontal wells to be drilled several thousands of feet long. However, field experience and flow meter surveys in long horizontal drain-holes revealed that the frictional pressure loss 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. Flow meter surveys revealed that the productivity of long horizontal wells is not proportional to well length because the increase in the length of horizontal section results in significant frictional losses in the wellbore. 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.This paper presents a new approach to maximize the use of the full length of long horizontal drain-holes by producing these long horizontal wells from both ends (heel and toe) and/or intersecting the second half of the horizontal well at an optimized location. This approach is supported by development of a rigorous semi-analytical model for the transient pressure analysis and well productivity evaluation for the horizontal well producing from both wings at the desired rates from both wings. The model incorporates the impact of wellbore hydraulics into the solution and used to calculate the flux distribution and pressure profile along the horizontal section. The developed model can also be used to evaluate the impact of reservoir parameters on the horizontal well performance. Furthermore, the model can be used as an optimization tool to optimize the production of long horizontal well by producing the well at the desired flow rates from both wings. Also presented, are some results showing the impact of wellbore hydraulics on the flux profile along the horizontal wells. These results show that the flux profile is a function of combination of reservoir flow characteristics and well conductivity. Wellbore hydraulics changes the flux distribution (flow ingress profile) along the wellbore and, thus, results in additional pressure drop in the well. The proposed method is found to be superior to the conventional horizontal well in terms of productivity and flux profile.

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.