New approach for the performance of reservoirs depleted by long horizontal wellbores with closed sections

Abstract

This paper introduces a new approach for reservoir performance where long horizontal wellbores are extended in the porous media with the existence of closed sections. It focuses on the impact of these sections on the pressure behavior, flow regimes, and productivity index considering different characteristics for the closed sections in terms of the length and petrophysical properties. The methodology used in this approach includes different tasks. The first is developing analytical models for the pressure drop caused by the production at a constant sandface flow rate from a horizontal wellbore where a part of it is closed. These models are developed based on the fact that the porous media with the existence of the closed sections in the horizontal wellbores consists of three regions. The first represents the porous media in the vicinity of the open section of the wellbore and extends to a distance equal to half the formation thickness while the second is the porous media of the open section that extends beyond the first region and reaches the reservoir boundary. The third region represents the porous media of the closed sections that extend from the wellbore to the reservoir boundary. In the second task, the proposed models are solved for different reservoir configurations, wellbore lengths, and closed and open section characteristics. The impact of closed sections on transient and stabilized pseudo-steady state productivity indices are demonstrated in third tacks while the analytical models of the observed flow regimes in the porous media are presented in the fourth task with a major focus given to those impacted by the closed sections. The outcomes of this study can be summarized in the following points: 1) The pressure behavior, flow regimes, and productivity index are significantly influenced by the existence of closed sections. This influence is significant during early production time, but it decreases during intermediate production, however, it is not seen at late production time. 2) The impact of closed sections becomes more severe when the petrophysical properties of the closed sections are greatly different from those of open sections. 3) The pressure behavior of early production time is not affected by the petrophysical properties of the closed section porous media while pseudo-steady state flow is significantly impacted by these properties. 4) The pressure and pressure derivative behaviors of long horizontal wellbores with long closed sections are similar to those developed in reservoirs depleted by hydraulic fractures. 5) Reaching pseudo-steady state flow may need a longer time when there is a great difference in the petrophysical properties between closed and open sections, however, the length of the closed sections may not have such impact. The novel point that has reached in this study is observing a new bi-linear flow regime instead of a linear flow regime. This flow regime represents a simultaneous linear flow from the closed section porous media to the open section and from the open section to the porous media in the vicinity of the open section of the wellbore. New analytical models for the pressure and pressure derivative of this flow regime is introduced in this study.