Abstract

One of the main characteristics of horizontal wells is their extended contact with the reservoir. This extended contact provides many benefits for horizontal wells - including lower drawdown, lower critical rates/drawdown's for reservoirs susceptible to gas and/or water coning, higher sweep efficiencies in displacement recovery processes. The extended contact also means that the behavior of horizontal wells _ in terms of the flow into, and inside them _ will have a significant impact on reservoir recovery performance. As such, wellbore hydraulics cannot be ignored in reservoir performance analysis. This is especially true in the case of multiphase flow inside the wellbore, and the case of enhanced recovery processes.

This study examines the impact of horizontal wellbore hydraulics on recovery performance. The investigation focuses on physical modeling of the flow into, and inside a horizontal well. Scaling criteria are derived using two independent methods (Inspectional Analysis and Dimensional Analysis). Theoretical analyses demonstrate the impact of improper scaling of the horizontal well size on recovery performance, for a variety of situations _ including low-pressure reservoirs, and heavy oil reservoirs being steam flooded using horizontal wells. Experimental data are also collected to support theoretical findings.

Theoretical and experimental results show wellbore hydraulics to be an important parameter affecting the recovery performance, when horizontal wells are utilized in the recovery process. In addition, improper scaling of horizontal well for physical modeling studies lead to inaccurate prediction of various parameters, including the pressure drop across the wellbore. It can also lead to flow phenomena unrepresentative of those in field scaled recovery processes.

Introduction

The principal advantages commonly attributed to horizontal wells include their extensive contact with the reservoir, ability to alleviate coning of unwanted fluids in reservoirs susceptible to gas and/or water coning, and high productivity as a result of their high probabilities of intersecting networks of vertical fractures in naturally fissured reservoirs [1]. The first two advantages are believed to be due mainly to the reduced pressure drawdown in the vicinity of the horizontal wellbores, as a direct result of their extensive contact with the reservoir. In secondary and tertiary recovery processes, horizontal wells have been shown to be capable of improving the sweep efficiency - leading to improved oil recovery when compared to the performance of vertical wells.

Many of the earliest studies into the recovery performance of horizontal wells typically treated the horizontal well, mathematically, as an infinite-conductivity fracture [2–5]. In such cases, the pressure drop across the horizontal well was implicitly assumed to be negligible. Dikken [6] was the first investigator to couple the flow from the reservoir into the horizontal well with the flow inside such a wellbore. A second-order differential equation linking single-phase turbulent flow inside the horizontal wellbore with stabilized reservoir inflow was derived and solved numerically for various boundary conditions. It was shown that, among many important findings, turbulent flow inside the horizontal wellbore could result in an appreciable reduction of drawdown at various points away from the lifting end of the horizontal section.

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