Flow of Oil And Sand In a Horizontal Well
Authors: Doan Q. , Ali S.M. Farouq , George A.E. 
Published: March 2010

Abstract
Despite the increasing acceptance of horizontal wells as a potentially productive means of recovering oil and gas from underground reservoirs, the hydrodynamics of flow inside a horizontal well remains incompletely understood, especially for multiphase flow. Sand production into a horizontal well presents a formidable problem as the sand deposits at the bottom of the horizontal well, and thus reduces the effective size of the flow conduit. This study focusses on the flow of oil and sand in a horizontal well.
The model developed in this study treats the flow of oil and sand as that of a monodisperse, dilute suspension. The fluid phase (oil) is assumed to be incompressible and Newtonian. The particulate phase, composed of spherical sand particles, is assumed to behave as a continuum. The diffusive movement of the particulate phase is controlled by gravity force. The model allows for the determination of the axial velocity of the fluid phase and particulate phase, and the particulate phase density distribution at different positions along the horizontal well length.
Examination of the dimensionless groups allows for an analysis of the dominant parameters controlling the transport of sand in a horizontal well, including condition(s) promoting sedimentation. The rate of sediment bed buildup is correlated with fluid phase flow and interaction between the fluid phase and the particulate phase.

Introduction
Solid-liquid multiphase flows encompass many different areas of science and engineering, ranging from transport of colloids in rain water, sediment transport in river streams, waste transport in sewers, bed fluidization, flotation to slurry pipeline transportation, drill cuttings removal, and transport of fracture proppants, etc. As more horizontal wells are drilled to recover oil and gas from oil reservoirs, problems associated with sand production into, and their transport inside these horizontal wells become more prominent- particularly for wells drilled in unconsolidated or fractured formations. Deposition of sand and fines inside these horizontal wells could have adverse impact on their productivity, even negating many of the advantages of horizontal drilling. In particular, the produced sand particles tend to collect in the low spots (doglegs) along the horizontal well, and thus constrict the flow of oil through the well at these points. Sand removal techniques have been successful in fluidizing the settled sand particles and removing them from the wellbores. However, these operations are time consuming, expensive, and require a knowledge of where the sand deposits are. Few studies investigating the hydrodynamic transport of sand and fines in horizontal wells are available in current petroleum literature. This paper attempts to identify parameters governing the flow of oil and sand inside a horizontal well, including conditions promoting sand deposition, as well as the rate of sediment buildup at different positions along the horizontal well length.

Hydrodynamic Fundamentals
From a hydrodynamic viewpoint, the most important and fundamental aspects of solid-liquid multiphase flow are interphase interaction (i.e., interaction between the fluid phase and the particulate phase) and intraphase interaction (i.e., interaction among solid particles making up the particulate phase).