Particle Transport Through Perforations

Abstract

Abstract This paper describes a new procedure for determining particle-transport efficiency through perforations. Transport efficiency is the mass fraction of particles that are transported through the perforations relative to the total mass of particles injected. Our conclusions are based on laboratory studies of the transport of solid particles carried through perforations by different fluids having a wide range of physical properties. Prediction of particle-transport efficiencies based on theoretical considerations described in this paper gives an accurate representation of experimental results. Introduction Transport of solid suspensions through perforations in a pipe wall presents special flow problems during gravel prepacking and hydraulic fracturing operations. Both of these operations commonly are practiced in the field, yet surprisingly little experimental or analytical work is available to guide engineers in selecting operating conditions that ensure that the solid particles are transported efficiently through the perforations and into the formation. Torrest and Savage1 and Haynes and Gray2 studied the transport of sand slurries in a casing with perforations. In these studies, however, no attempts were made to assess either the effects of fluid properties or the number of perforations on particle transport. Furthermore, no attempts have been made to establish a theoretical basis for estimating particle-transport efficiency. This paper describes a new procedure for determining particle-transport efficiency through perforations. Transport efficiency is the mass fraction of particles that is transported through the perforations relative to the total mass of the particles injected. The design procedure described in this paper can be used (1) to ensure that particles are transported through each perforation that accepts fluid, (2) to ensure that a high-density pack is placed outside the perforated casing during gravel prepacking operations, and (3) to prevent bridging of proppant particles in the perforation tunnels during hydraulic fracturing treatments. The conclusions of this work are based on laboratory studies of the transport of solid particles carried through perforations by different fluids having a wide range of physical properties. Predictions of particle transport efficiencies based on theoretical considerations described in this paper give an accurate representation of experimental results. This paper is divided into two main sections. The first section discusses experiments performed to measure the transport efficiency of particles through perforations in casing. The second section describes a particle-transport theory that can be used to extend the laboratory results to full-scale field systems. Measurement of Transport Efficiency Particle-Transport Apparatus The dynamics of particle transport through perforations were studied with two transparent Lucite wellbore models. Both a 3-in.-ID and a 7-in.-ID Lucite casing were fitted with perforations as shown in Fig. 1. The 10-ft-long sections had a 3-ft-long flow-development section, a 4-ft-long perforated zone, and a 3-ft-long rathole section. A maximum of 30 perforations could be used in an experiment by inserting small lucite perforation tunnels in the casing wall. The diameter of the perforation tunnels could be changed from 1/4 in. through 1/2 in. Particle-Transport Apparatus The dynamics of particle transport through perforations were studied with two transparent Lucite wellbore models. Both a 3-in.-ID and a 7-in.-ID Lucite casing were fitted with perforations as shown in Fig. 1. The 10-ft-long sections had a 3-ft-long flow-development section, a 4-ft-long perforated zone, and a 3-ft-long rathole section. A maximum of 30 perforations could be used in an experiment by inserting small lucite perforation tunnels in the casing wall. The diameter of the perforation tunnels could be changed from 1/4 in. through 1/2 in.