Targeted Steam Injection Using Horizontal Wells With Limited Entry Perforations
Authors: Boone T.J. , Youck D.G. , Sun S. 
Published: March 2010

Limited-entry perforations have been used in vertical wells in both California and at Imperial Oil Resources' Cold Lake field as a method for distributing steam to different zones. The technology relies simply upon designing the number, size, and placement of the perforations so that critical or choked flow occurs across the perforations during steam injection, and steam exits the well with the desired distribution. This paper describes an experimental horizontal well where this same technology was used to replace ten vertical injection wells with a single horizontal well. The well was located between rows of vertical wells in a reservoir that had been subjected to more than ten years of operations under cyclic steam stimulation. The limited-entry perforations enabled steam to be targeted at the cold regions of the reservoir. A more typical completion such as a screened or slotted liner would not have provided any control over the placement of steam in the reservoir. The 1,000 m long liner was cemented in place with a completion design consisting of only 28, 9.5 mm diameter, perforations which were drilled through the casing and cement. The design injection rate for the well was 2,000 to 3,000 m3/day of 70 % quality steam. This paper presents an assessment of the performance of the well based on theoretical calculations, measured injection pressures and rates, and 3D seismic imaging.

Introduction

This paper presents the results from a pilot at Imperial Oil's Cold Lake field where a horizontal well with a unique completion design was employed as a dedicated steam injector. The well was completed with a liner that was cemented in place and perforated with only 28 limited-entry perforations, which served to distribute the injection of steam along the horizontal well.

Limited entry perforations have been used extensively in vertical wells, in thermal operations in California, as a mechanism for distributing steam to several zones within a formation(1, 2). More recently limited entry perforations have been employed in at least one horizontal well in California(3). The term "limited-entry" implies that the size or area of the perforations has been specifically selected to limit the flow rate into a zone at a given injection pressure. This limit occurs because the velocity of the steam exiting the perforation is approaching the sonic velocity and is therefore choked or throttled. Generally, this results in a large reduction in the number and size of perforations relative to what is typically used for production purposes. For example, the pilot well described in this paper has a 1,000 m long liner section which was completed with only 28, 9.5 mm diameter perforations. The well was designed for injection of up to 3,000 m3/day of 70 % qualitysteam (cold water equivalent volume) with well pressures of 10 MPa.

The specific application for this well design at Cold Lake is as a "follow-up process" where infill wells would be drilled amidst a regular pattern of vertical wells that had been operated for ten years under Cyclic Steam Stimulation (CSS).