Real-Time Optimization of SAGD Operations
Authors: Denney Dennis 
Published: February 2015

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 157923, ’Real-Time Optimization of SAGD Wells,’ by Luis E. Gonzalez, SPE, Peter Ficocelli, SPE, and Tad Bostick, SPE, Weatherford, prepared for the 2012 SPE Heavy Oil Conference Canada, Calgary, 12-14 June. The paper has not been peer reviewed.

The steam-assisted-gravity-drainage (SAGD) process along with an efficient steam-use process can reduce production costs and increase the oil-recovery rate. The use of real-time downhole monitoring is an effective approach to achieve this optimization. The use of downhole distributed-temperature sensing (DTS) and array-temperature sensing by use of fiber-optic technology has led to instrumented wells that enable data access on a real-time basis, leading to better control of operations, and to optimizing the steam process. Also, fiber-optic technology enables measuring pressure and temperature over the same fiber and in close proximity along the wellbore.

Introduction

At reservoir conditions, bitumen is essentially immobile, and recovery of these highly viscous fluids requires viscosity reduction, often by applying heat. The SAGD process is an effective recovery method for heavy oil and bitumen. The SAGD process typically uses two parallel horizontal wells that normally are separated vertically by approximately 5 m. The top well is the steam injector, and the bottom well is the producer. As steam is injected, a steam chamber will grow around and above the injection well. Despite its effectiveness, the SAGD process has many economic risks including a high initial investment for constructing the surface facilities and uncertainties related to product prices.

Displacement efficiency is a critical factor in controlling oil recovery from the steam chamber, and, although increased volumetric sweep is beneficial, the chamber-growth rate greatly affects the rate at which the displacement efficiency increases in the steam chamber. Increasing the volume of the steam chamber too quickly may decrease the effectiveness of the SAGD process.

Uniform distribution of steam along the entire length of the wellbore could lead to a more-uniform steam-chamber growth, making the entire length of the well productive and developing optimum performance of a SAGD well pair. Traditionally, the SAGD injection well is completed with dual injection strings (one injection string ending at the heel and the other injection string ending at the toe) and the production well is completed with a slotted liner, as shown in Fig. 1. Steam distribution along the well is governed by different factors. The most important factors include pressure in the injector and producer wells, fluid-flow regime, fluid velocity, wellbore trajectory, and heat loss along the length of the wellbore. A new well/injector configuration is proposed that includes steam diverters, inflow-control devices, centralizers, fiber-optic pressure gauges, a fiber-optic DTS system, and control lines. An inter-mediate configuration could be the traditional dual string with the addition of temperature and pressure measurement by use of fiber-optic technology to help control the shape of the steam chamber.