Analysis Of Heat Losses And Casing Temperatures Of Steam Injection Wells With Annular Coolant Water Flow
Authors: Back Lloyd H. , Cuffel Robert F. 
Published: December 2007

Circulating coolant water from the ground level through the annulus between insulated steam tubing and the casing of injection wells was investigated analytically. Calculations indicated that the annular water flow decreased the percent energy loss to the surrounding rock and reduced casing temperatures. The analysis has application to oil recovery in deeper wells and for higher pressure and, thus, temperature steam.

This work presents the results of one phase of research carried out on Applications of Aerospace Technology to Petroleum Extraction and Reservoir Engineering at the Jet Propulsion Laboratory, California Institute of Technology, under Contract No. NAS 7–100, sponsored by NASA.

Introduction

Current interest in steam injection oil-recovery methods is toward the use of deeper wells and higher pressure wet steam with correspondingly higher pressure wet steam with correspondingly higher saturation temperatures. Particular problems are higher heat losses from the flowing steam to the surrounding rock, higher casing temperatures and thermal stresses, and packing failure because of the high temperature steam with the intrusion of steam, formation water, oil, and mud at the well bottom into the annulus between the steam pipe and the casing.

Wellbore heat transfer analyses have been carried out by Moss and White, by Ramey, and subsequently by others, but there apparently has not been an investigation of circulating water through the annulus to cool the casing and to pick up some of the heat that would otherwise be lost to the surrounding rock. Such a cooling method is common practice in liquid propellant rocket engines where practice in liquid propellant rocket engines where some of the propellant is used to cool and maintain the integrity of the nozzle wall.

Of primary concern is the reduction of heat losses from the steam to the surrounding rock since this energy that was supplied to produce steam from water is not available for oil recovery in the formation below, and the net yield of recoverable oil is reduced thereby.

Also of concern is the avoidance of lateral deformation and buckling of the casing due to thermal stresses. Whillhite ana Dietrich estimated that the change in casing temperature for J-55 grade material (minimum yield stress 55,000 psi) is about 250 degrees F for casing yield and about 500 degrees F for joint pullout in tension during the cooling cycle following steam injection for a new well. However, allowable thermal stresses and thus casing temperature changes are expected to be less for older wells often used for steam injection. Since most states require cementing the casing, lack of uniformity of cement also can lead to local failure and buckling at lower tempera-changes of the casing.

The consequences of packing failure are not well known with regard to thermal conditions near the well bottom; however, the use of coolant water flow through the annulus would obviate the need for a packer and prevent intrusion of steam in particular packer and prevent intrusion of steam in particular into the annulus.

ANALYSIS OF COOLANT WATER FLOW IN ANNULUS

The wellbore configuration is depicted in Fig. 1. Steam flows through the insulated tubing and water flows through the annulus between the sealed insulation and the casing from the ground level. Heat is transferred from the steam flow through the tubing and insulation to the water flow. Part of thus heat is picked up by the water flow and part is transferred through the casing and cement to the surrounding rock. At the bottom of the wellbore the steam and water flows mix before entrance into the formation.

In the analysis that was carried out, quasisteady heat transfer was considered; i.e., the thermal capacity of the tube wall and casing and to a lesser extent the insulation and cement were not taken into account, but the heat transfer from the cement to the surrounding rock was taken as time-dependent in the way considered by Ramey for the infinite radial rock.