Some Practical Considerations in the Design of Steam Injection Wells

Abstract

In planning the completion and injection program for a steam injection well, it is important to consider the effects of fluid dynamics and heat loss on the wellbore and on the steam so that steam with the desired properties will reach the formation and so that wellbore equipment will properties will reach the formation and so that wellbore equipment will not be damaged. Introduction Normally, completion of a steam injection well must be designed so saturated steam can be injected into an oil reservoir at the desired rate, pressure (or temperature, since one determines the other) and heat content It is also necessary to prevent thermal damage to wellbore equipment during the steam injection process. To achieve this, both heat loss and pressure process. To achieve this, both heat loss and pressure change effects must be considered. Pressure change in the injection string includes frictional pressure drop, pressure increase due to the weight of the steam column (static pressure change), and pressure change due to change in fluid velocity (kinetic energy change). Heat is lost to the surrounding wellbore equipment and to the earth due to the high temperature of the steam. Generally it is desirable to design the completion so that the cost of heat lost is minimized and so the casing temperature is kept low enough to prevent casing damage. Willhite and Dietrich as well as Leutwyler and Bigelow have discussed the effects of high temperature on casing. For laterally supported casing, Willhite and Dietrich propose that the completion be designed so the thermal compressive stress will be less than the yield point of the casing. To calculate casing temperature and casing stress it is necessary to calculate the heat lost by the injected steam. Satter has presented a depth-step method for calculating heat loss and steam quality for saturated steam as a function of depth. Since Satter assumed no pressure change with depth, he assumed, in effect, that the temperature of the injected saturated steam remains constant, and that only the quality varies with depth. Holst and Flock improved the accuracy of the heat loss calculation by including the effects of frictional pressure drop in the injection string. However, they neglected static pressure change. In this paper steam and casing conditions are presented as functions of depth for several steam presented as functions of depth for several steam injection and well completion situations. This information, which has been obtained from heat loss calculations, is used to indicate the types and magnitude of various problems that should be considered in designing problems that should be considered in designing completions for steam (or any hot fluid) injection wells. The technique used for calculating heat loss and down-hole conditions is described briefly in the Appendix. Conditions During Steam Injection Heat loss calculations have been used to investigate the effects of well completion on steam injection well behavior. Figs. 1 through 4 show down-hole conditions for five different completion schemes. These figures apply after one week of injection of 500 psia, 467F, 80 percent quality steam (surface conditions) at 6,000 lb/hr. Table 1 gives the physical characteristics of the injection well. Table 2 gives completion details for the five cases shown in Figs. 1 through 4. For convenience in showing calculated results for the completion conditions involved, the low injection rate is used. JPT P. 79