Wellbore Heat Losses In Deep Steam Injection Wells S1-B Zone, Cat Canyon Field

Abstract

Abstract Plans to initiate a pilot steam displacement project with injection into zones as deep as project with injection into zones as deep as 2700' prompted concern for the wellbore heat losses that could be expected. To evaluate this aspect of the pilot design, a computer program was developed. The program and predictive technique were tested by comparing with other published methods and with measured casing temperature data. Agreement of predicted casing temperatures with measured temperature data was within three percent. The program was then used to predict wellbore heat losses under a variety of possible completion designs for steam injection wells in the S1-B zone of the Cat Canyon Field located near Santa Maria, California. These results show that under certain completion conditions, heat losses could be as high as 22 percent. Introduction In 1974, Getty Oil Company began design of a pilot steam displacement project in the S1-B sand of the Cat Canyon Field, Santa Barbara County, California. This zone is a thick, unconsolidated sand which produces nine degree API crude oil through use of cyclic steam stimulation. Wells range to 2700' in depth. In addition, the relatively high injection pressures required (1600 - 2000 psig) result in steam temperatures of approximately 620 degrees F. This combination of deep wells and high steam temperatures prompted concern about the wellbore heat losses which would be sustained. A review of published heat loss calculation methods indicated that very high heat losses could occur under some completion conditions. This review also revealed that each calculation technique had limitations which were of concern. A computer program was then developed which incorporates the best features of the various published techniques, but which is capable of handling more complicated well completion techniques. It is capable of handling cases in which steam quality varies as a function of depth, and also performs a complete heat balance of the steam injection system from steam generator discharge to sand-face. Following program verification, a study of various steam injection completion alternatives was conducted. COMPUTER PROGRAM DESCRIPTION The computer program developed (hereafter called HEATLOSS) calculates wellbore heatlosses based upon conservation of radial heat flow. That is, the steady-state heat flow due to thermal energy lost by the injected steam is assumed to be equal to the transient radial heat flow to the formation. An overall heat transfer coefficient, Uti, is calculated based upon equations for the conductive heat flow through various components of the injector completion and conduction-convection and radiation heat transfer coefficients in the annulus. An iterative procedure is used for this purpose (see the appendix for a detailed discussion of the calculation methods). Having calculated the heat transfer rate (from uti), knowing the steam mass flow rate, and by implicitly determining the steam pressure change, the variation in steam quality is calculated. In addition to the wellbore heat losses, surface steam line heat losses are also considered. These surface lines can be as long as one-half mile, in which case the heat losses can be substantial. The surface lines can be simulated as buried, exposed and not insulated, or exposed and insulated.