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The high temperature and pressures encountered in steam flooding have necessitated the use of premium and, in many cases, unique equipment. Field results from three steam flood installations give an insight as to the performance of high-pressure equipment when subjected to the accompanying high temperatures. Performance of the equipment and factors entering into the selection of equipment for steam flood installations are discussed.
Recovery of low-gravity, high-viscosity crude oil from relatively shallow reservoirs is becoming feasible through the application of steam flooding. Pan American Petroleum Corp. initiated a pilot steam flood with a 5.36 million Btu/hour, 1,500-psi steam generator at the Winkleman Dome field in west central Wyoming in March, 1964. After one year of operation, this steamer was replaced with a larger unit capable of 12 million Btu/hour at 2,500 psi. Two other pilot steam flood projects were started at that time using 12 million Btu/hour, 2,500-psi steam generators, one at the Salt Creek Shannon field and another at the Fourbear field, both in Wyoming. This paper discusses the equipment used in high-pressure steam flooding and reviews some of the problems encountered in the application of the equipment. Where determined, a suggested solution is presented. The discussion follows the conventional flow of water and steam: water treating. steam generation, steam control and transmission, wellhead and subsurface equipment, and instruments and data collection (Fig. 1). The steam generation and transmission equipment discussed in this paper has been designed for 2,500-psi saturated steam service. Maximum operating conditions have been 1,875 psi and 626F.
Successful operation of steam generation equipment depends primarily upon a good source of water combined with an effective water treating system. Experience gained in the past two years of pilot steam flood operation indicates the majority of steamer down-time is caused by water treating problems.
The quality of raw water dictates the amount of treating required; therefore, it is imperative that the best water available should be used. Some criteria for a good quality raw water are: (1) the water should be free of oil or filming amines; (2) dissolved gases such as O2, C2 and H2S, should be absent or at least present only in trace amounts; (3) total hardness should be low; and (4) suspended solids concentration should be low. Since the quality requirements of water used in a single-pass steam generator are extremely stringent, it is unlikely that the available raw water can be used without some form of treatment.
An experimental steam injection project conducted by Northwestern Refining Co. and McWood Corporation during 1966 at Hughenden, Alberta has shown that it is feasible to inject high-pressure steam (1,500-1,600 psig) at high rates (22 MM Btu per hour) into a sandstone reservoir containing an 18°-A.P.I.-gravity crude oil at a depth in excess of 2,500 feet without experiencing serious mechanical problems and without excessive heat losses. Conventional gas-fired treaters have proved adequate in handling any emulsion problems encountered to date.
This paper reviews the design concepts pertaining to the forced-circulation once-through steam generator. To aid the production engineer in evaluating different generators for application in different situations, this paper discusses elements of feedwater treatment, aspects of design, defines common terms the production engineer might not be familiar with, and describes several figures included for determination of heat requirements, pressure loss, generator thermal efficiency, heat losses, working pressures and tube spacing.
The advent of high-pressure steam injection as a secondary recovery technique has created a requirement for a generator suitable for this application. The generally satisfactory and sometimes spectacular results achieved in several of the initial commercial steam flooding projects has created a rapid increase in the requirement for suitable generators. The result has been the appearance on the market of several competitive designs of thermal recovery generators. The production engineer is thus faced not only with the problem of understanding an unfamiliar piece of equipment, but evaluating the merits of several competitive designs.
This paper is concerned only with reviewing the design concepts pertaining to the forced-circulation once-through generator. The high operating pressures used in this service dictate the use of a water tube design where the pressure is contained in relatively small tubes with resultant economy in manufacture and decrease in operating hazard. The once-through steam generator was specifically developed for thermal recovery applications and features a single pass of water through the generator coil and no separating drum. The units are generally designed to produce approximately 80 per cent quality steam, so that the weight ratio of water to steam at the outlet of the generator is about 1:4, which is a much lower ratio than in conventional boiler designs. This water-steam ratio is not sufficiently high to insure complete wetting of the tube walls in the outlet portion of the generator coil, therefore the maximum tube wall temperature must be determined using a steam rather than a water heat transfer film coefficient. Since the steam film coefficient will be considerably lower than that achieved with water at an equal mass velocity, the maximum tube wall temperature would be considerably higher than in a conventional boiler unless a lower radiant absorption rate is used. The method of calculating the tube wall temperature will be outlined later.
The once-through generator was specifically developed for thermal flooding applications and provides features not available in conventional steam boilers. Among the important advantages are the following: 1. It will handle feedwater with a relatively high percentage of solids, provided the solids have been converted to soluble form. 2. It does not have a separating drum and is essentially only a pipe coil. Because of the small volume of water and/or steam contained in the coil and the lack of a drum, it does not conform to the classic definition of a boiler. 3. It does not have level controls, low level cutouts, etc., as required in a conventional boiler installation, and does not require continuous blowdown and constant operator attendance. Feedwater treatment is an important consideration in the satisfactory performance of a once-through generator, and deserves special emphasis. Some of the main considerations are as follows.
Hardness The special nature of the thermal recovery heaters where 80 to 85 per cent of the feedwater is vaporized in a single pass through the heater makes it essential to have zero hardness in the feedwater at all times. We recommend the dual-ion-exchange system as providing the minimum hardness leakage in spite of difficult raw waters, with the maximum assurance of always providing this minimum hardness leakage. We believe an ion exchange system is a prerequisite for the successful operation of a wet steam injection system for secondary oil recovery.
ABSTRACT ABSTRACT This paper describes some of the problems encountered in cyclic steam injection in the Guadalupe Field, San Luis Obispo County, California. Traditional problems, inherent to steam stimulation - such as casing failure, sand control, and adaption of existing facilities to greater volumes of high-temperature production - were encountered. Innovations in methods and equipment used to implement cost reductions are discussed. INTRODUCTlON Development of practical techniques of thermal stimulation, including in situ combustion, steam drive, and cyclic steam injection, was received with enthusiasm by oil-production people associated with low-gravity, high-viscosity oil reservoirs Cyclic ? more popularly called ?huff-and-puff? ? steam injection was the technique first used by most operators because of lower capital investment and more rapid response. The response from many of these early projects was encouraging. However, within a short time it became apparent that a new set of problems would have to be solved if cyclic steam injection was to be a financial success. In some areas the most perplexing problem was the failure of well casings to withstand elevated temperatures. In others it was necessary to revamp or enlarge oil-treating facilities to enable dehydration of the larger volumes of high temperature crude emulsions. All operators found it necessary to refine techniques to reduce high operating costs. The objective of this paper is to present a case history of cyclic steam injection, the related problems, and how they were solved by one California operator. BACKGROUND The key to successful operation of the Guadalupe Field has frustrated oil men for over 15 years Continental Oil Company drilled the discovery well in 1949, but did not develop commercial production from this 10 API gravity reservoir which has an average thickness of 40 ft and an average depth of 2,700 ft The Thornbury Drilling Company acquired the lease by purchase in 1950 and drilling was resumed Union Oil Co of California became the operator in 1953.The low production rates resulting from the high viscosity of the crude and sand-control problems plagued Union as it had the prior operators. Recognizing the potential of viscosity reduction by thermal methods, Union experimented with bottom-hole electric heaters, but cable failures and sand-control problems proved too much. During this period of experimentation it was determined that the sand could be controlled by gravel-packing. This method has essentially eliminated sand production in the field. In February 1964, cyclic steam injection tests were initiated. The response was encouraging. Solution of the new set of problems presented by steaming operations has encouraged Union to drill additional wells. CASING DESIGN AND CEMENTING TECHNIQUES Casings in 15 of 37 wells failed after being subjected to high temperatures during steaming. It is possible that additional failures occurred which have not been detected because production has not been affected. This failure rate was understandably prohibitive, and ?puff-and-puff? steaming operations were suspended until the problem could be solved. Casing design for, and failures from, thermally induced stresses has been discussed at length in numerous papers and reports and will not be further discussed in technical detail in this paper.