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This paper was to be presented at the 40th Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Denver, Colorado, October 3-6, 1965, and is considered to an abstract of not more than 300 words, with no illustrations, unless the paper is specifically released to the press by the Editor of the Journal of Petroleum Technology or the Executive Secretary. Such abstract elsewhere after publication in the Journal of Petroleum Technology or Society of Petroleum Engineers Journal is granted on request, providing proper credit is given that publication and the original presentation of the paper.
Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.
Water to be used for steam injection projects must contain a very small amount of hardness ions and oxygen. corrosion should be monitored at several locations. Methods used to accomplish these objectives are described.
Steam has been used to transfer energy for many years. In the oil field, steam has been used to heat oil for demulsification and viscosity-reduction purposes, as well as used as a source of power to drill oil wells. During the past few years, much emphasis has been placed on thermal recovery of low-gravity viscous crude by the injection of steam into the reservoir. This use of steam was tried in the 1930s, but it has reached real prominence in the oil industry only during the past five to ten years. Today, much interest exists in the generation of steam for injection into oil bearing strata, and many approaches are offered to the handling of this fluid.
Steam Generator Equipment and Water Sources
Many authors describe the qualities of the waters that are necessary for steam generation. The pitfalls of poor handling of boiler feed water are well known, and they have been made the subject of books and other literature. This paper deals with water treatment and handling designed for a steam product of approximately 80 per cent quality. The equipment referred to includes only the once-through steam generator where there is neither recirculation of the water phase nor blowdown of concentrated, soluble or insoluble, salts from the steam generator.
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.
The heavy oil sand reservoir of Kuwait containing a viscous, low API oil occurs at a shallow depth of about 422 feet subsea. Its reservoir temperature and pressure are generally low because of the shallow depths involved. The heavy oil reservoir has not been produced till now by the primary techniques. Primary recovery is expected to be low mainly due to lack of a natural driving mechanism.
Various studies were made to find out ways and means to recover the heavy crude oil from the shallow deposits in Kuwait. The viscosity, temperature behaviour of Kuwait heavy oil is such that its viscosity is reduced by a factor of more than 100 when the temperature is increased to 300 degrees F which suggests that the oil might be produced successfully with thermal recovery processes. Other favorable Conditions for such a process are the shallow depth of the accumulation and the relatively high oil saturation. In view of their size and favorable characteristics, Kuwait's heavy oilfields are obvious candidates for the application of thermal recovery methods. It was concluded that injection of limited amounts of steam might be a very effective method for stimulation of heavy-oil wells. To obtain an early answer on the suitability of thermal process a pilot project of four wells for steam stimulation was project of four wells for steam stimulation was initiated in an area near light oil production facilities. This helped in transportation of produced crude. The other favorable factors for produced crude. The other favorable factors for selecting the pilot area are :
1) Net pay thickness is the highest in the known area, 2) The oil viscosity is moderate compared to other areas, 3) Nearer to fresh water station. This is required as water needs to be transported by road tankers.
The pilot project was initiated with simplest design and was handled with in-house expertise with minimum input from outside consultants, to achieve the following objectives:
1) To determine the applicability of thermal recovery process for Kuwait's heavy oil deposits, 2) To determine optimum steam injection rates, 3) To observe reservoir response under different conditions of steam injection, 4) To obtain information for future implementation of large scale project, 5) To gain operating experience under local conditions and to determine problem areas.
The first steam injection was started in September 1982. This paper describes the performance until the end of September 1986. The performance until the end of September 1986. The operating practices and well performances are discussed in some detail.
In view of the favorable results obtained so far, steam soak projects have been expanded considerably since the start of this project. Presently another pilot of the same size as the Presently another pilot of the same size as the one under discussion is underway. Further extension in the two pilot areas is being programed. programed. PROJECT DESCRIPTION PROJECT DESCRIPTION The reservoir data, well completions, surface facilities and source water are discussed in the following:
Recycle of high hardness, high TDS(total dissolved solids) waters (hardness>1000 parts per million (ppm) as CaCO3 and TDS>10,000 ppm) water for steam generation or other reuse such as irrigation or drinking water is very expensive. Silica content is usually above 250 ppm in such waters which can cause problems in steam generation and with desalination. Many of the these high hardness waters are oil field produced waters but there are other processes which generate waters which require additional treatment. For those high hardness waters, hot lime or hot caustic, followed with strong acid/weak acid resin or just weak acid resin softeners are used in conjunction with oil field steam generation. Treatment of these waters for irrigation or drinking waters involves thermal desalination or reverse osmotic(RO) treatment with biological control.
Silica removal is not required for normal wet steam genera tion. However for desalination operations, whenever the feed water concentrate is to be used for the steam generator feed and the fresh water sold, silica removal is required to aid in scale formation in desalination plus silica level in the concentrate water. The known limits on the concentrate feed water to a wet steam generator are 500 ppm silica and 25,000 - 30,000 ppm TDS of total water ions, based on soluble salts solubility. Silica removal is also required in other waters such as 210,000 ppm TDS water containing sodium carbonate where silica removal is required prior to crystallization of sodium carbonate crystals.
In the softening test work, the high solids addition and disposal associated with a hot lime system was not desired so alternatives were investigated. In addition, better silica removal than silica absorption on magnesium hydroxide or alumina or aluminum was required. Steam stripping of the high pH water and removal of the precipitates using a ceramic crossflow filter for which a special crossflow filter back pulse unit for cleaning was developed. Temperature and pH were increased prior to the steam stripping to decrease steam condensation and drive the reaction. When silica removal was required, a bed of alumina or aluminum was used at the high pH and temperature to put aluminum into solution so aluminum silicates were removed with the hardness precipitates. The solids often contain some oil when using oil field waters so an odor chemical was also developed for the microbiological soil remediation site.
The steam stripping was tested first in a countercurrent mode in a stainless steel column clad with a Hastelloy C 22, packed with stainless steel packing. The second test was by injecting the steam on the outside circumference of a crossflow ceramic microfilter in a cocurrent mode with flashing in a exit vessel. In the countercurrent tower operation, the control of the equili brium of the carbon dioxide, the carbonate and bicarbonate at the top of the tower was more difficult than when contacting with the microfilter. With the microfilter, the equilibrium approach was not a large concern as fresh steam was contact ing the water and was then flashed. However the exact control of the steam to water ratio was more difficult in the second case.
Both thermal desalination and RO were pilot tested with wa ters from 10,000 to 36,000 ppm TDS to produce potable water with a quartz ultraviolet light for biological (disinfection) control. For wet steam generation, the field produced waters(10,000-24,000 TDS) were tested using strong acid/weak acid resin softening with no silica removal in a 1 MM BTU/Hr wet steam generator.1
The overall operational costs were less than normal sequence of processes mentioned in the literature while the capital costs were in the same range. Patents were obtained on the(1) steam stripping softening, (2)silica removal,(3) back pulse on the micro filter and(4) the odor chemical. A patent on the sour gas treatment is pending.