Experimental and Calculated Relative Permeability Data for Systems Containing Permeability Data for Systems Containing Tension Additives American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. This paper was prepared for the Improved Oil Recovery Symposium of the Society of Petroleum Engineers of AIME, to be held in Tulsa, Okla., March 22–24, 1976. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made. provided agreement to give proper credit is made. 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. Abstract In order to predict recoveries for low tension waterfloods, one must have information on the relative permeabilities of oil and water under conditions approaching miscibility. In this study relative permeability data were obtained by two conventional methods, the displacement method and the steady-state method, in fired Berea cores for a crude oil-water system containing tension reducing additives (surfactants). Four surfactants were utilized, two being preferentially water-soluble and the other two being preferentially oil-soluble but not to the same degree. From the measured data, equations were developed for calculating relative permeability data for the systems examined. As a test, the equations developed were utilized in a one-dimensional reservoir simulator program for computing laboratory waterflood performance. The comparison given in the paper shows that the calculated values were in good agreement with the measured results. Introduction In order to mathematically simulate laboratory waterfloods one must have accurate relative permeability data. These data are usually obtained in one of several ways, namely,Direct MethodsSteady-StateDisplacementStationary-PhaseNuclear Magnetic ResonanceIndirect Methods (by calculation, using proven equations)Naar-Wygal EquationsLand Equations The direct methods, as listed above, are much preferred over the indirect methods; however, a complete set of relative permeability data is rarely found.
Distinguished Author Series articles are general, descriptiverepresentations that summarize the state of the art in an area of technology bydescribing recent developments for readers who are not specialists in thetopics discussed. Written by individuals recognized as experts in the area, these articles provide key references to more definitive work and presentspecific details only to illustrate the technology. Purpose: to informthe general readership of recent advances in various areas of petroleumengineering. Introduction An essential key to a successful waterflooding project is a well-planned andwell-executed program of surveillance and monitoring. This program should betailored to address individual projects or fields because each waterflood willhave different characteristics. There are, however, some basic ingredients thatshould be common to all surveillance programs. In general, three majorcategories of field conditions must be included in any waterflood surveillanceprogram: reservoir conditions, injection/production-well conditions, andfacilities/operating conditions. The last and probably the most importantingredient is record keeping/performance control. There are, of course, economic conditions that must be taken into consideration. For the purposes ofthis paper, however, only the technical aspects of a waterflood surveillanceprogram will be addressed. The purpose of this paper is to provide an overviewof waterflood surveillance programs and to outline the various items to bemonitored. Selected tests for diagnosis of problems commonly associated withwaterfloods are discussed briefly, along with a look at developing surveillancetechnology. Surveillance Program Waterflood surveillance programs of the 1980's have been influenced to somedegree by the chemical waterflood projects of the 1970's. The desire tounderstand chemical-recovery-process applications better led to a significantincrease in project surveillance activities. Much time and effort was spent inevaluating both waterflood and tertiary recoveries. It was shown that byclosely monitoring field activities, improvement in waterflood recoveries couldbe achieved. Fig. 1 shows the key monitoring points in the traditionalwaterflood cycle. There was a time when most of the attention given awaterflood project focused on reservoir performance, and this usually waslimited to monitoring water cuts. Today we realize that it is equally importantto include well, facilities, and operating conditions in our surveillanceprograms. Thus, all the components of the waterflood cycle diagrammed in Fig. 1should be included in a well-planned surveillance program. Table 1 lists itemsthat should normally be included in the three major categories of surveillance. This is by no means a complete listing because waterfloods can have ratherunusual characteristics or conditions requiring additional items forobservation and evaluation-e.g., environmental and regulatory conditions. Reservoir Surveillance As listed in Table 1, reservoir pressures, injection and production rates, fluid volumes, WOR/GOR's, and fluid samples require constant surveillance. Adiscussion of these items and proposed schedules for obtaining the data waspresented by Barnes and Tinker. When these data are coupled with thereservoir-description information, waterflood-performance calculations can bemade. Reservoir-description information generally includes core, well log, andgeologic data. Holbert and Zeito list the reservoir-description data in moredetail. Numerous methods or techniques for estimating waterflood performancehave been reported in the literature. These methods range from the classictypes to sophisticated reservoir simulator models. There are four types ofwells requiring surveillance: production, injection, water-supply, andwater-disposal wells. Of these, production and injection wells require the mostattention. Monitoring well performance requires a program of selected welltests to be conducted regularly. The types of well tests selected will dependon surface/downhole equipment, well-completion characteristics, produced orinjected fluids, the stage of the waterflood project (early, middle, or late), and the reservoir description. Key items for surveillance are fluid entry intoor exit from target zones, cement/completion integrity, and mechanicalequipment, both downhole and surface. Well testing is discussed later. The wellsurveillance program should include plans for recording the information in asuitable manner or format such that it is both easily accessible and "userfriendly." Finally, the program should provide a systematic approach to dataanalysis, evaluation, recommendations, and corrective measures, as needed. Facilities/Operations Surveillance Waterflood operating procedures and conditions, along with the associatedproject facilities, are often taken for granted, yet they are key ingredientsto successful project management. Tinkers reported on the operating factorsthat affect waterflood performance, including well completions, injectionpatterns, high-volume lift, injection profiles, and bottomwater production. Operations and facilities vary considerably from project to project and undergochanges during the several stages of waterflood development. Injection-patternconfigurations, surface topography, reservoir characteristics, deviated wells, and field operating constraints are only a few of the conditions that can leadto problems associated with project management.
In late 1973, Mobil Producing Texas and New Mexico Inc. and Mobil Research and Development Corp. initiated a cooperative, low-tension waterflood (LTWF) project in Mobil's West Burkburnett waterflood, Wichita County Regular field. TX. The LTWF project encompasses ten 20-acre, five-spot patterns. A low-concentration surfactant slug was injected from Oct. 1975 to June 1976, followed in turn by biopolymer and freshwater drives. Tertiary oil production response first was noted near the completion of surfactant injection. and, to date, 17 of the original 20 producers are yielding incremental oil. Four producing wells outside the LTWF area have also shown some oil production response. The total tertiary oil production to the end of 1980 (actual) and to anticipated project termination in 1984 (projected) are estimated to be 238,000 and 320,000 bbl, respectively-equivalent to recovery factors of 17.6 and 24% of the OIP at project initiation. These figures pertain to total oil production, since the project area would have been abandoned if the LTWF project had not been initiated. To the end of 1980, the oil recovery attributed directly to effects of the LTWF process is 105,000 bbl, that projected to the anticipated project termination in 1984 is 180,000 bbl. The corresponding recovery factors are 8 and 13%, respectively. This paper summarizes the engineering studies associated with this chemical waterflood field test. Introduction Mobil's West Burkbunett waterflood is about 4 miles southwest of Burkbunett (TX) and is classified in the Wichita County Regular field. The pool discover)/ well was C. Schmoker No. 1. completed in June 1912. The producing sand is found at 1,600- to 1,800-ft depth and is designated the Gunsight sand in the Cisco series of Pennsylvanian age. The structure of the Gunsight sand in the area is lenticular, with the major axis running east and west. The sand dips approximately 250 ft from the south to the north. The producing sand is interspersed with shale and lenses into shale on all sides of the pool. Waterflooding began in 1944 with a pilot flood developed on 20-acre five-spot patterns. Expansion to full development occurred during 1948–50. The current waterflood is a group of 100% Mobil working-interest leases being waterflooded on a cooperative 20-acre five-spot pattern arrangement. In 1971, all the leases in the waterflood project either had become uneconomical to operate or were being projected to reach the economic limit by 1972 or 1973. Several leases on the east side of the project already had been abandoned. As a final step in exploitation. the project was evaluated for tertiary recovery by our LTWF multislug process. The functions of each of these slugs have been described by Foster and by Murphy et al. Plans were developed for application of the LTWF process in 10 adjacent, 20-acre patterns with 10 injectors, 20 producers, and 2 observation wells. This 200-acre development is shown in Fig. 1 as the enclosed area on a partial field map. Mobil Producing Texas and New Mexico operated the project, with personnel from Mobil Research and Development serving as technical consultants. The LTWF project began in Nov. 1973 with a freshwater preflush. Injection of the surfactant slug started in Oct. 1975 and ended in June 1976. This was followed by a polymer drive until April 1978. Since then, fresh water has been injected and is continuing. The injection schedule of this chemical flood is summarized in Table 1. From 1974 through 1977, an injection rate of approximately 3,000 B/D into 10 injectors was being maintained. JPT P. 2495^
A test of a low-tension waterflood process was conducted in a single five-spot pattern in the Salem field. The presence of a regional pressure gradient across the pattern is believed to have caused migration of injected chemicals and displaced oil from the pattern area, resulting in less encouraging recovery than had been anticipated. Introduction A comprehensive discussion of the results and performance of the Salem Unit low-tension waterflood pilot has performance of the Salem Unit low-tension waterflood pilot has been presented by Whiteley and Ware and Widmyer et al. Their papers present an overview of the project and the basic data relating to the execution and performance of the pilot. As is frequently true of pilot tests, conditions and performance did not conform to expectations in all respects, and Widmyer et al. conclude that inadequate or incomplete pore flushing and high surfactant retention ted to lower-than-expected oil recovery. Although the data and methodology leading to their interpretation are presented, they also recognize alternate interpretations presented, they also recognize alternate interpretations that may apply to part of the data. This paper presents alternative interpretations of those results, particularly relating to surfactant adsorption and fluid flow in the test area. Specifically, the interpretations described here indicate that surfactant retention was significantly less than the value arrived at by Widmyer et al. and that the less-than-planned oil recovery resulted from migration of injected and displaced fluids out of the test pattern. This migration was affected by a prevailing pattern. This migration was affected by a prevailing pressure gradient across the test pattern and possibly was pressure gradient across the test pattern and possibly was aggravated by operating one or more of the injectors at pressures sufficient to sustain fracture-open conditions. pressures sufficient to sustain fracture-open conditions. Test Description The Salem low-tension waterflood test is being conducted in the Salem Unit, Marion County, Ill. The test reservoir is the Benoist sandstone, which essentially is at waterflood residual oil saturation (about 30 percent). Further details of reservoir characteristics have been reviewed previously. The experimental pattern is a 5-acre, normal five-spot centered in an existing 20-acre waterflood pattern. The secondary injectors are operated as backup injectors to confine the tertiary flood chemicals. There are two observation wells located on one of the direct lines between a tertiary injector and the producer to provide data on chemical transport, stratification, and oil provide data on chemical transport, stratification, and oil cut. The producer served earlier as the secondary producer; all other wells are new completions. Fig. 1 is a plat of the test area, The low-tension waterflood process is a multislug process; the slug sizes and constituents used in the Salem process; the slug sizes and constituents used in the Salem Unit are summarized in Table 1. Slug a-1 serves to displace the saline, divalent, ion-containing formation water that is not compatible with the surfactant. The carbonate and phosphate in Slugs a-2 and a-3 precipitate any remaining divalent ions and serve as sacrificial adsorbents to minimize surfactant retention. The sodium chloride provides a salinity level that yields optimum interfacial-tension behavior by the surfactant. Slug b, the surfactant slug, mobilizes the secondary residual oil. Slug c is a mobility-control slug that precludes fingering of the Slug d drive water through the surfactant and oil banks. Nonadsorbing tracer chemicals were injected into the injection quadrant containing the observation wells during Slugs a-2 and b and into the other three quadrants during Slug b only. JPT P. 1380
Previously published preliminary evaluations of a low-tension waterflood Previously published preliminary evaluations of a low-tension waterflood pilot reported less-than-expected oil recovery, partly the result of flow pilot reported less-than-expected oil recovery, partly the result of flow path distortion. Based on data from postflood tracer tests, tertiary path distortion. Based on data from postflood tracer tests, tertiary recovery was 37 to 43 % of the oil in the affected reservoir volume. Causes of the distortion and production shortfall are discussed. Complete reservoir definition when designing tertiary floods is necessary. Introduction In 1974, a joint Texaco Inc.-Mobil Research and Development Corp. test to evaluate a low-tension waterflood (LTWF) process was initiated in the Benoist sand at Salem Field, Marion County, IL. The process used a sequence of freshwater preflush, process used a sequence of freshwater preflush, chemical pretreatment, surfactant solution, a mobility-control (polymer) solution, and field brine. Descriptions of the process, its implementation, and preliminary evaluations are found in earlier studies. preliminary evaluations are found in earlier studies. Tertiary oil recovery was less than expected from the original flood plan, and various explanations of the flood performance were proposed. To provide additional information, further testing began in 1976. This paper describes the results of those tests and presents revised evaluations of the Salem LTWF pilot performance. pilot performance. Review To summarize pilot test performance briefly, the Salem LTWF program was designed to provide balanced injection with symmetrical fluid flow distribution in a 5-acre (20 x 10(3) m2), normal five-spot pattern. Four existing backup injection wells on 20-acre (81 x 10(3) m2) spacing (Fig. 1) were used to help confine the injected chemicals to the pilot area and to increase effectiveness of chemicals in the pilot. Studies indicated that 50 % of the injected chemicals should displace tertiary oil to the producing well, with the balance exiting the pattern.Oil recovery was substantially less than expected, only about 25 to 30 % of the recovery predicted using the concept of symmetrical displacement in all pattern quadrants, with recovery factors based on pattern quadrants, with recovery factors based on earlier laboratory investigations. Various explanations for the production shortfall were considered, including lower-than-expected oil displacement efficiency for the chemical system or a smaller pattern reservoir volume that actually was flooded and contributed to oil production. If the tertiary oil originated from a smaller swept reservoir volume, then the recovery efficiency assigned to the process obviously would be larger than that process obviously would be larger than that associated with a larger swept volume. Postflood Tests Postflood Tests To resolve the questions raised in preliminary evaluations, and to define better the amount of tertiary chemicals captured and the reservoir volume contributing to oil recovery, further testing began in 1976. A major goal of the postflood testing program was to ascertain whether flow path distribution was symmetrical (as intended) or distorted. Accordingly, for 1 month different tracers were injected into the respective injectors of the north and south quadrants. Response was measured using producing well samples. JPT P. 1185
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