PETROLEUM BRANCH, AIME PAPER Fidelity Union Building NUMBER 106-G Dallas, Texas THIS IS A PREPRINT --- S~T TO CORRECTION Use Of Sewage Effluent As A Water Flood Medium Mattoon Pool, Illinois

By

J. D. Simmons, The Carter Oil Co., Mattoon, Ill.

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This paper is to be presented at the 31st Annual Fall Meeting of the Petroleum Branch of the American Institute of Mining, Metallurgical, and Petroleum Engineers in Los Angeles, October 14-17, 1956, and is considered the property of the Petroleum Branch. Permission to publish is hereby re­ stricted to an abstract of not more than 300 words, with no illustrations, unless the paper is specifically released to the press by the Branch Publications Committee Chairman or the Executive Secretary on his behalf. Such abstract should contain appropriate, conspicuous acknowledgments. Publication elsewhere after publication in Journal of Petroleum Technology 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 Petroleum Branch office; it will be presented at the above meeting with the paper and considered for publication in Journal of Petroleum Technology.

ABSTRACT jected is greater than for similar floods using subsurface brines, and considerable time is re­ The Mattoon water flood, located in south­ quired to control quality, sewage effluent has central Illinois, encompasses 450 acres and in­ proven to be a satisfactory injection water. cludes 28 injection and 32 producing wells. A pilot flood utilizing Pennsylvanian age brine prov INTRODUCTION ed the feasibility of flooding the Mississipian age formations at Mattoon pool. However, since The Mattoon pool, located along the west side usable subsurface brines were limited in availabil of the city of Mattoon, Illinois, was discovered ity, an expansion of the project could be achieved in June, 1940. Development of the pool proceeded only after another source of compatible water was at a moderate pace and was not essentially com­ found. One such source was the effluent from the pleted until 1948. Final development included municipal sewage disposal system of the city of approximately 420 producers and 90 dry holes Mattoon. This effluent carries considerable sus­ drilled on 10-acre spacing. The principal produc­ pended matter in addition to aerobic and anaerobic ing horizons are the Cypress and Rosiclare sands bacteria. Following a series of tests, a satis­ of the Mississippian Chester series. factory treating method was developed, consisting of chlorination, settling, and filtration. A con­ During May, 1952, a 70-acre pilot water flood tract was negotiated with the city of Mattoon to was initiated to evaluate the feasibility of purchase the sewage effluent and injection began flooding the Cypress and Rosiclare sands. Pro­ in May, 1954. duction increases were realized in November, 1952, and by late 1953, results of the pilot indicated During the summer of 1955, additional tests that large-scale flooding would be economically revealed that produced water from the oil wells attractive. Water requirements for the proposed could be mixed with the effluent without addition­ expansion of the project were in excess of that al treating and, during September, 1955, thepro­ available from the Pennsylvanian brine used in the duced water was introduced into the injection sys­ pilot. The only other subsurface water source was tem. Currently, some two ffild one-half million bbl the Devonian limestone, found at a depth of ap­ of sewage effluent have been injected with no per­ proximately 3,000 ft. However, since the Devonian manent plugging of input wells being evidenced. brine was sour, its use would be accompanied by Phosphates, principallY.of iron, resulting from thE relatively high lifting and treating costs, and presence of detergent soaps in the sewage effluent its availability in sufficient quantities to meet continue to form after filtrat~on but are readily ultimate requirements was uncertain. The contin­ removed by periodic acid treatments of the well­ ued agricultural and industrial growth envisioned bores. Although the cost per barrel of water in­ for this area of Illinois will require the bulk of References and illustrations at end of paper 2 USE OF SEWAGE EFFLUENT AB A WATER FLOOD MEDIUM MATTOON POOL, ILLINOIS 706-G the potable surface water availablej consequent. carrying considerable suspended matter and is ly, the oil operators in the Mattoon pool were re­ heavily loaded with aerobid and anaerobic bacte­ luctant to place their needs for injection ~ater ria. Samples of the water were obtained and com­ on this supply. One source of surface water readi­ plete chemical and bacteriological analyses were ly available in adequate quantities was the efflu­ made. The tests indicated that prior to using the ent from the municipal sewage disposal system of sewage effluent, methods must be devised for: the city of Mattoon. Although it was known that this water carries considerable suspended matter 1. Removing the suspended matter along with bacteria, a series of laboratory tests 2. Destroying the living organisms' indicated that by utilizing a rather simple treat­ 3. Reducing the corrosive tendencies of ing method, the sewage effluent could be used. the water 4. Removing any residual suspended solids This paper presents a brief resume of the Mattoon reservoir ch2.racteristics and flood per­ For ease of operation and optimum use of existing Downloaded from http://onepetro.org/SPEATCE/proceedings-pdf/56FM/All-56FM/SPE-706-G/2086340/spe-706-g.pdf/1 by guest on 25 September 2021 formance and describes in detail the problems en­ personnel, it was determined that the most effi­ countered and methods devised to make the sewage cient method of handling the water would be to effluent a satis1'actory flood medium. confine the treating facilities to the injection plant side and, as a consequence, transport the RESERVOIR AND FLUID CHARACTERISTICS raw sewage effluent through 3-1/2 miles of pipe­ line. To prevent the suspende~ solids from The Mattoon pool lies on a north-south trend­ settling in the line, a diameter was selected to ing ar:~ticline at the northern edge of the Illinois insure turbulent flow and yet be large enough to basin. The Cypress and Rosiclare sands, found at avoid excessive pressure and attendant high power subsurface deptns of approximately 1,750 ft and costs. It was determined that an 8-in. ID pipe­ 1,950,ft, respectively, are the principal produc­ line would meet these requirements at the design ing horizons and are the only sands being water throughput rate of 8,000 B/D. flooded. The Cypress sand exists in four distant breaks separated by continuous shale barriers, Filtration tests were conducted to determine over a gross interval of approximately 80 feet. settling and filtration requirements. It was The Rosiclare sand exists as two erratically de­ found that 24-hour settling followed by filtration veloped productive zones. Table I presents perti­ resulted in a water with plugging qualities no nent average rock and fluid data for the two sands worse than those of tap water. Furthermore, 90 The primary producing mechanism for both sands has per cent of the suspended matter settled out in been a solution gas drive. four to six hours, resulting in a water that would not overload a conventional pressure type filter. FLOOD DEVELOPMENT Thus, the bulk of the suspended matter could be removed by providing a pit of 10,000-bbl capacity The pilot project, initiated in May of 1952, which, at an injection rate of 8,000 B/D, would consisted of four producing wells converted to result in a nominal settling~ime of some 30 input duty on a 20-acre, 5-spot pattern, and eight hours. producing wells. Because of sand discontinuity, only 70 surface acres were effectively placed Bacteriological counts showed that aerobes under flood. Flood water was obtained from a averaged 1,150,000/cc and anaerobes 22/cc, none Pennsylvanian sand found at approximately 1,500 ft of which were sulfate reducers. Tests with var­ subsurface. This brine was produced by a conven­ ious bactericides revealed that chlorine was the tional beam pumping unit and the water was filter­ most suitable. Dosages of 8 ppm or less chlorine ed through a pressure type anthracite filter prior were found to have little effect on the bacterial to injection. Injection averaged approximately count. However, 20 ppm resulted in a reduction 850 B/D, with surface pressures of 550 psig. from the 1,150,000 aerobes/cc to less than 10/cc. First gains appeared six months after initial in­ On the basis of these results, a dosage of 20 ppm jection, or during November, 1952, and first ex­ chlorine to achieve initial kill was recommended. pansion to the project occurred in May, 1954. Additional studies were undertaken to determine the residual chlorine content and the number of bac­ DETERMINATION OF SUITABILITY OF SEWAGE EFFLUENT teria remaining in the water as a function of time AS A FLOOD MEDIUM following a dosage of 20 ppm. It was found that of the 20 ppm chlorine added, 16 ppm were removed Prior to the first expansion, an additional within 10 minutes, presumably by the oxidation of sour~e of injection water was needed. After ex­ H2S and/or organic matter. It was also determined ploring and discarding the possibility of using that following an initial dosage of 20 ppm the sour Devonian brine, the city of Mattoon was con­ water remained effectively sterile if a residual tacted regarding the use of effluent from the chlorine content of 2 ppm were maintained. municipal sewage disposal plant. Mattoon is a city of some 18,000 persons and has' a sewage Corrosive tendencies of the water were found through-put averaging 54,000 B/D. The plant uses to be approximately 10 mdd or less than 0.002 IPY an activated sludge type treatment with primary and, as a consequence, use of corrosion inhibitor and final clarification, which yields an effluent 706-G J. D. SIMMONS 3 was deemed unnecessary. views of the treating system are shown in Fig. 2.

Filtration to remove the residual suspended Following post-chlorination, the effluent solids could be accomplished by the use of two passes through two rapid sand filters containing pressure type filters utilizing anthracite media graded anthracite filter media, through a master at a filtration rate of less than 3 gpm/sq ft of meter, and into the clearwell tank. The treated filter area. effluent from the clearwell flows by gravity into a suction supply header for two horizontal triplex SYSTEM DESIGN pumps whose operation is automatically controlled by electrodes suspended in the clearwell tank. A Based on the foregoing field and laboratory pressure type regulator provides a by-pass to the tests, an injection water system was installed. suction header and thereby controls discharge pres As shown in Fig. 1, it is composed of three major sures. In addition, safety relief valves prevent parts: a supply system, a treating and pumping exceeding rated pressures. To prevent freezing in station, and a distribution system. The sewage the pump and header building, temperature is main­ Downloaded from http://onepetro.org/SPEATCE/proceedings-pdf/56FM/All-56FM/SPE-706-G/2086340/spe-706-g.pdf/1 by guest on 25 September 2021 effluent is obtained from a sump following sludge tained above 400 F. treatment by the City and is pumped through ap~ proximately 3-1/2 miles of B-in steel line to the The distribution system is constructed of a waterflood treating plant. In addition to main­ cement-lined steel pipe buried at a depth of 30 taining turbulent flow, to combat the build-up of in. to avoid freezing. Further freeze protection suspended SOlids, scraper traps were installed is provided at the input wellheads by the use of and line clean-out with a flexible wire brush­ insulation-filled wooden boxes containing all the type of scraper is performed every three months. aoove-ground connections. The supply pump at the City plant is operated through a time clock, regulated to avoid pumping OPERATION at times the City p1ant experiences flash indus­ trial loads resulting in a poor quality effluent. QUALITY CONTROL The time clock is adjusted to meet major changes in water requirements such as those occurring Following the start of sewage effluent in­ when the flood Is expanded. jection, a program of water sampling and testing was set up to assure satisfactory water quality. Treating, settling and pumping are accom­ Basically, tests are required to determine: (1) plished at the plant site centrally located in sediment content; (2) residual chlorine content; the Mattoon pool. Sewage effluent arriving at (3) bacterial content; and (4) corrosiveness. the plant passes through the chlorinator building into the settling pit. Two semi-automatic chlori Sediment concentration is determined by use of nators, using gaseous chlorine obtained in 150-lb a squeese type test filter using pre-weighed fil­ cylinders, are used for chlorination prior to and ter papers. Test samples are obtained at the fol­ following settling. Pre-settling chlorination is lowing locations: at the rate of 20 ppm chlorine and is sufficient to destroy the bacteria. Following the removal (a) Sewage effluent entering pit following of suspended solids by settling in the pit, the pre-chlorination; water is again treated with chlorine to insure a (b) Settled water entering filters following residual chlorinecontent'of 2 ppm. Since chlo­ post-chlorination; rine hydrate forms at temperatures below 490 F, (c) Filtered water entering clearwell; which would cause interruption of the chlorine (d) Injection water leaving station; operation, the chlorinator building is insulated (e) Injection water at the wellheads of and heated during cold weather to maintain a two key inputs. temperature of 600 F. As a safety precaution, gas masks are readily available and exhaust fans In additionl, periodic checks have been made controlled from outside the building have been with a standard turbidimeter. This instrument installed. measures the diffusion or' light through the water sample, calibrating the answer in terms of the The 10,OOO-bbl settling pit, with dimensions equivalent diffusion of Si02 in distilled water. of 113 ft x 113 ft x 7 ft, was constructed with The turbidity of the sewage effluent ranges from 2-1/2-iri. thick "Gunite" type cement reinforced 21 to 56 ppm Si02 equivalent, and averages 30 ppm with 4ft x 4 ft steel mesh. A concrete pit was of Si02 equivalent. The filtered water, after selected rather than an earthen sump to avoid con treatment, has turbidity ranging from [) to 20 ppm tamination of the water with silt. A baffle of Si02 equivalent, with a maximum of 20 ppm Si02 cypress wood extends two-thirds of the length of equivalent having been found to be the minimum the pit, resulting in the water traveling approxi quality acceptable. Should unsatisfactory water mately twice the length of the pit before it is be encountered, the system is shut down and the pumped into the filters. In addition, the en­ pit cleaned. Cleaning the pit each Spring has trance section of the pit is divided by a spread­ been found adequate. The eight-inch line is clean­ er weir which encourages diffusion of the incom­ ed every three months by pumping a scraper from the ing water and provides a sediment trap. Selected treating end back to the sewage plant and allowing 4 USE OF SEWAGE EFFLUENT AS A WATER FLOOD MEDIUM MATI'OON POOL, ILLINOIS 706-G thfs water to enter the City disposal system. meet the increased demand, and residual chlorine Residue obtained on xhe pre-weighed filter papers content dropped from 2 ppm to zero. To avoid a using the squeeze test filter, are occasionally recurrence and to sterilize the eight-inch pipe­ sent to a laboratory for qualitative and quantita­ line which had probably become a bacteria breeding tive analyses. Solids are reduced from an average ground, a chemical pump to inject sodium hypochlo­ of 50 Ib/l,OOO bbl in the untreated water to less rite into the supply line was installed at the than 5 Ib/l,OOO bbl in the injection stream. City sump. Hypochlorite is injected at this point whenever the tests at the injection station indi­ Chlorine content is determined by use of a cate that water quality is falling and chlorine residlffil chlorine comparator which determines demand will exceed the ability of the chlorinators chlorine concentration by a visual color inspec­ to restore sterility. tion. Water is sampled daily from the following locations: FORMATION OF PRECIPITATES WITHIN THE Downloaded from http://onepetro.org/SPEATCE/proceedings-pdf/56FM/All-56FM/SPE-706-G/2086340/spe-706-g.pdf/1 by guest on 25 September 2021 (a) Downstream from pre-chlorinator (minimum INJECTION SYSTEM 20 ppm); (b) uPstream from post-chlorinator; Use of the sewage effluent began duriniS May, (c) Downstream from post-chlo~inator (minimum 1954. Within one month, a soft deposit of fine 2 ppm); yellow-colored material was found in the discharge (d) At the wellhead farthest from plant (min J of one of the pressure type filters. Chemical ana- imum 2 ppm). lysis revealed that it was primarily iron oxide, aluminum oxide, and iron phosphate. It was 95 per If the water is found to be below the standr cent soluble in dilute and 19 per c~nt hydrochloric ards set, the rate of chlorine injection is in­ acid. Deposits of similar material have been, and creased. This occurs when the effluent delivered are now being, found throughout the entire system, by tbe City suffers a decrease in quality, which including input well tubing and in water backflow- is fairly frequent in the summer months. During ,ed from input well sand faces. A representative warm weather, optimum conditions for bacteria . analysis of this material is shown in Table II. growth occur and, furthermore, the City plant ex­ The phosphates are thought to be a result of deter periences increased throughput. gent soaps used in both home and commercial laun­ dries. 'Tests of additional filtration using a Bacteriological tests are conducted every diatomaceous earth type filter-aid did not appre- three months to determine if any strains of bac- ciably reduce the amount of this very fine precipi teria are building up an immunity to the chlorine tate. The problem has been accepted as one best treatment. Samples are obtained and tested for controlled by periodic acid ~reatment of the input aerobic, anaerobic, and sulphate reducing bacteria wells. at the following locations:

(a) After pre-chlorination; Beginning in August, 1955, a program of input (b) After' post-chlorination; well testing·was initiated to determine if any per. (c) At several key injection wells. . meability impairment was occurring near the well- ; bore. Using concepts developed by the. Carter Re- . To date, no decrease in the effectiveness of search Laboratory, A; F. Van Everdingenl and S. T. chlorine gas as a bactericide has been found. Yuster,2 relating to analysis of pressure fall-off data and well injection histories, it has been Corrosion rates are determined by weighing determined that no permanent plugging of the sand standard 1-1/4 in. x 5 in~ mild steel coupons ex­ faces is occurring. posed in the system at the following locations: ADDITION OF PRODUCED WATER TO (a) Ahead of the pre-chlorinator; SEWAGE EFFLUENT (b) Leaving the station; (c) At the wellhead of various key inputs; During the Summer of 1955, another series of (d) Down the hole in the key inputs. tests was conducted to deterimne if the produced Cypress and Rosiclare brines could be mixed with These tests were conducted every three months, treated sewage effluent for re-injection. Pro­ initially. Since no significant change in corro- duced water had been handled by segregated injec- sion rates has been found, and all are below 10 tion into a limited number of waterflood input mdd, no corrosion inhibitor is used and the fre- wellS, with the excess being eliminated by surface quency of testing has been reduced to semi-annual- evaporation and injection into a salt water dis­ lYe posal well. However, water producing rates were approaching the capacity of existing facilities. At only one time has the water quality fallen The principal problem in returning the two waters below the prescribed standards. This was in June, to a co~on injection system was the control of 1954, when the City treating plant was overloaded calcium carbonate precipitation. The calcium-bi­ and essentially raw ,sewer water was delivered for carbonate ratio in the combined produced water is several days. The chlorinator capacity could not high, tending to result in super-saturation of 706-G J. D. SIMMQNS 5 calcium carbonate. However, the sewage effluent REFERENCES is high in bicarbonates and it was postulated that a mixture of at least eight parts sewage water to 1. Van Everdi?gen, A. F.: "The Skin Effect and two parts produced water would help prevent super­ Its Influence on the Productive Capacity of saturation of calcium carbonate and its eventual a Well," Trans. AIME, (1953) 198,171. precipitation in the injection system. 2. Yuster, S~: "Graphical Prediction of Water Flooding Intakes," Prod. Monthly, (Nov., Field tests were conducted using a scale model 1945). of the settling and treating system. Water quality was determined by observing plugging teniencies of the water in alundum cores having permeabilities representative of the horizons being flooded; i.e., from 50 to 100 md. Several tests 'of various mix tures, ranging from 10 per cent brine and yo per Downloaded from http://onepetro.org/SPEATCE/proceedings-pdf/56FM/All-56FM/SPE-706-G/2086340/spe-706-g.pdf/1 by guest on 25 September 2021 cent effluent to 50 per cent brine and 50 per cent effluent, were run. Further tests with various brine-effluent mixtures, treated with alum in con­ centrations of 12 to 24 Ibll,OOO bbl of water were made. A final series of tests were performed on alum-treated mixtures which had been given addi­ tional filtration through a diatomaceous earth filter.

Results of the testing indicated that mixtures consisting of up to 20 per cent produced water had equal or slightly lower plugging tenden~ies than 100 per cent sewage effluent. Both the addi­ tion of alum and further filtration through dia­ tomaceous earth reduced plugging tendencies only slightly. Since the improvement in water quality is so slight, the additional investment for en­ larged treating facilities is not justified.

By July 1, 1956, a total of 3,540,000 bbl of water had been injected, of which approximately 2,600,000 bbl were sewage effluent. Current in­ jection averages 4,000 BID with surface injection pressures of up to 880 psig. Accumulated oil gains exceed 400,000 bbl, with June, 1956 production averaging 1,200 BID, of which 1,100 BID is the increase over normal primary.

COSTS

The cost of" injection water at Mattoon has ranged from $0.035 to $0.055/bbl of water, includ­ ing depreciation. Currently, water is being in­ jected at a cost of approximately $0.04/bbl, which is 30 to 40 per cent more than the cost of water at floods of similar size in the area using sub­ surface brine. The sewage effluent cost is greater because of treating expense, including depreciation of the additional investment in treating facili­ ties, and because the operating problems accompany­ ing its use require considerably more time of engineering and operating personnel. However, by devoting the necessary time and money to achieve and maintain proper water'qua~ity, it has been possible to utilize the sewage effluent as a satis­ factory waterflood medium. TABLE I

RESERVOIR AND FWID ANALYSES MATTOOO WATER FLOOD

Core Ana.l.ysis CyPress Rosiclare Porosity - Per Cent 20.1 14.1 Per.meabilit,r - Md 54 97

Estimated Connate Water - Per Cent 35 30 Downloaded from http://onepetro.org/SPEATCE/proceedings-pdf/56FM/All-56FM/SPE-706-G/2086340/spe-706-g.pdf/1 by guest on 25 September 2021

Fluid .Ana.J;r!is

Original Reservoir Pressure - PSIG @ Subsea DatUll 707 @ 1,037' 780 @ 1,200' Saturation Pressure - PSIG 707 450 Reservoir 'l'emperature _ 0 F 85 90 Solution Gas-Oil Ratio - Cu. Ft. per Bble 322 196 Fannation Volume Factor 1.209 1.130 Viscosity @ Original Reservoir Conditions - Cp 1.63 2.00 Viscosity @ Atm. !-'ress. & Reservoir Temp. - Cp 4.32 5.06 Oil GraVity - 0 A.P.I. 39 39

TABLE II

TYPICAL ANALYSIS UF PRECIPITATES FORMED AFTER WATER 'tREATMENT MATTOON wAitH FLOOD

Constituent Weight Per Cent Iron Phosphate 21 Iron Oxide 31 Aluminum Oxide 17 Calcium Oxide 2 Calcium Carbonate 2 Calcium Chloride 3 Calcium Sulfate 2 Silica 1 Acid soluble organic compounds and water of hy"dration 21

Tot a 1 • • • • • • •• 100 MATTOON WATER FLOOD PLANT MATTOON POOL, ILLINOIS

OVERALL PLANT INSTALLATION Downloaded from http://onepetro.org/SPEATCE/proceedings-pdf/56FM/All-56FM/SPE-706-G/2086340/spe-706-g.pdf/1 by guest on 25 September 2021

10,000 BBL. SETTLING PIT

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