Salt Cement for Shale and Bentonitic Sands

KNOX A. SLAGLE HAlLIBURTON CO. DWIGHT K. SMITH DUNCAN, OKLA. MEMBER A/ME

ABSTRACT water from the producing zones. However, the addition of salt to the mixing water for this specific application The application of salt for primary cementing in the was rarely considered, and only scattered uses are recorded. Downloaded from http://onepetro.org/jpt/article-pdf/15/02/187/2214379/spe-411-pa.pdf by guest on 29 September 2021 past has been restricted largely to salt formations. Recog­ nition of its value in cementing through fresh-water­ Perhaps the earliest significant use of salt cement sensitive shales and bentonitic sands has recently brought appeared in the Williston basin area of North Dakota and about wide usage. Montana. The problem of collapsed casing and tubing in salt sections and investigation of the reasons for this made Formations of this latter type from different areas have it a logical consideration. Here the application was to been sampled and tested for the applicability of salt provide good bonding to salt sections. Previous develop­ cement with emphasis on improved cement-formation ments in blending equipment made the dry blending of bonding and minimization of formation deterioration by salt with the cement practical for the first time. Tests water contact. Field surveys indicate this economical addi­ revealed that granulated salt added to the dry cement tive has helped to reduce remedial work and to greatly in sufficient quantity to saturate the mixing fluid was a improve the success of primary and squeeze cementing practical approach to overcome previously objectionable jobs. features. Wellhead sampling showed that the mixing pro­ A study has also been made of the effects of various vided by pumping equipment resulted in solubilization of concentrations of salt in cement systems and how these the salt before entering the wellhead. Today, practically concentrations modify their slurry properties. all saIt used in oilwell cementing is dry-blended with cement before delivery to the wellsite. INTRODUCTION In studying troublesome and often expensive squeeze The application and use of sodium chloride in oilwell jobs in shaly zones, salt cement was again given con­ cementing dates back over a decade. The initial recorded sideration. Success with squeeze cementing in shaly sec­ use of salt with cement appeared in the completion of tions in Southern Oklahoma might be considered the wells through salt domes along the Gulf Coast in the initial application of salt slurries for shales and bentonitic 1940's. In the absence of bulk blending facilities, salt was sands. added to the mixing water prior to mixing with cement. The use of salt has many unique properties for oilwell This practice was followed to help provide better bonding cementing. Ludwig' described the general effects of salt to salt formations, as illustrated in Fig. 1. Here it can be on cement and the basic chemistry involved when cement seen that the fresh-water slurry has dissolved a portion reacts with sodium chloride in concentrations ranging up of the salt, resulting in no bonding between the two, while to saturation of the mixing water. More recently, Beach' the salt-saturated slurry causes no solution problem and recognized the benefits of smalI quantities of salt in gel permits contact and bonding of cement and salt. The cements. Salt produces two opposite effects on the setting addition of sufficient sodium chloride to provide a sat­ of cement, depending on the concentration. In low per­ urated solution for mixing cement required considerable centages salt has an accelerating effect on cement and time and expense to the operator. Foaming, which was provides shorter pumpability and greater early compressive encountered during the mixing of salt water, necessitated lReferences given at end of paper. development of anti-foam agents and it became fairly com­ mon to add 1 pt of tributylphosphate /10 bbl of salt water to minimize this nuisance. These operational difficulties and misunderstanding of the effect of salt in cement systems probably account for the long delay in widespread use of such slurries. Another application of brines for mixing cement oc­ curred when early cementers found that certain shaly formations could be more effectively squeezed when using

Original manuscript received in Society of Petroleum Engineers frffi cc Sept. 4, 1962. Revised manuscript received Nov. 30, 1962. Paper pre­ sented at 37th Annual Fall Meeting of SPE, Oct. 7-10, 1962, in Los Angeles, Calif. Discussion of this and all following technical papers is invited. Dis· Fresh Water Slurry Saturated Salt Slurry cuss ion in writing (three copies) m ay be sent to the office of the Journal of Pet'roleu1n Technology. Any discussion offered after Dec. 31, 1963, should be in the form of a new paper. No discussion should ex­ ceed 10 per cent of the manuscript being discussed. FIG. I-BONDING OF CEMENT TO ROCK SALT.

FEBRUARY, 1963 187 strength. Salt saturation has an opposite effect on most mary cementing job. Each of these properties will be con­ slurries in that it provides longer thickening times and sidered in detail. slower strength development. For deeper wells, where higher temperatures are encountered (140 F and upward), TYPE OF SALT RECOMMENDED FOR this is a decided advantage. SALT CEMENT The principal benefit of salt cement evolves not from Salt is a commodity that is readily available in many its accelerating, dispersing or retarding properties but, parts of the world, and it is found in a variety of grades. rather, because of its influence on clay minerals, which Two general properties should be considered when select­ represent a predominant portion of shales and exist in ing a material for use in cement-fineness and amount of various quantities in sands and other producing formations. insoluble material. Excessively coarse particles may create Formation brines normally cause these minerals to be pres­ too slow a solubility rate, particularly in shallow wells and ent in a flocculated and unexpanded state. Introduction when using a saturated slurry. Extremely fine particles are into the system of water-base fluids of low ionic content subject to caking when handled in bulk or under pro­ will often cause deflocculation and expansion of the clays, longed storage. Generally, a material having a 20- to particularly those water-sensitive ones such as montmoril­ 100-mesh size is specified for dry-blending in oilwell lonite, illite and chlorite. These occurrences can result cements. Impurities or insolubles should be as low as in permeability damage to "dirty" sands and varying possible to minimize the presence of sulfates which may degrees of formation disruption in shales or zones where be detrimental to sulfate resistance of a cement. When shales predominate. Formation disruption can be a prob­ considering field brines for mixing with cements, tests lem because a flow channel may be created that can should be made prior to use to determine the per cent Downloaded from http://onepetro.org/jpt/article-pdf/15/02/187/2214379/spe-411-pa.pdf by guest on 29 September 2021 affect satisfactory zonal isolation. of salt and impurities. Waters containing more than 2,000- While a cement slurry contains a lime- (calcium hydrox­ ppm sulfates when mixed with cement could have a detri­ ide) saturated water, the extremely low solubility of this mental effect on durability. The presence of calcium chemical results in relatively low ionic content but does chloride in the brine might produce an undesirably short contribute to clay flocculation by maintaining a high pH. pumping time. It is probable that the improvement in formation compe­ tency noted with salt cement slurries is due to the influence RETARDATION AND ACCELERATION of both the pH control with lime and the ionic content created by the addition of sodium chloride. We have also In low concentrations salt is an accelerator, while above found that other inorganic salts in sufficiently high con­ approximately 12 per cent salt in the water, it functions centration can reduce the amount of deflocculation and as a retarder-except with the API Class E Cements. This formation deterioration - although, for the most part, effect may be best illustrated with Table 1 and Fig. 2. At neither as effectively nor as economically as sodium chlo­ low temperatures (60 to 120 F) when used for primary ride, while posing other problems with respect to proper­ cementing, 5 to 10 per cent salt by weight of mixing water ties of the cement slurry. An excellent study of clay may be used if the particular formations are compatible minerology has been published by Moore" which, while not with this low concentration and if sufficient placement time concerned with cementing slurries, does discuss some of is available. At higher temperatures (140 to 260 F) this these problems with other fluids. low concentration could cause too much acceleration, and concentrations of salt from 15 to 37 per cent by weight TESTING OF FORMATION SPECIMENS of water are commonly employed. For saturation of a slurry, 3.1 Ib of salt are used for each gallon of mixing Thus far, testing of samples of formation for the appli­ water to provide saturation at 140 F. Quantities of salt for cation of salt cement has been by immersion in various several different compositions are shown in Table 2. cementing slurries of several salt contents, rather than in Beach' recently reported on the dispersing action and either a salt solution or cement filtrate. After the cement acceleration gained from small concentrations of salt in has hardened, observation of the effects is made visually. gel cement. While not as effective as calcium chloride as Fig. 3 indicates the progressive improvement in formation an accelerator, 2 to 5 per cent salt water does offer bene­ integrity for a shaly formation with increasing concentra­ ficial properties in low-temperature cementing. Sea water tion of salt in the cement slurry. Substantial disintegration and many field brines contain chloride concentrations of the shale can be noted with the fresh-water slurry. In equivalent to these values (Table 3) and also have an all tests conducted to date, there have been no formation accelerating effect on cement (Fig. 2). specimens evaluated which have not reacted satisfactorily with a salt-saturated slurry, and those containing the clays The acceleration effect can be observed in the following comparison. most subject to expansion have required saturation in order to maintain competency. Some formations have been Compressive found to provide good results with salt content as low as Thickening Time Strength 10 per cent by weight of the slurry mixing water, and in at 6,000 ft 100 F, 24 hr (psi) Closs A Ceme.lt-Fresh Water 2:41 2,108 these cases selection of a slurry has been based on other Class A Cement-Sea Water 2:07 3,145 factors, such as acceleration or retardation properties, which could be of benefit. SALT AS WEIGHT MATERIAL In deep wells, cement slurries are often saturated with GENERAL EFFECTS OF SALT ON CEMENT

TABLE l-EFFECr OF SALT CONCENTRATIONS ON THICKEN'ING TIME While not considering specific quantities of salt, the (HOURS,MINUTES) following effects may be observed when using salt for Per Cent API Class A Cement Pozzola" Cement Retarded Cement oilwell cementing: (1) improved flow properties; (2) good Salt* API 8,000·£! Csg. API 8,OOO·£! Csg. API 14,OOO·ft Csg. dispersing agent; (3) compatible with most other additives; o 2,13 2,]0 3,00+ 5 1,27 ],48 2,] 5 (4) better bonding-salt, shales, swelling clays; (5) accel­ 10 ],56 2,05 2,39 erator-low concentrations; (6) retarder-high concen­ 18 2,51 2,'6 3,]0 Sat. 3,25 4,00+ 2,59 trations; (7) increases slurry weight; and (8) better pri- *By weight of mixing water.

188 JOURNAL OF PETROLEUM TECHNOLOGY salt to obtain increased density. .:>amrallon of water with TABLE 2-SALT FOR SATURATED SLURRY Woter Salt salt will increase its density about 1.7 Ib/gal. Since cement Composition (gal/lock) (Ib/.ack) slurries have a somewhat higher initial density than water, API Class A Cement-O% Gel 5.2 16.10 the effect of salt on the slurries will not be this great, but API Class A Cem ..nt~% G.I 7.8 24.18 API Closs A Cenlent-8% Gel 10.4 32.24 will range from an increase of 0.5 to about 1.0 Ib/gal API Class C Ce."ent 6.3 19.54 API Class D· E Cemenl 4.5 13.95 depending on the weight of the selected cementing com­ Pozzolan X Cement 5.75 17.n position (Fig. 4). In instances where a heavier weight is Pozzola" Y Cement 5.34 16.50 desired, it will be noted that less weight material will be required with the salt slurries (Table 4). TABLE 3-(FROM REF. 4) Gulf of Mexico Pacific Ocean COMPATIBILITY OF SALT WITH ADDITIVES Specific Gravity 1.019 1.026 pH Factor 6 .5 7 .6 Due to the many specialized problems encountered Total DiSSOlved SOl ids I ppm) 29,.480 33,660 Calcium (ppm) 380 .452 whIle cementing wells, many additives are used with Magnesium (ppm) 736 1,163 Chlorides (ppm) 14,780 18,820 cement to modify its properties for specific applications. Sulfates (ppm) 1,950 2,610 Compatibility necessarily becomes of concern, particularly Carbonates (ppm) None None Bi -Carbonates (ppm) 177 185 when considering the wide temperature ranges over which oilwell cements are used. Salt cements are generally com­ patible with all light and heavyweight additives, accelera­ compatible with such combinations and aids not only tors, retarders and other special additives in common

dispersion, but also in low percentages accelerates early Downloaded from http://onepetro.org/jpt/article-pdf/15/02/187/2214379/spe-411-pa.pdf by guest on 29 September 2021 usage. Low-water-loss materials have exhibited very good strength. Properties of such mixtures are illustrated in results in certain situations, both for primary and squeeze Table 6. While viscosity reduction in these systems permits cementing. The mixing of salt with some of these products the use of lower water ratios than normally employed with results in a slight increase in slurry viscosity which can gel cement, as indicated in Table 7, it is by no means usually be corrected with a slight increase in mixing necessary to have the reduction when maximum slurry water. Most low-water-loss materials are adversely affected volumes are desired. Despite the presence of the salt in by the presence of chloride ions, some to the extent of a gel cement slurry, tests have shown that there is no being ineffective. With some additives, the decrease in significant change in the free water for these slurries fluid-loss control may be insignificant, but when minimum (Table 8) when tested by the methods in Section 3 of fluid loss is desired it can normally be regained in the salt API RP lOB, "Recommended Practice for Testing Oil­ slurries by a slight increase in the amount of fluid-loss Well Cements and Cement Additives". In fact, the cubic­ additive (Table 5). feet-per-sack yield will increase by the absolute volume The corrosiveness of a pure sodium-chloride solution on of salt in solution (Fig. 4). steel has been found to be very low, being less than 0.5 Table 7 will illustrate the comparative properties of mils per year for temperatures up to 210 Fo' Salt will fresh and salt-saturated slurries with 0 to 12 per cent react with normal hydration products in cements and, bentonite. when set, should offer comparable protection to fresh­ Comparative tests have also been made with salt slurries water slurries. containing bentonite and the attapulgite-type salt-water clay. These data illustrate that bentonite has the greater SALT IN GEL CEMENT water-absorbing capacity in gel cements. When sodium In gel cements, a calcium lignosulfonate is commonly used as a dispersant to reduce the slurry viscosity. Salt is

Thickening Time Hrs.-Min. 5:00 4:00 3:00 ~

2:00 Fresh Water 5% Sail ~ 8,000 Ft. API Casing Test 1 :00 ------0:00 o 15 30 45 Percent Salt by Weight of Water

Compressive Strength - 24 Hrs . API Class A Cement ~ .lQQ..L 140 F o 2110 4025 5 3145 4630 Saturated Salt 10 3065 3515 IS"/. Salt 20 2470 2960 Sct. 1480 1780 FIG. 3-EFF[CT OF SALT CEMENT ON SHALE-REO CAVE FIG. 2-SALT CEMENT THICKENING TIME. FO R~I A T ION, TEXAS PANH ANDLE.

FEBRUARY. 1963 189 bentonite is blended with cement and slurried with water, Slurry Weight it becomes partially converted to calcium bentonite. While Lbs./Gal. less swelling occurs with this form of the mineral, it still 18.01...--...,.--...--- performs better in cement than the salt-water type clays, 17.01~--+_--_+_-_-IEffect of Salt on Weight as indicated by the viscosity and free-water separation data 16.0 ...... - in Table 8. ·······API Class 0-£ 15.0·~-_+-_--J ___ 1 - API Class A -0 ~6d 14.0 -::-"7.- :;::;:c:. EFFECTS OF SALT ON STRENGTH _::-==_-=- -- API Class A- 4 ~Gtl - .. - Pozzolan G~mt:nt RETROGRESSION 13.0~--~-=-~-_-~------____ ~~ ____ ~ ---API Class A-S%Grl At temperatures above 250 F, cementing compositions 12.0L-._.....J.__ -I.. __ ...1 o 15 30 45 undergo a retrogression phenomenon. This inherent prop­ Slurry Volume erty in cement at high temperatures causes a strength loss Cu. Ft./Sk. and results in a substantial increase in permeability. This normally occurs within the first three to seven days of 2.20 hydration, and apparently changes very little beyond this 2.001-_-_-_-_.,-,-""-",j...-c=::.::;:-=.------I Effect of Salt on Volum e period. To counteract this behavior, 30 to 40 per cent 1.80,--r--t---=-:-tr--_____ silica flour is commonly used in cements for elevated 1.60~==-+_-==+_--~I--API Class A-8~6d temperatures. The use of salt in cement does nothing to 1.40 -'-API ClassA-4%Gd change this property in cement, as illustrated in Table 9. _ -API Class A-0%6cl Downloaded from http://onepetro.org/jpt/article-pdf/15/02/187/2214379/spe-411-pa.pdf by guest on 29 September 2021 The addition of salt does not cause any appreciable change 1.20 """API Class D-£ in strength, but with silica flour the normal strength loss 1.00 - L-.----~--~----~5 does not take place. 0 15 30 4 Percent Salt by Weight of Water

FIG. 4--SLURRY PROPERTIES. TABLE 4 Pounds of Ilmenite Specific Grovity-4.7 ELECTRICAL CONDUCTIVITY OF CEMENTS API Class A API Class E Slurry Weight (lb/gal) Fresh Salt Fresh Salt Relative data on the electrical conductivity of cements 16.0 5 o o o have been determined for fresh and salt-saturated cement 17.0 22 15 12 5 slurries. The values were measured on cylinders 111/16 X 18.0 39 33 28 21 19.0 58 54 46 39 23/4 in. after curing at 100 F for 24 hours. Results in Table 10 indicate a slight increase in conductivity for the salt, but this has little recognizable significance in primary TABLE 5 cementing. API Class A Cement Filtration Rate (cc/30 minutes) 325 Mesh Screen @ 1,000 psi EXPANSION OF SET CEMENT Per Cent Salt 1.0% Additive 1 .2% Additive 0 80 35 Most cement slurries, if mixed with recommended max­ 5 84 44 10 80 40 imum water ratios and moist-cured, will produce set vol­ 15 78 48 umes of cement comparable to slurry volumes without Sat. 197 58 shrinkage. Some compositions will actually produce a slight expansion after hardening. This should result in TABLE 6-API CLASS A CEMENT, SALT 3.0 PER CENT (BY WEIGHT OF CEMENT), improved bonding in oilwell cementing applications; in 6 CALCIUM llGNOSUlFONATE 0..01 PER CENT fact, the conventional bonding tests being performed ,8 as Fluid loss well as acoustic attenuation data (bond logging) indicate 325 M.S. (cc/30 min.) Thickening Time Bentonite Water .API 6,000·ft Casing this excellent bonding. (The bonding strength of fresh­ (per cent) (gal/sack) 100 psi 1,000 psi (hours:minutes) water cement to pipe, at 140 F, increased from 108 psi 6 8..01 176 402 2,10 8 9.0 183 390 2,30 after one day to 231 psi after 28 days; whereas, bonding 10 9.9 184 340 2.12 12 10.8 176 360 2,05 strength of saturated salt-water cement increased from 14 11.6 82 330 1049 95 psi after one day to 400 psi at the end of 28 days.) 24-Hour Compressive Strength (psi) To detemine expansion of cements, comparative fresh­ Bentonite 80 F 140 F water and saIt-saturated cement slurries were poured in (per cent) o psi 3,000 psi standard 1- X 1- X 6-in. bar molds. Stainless-steel pins were 6 660 1250 8 550 1155 inserted in each end for accuracy in measuring the length 10 425 900 of the set specimens. After curing 24 hours at 80 F, these 12 360 880 14 345 870 specimens were removed and measured for their relative

TABLE 7-API CLASS A CEMENT WITH BENTONITE, 3.1 lB SALT/GAL WATER, SATURATED SOLUTION @ 140 F Initial 8,000·ft Slurry Slurry Thickening 24·Hour Bentonite Water Salt Viscosity Weight Time Strength (psi) (per cent) (gal/sack) (per cent) (poises) (Ib/gal) (hromin) 100 F 140F 0.0 5.2 0 6 15.6 2,13 2110 4025 0.0 5.2 Sat. 4 16.1 3,25 1485 1780 4.0 7.8 0 13 14.1 1,54 1265 2025 4.0 7.8 Sat. 8 14.8 4:20 540 875 8.0 9.7 0 20 13.1 1,46 680 1070 8.0 9.7 Sat. 7 14.0 3,00+ 340 605 12.0 12.3 0 26 12.6 1,56 305 560 12.0 12.3 Sat. 6 13.5 3,00+ 230 405

190 JOURNAL OF PETROLEUM TECHNOLOGY TABLE 8 TABLE ll-LINEAL EXPANSION, IN INCHES, fOR A 6-IN. S,PECIMEN LENGTH (AVERAGE Of DUPLICATE BARS CURED AT 95 f-800·PSI PRESSURE) Bentonite Cement Attapulgite Expansion after Hardening (in.) Fresh Water Sa It SaiD rated Cement- 7 Days 28 Days 60 Days 4% 8% 4% 8% 4% 8% API Class A Cement 0.056 0.073 0.077 Water (gal/sack) 7.8 9.7 7.8 9.7 7.8 9.7 API Class A Cement' 0.060 0.100 0.120 Viscosity (poises) 13 20 8 7 6 5 Pozzola" X Cement-OO/o Gel 0.037 0.050 0.055 Free Water (ee) 1.3 1.0 2.3 2.1 4.0 4.0 Pozzolan X Cement-OO/o Gel'" 0.037 0.075 0.090 *Salt saturated. Pozzolan X Cement-2% Gel 0.050 0.072 0.083 Pozzolan X Cement-2% Gel'" 0.051 0.080 0.095 *Salt-saturated slurries. TABLE 9-API CLASS E CEMENT, 35 PER CENT SILICA flOUR Compressive Strength (psi) TABLE 12 230 F (days) 290 F (days) Per Cent Salt Flow Behavior Consistency 7 28 3 7 28 Basic Slurry By Wt. of Water Index (n') Index (K'J fresh Water 3265 5625 8475 9000 8875 8200 API Class A Cement 0 0.30 0.1950 Saturated Salt Water 3540 5700 6040 5015 5690 5890 10 0.20 0.3800 Saturated 0.20 0.1800 4 Per Cent Gel Cement 0 0.10 0.9500 10 0.21 0.1724 TABLE 10 Saturated OAO 0.0522 Electrical Electrical 12 Per Cent Gel Cement 0 0.10 0.7600 Composition .salt Resistance (ohms) Conductivity (mhos) 10 0.05 0.7103 Saturated 0.25 0.0948 API Class A Cement None 40,000 0.000025 API Class A Cement Saturated 18,000 0.000056 Pozzola" Cement 0 0.10 0.8100 Pozzolan Cement None 19,000 0.000055 10 0.31 0.0919 Downloaded from http://onepetro.org/jpt/article-pdf/15/02/187/2214379/spe-411-pa.pdf by guest on 29 September 2021 Pozzolan Cement Saturated 12,000 0.000083 Saturated 0.56 0.0148 initial lengths. These bars were then submerged in fresh for the more-or-Iess average pipe size-hole size condition water in an autoclave where pressure was applied for of 5V2 -in. casing in an 8¥

TOPOfCE~NT-6.200fT. CON01TlONS CAlClJlATEO fOR TURBlIL[ut fLOW OF CEHWT SLURRY Displacement ~t~lg ~ :,iSZWa8 P~Bf!ii t i Pf§d,f UUot!lU WJ StT!!8tuRi Rat e FLUID) - to tr~/(,;Al SRl/lE FOR OISf'lACEMENT Bbl s./Min. -- API Closs A Cement FlUIOPRDf'ERTIES flUID WEIGHT fLUIO WEIGHT Il~. lSS/GAL N··PRIME K-PRll<£ >0. lBS/GAl }I-PRIME K-f'R1HE 35 --12% Gel-Cement 10.200000 .67000000 ).)OOooOOE-O) t 10.200000 .67000000 , 11+.100000 .10000000 .81000000 , 14.800000 .56000000 {:l~ogggt2 3 10.000000 1.0000000 4.0000000[-05 3 10.000000 1.0000000 4.0000000£-05 ----4% Gel-Cement HOLE CIAMOER USEO HI CALCULATIONS HOLE OIAMHER US(O IJoiCAlCULATIONS 9.375000011.1. 9.3750000 Ill. 30 ~" ___ Pozzolon Cement HOWRA!E VElOCllY HOW RATE VELOCITY VELOCITY BBLS/HIN III f'IPE VElOClTY IISlS/HIN INPIf'E 10.642200 35.781918 25.035119 ).7905646 12.7448 8.9170694 \\\, FRICTIONAL PRESSURE-PSt/IOOO H. FRtCTIONAtPRESSURE-PS1/1000fT. ''-. CAS I t.lG ANNULUS CAS I NtO AtlNUlUS 25 \' 243.87367 61.50171 3/0.05%800 9.5916707 )82.97654 122.45825 52.933553 16.)07057 ----"\' ...., ... , 227.06179 53.H12585 29.1926/06 6.93%562 'ijEll-HEAOPRESSUflE-KJDC1RCUlATlNG WELL-HEAOPRESSURE-1iUOCIRCUlATING \ " .... , 2308.7245P51 329.95219P51 "" ".... OEJ>THOF WEll-HEAO 20 ~ TO~ PLUG PRESSURE ...... 00000000 2105.6859 " 500.00000 2\02.4739 ..... , ...... 1000.0000 2099.2618 . :.-::...,. 1500.0000 209(>.01199 ...... 2000.00PO 2092.8380 2500.0POO 2089.6260 3DOO.00PO 2086.411+1 15 ~ 3500.0000 2083.2022 '-'" 4000.0000 2079.9902 4S00.POOO 2101.2256 -01'----- 5000.0000 2185.7532 - 5500.0000 2270.2807 ...... 6000.0000 2354.8086 --- 6500.0PPP 2439.3360 7000.0000 2523.8638 ---- 7500.00PP 2608.3914 10 7560.0POO 2618.5349

ANNULAR Flll-UP IN ABOVE HOtEDIAHETER ANNUlARFlll-UPH/ABOVEHOLEOIAMETER 059.9999 fT. \J59.9999fT. SACKS fOR A60VE ANNUU,R Fill-UP SACKS FOR ASOVE ANNULAR FILL-UP o 15 30 45 3n.32212 312.07728 1";::;':S)~;l~S~AO PRES5UREr Percent Salt by Weight of Water \'DRAULICIfOftSEPOWERREQUIR 2295.5569 FIG. 5-SALT CEMENT SLURRIES-DISPLACEMENT RATE FOR TURBULENT FLOW (8%.IN. HOLE, 51h-IN. CASING). FIG. 6---EXAMPLE OF HYDRAULIC WELLBORE ANALYSIS.

FEBRUARV, 1963 191 When either of the two fluid indices is lowered by montmorillonite, an extremely water-sensitive clay more inclusion of an additive in the slurry, while the other commonly associated with the bentonite used for produc­ remains constant, some degree of reduction in fluid con­ ing drilling muds and as an additive for cements. Among sistency or thickness has been achieved. However, the the formations where salt cement has been used success­ usual tendency of a dispersant additive is to depress the fully are the Wilcox, Frio and Miocene formations. consistency index which is analogous to viscosity in a In South Texas, the Upper Wilcox is characterized by Newtonian fluid, and increase the flow behavior index four primary producing intervals of shaly sands, separated toward the value for a Newtonian fluid, where it is 1.0. most often by several hundred feet of shale. Practically all Salt is most effective in reducing the consistency index wells are drilled through the producing zones, cased and and critical displacement rate when used in sufficient tested, so it becomes very important to have a good pri­ quantity to saturate the slurry mixing water. It also has a mary cement job. Similarly, the Deep Wilcox consists of more pronounced effect when used with slurries containing a series of shaly sands separated by 50- to 100-ft shale bentonite. This would naturally be expected because of the sections. The water-sensitive nature of these shales has effect of salt on montmorillonite in reducing water absorp­ created considerable difficulty in obtaining satisfactory tion and swelling, thereby permitting improved fluidization cement jobs because of formation deterioration when con­ of the slurry by its mixing water. Because of this property, tacted by a fresh-water slurry. it is often possible to significantly reduce critical displace­ Thus far, some 47 cementing jobs have been performed ment rate with gel cement using concentrations of salt less using salt slurries for Wilcox protection in this area. than saturated. This also minimizes the retardation encoun­ Depths have ranged from 4,700 ft at the top of the Upper tered with higher salt percentages so that satisfactory com­ Wilcox in some fields to 13,600 ft for the Deep Wilcox. Downloaded from http://onepetro.org/jpt/article-pdf/15/02/187/2214379/spe-411-pa.pdf by guest on 29 September 2021 pressive strengths can be attained at low temperatures. Included in these jobs are 13 liners principally in the Deep In areas where lost circulation may be a problem during Wilcox, 18 production strings mostly in the Upper Wilcox, critical-displacement-rate cementing operations with the and 6 intermediate strings, for a total of 37 primary jobs. usual slurries, dual benefits may be realized with salt On these wells, there has been no reported remedial work slurries. Many of these lost-circulation formations con­ created by communication, in direct contrast to the usual tain shale, shaly sands, shaly limestones or combinations magnitude of squeeze work when fresh-water slurries were thereof. When this condition exists, maintenance of exist­ used in nearby wells. The remaining 10 jobs consisted of ing formation integrity may be materially improved by a two plugbacks and eight squeeze jobs, one at the top of a salt slurry, while the displacement rate for efficient mud liner because of lost circulation and others to help shut-off removal can be reduced and the circulating pressure cre­ nonproductive zones which had been perforated and ated in the annulus minimized. This combination of prop­ tested, or to help correct a problem in wells cemented erties can possibly permit satisfactory circulation of cement with other than salt slurries. across the zone of loss and yield a good primary cement­ ing job, at reasonable cost for both materials and horse­ In the Frio wells, at 5,000 to 6,200 ft, formation characteristics are again shaly sands separated by shales. power. Results have been similar to those in the Wilcox, with FIELD EXPERIENCE four liners and three production strings requiring no reme­ dial work except one squeeze job for nonproductive per­ As with any technique or material, the ultimate proof forations. Four other successful squeeze jobs have been of the benefits of a change exists only in satisfactory done with salt cement on wells originally cemented with a performance upon application in the field. From this fresh-water slurry. standpoint, the salt cement slurries have been exemplary In all of the situations just mentioned, a saturated salt in that superior primary cementing results have been slurry has been used. For the Deep Wilcox wells, the achieved in all areas where salt has been used (Table 13). basic cement has been an API Class E containing silica In several of these areas, the salt slurries are also being flour to help prevent high-temperature retrogression of the used successfully for remedial cementing operations. set cement. Since salt saturation of a Class E cement does GULF COAST not cause appreciable retardation with most brands, some Published literature' indicates that along the Gulf Coast 50 per cent of the slurries also contained a modified ligno­ the predominant clay mineral in producing intervals is sulfonate retarder for adequate pumping time at the temperature encountered. The principal function of salt in these slurries was twofold: (1) to help provide protec­ TABLE 13-FORMATIONS BEING CEMENTED WITH SALT SLURRIES tion for, and better bonding to, the shale formations Depth separating the producing zones, thereby providing zonal Formation Area ~ isolation without the necessity of block squeezing; and Sand and Shale (2) many of these wells required higher than normal Wilcox 4,700 to 13,600 South Texas density fluids to control wellbore pressure, and salt satura­ Frio 5,000 to 6,200 South Texas Miocene 9,000 to 15,000 South louisiana tion in most cases yielded sufficient slurry weight to obviate W'Ood"bine 7,400 North Texas the necessity of adding weight material to the slurry. Strawn 3,400 North Texas KMA 4,000' North Texas When necessary, the conventional weight materials can be Penn. Age To 10,000 Oklahoma Woodford 2,500 to 10,000 Oklahoma and have been used with salt slurries. Delaware 5,000' West Texas Red Cave 2,000 Texas Panhandle In the remaining wells, ranging from 5,000 to 10,000 ft, Morrow 8,000 Texas Panhandle Wasatch 5,000 to 7,000 Utah the basic slurry has been either API Class A cement or Lime and Shale a pozzolan cement blend. The salt-saturated slurries pro­ vided several benefits here, again with the major factor Pettit 7,200 North Texas Hope 2,800 West Texas dictating their use being better primary cementing of the Kansas City 3,400 Kansas shales and minimization of squeezing to obtain isolation. Dolomite and Shale Other advantages utilized were retardation of the slurry Queens 3,000' West Texas and minimization of the amounts of more expensive addi­ Arbuckle 3,000 to 4,000 Kansas *18 per cent salt, other zones being cemented with saturated salt slurries. tives for retarding, and to some extent the added slurry

192 JOURNAL OF PETROLEUM TECHNOLOGY weight obtained. Additives used in conjunction with salt also been done on older wells using the salt-saturated in these slurries have included silica flour, calcium ligno­ slurries with very good results. sulfonate and cellulose retarders, granular lost-circulation materials, bentonite and selected low-water-Ioss additives !\lID·CONTINENT that are not significantly deteriorated by the presence of In North Texas, salt-water slurries have been used for the chloride ion. cementing the Woodbine sand, Strawn sand, KMA sand and Pettit lime. Shales surrounding these formations have In some other areas of South Texas, the salt-saturated created the same difficulty in obtaining separation of pro­ slurries have been used quite extensively for improvement ducing zones that has been the problem in other areas. of the flow properties of slurries and attainment of better Depths in this area range from 3,400 ft for the Strawn circulation characteristics at lower displacement rates. to 7,400 ft for the Woodbine, and concentration of saIt Concurrently with this property, the protection of shales has varied accordingly. In the deeper wells, where retarda­ and shaly sands is also realized, as well as useful retarda­ tion is desired, saturated salt-water cement is used; for the tion of the slurry. Resultant superior cementing jobs have shallower wells, in order to provide shorter waiting-on­ been indicated by both communication tests and acoustic cement times, the amount of salt has been 18 per cent logs for bonding to pipe and formation: by weight of the mixing water. Results have been excellent In one section of Louisiana, a major oil company has with no reported failures on any of the salt cement jobs; been using salt-saturated API Class A cement with calcium where acoustic bond logs have indicated indifferent bonds lignosulfonate retarder for cementing through the Miocene previously, they are indicating very good bonding for the at 9,000 to 10,000 ft. This is another of the situations salt slurries. Downloaded from http://onepetro.org/jpt/article-pdf/15/02/187/2214379/spe-411-pa.pdf by guest on 29 September 2021 where interbedding of sands and shales exists, creating In Oklahoma various shales of Pennsylvanian age ex­ difficulty in maintaining formation competency when a hibit a high degree of sloughing in the presence of fresh fresh-water slurry contacts the clay minerals of the for­ water, causing severe washouts above and below sand mation. formations which it is desired to isolate. This situation Further work has also been done in the shaly Miocene exists to some degree in practically all parts of Oklahoma formation at 13,000 to 15,000 ft where fairly close water and includes formations of other ages such as the Wood­ or gas contacts are encountered. Indications thus far are ford shale. For the past few years, salt-saturated cements that better segregation of these various fluids is obtained by and displacement rates as high as practical have been used use of the saturated salt slurries because of their improved as a remedy for this problem, with very good results. formation bonding characteristics. In addition to the The Layton and Bartlesville formations are two ex­ properties of salt in this situation, attainment of turbulent amples of shaly sands where saturated slurries have been flow at minimum displacement rates has also been accom­ helpful. In one area where five wells were driIIed through plished by use of an additive to help provide exceptional this type of problem shale without obtaining a satisfactory dispersion and viscosity reduction of the slurry. primary cement job, a change was made to salt-saturated cement preceded by a suitable chemical wash for the Another oil company was encountering considerable drilling mud involved. Acoustic bond logging indicated expense in completing wells in Southwestern Louisiana due excellent bonding, and final completion bore out this result to extensive block squeeze requirements for effective sep­ by being trouble-free. This type of slurry has also been aration of zones. A very effective mud program was being used extensively on squeeze jobs where shales have been used to minimize washout in the shale sections and, heaving around the producing formations. Predominantly, apparently, a nearly gauge-size hole was being obtained. the basic slurry has been either API Class A cement or a However, primary cementing results with fresh-water slur­ pozzolan cement-although, as deeper wells are being ries were generally poor. On a few occasions when slurry drilled, the use of salt in Class E cement is also increasing. was actually circulated to the surface, large pieces of shale formation were brought out of the hole with the slurry, Salt cement in West Texas has been used primarily to indicating a severely water-sensitive, sloughing formation. help prevent channeling through the shales around the Inhibition of shale heaving was being accomplished in the Delaware sand, Queens dolomite and Hope lime. Many drilling program, and immediately undone upon circula­ of the shaly and dirty sands of this area are sensitive to tion of the fresh-water slurry even though it contained a the filtrate from a fresh-water cement. Salt at 16 to 18 low-fluid-Ioss additive to reduce filtrate damage in the per cent by weight of mixing water has been added to sands. cement, and has been effective in controlling formation damage and communication between zones in these for­ The subsequent change to salt-saturated slurry yielded mations. Use of these lower salt concentrations is dictated 11 successful primary cement jobs out of 12, compared in this area by the relatively low formation temperatures to the previous success ratio of practically zero. Since where retardation of the slurry would create unduly long these were deep, high-temperature wells in the range of waiting-on-cement times. 13,000 ft with high-pressure zones necessitating 17.5-lb/gal Also, quite a bit of cementing has been done in this fluid densities, the slurry used was API Class E cement, area using salt concentrations in the accelerating range­ silica flour, weight material, retarder, salt saturation (which that is, 2 to 5 per cent by weight of water. Specifically, also reduced the amount of weight material) and mainte­ these concentrations have been used in conjunction with nance of low fluid loss by use of a salt-compatible addi­ high percentages of gel to overcome the retarding effect tive. of the calcium lignosulfonate dispersant, although there Other salt slurries have been used to a limited extent are probably several shales where these concentrations in this same general area for similar problems at depths could provide some degree of formation stability. On sev­ ranging from 5,000 to 17,000 ft. In the shallower wells, eral occasions, the salt has also been used to lower the the cement has usually been API Class A where the salt critical velocity or rate for turbulence with the slurry, functions as a retarder, and in the deeper wells API Class particularly in the pozzolan cements. On wells in the Hope E cement is used with the additional salt advantage being lime, it has usually been necessary to squeeze the shale its increased slurry weight and inability to dissolve salt above and below the lime to get a water-free completion. stringers. A considerable number of squeeze jobs have Use of salt-saturated slurries has largely eliminated this

FEBRUARY, 1963 193 remedial work. On occasion, when low fluid loss is also ing, but the field work thus far has not been extensive indicated as probably beneficial to the completion, an addi­ enough for complete evaluation. Similarly, in the eastern tive for this purpose has been used with the salt slurry. part of the country, very little cementing has been done Central Kansas is an area which has, perhaps more with these slurries although a great deal of interest has dramatically than any other, exhibited the extent to which developed recently. the salt slurries can provide successful cementing results. Predominantly, the producing formations are the Arbuckle ACKNOWLEDGMENT lime and Kansas City lime at 3,000 to 4,000 ft, inter­ bedded extensively with clays and shales. In the past on The authors wish to thank the Halliburton Co. for per­ some of these wells, it has been impossible to obtain a mission to publish these data, and those in the laboratory primary cement job with any type of cementing composi­ and field organizations who assisted in its preparation. tion. Salt-saturated cement has been so successful in ob­ taining results that some 80 per cent of the jobs performed REFERENCES now are done with it, despite the retardation occurring at 1. Ludwig, N. c.: "Effects of Sodium Chloride on Setting Prop· the low temperatures and the somewhat longer waiting erties of Oil Well Cements", Drill. and Prod. Prac., API time required. The shales encountered here create a prob­ (1951) 20. lem in that they apparently require a saturated slurry to 2. Beach, H. J.: "Improved Bentonite Cements Through Partial maintain their competency. Acceleration", Jour. Pet. Tech. (Sept., 1961) 923. In the Texas Panhandle, similar results occur with the 3. Moore, John E.: "Clay Mineralogy Problems in Oil Recovery", Red Cave formation (Fig. 3) around 2,000 ft and the Pet. Eng., Parts 1 and 2 (Feb., March, 1960). Downloaded from http://onepetro.org/jpt/article-pdf/15/02/187/2214379/spe-411-pa.pdf by guest on 29 September 2021 4. Owsley, W. D.: "Surface Cleaning Equipment and Supplies", Morrow formation around 8,000 ft. These two sands and Oil Well Cementing Practices in the United States, Chapter 7, the ever-present shales again appear to be most success­ 88·89. fully cemented with the salt slurries. 5. Hudgins, C. M., McGlasson, R. L. and Gould, E. D.: "Devel· Use of salt cement has not been very extensive in the opments in the Use"of Dense Brines as Packer Fluids", Drill. Rocky Mountains or in Canada. In these areas, the major and Prod. Prac., API (1961) 160. 6. Evans, George W. and Carter, L. Gregory: "Bonding Studies use of salt has been for cementing through salt sections of Cementing Compositions to Pipe and Formations", Paper or potash sections where the application is quite obvious presented at Spring Meeting of API Southwestern Dist., Div. -to help avoid dissolving large portions of the formation. of Production, Odessa, Tex. (March 21-23, 1962). Recently, there has been some use of salt-saturated 7. Slagle, KI10X A.: "Rheological Design of Cementing Opera­ slurries in northeastern Utah for cementing in the Wasatch tions", Jour. Pet. Tech. (March, 1962) 323. 8. Walker, Terry: "Report of Bond Logging", Paper presented at and Mesa Verde formations, both shaly sands. Laboratory Spring Meeting of API Mid·Continent Dist., Div. of Produc­ tests indicate very definite advantages of improved bond- tion, Oklahoma City, Okla. (April 4-6, 1962). ***

194 JOUIINAL OF PETIIOJ.EUM TECIINOLO(a