SQUEEZE CEMENTING

Field Results of Cementing Operations Using Slurries Containing a Fluid -Loss Additive for Celnent

J. P. PAVLICH DOWELL DIV. OF THE DOW CHEM/CAL CO. MEMBER A/ME HOUSTON, TEX. W. W. WAHL TULSA, OKLA. Downloaded from http://onepetro.org/jpt/article-pdf/14/05/477/2213292/spe-133-pa.pdf by guest on 26 September 2021

Abstract Casing cementing operations utilizing low-fluid-loss slurries showed an extremely high success ratio, confirm­ A survey of 1,000 squeeze-cementing jobs in different ing the fact that this type of cement will help minimize areas of the United States indicates that cement slurries channeling, prevent sticking of casing during cementing, having low-fluid-loss properties can be used successfully increase the probability of desired fill-up and reduce the in conventional squeeze operations employing the "hesi­ necessity for block squeezing. tation" technique. It has been found that high pressures are not essential to obtaining a successful dry test follow­ The application of cement slurries during oil well ce­ ing squeeze. Also, zone isolation to reduce high gas-oil menting operations is frequently complicated by excessive or water-oil ratios has been achieved by notching the water loss into permeable formations. This results in pre­ casing with high-velocity jets of an abrasive-laden fluid mature thickening of the slurry and possible bridging of and subsequent displacement of low-fluid-loss cement at cement solids before placement of the slurry is complete. high injection rates. The attainment of high squeeze pressures is frequently misleading in that they may be due to blockage by Bridging agents in gel-cements containing the fluid-loss additive have been used to squeeze naturally fractured dehydrated slurry in a region of fluid-loss, rather than in the zone to be sealed off. The inclusion of fluid-loss addi­ formations which previously required numerous stages tives in cement slurries reduces premature fluid-loss and with large volumes of cement. Drilling-out was not re­ minimizes the possibility of improper placement of the quired in many cases, because the cement was circulated cement and subsequent job failure. out of the perforated interval. Casing cementing opera­ tions have been particularly successful when using light­ In the past, many fluid-loss control additives have re­ weight slurries containing pozzolanic extender, bentonite sulted in undesirable modification of many slurry proper­ and sufficient fluid-loss additive to reduce the fluid-loss ties, complicating application procedures and often requir­ to 120 eel 30 minutes at the cementing temperature. ing the use of additional corrective additives. A recently Cement bond logs indicate that these slurries, when used developed fluid-loss additive, FLAC, is relatively inert with scratchers and reciprocation of the pipe during the and in most cases does not affect the desirable properties cementing operation, increase the probability of desired of either the cement slurry or the set cement.' The sum­ /ill-up and minimize the necessity for block-squeezing. mary chart shown in Table 1 is a breakdown of over 1,000 cementing jobs using this fluid-loss-control additive Introduction which have been performed in the major oil fields of the U. S. and Canada. These treatments are divided into the A study of treatment reports from over 1,000 cement­ following broad categories. ing jobs, using slurries with controlled fluid-loss properties, 1. Zone Abandonment-shutting-off perforations to ex­ indicates that in most applications controlled filtration clude undesirable fluids and to permit reworking of well. provides ,definite advantages in achieving the purpose of the cementing operation. Analysis of the economic aspects lReferences given at end of paper. of squeeze cementing indicates that the use of a low-fluid­ TABLE I-CEMENTING JOBS PERFORMED USING LOW-FLUID-LOSS loss additive in the slurry provides at least 10 per cent CEMENT SLURRI ES lower cost over conventional squeeze-cementing operations Zone General Block Zone IPrimary employing neat cement by eliminating extra stages. Un­ Area ~andonmen! Repair Squeeze L~!ati~~ ~mpleti?~~ Misc!. successful squeeze jobs were studied from the standpoint Gulf Coas~ 289 65 57 2 24 73 Permian Basin 165 63 of formation characteristics, cementing materials and tech­ Kansas-Okla.- Texas Panhandle 64 40 .5 niques in an effort to determine causes of failure and Rocky Mountain possible remedies. and 4-Corners 45 ~O Ark-La·Tex 20 10 15 Appalachian 45 18 Original manuscript received in Society of Petrolewn Engineers office Canada 45 20 Sept. 7, 1961. Revised manuscript received April 10, 1962. Paper pre­ Per Cent of ' sented at 36th Annual Fall Meeting ef SPE, Oct. 8-11, 1961, in Dallas. Jobs Succesc;ful 80 VO 72 60 100 70

MAY, 1962 SPE 133 477 2. General Repair-squeezing-off channels and repair­ in the cement slurry is more than offset by eliminating ing holes in pipe. the expense of additional squeeze stages that might other­ 3. Block Squeeze-isolating a zone before perforating wise be necessary to obtain a dry test. Additional savings for production. are effected by omitting the drilling-out step normally 4. Zone Isolation-Squeezing to eliminate vertical mi­ required after squeezing with conventional high-water-loss gration of fluids or gases (often referred to as "pancake" slurries. squeeze) . The success ratio of cementing jobs using low-fluid-loss 5. Primary Completion-setting casing or liners. slurries has been relatively high. In areas where formations are highly permeable, fractured or vuggy, and perfora­ 6. Miscellaneous-tubingless and permanent-type well tions cover an extended interval, these techniques have completions. proved 85 per cent successful. A successful job is defined as one in which a dry test was obtained following a single-stage application. Zone Abandonment Some of the early low-fluid-loss jobs were unsuccessful Conventional squeeze techniques designed to seal off a because of improper squeeze techniques. Multiple stages specific zone or set of perforations rely upon spotting were necessary because field personnel were unable to the cement slurry at the desired depth and then dehy­ accept the idea that a satisfactory shut-off could be drating it by the application of high pressure, forcing obtained without using high squeeze pressures. Many excess liquid from the slurry out into the formation. If, times, an adequate squeeze pressure was obtained, indi­ Downloaded from http://onepetro.org/jpt/article-pdf/14/05/477/2213292/spe-133-pa.pdf by guest on 26 September 2021 after placement, the well does not give a "dry test", addi­ cating that cement filter-cake build-up had progressed tional stages of cement must be applied until a successful satisfactorily. However, in an attempt to attain still higher seal is obtained. squeeze pressures, the formation was hydraulically frac­ tured and once more opened up. Additional slurry was Many things can contribute to job failure during a only pumped away into the formation, rather than being squeeze-cementing operation. A frequent cause of failure dehydrated to form a permanent seal at the wellbore, is premature dehydration resulting from rapid fluid-loss and the job was considered a failure. Obviously, the ideal and subsequent immobilization of the slurry.' Sometimes, procedure is a slow pressure build-up which will gradually when a long perforated interval is to be shut off, dehydra­ force the excess water from the slurry without pushing tion occurs rapidly when the first perforations are con­ the slurry away from the wellbore, possibly resulting in tacted, and the resulting cement filter-cake that builds up formation damage. blocks the slurry from reaching the remainder of the Normally, it was found that pressures ranging from perforations. As a result, even if only a few of the 500 to 1,000 psi in excess of the bottom-hole injection perforations remain open, fluid can enter the well bore and pressure were sufficient to attain a successful squeeze. the job must be considered a failure. The value of a The bottom-hole injection pressure is that pressure at­ fluid-loss additive to prevent premature water loss before tained once injection has become stabilized. The surface the slurry can be properly placed and squeeze pressures squeeze pressure can be calculated from the bottom-hole applied is readHy apparent. squeeze pressure and the hydrostatic head of the fluid The use of "hesitation" squeeze techniques has been column in the well. found beneficial in attaining an effective seal by the Table 2 illustrates that low final squeeze pressures can gradual building-up of a cement filter cake. Essentially, this consists of applying successively higher pressures at intervals, with pauses between, to allow controlled deposi­ TABLE 2-EfFECT OF SQUEEZE PRESSURE ON JOB SUCCESS tion of cement solids. This procedure is not recommended Squeeze Pressure In Excess of Bottom-Hole for use with high water-loss slurries because there is ,Well i.njection Pressure Depth danger of dehydrating the entire column of slurry. With County State ----'!tL Attempted lAttained -Remorks* controlled water-loss slurries, however, the desired cement Chambers Tex. 11,000 2000 i200 PC R filter cake can be slowly built up in the perforations until Qnd Stage ;1000 1000 PC they are completely sealed, while the slurry in the hole R 3rd Stage 1000 1000 DT remains fluid and may be reversed out when squeeze Chambers Tex. 9,500 ·1000 1000 DT Chambers Tex. 5,000 2000 850 DT pressures indicate that an effective shut-off has been Jeff. Davis Miss. 14,565 2700 2700 DT attained. Jeff. Davis Miss. 12,800 750 750 DT Simpson Miss. 13,750 2800 800 PC R As cement fills a perforation, the filter cake continues 2nd Stage 800 800 DT to grow, forming a protrusion into the interior of the Jeff. Davis Miss. 14,490 2700 2700 DT Jeff. Davis Miss. 14,340 1700 1700 DT pipe known as a "node". The extent of node build-up is Andrews Tex. 4,275 2000 300 DT closely related to the fluid-loss characteristics of the Midland Tex. 7,261 2000 2000 DT Midland Tex. 7,345 1500 500 DT slurry. If the fluid-loss of a slurry is too low, the time lea N. M. 5,470 .11800 1100 PC R required to deposit an adequate filter cake in a perfora­ 2nd Stage 4800 1500 DT tion will be excessive. On the other hand, too high a lea N.M. 5,552 '000 1000 DT Harper Okla. 4,160 3000 1100 PC fluid-loss will result in large nodes being formed within R \2nd Stage 3000 800 R the pipe which must be removed by means of "node­ Jrd Stage 3000 500 R cutters" to allow free passage of tubing, packers and 4th Stage 500 500 DT Harper Okla. 4,615 500 500 DT down-hole tools through the perforated interval. Harper Okla. 4,145 500 500 DT Beaver Okla. 6,527 850 850 DT The advantage of the "hesitation" squeeze technique is Pecos Tex. 2,328 1750 800 PC R that the slurry remains fluid, assuring filter-cake build-up 2nd Stage 1000 1000 DT in all perforations-not merely those first contacted. Garvin Okla. 4,596 ·1600 600 PC R Thus, a shut-off can be achieved in a single stage. The 2nd Stage 800 800 DT Garvin Okla. 4,778 800 gOO OT additional cost of including a fluid-loss control additive * PC = perforations cleared; R = resqueezed; DT = dry test.

·1.78 JOl"R,,"AL OF PETROI.EI''I TECH,,"OI.OGY be as effective in obtaining a successful squeeze as high becomes immovable before complete penetration of the pressures. This table also indicates that attempts to obtain channel has been attained. Controlled fluid-loss slurries unnecessarily high pressures have resulted in mUltiple can completely fill the channel before sufficient leak-ofl' stages. takes place for them to become immovable. Unsuccessful jobs have also resulted from attempts to Where bond logs have indicated the presence of voids squeeze off highly fractured formations having low perme­ in the cement behind the casing. the volume of the void abilities and low bottom-hole pressures. Often, the hydro­ is first calculated assuming no cement behind the pipe. static head of the fluid column alone was sufficient to This volume of cement is injected, if possible, at a low force the cement back into the formation. This problem injection rate or until an injection-pressure increase is has been overcome by the use of (1) multiple small-batch noted. Pumping is then discontinued for a 5-to 10-minute stages and (2) bridging materials. interval and the normal hesitation technique of alternate The multiple small-batch technique consists of injecting pumping and shutting-down is employed. Flow-back of a series of slurry increments (10 to 25 sacks each) of low­ cement slurry can often be avoided by holding the final fluid-loss cement. The initial batch usually contains an pressure, releasing the pressure and then repressuring, as accelerating agent, such as salt, to speed up the initial previously described. set and prevent further penetration. When a pressure Fig. 1 shows a bond log of a primary cementing job, rise is noted, indicating cement filter-cake build-up in indicating either channeling or incomplete fill-up in the fractures and perforations, the hydrostatic pressure of the potential producing interval, and a second log made cement slurry in the tubing is sufficient to achieve the following a remedial low-fluid-loss squeeze operation. squeeze. The success of this technique depends upon The initial log on this well showed little, if any, bond Downloaded from http://onepetro.org/jpt/article-pdf/14/05/477/2213292/spe-133-pa.pdf by guest on 26 September 2021 relying on low pressure to accomplish the shut-off. from 6,950 to 6,700 ft; since it was desired to produce One disadvantage of this technique is that, if the first from the Viola at 6,825 to 6,829 ft, it was necessary batch of accelerated slurry does not enter the perforations to isolate this zone by squeezing. The annular volume to be sealed but remains in the pipe, it may harden to be filled was calculated to be 34 sacks. The well was sufficiently to prevent reversing-out of excess slurry at the squeezed through perforations at 6,860-61 ft (4 shots/ft) end of the job. with 25 sacks of low-fluid-loss cement. Final bottom-hole The most successful bridging material used in cement squeeze pressure was 4,000 psi. A second bond log was slurries has been polymerized plastic, ground and graded run showing good bonding from 6,772 to 6,880 ft. The to provide a predetermined ratio of different particle sizes. Viola was perforated and treated with acid at 3,200 psi. Walnut shells, gilsonite and perlite also have been used Limited testing indicated a good oil show with a small for bridging with some success. As soon as the bridging amount of water. particles in the slurry have built up and a pressure rise The success of this type of cement squeezing, using is noted, the job can be completed employing normal low-fluid-loss slurries, has been approximately 70 per cent. hesitation techniques, with low final squeeze pressures. In wells where the perforated interval is completely void Some job failures can be attributed to impatience, or of cement, the probability of obtaining a successful anxiety to get the cement slurry out of the hole as quickly squeeze in one stage is reduced, although a larger volume as possible. When using high-water-loss cements, the of slurry can be introduced before dehydration occurs. danger of premature dehydration and immobilization of Only moderate success has been experienced in attempt­ slurry is ever-present. Field personnel are not always ing to repair holes in casing or production strings. Treat­ willing to rely on thickening time as the sole criterion in ment reports show that, on the average, three 50-sack determining how long the slurry can be safely left in the stages were required before an effective squeeze was well, even though a low-fluid-loss slurry is used. obtained in 25 jobs of pipe repair. At the completion of a squeeze, it is necessary to re­ BEFORE SQUEEZE lease the tubing pressure to determine whether the cement will flow back from the formation. In many instances, POOR BOND-, ! I the squeeze has been considered successful if there was ~ I hi ~ I I no visible change in fluid volume in the displacement tank IA after checking flow-back. Unfortunately, small volumes W~, II i i I 1 leaking through one or two perforations cannot be meas­ IV I ~ ~ W iY ~i~ Vh ~ ured with field equipment. Because of this, it is always 66 50 6700 6750 6800 685~ 6900 6950 7000 7050 good practice to repressure to final squeeze pressure and maintain this pressure for at least 10 minutes. It has been « --l a:f2 found that many times the formation will accept slurry 0 w :> Cl. after the initital test, so that continued injection is re­ AFTER SQUEEZE quired. Patience in executing a squeeze is of utmost importance and cannot be stressed too greatly. Attempting GOOD BON~)-+ I to attain pressure build-up too quickly can only result h. I I in job failure and the need for additional squeeze stages. lA II i ! I I [IIIV' t"'iJ. ~Il ~ v. v~ General Repair -No It- 6650 6700 6750 6800 6850 6900 6950 7000 7050 Of the cementing jobs surveyed, approximately 25 per '- WELL DEPTH (FEET) cent were remedial squeeze operations performed to re­ Fig. I-Comparative bond logs of a well in the Helsel Field, pair faulty primary cement jobs that resulted in channel­ Cleveland County, Okla. The upper log, made after primary ing, improper bonding, or insufficient fill-up. The use of cement job with conventional high-fluid-loss slurry, shows poor bonding above 6,950 ft. The lower log, made follow­ conventional, high-fluid-loss slurries for channel repair is ing remedial squeeze with low-fluid-loss slurry, shows good not always satisfactory because the slurry dehydrates and bonding over the producing interval.

MAY. 1962 ,179 Block Squeeze result, many times the slurry quickly becomes dehydrated and immobilized so that desired fill-up is not attained The block-squeeze technique is used to isolate the and different formation zones are not properly isolated. production zone before completion by perforating above ~so as ~ result of this premature thickening of the slurry, and below the pay section, followed by a cement-squeeze high surface pressures are required for displacement and application. Normally, the technique requires two perfo­ the low pump rates result in inadequate removal of drill­ rating steps, two squeeze steps and a drilling-out step. ing mud ahead of the cement slurry. As a result, residual In contrast, by using a controlled fluid-loss slurry, both streaks of mud through the slurry later wash out leaving sets of perforations can be squeezed simultaneously. Then, channels in the set cement. It has been demonstrated after squeeze pressures indicate that satisfactory shut-off that cement slurries in plug flow displace only 60 per cent of both zones has been achieved, excess slurry can be of muds capable of being circulated, whereas 90 to 95 reversed from the hole in preparation for perforating and per cent of the mud may be displaced by slurries in completing the pay zone. The lower over-all cost of the laminar and turbulent flow.' latter procedure makes it economically attractive. Al­ though fewer jobs of this type have been performed, Another cause of channeling is localized dehydration of success ratios have been in the 70 to 75 per cent bracket. the sl~rry across zones of high permeability. The resulting nonumform slurry causes regions of irregular flow in The failures experienced using low-fluid-loss slurries the annulus, producing voids in the set cement. have been attributed to the fact that, in block-squeezing, the zones above and below the pay section were often .The use of a controlled fluid-loss cement slurry mini­ mizes these problems so that the slurry is kept in a

dense, impermeable sections. As a result, longer time is Downloaded from http://onepetro.org/jpt/article-pdf/14/05/477/2213292/spe-133-pa.pdf by guest on 26 September 2021 required to build up the necessary cement filter cake. readily pumpable state until desired fill-up has been at­ Where such conditions are known to exist, it is recom­ tained and the well is shut in for the cement to set. mended that the concentration of fluid-loss additive in ~revious investigators have shown the utility of low­ the slurry be lowered, so as to increase the leak-off rate flUl~-loss cerne~t slurries in minimizing sticking of casing and provide a slightly faster filter-cake build-up. dunng cementmg operations.' High-yield, low-fluid-Ioss cements have been used successfully in areas where con­ ventional neat cements resulted in incomplete fill-up and Zone Isolation cement left in the pipe. For example, in an 11,000-ft well in Mississippi, over 4,000 ft of high-fluid-Ioss cement This technique is sometimes known as a "pancake 0 slurry was left in the pipe during the primary cementing squeeze". The achievement of a 360 radial spread of o?eration. During displacement, the slurry had to pass a cement has been attempted by first cutting or notching ~Ighly permeable zone, and it was evident that dehydra­ the pipe by means of high-velocity, abrasive-jetting tech­ tion of the slurry was responsible for the pressure build­ niques: This insures a single point of entry for the cement up and subsequent lock-up. slurry into the formation and enhances the probability of a "pancake" pattern for the set cement. Radial pancake In contrast, an offset well of the same depth was ce­ layers can only be accomplished where formations tend mented using an API Class E cement containing 4 per to fracture horizontally. The achievement of an imperme­ cent bentonite and sufficient fluid-loss additive to yield a able layer of cement between zones is beneficial in elimi­ fluid-loss of 120 ml/30 minutes at bottom-hole tempera­ nating or reducing the vertical migration of unwanted tures. No increase in displacement pressure was discernible fluids, such as gas and/or water, from one zone to another. during pumping, and it was possible to reciprocate the pipe for some 30 minutes after the plug landed. The radial extent of the cement layer is governed by the amount of cement injected into the zone during the Another case history may be cited to show the ad­ squeezing operation. This can be determined by use of ~antages of using low-water-Ioss slurries for casing cement­ fundamental calculations similar to those used in plan­ mg. An 11,466-ft well in Citronelle field, Mobile County, ning fracturing treatments.4-0 A more detailed explanation Ala., was equipped with 5Vz-in. casing. It was desired may be found in the Appendix. to place high-strength cement opposite the pay and a filler cement. above the pay to a depth of 7,000 ft, thus covering In field application, the volume of slurry required to the entire Tuscaloosa section in which the pipe-corrosion obtain the desired radial penetration is injected into the problem is severe. Similar cementing operations in this formation before the hesitation technique is employed. field using high-fluid-loss slurries containing lost-circulation An additional 10 to 15 cu ft of slurry is always used to materials have failed, and subsequent logs showed no insure good cement in the notched zone. cement behind the pipe. In one case, 8,800 ft of slurry Several jobs have been performed using low-fluid-loss was left in the pipe. cement slurries to achieve greater formation penetration In the subject well, the pipe was reciprocated for one and to provide a more effective barrier between zones. In hour prior to starting cement. Fifty scratchers were used one particularly noteworthy zone-isolation squeeze in the to facilitate removal of mud cake from the wellbore. Mississippi formation in Kansas, the gas-oil ratio was Some 2,275 cu ft of a filler cement--consisting of cement reduced from 19,000: 1 before squeezing to 1,700: 1 fol­ pozzolanic extender, 4 per cent bentonite and sufficient lowing the squeeze job. fluid-loss-control additive to limit the filtration rate to 120 mlj30 minutes-was mixed and displaced at 11.1 bbljmin. Primary Completion This was followed by 603 cu ft of an API Class E cement containing 4 per cent bentonite and the fluid-loss additive. The benefits of using a low-fluid-Ioss cement slurry The plug was ~isplaced at the rate of 18 bbljmin, which during primary cementing operations are even more pro­ would be suffiCient to cause turbulent flow in the annulus. nounced. As the slurry is circulated upward through the ~o. slurry was left in the pipe, and a temperature survey annulus between the casing and the open hole, it comes mdlcated the top of the high-strength cement to be at 10,- in contact with broad expanses of permeable formation 650 ft. A subsequent cement bond log indicated the top of rock, greatly intensifying the leak-off problem. As a the pozzolanic cement to be at 7,550 ft. Completion of the

480 JOURNAL OF PETROI,EUM TECHNOI,OGY well resulted in water-free production without the neces­ but the fluid-loss values of the two slurries were 40 and sity of block-squeezing. 65 ml/30 minute, respectively. The outline of the per­ All of the primary cementing jobs performed to date foration can be seen on the nodes and the node dimen­ using low-fluid-Ioss slurries have been successful. As far sions are given. The relationship between the fluid-loss as it is possible to ascertain, no channeling occurred and properties of the slurry and the extent of node build-up in every case the entire calculated volume of slurry was can be clearly seen. displaced from the casing. Economic Evaluation Tubingless and Permanent-Type Well Completions The following evaluation in Table 3 shows typical The drilling-out of cement in small tubular goods sub­ comparative job costs of a conventional squeeze operation sequent to a squeeze operation is a particularly trouble­ and one employing a low-fluid-loss slurry in an 8,000-ft some job. Because of small diameter and low tolerances, well. It is assumed that excess low-fluid-loss slurry was there is a constant possibility of sticking and twist-off of reversed-out of the perforated interval following the drill pipe. A low-fluid-Ioss cement is fundamental in elimi­ squeeze. Table 3 reflects a 10 per cent decrease in job nating the drilling-out operation, and particular emphasis costs resulting from use of the low-fluid-loss additive. It must be placed on the filtration characteristics of the does not take into account additional savings resulting slurry so as to properly control node build-up during the from improved job success ratio (75 per cent success for squeeze. This is essential in order to allow the traversing low-fluid-loss squeezes vs 61 per cent success ratio for of the tubing-gun through the squeezed interval in the conventional high-fluid-loss squeeze' ) which, in turn, re­ Downloaded from http://onepetro.org/jpt/article-pdf/14/05/477/2213292/spe-133-pa.pdf by guest on 26 September 2021 event of reperforating. duces the need for additional stages. Squeeze-cementing operations in the Gulf Coast area involving concentric tubing strings have been performed Conclusions using the Bradenhead method. Perforations in 2-in. tubing were squeezed by pumping slurry through I-in. tubing 1. The use of a low-fluid-loss additive for cement facili­ without the use of packers. High displacement pressures tates placement of cement slurries by maintaining fluidity due to friction and high bottom-hole temperatures and and reducing the possibility of premature dehydration. pressures require cement slurries specifically tailored for 2. Use of the hesitation squeeze technique in connection these particular well conditions. It is essential that field with low-fluid-loss slurries provides positive shut-off and slurry compositions be carefully controlled so that the controlled filter-cake build-up. thickening time, fluid-loss properties and weight of the 3. High final squeeze pressures are not essential for the cement will conform to laboratory data. All laboratory success of a low-fluid-loss squeeze operation. tests are conducted in accordance with standard API 4. Lower job costs can be achieved by reversing-out testing procedures.' Fluid-loss tests are conducted in a high-temperature, pressurized Baroid tester using API excess slurry at the completion of the squeeze, thus elimi­ cement filter screens at maximum cementing temperature nating drill-out. and 1,000-psi differential pressure. 5. Evaluation of over 1,000 jobs indicates an over-all It has been shown that node height at perforations is a success ratio of 75 per cent. function of slurry fluid-loss and total filtration time.' Fig. 2 shows nodes recovered following squeeze operations Acknowledgments on offset wells in which the depth of the perforated in­ terval to be squeezed, the cementing temperature, and the The authors wish to express their appreciation to Dowell filtration time were approximately equivalent in the two Div. of The Dow Chemical Co. for permission to present wells. The slurries used were composed of an API Class A this paper, and to S. J. Martinez and D. R. Wieland of cement containing a calcium lignosulfonate-type retarder, the U . of Tulsa for their valuable assistance in its preparation.

References 1. Stout, C. M. and Wahl, W. W.: "A New Organic Fluid-Loss Control Additive for Oilwell Cement", Jour. Pet. Tech. (Dec., Q.I 1960) 12, No.9, 20. g 2. Beach, H. J., et al: "Controlled Filtration Rate Improves Cement Squeezing", World Oil (June, 1961) 152, No.6, 87. 3. Ousterhout, R. S.: "Field Applications of Abrasive-Jetting Techniques", Jour. Pet. Tech. (May, 1961) XIII, 41 3. 4. Hurst, R. E.: "An Engineered Method for the Evaluation and J=O.23 IN, __ C.0.55 IN. Control of Fracturi ng Treatments", Drill. and Prod. Prac., ~I API (1959) 168. 5. Howard, G. C. and Fast, C. R. : "Oplimum Fluid Charactel'-

TABLE 3-COMPARATIVE JOB COSTS IN AN 8,000· FT WEll-CONVENTIONAL SQUEEZE TECHNIQUE VS ONE EMPLOYING A LOW-FLUID-LOSS SLURRY Squeeze Cost Items Neat Cement Low-Fluid-loss ,Pump Truck $330.00 $330.00 Cement-50 sacks 55.00 55 .00 FlAC (61 Ib, 1.3 per cenl) 76.00 Fig. 2-Comparative photographs of nodes ret~ overed from Retrie vable Packer 250.00 250.00 "S Hours Extra Rig Time for Drilling­ two offset wells following squeeze operations. API fluid lo's Out and Round-Trip Tubing of slurry u sed in Well A was 65 ml/30 minutes, while fluid $21 .50/hour 172.00 loss in Well B was 40 ml/30 minutes. Total $807.00 $711.00

MAY, lY62 431 IStICS for Fracture Extension", Drill. and Prod. Pral'., API bined factors of fluid coefficient, pumping time and frac­ (1957) 261. ture width. 6, Perkins, T. K., et al: "Designing Aluminum·Pellet Fracturing Treatments", Paper presented at Spring Meeting of the South· X = 2C("t)' (3) ern Dist. of API Div. of Production (March 8·10, 1961). W 7. Howard, G. C. and Clark, J. B.: "Factors to be Considered in where X = constant, dimensionless, Obtaining Proper Cementing of Casing", Drill. and Prod. Prac., API (1958) 257. t = V /Q = total pumping time, minutes, 8. "Recommended Practice for Testing Oil· Well Cements and V = slurry volume, cu ft, Cement Additives", RP lOB, API, Ninth Ed. (Jan., 1960). Q = constant injection rate, cu ft/min, and 9. Binkley, G. W., Dumbauld, G. K. and Collins, R. E.: "Factors Affecting the Rate of Deposition of Cement in Unfractured W = fracture width, cu ft. Perforations During Squeeze.Cementing Operations", Trans., AIME (1958) 213, 51. Step 4 APPENDIX From the fracture area, determine volume of cement slurry necessary to fill the fracture void. The procedure for determining the volume of cement QW [ .. 2X slurry required is as follows. A = 4.rC' e \ .. erfc (X) + . -;ot (4)

Step 1 where e = numerical constant (natural logarithm base),

and Downloaded from http://onepetro.org/jpt/article-pdf/14/05/477/2213292/spe-133-pa.pdf by guest on 26 September 2021 Determine fluid coefficient of slurry which is a measure erfc (X) = complimentary error function of X. *** of the resistance to flow of fluid leaking off into the formation. K:::'P) , C = 0.047 --- (1 ) ( 100lt where C = fluid coefficient of slurry, ft/min;' K = permeability of cement filter cake, darcies, = porosity of cement filter cake, per cent. P = differential injection pressure, psi, and l.t = viscosity of cement slurry, cpo

Step 2 J. P. PAVLICH (left) is district engineer for Dowell Div. Based on the desired radial penetration, calculate the of The Dow Chemical Co. at Houston. An engineering area of one face of the fracture. graduate of Oklahoma State U. at Stillwater, he joined A = "r' (2) Dowell at Hobbs, N. M., in 1952 where he worked as a where A = fracture area, sq ft, and petroleum engineer and field service engineer until trans­ r = fracture radius, ft. ferring to Houston in 1959. W. W. WAHL (right) is Lab­ oratory Group Leader of Dowell's cement research and development group in Tulsa. He joined the company as a Step 3 chemist in 1957 after graduating from the U. of Kansas Determine the constant X which represents the com- with a BS degree in chemistry.

-1.82 ,10CR'\'AL OF PETROLEC'l TECH'iOLOGY