Patent Publication Number: US-6984611-B2

Title: Spotting fluid for differential sticking

Description:
This application is a division of and claims priority from U.S. patent application Ser. No. 10/117,957, filed Apr. 8, 2002, now U.S. Pat. No. 6,662,871, which is a division of U.S. patent application Ser. No. 09/758,754, filed Jan. 10, 2001, and issued as U.S. Pat. No. 6,435,276 on Aug. 20, 2002. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to compositions and methods for unsticking or freeing differential stuck pipe used in drilling a borehole for hydrocarbons in a subterranean formation. 
     2. Description of Relevant Art 
     Rotary drilling methods employing a drill bit and drill stems have long been used to drill wellbores in subterranean formation. Drilling fluids or muds are commonly circulated in the well during such drilling to cool and lubricate the drilling apparatus, lift cuttings out of the wellbore, and counterbalance the subterranean formation pressure encountered. The specific gravity of a well fluid is normally adjusted in such a way that the pressure of the fluid on the rock formations exceeds the formation pressure on the well. As a result, liquid components of the well fluid are forced into the formation surrounding the well while insoluble components settle on the walls of the well in the form of a stabilizing “filter cake.” 
     Inevitably in drilling a well, the path followed by the drill pipes will deviate some from the vertical or other desired path for the well. At such consequent deviations or “kinks,” the rotating drill pipes may come into contact with the filter cake and even with the wall of the well and become buried therein, resulting in jamming or sticking. 
     Such jamming or sticking is particularly common when pipe connections, which are larger in diameter than the drill pipes themselves, come into contact with the kinks. 
     The most frequent cause of jamming or sticking of drill pipes is differential jamming. Differential jamming can occur when the rotation of the drill pipes is stopped. If a drill pipe then comes into contact with the filter cake adhering to the wall of the well, the drill pipe is forced into the wall of the well by the hydrostatic pressure of the column of mud. The contact surface is then isolated from the mud pressure. If, as is usually the case, the mud pressure is greater than the formation pressure, the contact surface is held fast to the wall by suction forces. The suction force increases with the thickness and compressibility of the filter cake. With time, even relatively large sections of the drill pipe can become held fast. Thus, prompt treatment is best. 
     Prompt freeing of the stuck drill pipe is also needed to alleviate lost drilling time and the consequent costs which that involves. 
     Spotting fluids are used by those skilled in the art to free stuck drill pipe. Spotting fluids need a good lubricating effect and the ability to ensure good oil wettability of the surfaces of the drill pipe and of the walls of wells coming into contact with the drill pipe. 
     To maximize utility in freeing stuck pipe, the spotting fluid should be applied at exactly the point in the well at which the pipe has become stuck. This is accomplished in the same general way in which the well fluid is introduced into the well. Instead of the well fluid, the spotting fluid is forced through the interior of the drill pipe to the bit, which leaves the bit, and slowly ascends in the well to the point of the stuck pipe. Thus, it is critically important to be able to exactly adjust the specific gravity of the spotting fluid so that it will be such as to keep the spotting fluid at that location in the well of the stuck pipe for sufficient time for its lubricity-enhancing properties to act to free the stuck pipe. 
     Since prompt use of a spotting fluid is important, it is standard practice at the drill site to store spotting fluid or spotting fluid concentrates which may rapidly be adjusted to the required density and consistency by addition of barite or other weighting materials and optionally other additives and water. 
     Spotting fluids known in the art typically consist of hydrocarbon mixtures, often based on diesel oils or mineral oils. Emulsifiers and surfactants are typical additives. 
     Such prior art spotting fluids may cause environmental concerns if they come into contact with ground soil formations. Further, since oil based spotting fluids mix with the drilling fluid during discharge from the well, such oil based spotting fluids contaminate the water based drilling fluids which then have to be discarded and separately treated to avoid environmental concerns, adding further to the drilling costs. The environmental concerns are enhanced in off-shore drilling where there is less space to store discarded fluids for treatment. 
     U.S. Pat. No. 4,964,615 issued in 1990 to Mueller et al. discloses an ester based spotting fluid that is said to have fewer environmental concerns than the mineral oil or diesel oil based fluids. However, a need continues to exist for more efficient and improved, environmentally friendly spotting fluids that are effective in freeing stuck pipe. 
     SUMMARY OF THE INVENTION 
     The composition and method of the present invention are useful in treating and alleviating stuck pipe, particularly differential stuck pipe, during drilling of a wellbore in a subterranean formation. The preferred composition of the invention is an invert oil mud system comprising iso-butyl oleate as the external phase and glycerin (preferably) or calcium chloride (CaCl 2 ) solution as the internal phase. For application to stuck pipe downhole, this emulsion may be combined with, added to, or mixed with other fluids for carrying the emulsion to the treatment site and holding it there long enough to free the stuck pipe. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention provides a new composition and method of using such composition for freeing stuck drill pipes. The composition and method are particularly useful in freeing differential stuck pipe. 
     The composition of the invention comprises a water-in-oil emulsion or an invert oil mud system. The emulsion comprises iso-butyl oleate as the external phase and either glycerin (preferably) or calcium chloride as the internal phase, preferably in a ratio ranging from about 95:5 to about 50:50 oil phase to water phase or more specifically oleate to either glycerin or about 38% aqueous calcium chloride solution. This emulsion may be added to or mixed with other treatment products and with materials or products to facilitate delivery of the emulsion to the site of the stuck pipe and holding of the emulsion at such site sufficient time to enable the emulsion to cause or effect unsticking of the pipe. Such typical additives or additional materials include, for example, about 2 to about 14 pounds per barrel EZ-MUL NTE™ (an emulsifier/oil wetting agent), available from Halliburton Energy Services, Inc., Houston, Tex.; about 0.5 to about 3.0 pounds per barrel DRILTREAT™ (a supplemental oil wetting agent), available from Halliburton Energy Services, Inc., Houston, Tex.; about 2 to about 6 pounds per barrel GELTONE II™ (a viscosifier or suspending agent), available from Halliburton Energy Services, Inc., Houston, Tex.; and barite as needed for desired fluid density. 
     An example formulation of a preferred spotting fluid of the invention comprises, as the external phase, about 0.7 barrel (bbl) of iso-butyl oleate as the external phase and, as the internal phase, about 0.3 bbl of glycerin. This formulation is combined with about 8 lb/bbl of EZ-MUL NTE™; about 1 lb/bbl of DRILTREAT™; about 3 lb/bbl of GELTONE II; and barite as needed for desired density. 
     The iso-butyl oleate/glycerin invert emulsion of the invention has the advantageous ability to not only lubricate the surfaces involved in sticking of the metal (of drill pipe or other stuck equipment in the filter cake) but also to dehydrate or destruct the filter cake for enhanced performance as a spotting fluid. The iso-butyl oleate oil phase is effective at lubricating the surfaces and penetrating the filter cake. Glycerin is effective at dehydrating the filter cake. In fact, glycerin, with an a w ≅0.0 (a w  means activity, water phase), is even better at such dehydration than is calcium chloride, with an a w ≅0.30, which has been known to be effective at dehydrating filter cakes. 
     The emulsions of the invention were tested for performance as a spotting fluid in a differential sticking tester, or STICKOMETER™, manufactured by and available from Halliburton in Houston, Tex. The STICKOMETER™ consists of a modified filtration cell in which a mud cake to be tested is deposited by filtration of a mud under pressure. A flat plate is pressed under load onto the mud cake. Spotting fluid is then allowed to soak around the mud cake and stuck plate apparatus. After a period of time, typically about 16 hours, torque-to-flee is measured. This torque is a relative measure of sticking tendency. A typical test procedure follows. Already prepared mud was allowed to filter under 500 psi pressure, generating a mud cake, while collecting 10 ml of filtrate. The metal disk was then stuck in the mud cake, and 2 ml of additional filtrate was collected. For base mud, filtering was done overnight without collecting the 2 ml of filtrate. For spotting fluid evaluation, the pressure was relieved after 2 ml of filtrate, the base mud decanted, then spotting fluid loaded into the cell. Pressure was reapplied and filtration continued overnight, for about 16 hours. The torque was measured the next morning while maintaining 500 psi pressure on the cell. 
     In testing this invention, an invert-oil emulsion of iso-butyl oleate and glycerine was prepared and tested in a STICKOMETER™ and test results—torque to free in inch pounds (in/lbs)—and compared to results with other fluids, including known spotting fluids and commercially available spotting fluids such as COASTAL SPOT™, available from Coastal Mud and Coastal Fluid Technologies, Lafayette, La., a division of Coastal Chemical Co., LLC a Holland Chemical International Co. Tables 1 through 4 show the performance of various experimental and commercial spotting fluid treatments in selected mud systems. In each case, the isobutyl oleate/glycerine composition of the present invention yielded equal or better results than any product tested. 
                         TABLE I               Mud System/Spot   Torque-to-Free (in/lbs)                  Base A (16 ppg Freshwater Lignosulfonate)   350       Base A with addition of:       Diesel oil   170       11.6 CaCl 2  brine   110       12.7 NaBr brine   190       12.7 NaBr brine/3% TORQ TRIM II ™   150       12.7 NaBr brine/3% FSE Fluoro-surfactant   150       30% 12.7 NaBr brine/70% Glycerine   200       Squalane C 30 H 62     120       Squalene C 30 H 50     180       Isobutyl Oleate Neat    60       Oleyl Oleate Neat    80       16 ppg COASTAL SPOT ™/CaCl 2      50       16 ppg COASTAL SPOT ™/NaCl   170       16 ppg Phase 1 of DUAL PHASE ™   110       16 ppg Phase 1 &amp; 2 of DUAL PHASE ™   110       16 ppg Isobutyl Oleate/CaCl 2      70       16 ppg Isobutyl Oleate/Glycerine    40       16 ppg Oleyl Oleate/Glycerine    55                    
TORQ TRIM II™ is available from Halliburton Energy Services, Inc. in Houston, Tex.; COASTAL SPOT™ is available from Coastal Mud and Coastal Fluid Technologies in Lafayette, La.; and DUAL PHASE™ is available from Halliburton Energy Services, Inc. in Houston, Tex.
 
     The base mud in Table 1 is a 16 lb/gal freshwater/lignosulfonate mud. This base mud shows torque-to-free at 350 inch-pounds, a “high” number in terms of sticking tendency, indicating the mud alone likely will not be able to free a stuck pipe. A low torque-to-free number represents or indicates low sticking tendency. As shown in Table 1, all of the various spotting fluid treatments provided some improvement over the base mud for purposes of freeing stuck pipe. The isobutyl oleate/glycerine system of the present invention yielded the best performance, with a very low torque-to-free number of 40. 
                         TABLE 2                   Torque-to-Free       Mud System/Spot   (in/lbs)                  Base B (16 ppg Seawater Lignosulfonate)   280       Base B with addition of:       16 ppg COASTAL SPOT ™/CaCl 2     300       16 ppg ENVIRO-SPOT ™/Freshwater   270       16 ppg Phase 1 of DUAL PHASE ™   290       16 ppg Phase 1 &amp; 2 of DUAL PHASE ™   290       16 ppg Isobutyl Oleate/Glycerine   210       16 ppg Isobutyl Oleate/Glycerine (after 250° F. hot roll)   180                    
COASTAL SPOT™ is available from Coastal Mud and Coastal Fluid Technologies in Lafayette, La.; ENVIRO-SPOT™ is available from Halliburton Energy Services, Inc. in Houston, Tex.; and DUAL PHASE™ is available from Halliburton Energy Services, Inc. in Houston, Tex.
 
     Table 2 shows results with a 16 lb/gal seawater/lignosulfonate mud system. The control or base mud has a torque-to-free value of 280 in/lbs. Best performance again was with the isobutyl oleate/glycerine composition of the present invention, providing a torque-to-free of 210 in/lbs. Hot rolling this spotting fluid at 250° F. before conducting the STICKOMETER™ test yielded further improved results. 
                                 TABLE 3                       Mud System/Spot   Torque-to-Free (in/lbs)                          Base C (16 ppg POLYNOX ™)   380           Base C with addition of:           16 ppg COASTAL SPOT ™/CaCl 2     240           16 ppg Phase 1 of DUAL PHASE ™   260           16 ppg Isobutyl Oleate/Glycerine   160           Base D (16 ppg PHPA Mud)   205           Base D with addition of:           16 ppg COASTAL SPOT ™/CaCl 2     160           16 ppg Phase 1 of DUAL PHASE ™   155           16 ppg Isobutyl Oleate/Glycerine   170                        
POLYNOX™ is available from Halliburton Energy Services, Inc. in Houston, Tex.; COASTAL SPOT™ is available from Coastal Mud and Coastal Fluid Technologies in Lafayette, La.; and DUAL PHASE™ is available from Halliburton Energy Services, Inc. in Houston, Tex.
 
     Table 3 shows some limited results with a POLYNOX™ mud and with a PHPA (partially-hydrolyzed, polyacrylamide) based mud, both at 16 lb/gal. Again, isobutyl oleate/glycerine of the present invention showed the best results in the POLYNOX™ system. COASTAL SPOT™, DUAL PHASE™ and isobutyl oleate/glycerine of the present invention showed about the same performance in the PHPA mud system. 
     
       
         
           
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                 Mud System/Spot 
                 Torque-to-Free (in/lbs) 
               
               
                   
               
             
            
               
                 Base E (12 ppg Freshwater Lignosulfonate) 
                 185  
               
               
                 Base E with addition of: 
               
               
                 12 ppg DUAL PHASE ™ 
                 115  
               
               
                 12 ppg COASTAL SPOT ™-old 
                 75 
               
               
                 12 ppg COASTAL SPOT ™-new 
                 70 
               
               
                 12 ppg Isobutyl Oleate/Glycerine 
                 80 
               
               
                   
               
            
           
         
       
     
     Table 4 shows results with a 12 lb/gal freshwater/lignosulfonate mud system. Three commercial products and the isobutyl oleate/glycerine composition of the present invention showed similar performance in this mud system. With each, torque was reduced by over 50%. 
     Further, the iso-butyl oleate/glycerin composition of the present invention is environmentally acceptable. Mysid shrimp LC 50  tests were conducted according to industry standards. An invert emulsion comprising the oleate/glycerin composition was evaluated at 5 and 10 volume % in generic #7 drilling fluid (industry standard). Results for 96-hour LC50 in mg/L SPP were 267,600 and 227,700 respectively. Gulf of Mexico minimum by regulation is 30,000. Operators prefer 100,000 or more. 
     Without wishing to limit the invention, it is expected that the isobutyl oleate/glycerine composition of the present invention would be used over a density range of about 10 to about 16 lb/gal., depending on the circumstances of the case, and likely particularly associated with the well and the stuck pipe. Table 5 shows rheology and mud properties for an isobutyl oleate/glycerine invert mud system at 10, 13 and 16 lb/gal densities. These values in Table 5 are consistent with a reliable and stable mud system over this density range. 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Study of Mud Properties or 10, 13, &amp; 16 lb/gal experimental spotting 
               
               
                 fluid pills comparison of GELTONE II &amp; SUSPENTONE 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Sample Mark 
                 A 
                 A 
                 B 
                 B 
                 C 
                 C 
                 D 
                 D 
                 E 
                 E 
                 F 
                 F 
                 G** 
                 G** 
                 H*** 
                 H*** 
               
               
                   
               
               
                 Experimental Spotting Fluid, 
                 0.66* 
                   
                 0.62* 
                   
                 0.57* 
                   
                 0.66* 
                   
                 0.62* 
                   
                 0.57* 
                   
                 0.57* 
                   
                   
                   
               
               
                 bbl 
               
               
                 Glycerine, bbl 
                 0.23 
                   
                 0.17 
                   
                 0.11 
                   
                 0.23 
                   
                 0.17 
                   
                 0.11 
                   
                 0.11 
                   
                 SEE 
                 SEE 
               
               
                 Barite 
                 124 
                   
                 293 
                   
                 456 
                   
                 123 
                   
                 293 
                   
                 456 
                   
                 456 
                   
                 B 
                 B 
               
               
                 GELTONE II ™, lb 
                 4 
                   
                 3 
                   
                 2 
                   
                 — 
                   
                 — 
                   
                 — 
                   
                 — 
                   
                 E 
                 E 
               
               
                 SUSPENTONE ™, lb 
                 — 
                   
                 — 
                   
                 — 
                   
                 4 
                   
                 3 
                   
                 2 
                   
                 2 
                   
                 L 
                 L 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
                 O 
                 O 
               
               
                 Density, lb/gal. 
                 10.0 
                   
                 13.0 
                   
                 16.0 
                   
                 10.0 
                   
                 13.0 
                   
                 16.0 
                   
                 16.0 
                   
                 W 
                 W 
               
               
                 Stirred, min. 
                 30 
                 — 
                 30 
                 — 
                 30 
                 — 
                 30 
                 — 
                 30 
                 — 
                 30 
                 — 
                 30 
                 — 
                 30 
                 — 
               
               
                 FANN 35: 
                 80 
                 120 
                 80 
                 120 
                 80 
                 120 
                 80 
                 120 
                 80 
                 120 
                 80 
                 120 
                 80 
                 120 
                 80 
                 120 
               
               
                 Temp ° F. 
               
               
                 600 rpm 
                 76 
                 52 
                 102 
                 72 
                 151 
                 108 
                 75 
                 53 
                 108 
                 75 
                 154 
                 112 
                 OFF 
                 290 
                 O/S 
                 170 
               
               
                 300 rpm 
                 45 
                 30 
                 59 
                 41 
                 85 
                 60 
                 46 
                 31 
                 64 
                 43 
                 88 
                 63 
                 S 
                 180 
                 212 
                 91 
               
               
                 200 rpm 
                 34 
                 20 
                 43 
                 30 
                 63 
                 49 
                 35 
                 20 
                 44 
                 32 
                 64 
                 51 
                 C 
                 140 
                 150 
                 70 
               
               
                 100 rpm 
                 22 
                 14 
                 27 
                 20 
                 39 
                 28 
                 20 
                 15 
                 28 
                 22 
                 40 
                 30 
                 A 
                 95 
                 85 
                 40 
               
               
                  6 rpm 
                 6 
                 4 
                 7 
                 5 
                 9 
                 7 
                 6 
                 4 
                 7 
                 6 
                 9 
                 8 
                 L 
                 35 
                 15 
                 10 
               
               
                  3 rpm 
                 5 
                 3 
                 6 
                 4 
                 8 
                 6 
                 5 
                 3 
                 6 
                 5 
                 8 
                 7 
                 E 
                 31 
                 12 
                 8 
               
               
                 Plastic Viscosity, cp 
                 31 
                 22 
                 43 
                 31 
                 66 
                 48 
                 29 
                 22 
                 44 
                 32 
                 66 
                 49 
                 — 
                 110 
                 — 
                 79 
               
               
                 Yield Point, lb/100 sq. ft. 
                 14 
                 8 
                 16 
                 10 
                 19 
                 12 
                 17 
                 9 
                 20 
                 11 
                 22 
                 14 
                 — 
                 70 
                 — 
                 12 
               
               
                 10 sec gel, lb/100 sq. ft. 
                 4 
                 3 
                 5 
                 4 
                 6 
                 5 
                 5 
                 3 
                 5 
                 4 
                 8 
                 7 
                 — 
                 30 
                 12 
                 7 
               
               
                 10 min gel, lb/10 sq. ft. 
                 6 
                 5 
                 7 
                 6 
                 9 
                 7 
                 9 
                 6 
                 10 
                 8 
                 12 
                 11 
                 — 
                 52 
                 20 
                 12 
               
               
                 Electrical Stability, V 
                 312 
                 288 
                 512 
                 609 
                 612 
                 714 
                 504 
                 512 
                 761 
                 832 
                 1124 
                 1180 
                 1312 
                 1406 
                 395 
                 412 
               
               
                 Filtrate, 200° F., 500 psi, ml 
               
               
                 Oil, ml 
                 27.4 
                   
                   
                   
                   
                   
                 36.4 
                   
                   
                   
                   
                   
                   
                   
                 17.2 
               
               
                 Water, ml 
                 8.8 
                   
                   
                   
                   
                   
                 14.6 
                   
                   
                   
                   
                   
                   
                   
                 0.8 
               
               
                   
               
            
           
         
       
     
     The single asterisk in Table 5 designates values for the experimental spotting fluid which comprised 8 lb EZ MUL NTE™ and 1 lb DRIL TREAT™ in a barrel of isobutyl oleate. Double asterisks in Table 5 designates values for Experimental Spotting Fluid (Sample G) which comprised 8 lb EZ MUL NTE™ and 1 lb DRILTREAT™ in a barrel of oleyl oleate. Triple asterisks in Table 5 designates values for Sample H which comprised COASTAL SPOT™ which comprised a 16.0 lb/gal pill mixed according to COASTAL SPOT™ guidelines. 
     Table 6 shows a decided advantage of the invention. The test results of Table 6 show not only the effectiveness of the oleate/glycerin invert emulsion as a spotting fluid, but also that such spotting fluid in the water-based drilling fluid does not have to be separated and removed from the operating mud system after use, saving time and money. Spotting fluid volumes are typically about 50 to about 100 barrel “pills” in operating mud systems of about 1000 barrels or more. Once stuck pipe is no longer stuck, i.e., is free, the spotting fluid composition of the present invention used to free the pipe can be circulated in with the operating mud system. Table 6 shows that up to about 10 volume percent of isobutyl oleate/glycerine fluid mixed in with a seawater/lignosulfonate mud creates no final mud problems. To the contrary, the lubricity of the final mud mixture is improved some by leaving in the isobutyl oleate/glycerine, a further advantage of the invention. 
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 CONTAMINATION TESTS (sea water mud) 
               
               
                 Initial Properties and Properties After Hot Rolling at 150° F. and 250° F. 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Sample Mark 
                 A 
                 A 
                 B 
                 B 
                 C 
                 C 
                 AA 
                 D 
                 D 
                 DD 
               
               
                   
               
               
                 Base Mud*, bbl 
                 1.0 
                 1.0 
                 1.0 
                 1.0 
                 1.0 
                 1.0 
                 1.0 
                 1.0 
                 1.0 
                 1.0 
               
               
                 Experimental 
                 — 
                 — 
                 0.05 
                 0.05 
                 0.10 
                 0.10 
                 — 
                 0.10 
                 0.10 
                 0.10 
               
               
                 Spotting Fluid Pill, 
               
               
                 bbl 
               
               
                 Q-BROXIN ™, lb 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 2.0 
                 2.0 
                 2.0 
               
               
                 CARBONOX ™, lb 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 2.0 
                 0.0 
                 1.0 
               
               
                 Caustic soda, lb 
                   
                   
                   
                   
                   
                   
                   
                 1.0 
                 1.0 
                 1.0 
               
               
                 Stirred, min 
                 15 
                 15 
                 15 
                 15 
                 15 
                 15 
                 15 
                 15 
                 15 
                 15 
               
               
                 Rolled at 150° F., hr 
                 0 
                 16 
                 0 
                 16 
                 0 
                 16 
                 16 
                 0 
                 16 
                 16 
               
               
                 Rolled at 250° F., hr 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 16 
                 — 
                 — 
                 16 
               
               
                 Test Temp., ° F. 
                 80 
                 80 
                 80 
                 80 
                 80 
                 80 
                 80 
                 80 
                 80 
                 80 
               
               
                 Mud Density, 
                 16.0 
                 16.0 
                 16.0 
                 16.0 
                 16.0 
                 16.0 
                 16.0 
                 16.0 
                 16.0 
                 16.0 
               
               
                 lb/gal. 
               
               
                 Plastic Viscosity, 
                 40 
                 44 
                 34 
                 38 
                 39 
                 38 
                 37 
                 35 
                 41 
                 39 
               
               
                 cp 
               
               
                 Yield Point, lb/100 
                 18 
                 13 
                 36 
                 31 
                 41 
                 36 
                 13 
                 25 
                 19 
                 13 
               
               
                 sq. ft 
               
               
                 10 sec gel, lb/100 
                 7 
                 6 
                 16 
                 12 
                 20 
                 17 
                 4 
                 8 
                 7 
                 5 
               
               
                 sq ft 
               
               
                 10 min gel, lb/100 
                 21 
                 18 
                 40 
                 30 
                 50 
                 41 
                 12 
                 24 
                 18 
                 15 
               
               
                 sq ft 
               
               
                 pH 
                 9.7 
                 9.4 
                 9.8 
                 9.5 
                 9.7 
                 9.2 
                 8.9 
                 11.7 
                 11.2 
                 9.2 
               
               
                 API Filtrate, ml 
                 — 
                 2.6 
                 — 
                 3.2 
                 — 
                 3.6 
                 — 
                 — 
                 3.0 
                 — 
               
               
                 Filtrate, 250° F., 500 
                 — 
                 8.4 
                 — 
                 10.0 
                 — 
                 9.8 
                 — 
                 — 
                 8.2 
                 — 
               
               
                 psi, ml 
               
               
                 FANN 35: 
               
               
                 600 rpm 
                 98 
                 101 
                 104 
                 107 
                 119 
                 112 
                 87 
                 95 
                 101 
                 91 
               
               
                 300 rpm 
                 58 
                 57 
                 70 
                 69 
                 80 
                 74 
                 50 
                 60 
                 60 
                 52 
               
               
                 200 rpm 
                 45 
                 43 
                 55 
                 57 
                 65 
                 63 
                 38 
                 50 
                 48 
                 44 
               
               
                 100 rpm 
                 30 
                 27 
                 37 
                 38 
                 48 
                 45 
                 21 
                 30 
                 28 
                 22 
               
               
                  6 rpm 
                 9 
                 7 
                 18 
                 14 
                 24 
                 19 
                 5 
                 9 
                 8 
                 6 
               
               
                  3 rpm 
                 7 
                 6 
                 16 
                 12 
                 22 
                 17 
                 4 
                 8 
                 7 
                 5 
               
               
                 LUBRICITY 
                 — 
                 0.23 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 0.18 
                 — 
               
               
                 COEFFICIENT 
               
               
                 % Lubricity 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 — 
                 21.7 
               
               
                 Improvement 
               
               
                   
               
            
           
         
       
     
     The Base Mud in Table 6 is comprised of 0.72 bbl sea water, 12 lb AQUAGEL™, 30 lb Rev Dust, 4 lb Q-BROXIN™, 1 lb caustic soda, 416 lb barite and 0.5 lb BARAZAN PLUS™. AQUAGEL™ is available from Halliburton Energy Services, Inc. in Houston, Tex.; Q-BROXIN™ is available from Halliburton Energy Services, Inc. in Houston, Tex.; and BARAZAN PLUS™ is available from Halliburton Energy Services, Inc. in Houston, Tex. 
     In the method of the invention, a spotting fluid comprising an invert water-in-oil emulsion of the invention—glycerin or calcium chloride brine in isobutyl oleate—is used to free stuck pipe, particularly differentially stuck pipe. 
     The foregoing description of the invention is intended to be a description of preferred embodiments. Various changes in the details of the described composition and method can be made without departing from the intended scope of this inventions as defined by the appended claims.