Experimental Research of Gas Hydrate Drilling Fluids Using Polyethylene Glycol as an Inhibitor

urnal of China University of Geosciences, Vol, 17, No 3, P. 276-282, September 2006ISSN1002-0705Printed in ChitExperimental Research of Gas Hydrate DrillingFluids Using polyethylene glycol as an InhibitorZhang Ling'(张凌) Jiang guosheng(蒋国盛) Tu Yunzhong(涂运中Cai jihua(蔡记华) Dou Bin(窦斌) Zhang Jiaming(张家铭) Ning Fulong(宁伏龙)Faculty of Engineering, China University of Geosciences, Wuhan 430074, ChinaABSTRACT: Low temperature is the key for maintaining the wellbore stability of the gas hydrate welland for ensuring the safety in the well. In this article, the characteristics of drilling in the permafrostcontaining gas hydrates are analyzed initially. And later, the relative properties and the inhibitory mechanisms of the polyethylene glycol and the hydrate inhibitor of the drilling nuids ensuring drilling safetyare discussed. On the basis of these, the effects of the molecular weight and the content of the polyethy-lene glycol, and its interaction with the salts on the performances of the four groups of drilling fluids un-der low temperature are mainly analyzed. The results of these analyses show that for the relative drillingfluid system, the 5% content of polyethylene glycol with a molecular weight of 10 000 combined with15%NaCl+5% KCl or 20% NaCl is suitableKEY WORDS: drilling fluids, gas hydrate, polyethylene glycol, inhibitor.INTRODUCTIONand the relative characteristics and inhibitory mechaGas hydrate is an ice-like crystal compound gen nisms of the polyethylene glycol(PEG )have beenerally formed by water and natural gas molecules, discussed and analyzed in this article. Subsequentlywhich is mainly distributed under the ocean floor and on the basis of the relative experiments(ning et alin the permafrost and is viewed as an energy resource 2006), experimental research of the relative lowwith great potential (Jiang et al., 2002). For the rel- temperature performance of the four groups of drillative exploration and development of gas hydrate in ing fluids containing PEG has been carried out.China, some specialists and scholars have suggestedthat relative test drilling exploitation should be done CHARACTERISTICS OF DRILLING IN THE PER-in the permafrost(Liu, 2005; Li and Geng, 2000). MAFROST CONTAINING GAS HYDRATESDrilling in the permafrost has unique characteristicsThe temperature increment and the groundin which controlling the formation and decomposition stress release of the formation are made by drilling inof gas hydrate is the most important, and all of these the permafrost containing gas hydrates, which easilyhave a considerable relationship with the low- leads to the decomposition of the gas hydrates andtemperature performance of the drilling fluids contai- the release of large amounts of gas that decreases thening gas hydrate inhibitors. The characteristics of density of the drilling fluids. The gas hydrates maydrilling in the permafrost containing gas hydrates, be reformed in certain areas by the released gas andy the water in the drilling fluids. When drilling isThis paper is supported by the National Natural Science Foundation of carried out in these formations, the stability of theChina(No. 50504012), the New Century Excellent Talent Supporing gas hydrates is maintained by increasing the pressureProgram of Ministry of Education of China, China Postdoctoral Science in the well, cooling the drilling fluids, adjusting theFoundation( No. 2005037681)and the Excellent Young Teachers Spon- relative drilling parameters, and adding the inhibied Program of CUG(No. CUGQNL0623).tors, which makes drilling safe ( Jiang et al., 2001)Corresponding author: flyzlingfly 163 corle using drilling flu-Manuscript received March 22, 2006id中国煤化工maintaining the staManuscript accepted June 25, 2006.bilitC N MH Guring the safety inExperimental Research of Gas Hydrate Drilling Fluids Using Polyethylene Glycol as an Inhibitor277he well. During drilling in the formations, the spe- the temperature increases, the more PEg is separatedcial requirements are low temperature and inhibition out and the stronger is its inhibition(Liu et alof decomposition of gas hydrates. Good antifreeze 2001: Chen, 1998: Guo et al., 1997: Lu et alperformance and rheological performance are required 1997: Aston, 1994)by the former, which can be obtained by adding antThe greater the molecular weight of PEG, thefreeze agents and using flow-pattern adjustors, and stronger its inhibition. PEG with high moleculargas hydrate inhibition is required by the latter, which weight acts as an agent that decreases fluid loss bycan be obtained by adding relative inhibitors, such as increasing the viscosity When the content of PEG isthermodynamics inhibitors, kinetic inhibitors, and increased, the fluid loss of drilling fluids is controlledantr-agglomerants.and stronger shale inhibition is achieved. Adding agiven polymer also enhances the inhibition by PEGCHARACTERISTICS AND INHIBITORY MECHA-( Liu et al., 2001)NISMS OF PEGThe PEG is a water-soluble polymer that can be EXPERIMENTAL RESULTS AND DISCUSSIONtransformed from white viscous fluid to a waxy solidAccording to the above statements, PEG haswith increment of molecular weight, and it is com- many properties, such as shale inhibition and welpletely soluble in water and also soluble in other sub- bore stabilization. At the same time. it is a thermostances. It has good stability and a lubricating prop- dynamic inhibitor with some amount of gas hydrateerty and has low toxicity and causes no irritation. inhibition, and is a common additive to deepwaterThe water-based PEG drilling fluids are composed of drilling fluids. The experiments on inhibition of gasPEG, polymers, and inorganic salts that have good hydrate formation with water-based PEG drilling flu-shale inhibition, lubricating ability, the ability of ids have been carried out by foreign researchersflow-pattern adjustment, low toxicity, and the biode- which show that a better inhibition of gas hydrategradability favorable to environmental protection. formation can be achieved using PEG, NaCl, andThese are viewed as oil-based-like water-based dKCI together Hege et al., 2001). relattive expering fluids and are paid a great deal of attention (Guo mental researches have also been carried out by re-et al., 1997: Lu et al., 1997: Aston, 1994 ). They searchers in China on the inhibition of PEG under ahave been applied to some foreign complex formaroom temperature ( Bai et al., 2005; Huang et al., 2005).tions and the Well Chevgu-l Wei et al., 2003On the basis of the above reasons, as a low tem-Zhang et al., 2001)perature has a relatively great effect on the rheologicThe three inhibitory mechatfollows. The first mechanism is the synergetic effect.of PEG are as behavior of drilling fluids and pressure commonly hasK+ adsorbed in the clay surface compresses the elec- an insignificant effect on the rheological behavior ofwater-based drilling fluids Sun et al., 2004), PEGtrical double layer and makes the hydration film thin- has been selected as a gas hydrate inhibitor. Severalner and more favorable for the absorption of PEG.experimental researches have been carried out, andAs a result of this, PEG is strongly adsorbed in the the experimental apparatuses and the methods haveshale surface and the water is discharged. So thisprevents the clay from having direct contact with thewater and the hydration and dispersion of the shale isnhibited. Also, PEG can have different degrees ofsynergetic effect with other inorganic salts. The sec-ond mechanism is osmosis. With the Peg the vis-cosity of the drilling fluid filtrate can be increasedNo 5and the water activity can be decreased so that osmotic pressure can be reduced, which is helpful tothe stability of the shale and the wellbore. The thirdmechanism is the cloud point behavior. When the中国煤化工1000100temperature is higher than the cloud point, the PEGis separated out and adsor bed in the clay surface and FigurCNMHGf No. 6. No. 7plugs the pore, decreasing the fluid loss. The moreo.8,and No. 9 formulations(-20 C).Zhang Ling, Jiang Guosheng, Tu Yunzhong, Cai Jihua, Dou Bin, Zhang Jiaming and Ning Fulongbeen described in the literature. The experimental re-Table 3 The second group formulationssearches have been discussed and analyzed in this arlo. Formulationticle, and the percentages in this article is in mass11 Water+20% NaCl+3%LG+percent.5% PAM12 Water +20%NaCl+5% PEG(20 000)+The First Group Formulations%LG+5% PAMThe aim of these group formulations is to study13waer+20%NaCl+10%PEG(20000)+the effect of the different contents of peg. with a3%LG+5%PAMmolecular weight of 10 000 on drilling fluids. Thecontent of Peg in these formulations is shown in TaTable 4 The experimental results of the secondble 1, and the results are shown in Table 2.group formulationsTable I The content of Peg of the first group formulations No. i(e) Boo Bae(mPa. s).(m Pa. s) PH(mL)123456789101110128.567.733.633.856 NMContent of Peg(10000)(wt%)344.555.5681012157537.737.537.36NM-101859292.5he base formulation is water+20%NaCl20235119117.5PAM. PEG. polyethylene glycol. LG is a kind of vegetable131572.237.736.134.5650gum developed by the drilling fluids project group of the Faculty of Engineering, CUG. PAM. polyacrylamide.1075.338.537.6536.8659394 6 NM60able 2 The experimental results of the first group formulations64220>300187THTM6 NMAVNo.t(℃)(mPa·s)(mPa·s)(mL)NM. not measured812775.163.52 136.5 7 68.25 65.56 0.5 of PEG are 8% and 10%, respectively. The FLs of3-20>300126.5THTM63 drilling fluids in which the contents of PEG are gr41054.52527.2529.5 6 3.8 ter than 8% are all too large, and the FLs of No. 420 250 106 125 1446 18.5 No. 5, and No. 6 are too small to meet the drilling51047.820.523.9demand. These results show that the content of peg96.5 94.26 15 in drilling fluids in the range of 5% to 6% is favora6 10 45.4 19.5 22.7 25.96 11 ble to control the viscosity and fluid loss of drilling fluids20280133For drilling in the permafrost containing gas hy7 8 36.6 18.7 18.3 17.9 6 90 drate, a good, low-temperature flowing property of8 10 36.4 17.9 18.2 18.5 6 92 drilling fluids is very important. So, the experimen-9844.221.122.1tal researches on the low-temperature flowing prop101053.226.526.66 85 erty have been carried out for No. 3, No. 4, No. 5THTM. too high to measure.and No. 6 formulations the Fls of which are controlled well. When the temperature is -20 C, thehas n the range of 8 to 10C, the content of PEG values of AV and pv of drilling fluids decreased ini-a considerable effect on the apparent viscosity tially and then increased with an increment in the(AV), the plastic viscosity (PV), and the fluid loss content of the PEG. The values of AV and Pv of the(FL) of drilling fluids(Table 2). In this tempera- No. 8 formulation are the smallest, and those of theture range, the corresponding values of AV and PV No. 7 formulation are slightly larger than those ofchanged with the increment in the content of Peg, the No. 5 formulation. Similarly, the low-hich increased initially, and then decreased, and temp…fNo.5 and no.again increased finally. In this group the values of form中国煤化工 d the fls of nAV and PV of No. 2 formulation, in which the con- 3, NC N MH Gormulations in thistent of PEG is 4%, are the highest, and those of No. temperature are 3, 18. 5, 15, and 25 mL, respective7 and No. 8 are relatively low, in which the contents ly. These results show that when the temperature ofExperimental Research of Gas Hydrate Drilling Fluids Using Polyethylene Glycol as an Inhibitordrilling fluids is C, the content of PEG in drill- been increased from 5% to 10%, the values of Aving fluids in the range of 5% to 5. 5% is favorable to and PV of No. 12 and No. 13 formulations decreasecontrol the viscosity and fluid lossin the range of -8 to 15 C, but, in the range of20 to-8C, the values of av and pv of noThe Second Group Formulationsand No. 13 formulations suddenly increase. ThiThe second group formulations are shown in Ta- shows that increasing the content of PEG, with able 3. As shown in Table 4, in the range of 7 to 10 molecular weight of 20 000, can decreC, relative to the No. 11 formulation, the values of Pv of drilling fluids, and this is favorable to controlAV and PV of No. 12 and No. 13 formulations have the flowing property of drilling fluids in the range ofbeen decreased apparently by adding PEG, which -8 to 15 C, but at lower temperatures, such as inshows PEG has the apparent ability of decreasing the the range of -20 to-8C, the increasing contentviscidity. With the lowering of temperature, the val- leads to the sudden increment of viscidity, which isues of AV and PV of No. 12 and No. 13 formulations unfavorable to the control and adjustment of the flowncrease rapidly.pattern of drilling fluids( Fig. 2).When the content of Peg in drilling fluids hasNo.137℃85℃020040060080010001200020040060080010001200r(1/s)Figure 2. The rheological curves of No. 12 and No. 13 formulations.Table s The third group formulationsFormulation14 Water+5% NaCl +5% PEG(10 000)+2% LG+5% PAM15 Water + 5% NaCI+5% PEG(20 000)+ 2%LG+5%PAM16 Water 5%NaCl+ 5%KCI+5% PEG(10 000)+2%LG +5% PAM +2% CMC17 Water 15% NaC+5% KCl 5% PEG(10 000)+2%LG+5% PAM+2% CMC18 Water +5% NaCl+5%KCI+ 5% PEG(20 000)+2%LG+5% PAM+2% CMCWater+15% NaCl+5% KCI +5% PEG(20 000)+2% LG +5% PAM +2% CMCCMC. carboxymethyl cellulose.Table 6 The experimental results of the thirdComparing the results of No. 12, No. 13, Nogroup formulations4, and No. 8, the values of Av and Pv of drillingNo,t(℃C),600(mPa.s)(mPa.)PH FL fluids containing PEG with a molecular weight of10 000 are lower than those of drilling fluids cont2714,113.5ning PEG with a molecular weight of 20 000. Whe18.529.615.914.813. 7 6 0. 5 the temperature of drilling fluids is in the range of 715 24.5 33.6 17.4 16.8 16.2 6 NM to 15C or-20 C, the values of AV and PV of No17-201826.551.2202531.2816.5ion,中国煤化工e latter is good.ThesCNMHGwith a molecular12>300192THTM19 -20 284 140.7142 34 weight of 10 000 has a stronger ability of decreasingZhang Ling, Jiang Guosheng, Tu Yunzhong, Cai Jihua, Dou Bin, Zhang Jiaming and Ning Fulong000, and the 5% content of PEG in drilling fluids No. 16, No. 17, No. 18, and No. 19 formulationsis helpful in controlling the viscidity and Fl of drill- in the range of -20 to-12C, for drilling fluidscontaining PEG either with a molecular weight of10 000 or 20 000, the increasing content of NaCl inThe Third Group Formulationsdrilling fluids can decrease the viscidity, but the exThe third group formulations and the relative re- tent of the decrease in viscidity is different, and theults are shown in Tables 5 and 6, respectively. In 24 extent in drilling fluids containing PEG with 20 000C, the values of AV and PV of No. 14 formulation molecular weight is greater.are lesser than those in the no. 15 formulation, AtSo, for these group drilling fluids, the increasing12 and -20 C, the values of AV and PV of No. content of NaCl in drilling fluids and the decrease in16 and No. 17 formulations are lesser than those of the molecular weight of PEg can also decrease theNo. 18 and No. 19 formulations, respectively. This viscidity of drilling fluids, and the former can en-also shows that the PEg with a molecular weight of hance the anti-freeze performance of drilling fluids10 000 has a stronger ability to decrease the viscidity The increasing content of NaCl is much more effec-than the PEg with a molecular weight of 20000.tive in controlling the Fl of drilling fluids containingAccording to the values of AV and Pv of Peg with a molecular weight of 10 000No.21℃12℃-10℃8.5℃020040060080020040060080010001200Y(1/s)Y(1/s)Figure 3. The rheological curves of No. 20, No. 21, No. 22, and No. 23 formulations.The Fourth Group FormulationsFor No. 20 and No. 21 formulations containingThe fourth group formulations and the experi- PEG with a molecular weight of 10 000, when themental results are shown in Tables 7 and 8. From temperature is higher than -12 C, the values of AVTable 2. the AV values of No. 20. No. 21, No. 22, and PV of No. 20 formulation containing 15%NaCIand No. 23 formulations in the range of 2. 7 to 6C +5% KCl, which change homogeneously, are lesserare greater than those of the preceding three groups than those of No. 21 formulation containing 20%of formulations. Just like the preceding three group NaCl, and when lower than -8C, both visciditiesformulations, corresponding values of Av and PV of haveincrement Fig 3). But the changehese groups of formulations also increase with the in v中国煤化工lon Is homogeneouslowering of temperatures. But atthe fls of at aCNMHG2℃. For No.22these groups of formulations are too large, 31, 33. 2, and No. 23 formulations containing PEG with a mo-60.6 and 28. 6 mL, respectivellecular weight of 20 000, the values of av and PV ofExperimental Research of Gas Hydrate Drilling Fluids Using Polyethylene Glycol as an InhibitorTable 7 The fourth group formulationsNo. Formulation20 Water+15% NaCl+5% KCI+5% PEG(10 000)+3% LG +0. 15% Na2 CO,+3% clay+0. 25%XC21ater+20%NaCl+5% PEG(10 000)+3% LG +0. 15% Na2 Co,+3% Clay-+0. 25%XC22waer+15%NaCl+5%KC+5%PEG(20000)+3%LG+0.15%Na2CO2+3%clay+0.25%XC23 Water+20%NaCl+5%PEG(20000)+3%LG+0.15%Na2CO2+3%clay+0.25%XCXC. xanthomonas campestris polymerTable 8 The experimental results of theature can be well controlled by using PEG with a mo-fourth group formulationslecular weight of 10 000 in combination with 15%No.t(℃)NaCl+5% KCl. However, further experimental re-(mPa·s)(mPa·s)searches on low-temperature FL need to be carried202.7102.56851.2534.58out for these groups of formulations.-8112.270.856.11214891.77456.38CONCLUSIONS20>300>300THTM1)The values of Av and PV of the four groups134of drilling fluids that have been studied increase with5 151.7 103.5 75.85 48.28 the lowering of temperatures, and there is a critical-12167.510783.7560.58temperature in the low-temperature range at which20>300190THTthe viscidity of drilling fluids suddenly increases. An226>300150THTMincrease in the content of NaCl can enhance the anti7>300156.7THTM20>300>300THTMfreeze performance of the four groups of drilling flu235.5ids that have been studied, in which NaCl has a grea-39.5810159.510779.7552.58ter effect on enhancing the anti-freeze performancethan Kcl20>300>300THTM(2)The molecular weight and content of PEGNo. 22 formulation containing 15% NaCl +5%KCIthe type and content of the inorganic salts, and theclay have a great effect on the viscidity and fluid lossare greater than those of No. 23 formulation contar- of drilling fluids. For drilling fluids that has beenning 20% NaCl. But, in the range of-12 to 6 C,studied without clay PEG with a molecular weight ofthe values of av and Pv of No. 21 and No. 22 for10 000 is more favorable to control the viscidity andmulations containing 20% NaCl are close to each other.These results show that the molecular weight offluid loss of drilling fluids than PEG with a moleculaweight of 20 000, and an increase in the content ofPEG and the inorganic salts have a considerable effect NaCl is also favorable to control the viscidity of drill-on the viscidity and fluid loss of drilling fluids, and ing fluids. Using 20% NaCl together with PEG withferent effects on drilling fluids containing 15% Nac/ a molecular weight of 10 000 is helpful to control the+5% KCl or 20% NaCl. Adding PEG increases the viscidity and fluid loss of drilling fluids.For thosewith clay, the relative apparent interaction of PEGviscidity, and the increasing content of NaCl canhance the anti-freeze performance of drilling fluids.with a molecular weight of 10 000, KCl, and the clayPEG with a molecular weight of 20 000, rather than is unfavorable to control the viscidity, but with thetemperature higher than the critical temperature, thePEG with a molecular weight of 10 000, has a greater interaction of PEG with a molecular weight ofeffect on the values of Av and pv of drilling fluidscontaining 15% NaCl+5% KCl. And for drilling flu- 10000, KCl, and clay is favorable to control the vistaining 20% NaCl, the changcidity. The performance of drilling fluids containinglar weight of PEG frorn 10 000 to 20 000 has few 20% Nacl is affected slightly by the lowering of tem-effects on the values of AV and PV of drilling fluids, peratt中国煤化工ange in temperature also has few effects onrilling fluids, thethese drilling fluids. The viscidity of drilling fluidsYHaCN GS on the tempera-with the temperature higher than the critical temper- ture of theg fluids. The 5% content of PEGwith a molecular weight of 10 000 combined with282Zhang Ling, Jiang Guosheng, Tu Yunzhong, Cai Jihua, Dou Bin, Zhang Jiaming and Ning Fulon15% NaCl+ 5%KCl or 20% NaCl can provide bet- Jiang, G. S, Ning, F. L., Li, Z, w., et aL., 2001. Inhibiter control of viscidity and fluid loss of drilling fluidstion and Induction Decomposition of Gas Hydrate onwith a better cost performanceDrilling Procedure. Geology and Prospecting, 11(6): 8687(in Chinese with English Abstract)Jiang, G. S, Wang, D, Tang, F. L, et al., 2002. TheACKNOWLEDGMENTExploration and Development of Gas Hydrate. China Uni-This study was supported by the National Natu-versity of Geosciences Press, Wuhan. 1-3(in Chinese)ral Science Foundation of China(No. 50504012), the Li, C.M., Geng, R.L., 2000. Pondering over Gas HydratesNew Century Excellent Talent Supporting Program Exploration Drilling. Exploration Engineering, 3: 5-8of Ministry of Education of China, China Postdoctor(in Chinese with English Abstract)al Science Foundation(No. 2005037681)and the Ex- Liu, G. Z, 2005. Suggestions on the Sustainable Developmentcellent Young Teachers Sponsored Program of CUGfor Drilling Engineering. Petroleum Exploration and De-No. CUGQNLO623velopment, 32(1):87-88(in Chinese with English Ab-Niu, Y. B, Wang, G. J, et al., 2001. A StudyREFERENCES CITEDof Shale Stability of Water-Base Polyethylene GlycolAston, M. P, 1994. Water-Based Glycol Drilling Mud Shaleing Fluid. Natural Gas Industry, 21(6): 57-59(inInhibition Mechanisms. SPE 28818. 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