Abstract: This paper summarizes the studies and applications of the mechanism of borehole collapse, the main methods used for stabilizing instable borehol, and the status quo of water base drilling fluid technology, discusses the major difficulties presently faced in shale gas drilling in China, analyzes the differences between the mechanisms of borehole collapse both in China and in the America, illustrates the misconceptions and deficiencies existed in the studies on water base drilling fluids for shale gas drilling in China, and points out the technical direction for the development of water base drilling fluids for shale gas drilling in China.
Abstract: An anti-freezing nano emulsified paraffin, PF-EPF, was prepared through multi-component phase transition method, using liquid paraffin as internal phase and water solution of polyhydric alcohol as external phase. A compound emulsifier was added to accelerate the reaction. Parameters affecting the performance of PF-EPF, such as the HLB value and content of surfactant, emulsification temperature, and the content of oil phase were studied, demonstrating that the freezing point of PF-EPF reached -30℃, and thus had good stability and excellent anti-freezing capability. Conventional nano paraffins, when used at low temperatures, always separates out and coagulates, making them difficult to use in drilling. The PF-EPF was synthesized to solve this problem. Compared with conventional nano-paraffin emulsions, the percent of successfully controlling seepage loss with PF-EPF treated mud was increased by 45%, indicating that PF-EPF has better plugging and sealing performance. In field use, PF-EPF has showed its capacity in preventing borehole instability, increasing ROP, and protecting reservoirs. Apart from its use in petroleum engineering, this research work also helps widen the use of nano emulsions in cosmetic, medicine, food and agricultural fields.
Abstract: Nano material has small particle size, is well dispersed and has stable properties, thus is always used in solving lost circulation and borehole collapse encountered in drilling operation. A nano material plugging agent, NF-1 was developed by adding SnCl4·5H2O and benzimidazole into a mixture of absolute alcohol and deionized water under certain conditions. The synthesis was done by combining hydrothermal method and solvothermalmethod, taking into account the effects of reaction solvent, molar ratio of reactants, reaction temperature, and surfactant used in the reaction. NF-1 has particle size of 91.4 nm. Laboratory evaluation showed that addition of 5% NF-1 into a base mud reduced the 30 min filter loss of the base mud to 12.8 mL at 105℃, 3.5 MPa, indicating that NF-1 had excellent plugging performance.
Abstract: Horizontal drilling has been used in developing the block Jiaoshiba in Fuling, Chongqing. The horizontal section, more than 1,500 m in length, penetrated the lower Longmaxi mudstone formation, which has high clay contents, and is brittle and full of micro fractures. The vertical depths of the wells drilled in this area were deeper than 3,500 m. Deep well shale gas development in this area has been faced with difficulties such as high well temperature, cutting carrying, borehole wall collapse in some wells, over-pulls during tripping, and lost returns of muds in some wells, all of these have caused waste of manpower and material resources. To solve these problems, a diesel oil base drilling fluid has been studied for use in shale gas drilling. The diesel oil base drilling fluid formulated had good high temperature stability; at low oil/water ratio (70:30) the fluid was still stable. Two LCMs, were added in the oil base drilling fluid; one was a high purity ultra-fine CaCO3 mixed with an organic gel LCM which can plug fractures of 2 mm in width, and can stand pressure of 7 MPa. The other LCM, a nano graphite powder mixed with ultra-fine sepiolite fibers, can be used to plug micro fractures of 0.1 mm in width, and can stand pressure of 20 MPa. Field application demonstrated that this oil base mud greatly stabilized the borehole wall in easy-to-collapse hole sections, and reduced the average rate of hole diameter enlargement to less than 3%. Good lubricity of the mud made trip very smooth. The property of the mud was stable during the whole drilling period and was easy to maintain. Downhole problems previously encountered such as lost circulation and borehole wall instability were mitigated to acceptable levels. Field application proved the suitability of diesel oil base drilling fluid in shale gas horizontal drilling in Fuling area.
Abstract: The well Keshen-15 is a key exploration well drilled in the Keshen 15# structure of the middle Kelasu tectonic zone, Kuche depression, Tarim. Difficulties that must be faced during drilling include highly deep formations, faults, large hole size, high temperature, high mud density, developed salt and gypsum formations, and narrow mud density window etc. High temperature high density complex organic salt drilling fluids were formulated to have "low water activity, low hydrating potential and low equivalent circulation density (ECD)", in an effort to deal with the difficulties as mentioned above. With these measures, no trouble had ever occurred during drilling, and all of the wireline loggings were successful at the first try. Compared with the well drilled nearby with oil base drilling fluid, the mud density was reduced by 0.05-0.08 g/cm3, indicating that this organic salt drilling fluid had strong inhibitive capacity, low ECD, good rheology, high temperature stability, and resistance to salt, gypsum and drill cutting contamination. Meanwhile, this drilling fluid was environmentally friendly, non-fluorescent, had low corrosion to tubular goods, and can be used as drill-in fluid to save drilling time. The successful drilling of the well Keshen-15 has proved the potential of wide application of the high temperature high density complex organic salt drilling fluid.
Abstract: Well SHB1-6H is an ultra-deep well drilled in Shunbei area by Sinopec, and is the first well in this area to use 4 casing string sizes. The second interval of the well, with open hole length of 4,460 m, 1,463 m of which is mudstones, has complex geology; The Trias, Carboniferous and Silurian systems are mainly hard and brittle mudstones, apt to cave-in. Lost circulations have been easy to occur in drilling the shattered Permian system. To avoid these problems, a high temperature salt-resistant filter loss reducer, RHPT-1 and a filming agent, CMJ-1, were used in the potassium- and amine-treated sulfonated polymer drilling fluid to improve the inhibitive capacity, plugging performance and filtration behavior. In field application, the improved polymer sulfonate drilling fluid had rheology easy to control. To maintain the inhibitive capacity of the drillingfluid, 5-7 kg/m3 of HPA (an amine based shale inhibitor) and 30-50 kg/m3 of KCl were kept therein. A high softening point asphalt was used to enhance the plugging performance of the drilling fluid, and to reduce the HTHP filter loss to less than 10 mL. With these measures, borehole instability in the formations below the Trias system was effectively solved. In drilling the Permian system, bamboo fibers, ultra-fine CaCO3 and polymerized gel LCM have been used to avoid mud losses. The hole enlargement for the second section of well SHB1-6H was 12%, reduced by 63.74% than the adjacent well.
Abstract: The Quantou Formation and the formations above in Longfengshan gas field are mainly water sensitive shales. Downhole troubles such as borehole wall collapse, pipe sticking, wellbone expansion and bit balling have frequently been encountered in drilling these formations. Lost circulation, on the other hand, has always been encountered in the Yingcheng Formation, which is full of fractures. To ensure safe drilling through these formations, a plugging inhibitive drilling fluid was formulated based on laboratory researches. A shale inhibitor, NK-1, was selected through shale core swelling test and bentonite hydration test. KFT-II and ZX-8, as plugging agent and anti-collapse agent, were selected through mud cake building test and core permeability experiment. Laboratory evaluation showed that this drilling fluid had stable rheology, good filtration characteristics, strong inhibitive capacity and plugging and anti-collapse performance. In field application, the well Bei-209 was drilled successfully with this drilling fluid. The drilling fluid had stable rheology, and no borehole wall collapse happened. Tripping of drill string, wireline logging and casing running were run with no hindrance, and the reservoir formations were fairly protected from being damaged.
Abstract: The formation rocks of the Kimmeridgian stage on the right bank of the Amu Darya River, Turkmenistan, are halite and gypsum stone. High density drilling fluids used to drill this formation have always been contaminated by calcium and magnesium from the high pressure formation water, resulting in poor mud rheology and high filtration rate. The deteriorated mud rheology and filtration performance in turn resulted in other downhole troubles. A calcium tolerant high density low clay drilling fluid, D-ULTRACAL was developed to deal with these problems. A filter loss reducer, DSP-1, was used in the drilling fluid. DSP-1 can increase the viscosity of the drilling fluid, in this way reducing the clay content, improving the calcium tolerance and minimizing the filter loss of the drilling fluid. The density of the drilling fluid was 2.0 g/cm3, sufficient to prevent well kick and to protect the borehole wall from collapsing. The drilling fluid had salt content almost to saturation to minimize the dissolution of the salt and gypsum rocks. The properties of the drilling fluid remained stable at temperatures up to 150℃, and the filtration rate was only slightly affected by high temperature aging. On a hot rolling test, the percent recovery of shale cuttings reached 113.7%, and on a shale core swelling test, the percent reduction in the expansion of shale cores was 80.5%, indicating the strong inhibitive capacity of the drilling fluid. Calcium tolerance of the drilling fluid was 4 936 mg/L. This drilling fluid has been used to drill the well Gir-24D, which is located in the Girsan gas field, right bank of the Amu Darya River, Turkmenistan, and the thick salt and gypsum rock formations were successfully penetrated with no downhole troubles.
Abstract: In the adjustment wells drilled in recent years in Block Suizhong, Bohai Oilfield, the percentage of highly deviated wells and horizontal wells have been increasing every year. This leads the formation pressure to deplete seriously, and the low molecular weight cationic polymer drilling fluid (JFC) is becoming unsuitable for the drilling operation because of the deficiencies of JFC in inhibitive capacity, rheology, contamination tolerance, and reservoir protection. To solve these problems, laboratory studies were conducted on the issues such as reservoir characteristics, the physical-chemical property of shales drilled, and the adaptability of drilling fluid to the formations penetrated. A drilling fluid additive, HAS, was selected through laboratory experiments to treat the drilling fluid presently in use. It was found that, compared with low molecular weight cationic polymers, polyamines and organic MMH etc., HAS was much stronger in inhibiting the hydration and swelling of clay minerals. Another additive PF-VIF was selected to replace the filter loss reducer RS-1 and XC, and the rheology and cuttings carrying capacity were improved. A combination of PAC-HV, PAC-LV and HAS can prevent the drilling fluid from becoming flocculated, and increase the solids tolerance of the drilling fluid. The use of plugging agents LPF and HTC together reduced the filtration rate of the drilling fluid, and enhanced the performance of the drilling fluid to protect the reservoir formations. In field application of this drilling fluid, drilling efficiency was greatly enhanced. The rate of back reaming in the conglomerate section below the Guantao Formation was increased by 30%, and drilling time was saved by 41.08 d. Wells drilled with this drilling fluid had oil production rates reached or exceeded the forecast.
Abstract: An invert emulsion gel lubricating plugging agent, XZ-RF has been developed. Evaluation of XZ-RF showed that it had good lubricating ability; addition of 1% XZ-RF reduced the friction coefficient of bentonite mud by 60%, and 3% of XZ-RF reduced the friction coefficient of bentonite mud by more than 80%. XZ-RF showed good lubricating performance in polymer drilling fluid. XZ-RF also showed good plugging performance. A weighted bentonite mud treated with XZ-RF had HTHP filter loss reduced by 65.8% at 160℃. An under-saturated weighted brine mud treated with XZ-RF had HTHP filter loss reduced by 86.8% at 120℃. XZ-RF is a drilling fluid additive free of fluorescence, it has been successfully used in drilling 2 exploratory wells in Xinjiang Oilfield.
Abstract: Common drilling fluid lubricants have problems such as low film strengths at extreme pressure, poor stability at elevated temperatures, and short lubricity persistence in extreme conditions. An extreme pressure lubricant, JM-1, has been developed by mixing an organic molybdenum friction reducer and the 10# white oil. The organic molybdenum friction reducer was made by reacting vegetable oils with organicmolybdenum containing sulfur, phosphorus and molybdenum. The percent reduction in friction at extreme conditions was 65% at 1.5% JM-1 concentration. The evaluation showed that the film has high strength, the lubricity lasts long, and the lubricity remains stable at 150℃. JM-1 is non-toxic, pollution-free, and has low fluorescence. Drilling fluids treated with JM-1 do not foam. JM-1 has been tried in the highly deviated directional well Yao1-1HF, in which the friction in the horizontal section was reduced by 50%, and tripping and casing running were conducted smoothly, and well Beigang1, in which reaming was done much easier after using JM-1 treated drilling fluid.
Abstract: An inhibitive filter loss reducer AMSC was synthesized with AMPS, acrylamide, methacrylamidoxy ammonium chloride and potassium acrylate as raw materials. AMSC was synthesized for clay swelling inhibition and filter loss control. The reaction conditions were optimized with the response surface method, and the performance of AMSC was evaluated. Laboratory experiments showed that a percent swelling inhibition of 84.76% can be obtained using the AMSC synthesized at these conditions:molar ratio of the four raw materials=2：1：7：1, reaction temperature=50℃, monomer concentration=15%, initiator concentration=0.5%, reaction time=4 h. The inhibitive capacity of AMSC at temperatures less than 100℃ is equivalent to the similar commercial products presently available. An increase in the concentration of AMSC from 0.06% to 0.6% reduced the volume of clay in an water-clay mixture from 1.2 mL to 0.2 mL. AMSC also had good filtration control performance in water base drilling fluids; reducing the filter loss of most water base drilling fluids by 87%.
Abstract: A series of studies have been conducted on lost circulation control to deal with severe mud losses into fractures and vugs. A self-cementation lost circulation control method is the product of the studies. This method uses cementation agents and bentonite as the raw materials in the "bi-slurry grouting method", to stay the lost circulation material (LCM) slurries in place in the mud loss channels. Chemical reactions take place in the LCM slurries and set LCMs are formed, plugging the channels. The LCM slurries have low density and high viscosity. The set LCM, after aging for 24 h at 80℃, has compressive strength that is less than 11 MPa, and is easy to drill out. The time required for the LCM slurries to set is controlled by the concentration of an additive. This technology has been applied in field operation, and severe mud losses into fractures and vugs of different sizes were successfully stopped, ensuring high quality and efficient drilling operation.
Abstract: Well Ming-1 is an exploratory well drilled in Block Puguang by the Puguang subsidiary of Zhongyuan Oilfield Company. Lost circulation has occurred many times during drilling the formations on top of the Leikoupo Formation, where fractures and faults develop. These formations are generally broken, have poor cementation and narrow density windows. Methods of controlling lost circulation, such as bridging and plugging, gels of different composition and properties and cement slurry, all failed. Conventional pressure bearing lost circulation control methods and Neotor pressure bearing lost circulation control method have also been applied, and the lost circulation was not satisfactorily controlled and stopped. A chemical solidification technology was then used to control mud losses, and a cross-linking filming fluid was applied to protect the open hole section above the mud loss spots from being fractured while squeezing. Using this technology, the pressure bearing capacity of the formations was strengthened, providing a safeguard for mud loss control. The chemical solidification lost circulation material (LCM) used was a high valent metal ion nano material, and has the ability of slight swelling. It has density that can be adjusted between 1.05 g/cm3 and 1.90 g/cm3, and is stable at temperatures up to 180℃. In the cross-linking filming fluid, a high strength bridging LCM was used to replace the conventional bridging LCM previously used, and a chemical cross-linking solidification material was added to the filming fluid. With this chemical cross-linking solidification material, flowback of LCM slurry will not occur at pressures even higher than 3 MPa. This filming fluid remained stable at temperatures up to 180℃, and when solidified, can stand differential pressures as high as 20 MPa. The successful operation with this chemical solidification LCM provides an effective way of enhancing the pressure bearing capacity of formation to control lost circulation.
Abstract: When lost circulation is encountered during drilling into big caves or macro fractures, squeezing cement slurry is the commonly used method to control the mud losses. When squeezing cement slurry, a highly thickened supporting fluid shall be spotted into the loss zones to support the cement slurry, making sure that the cement slurry stays in place and sets at the mouth of the cave, thereby stops mud losses. The supporting fluids commonly used presently are high viscosity bentonite slurries which are easy to be diluted by water, and therefore cannot support the cement slurries. To formulate a suitable supporting fluid, a high molecular weight polymer, YSZC-1, was synthesized. An oil base supporting fluid, viscosified when in contact with water, was formulated by mixing YSZC-1 with oil. The viscosity of this supporting fluid is adjustable to satisfy the special needs of field operation. Since this supporting fluid instantly becomes thickened as soon as it is in contact with water, it cannot be diluted with water, and the failure in controlling mud losses into caves can thus be avoided. When in contact with water or water base drilling fluid, the apparent viscosity of this supporting fluid increases exponentially, and to a maximum when the volume ratio of the supporting fluid and water base mud is 1：1. An apparent viscosity of 133 mPa·s was obtained by mixing one part (volume) of supporting fluid with 9 part of water base drilling fluid, rendering the supporting fluid strong resistance to water dilution. When aging for 16 h at 150℃, the apparent viscosity did not decrease apparently. This supporting fluid is resistant to salt contamination to saturation, and to calcium contamination to about 5%. It is compatible with cement slurry, and will not cause the cement slurry to "flash set". This supporting fluid satisfies the needs for controlling mud losses into caves, and maximizes the possibility of successful mud loss control in caved formations.
Abstract: Well cementing operations in Block Shunnan has been encountering technical difficulties such as active oil and gas, severe gas cut, narrow density window, deep well, high bottom hole temperature, and low pressure bearing etc. To deal with these difficulties, a precise dynamic pressure control well cementing technology was applied in Shunnan, and well cementing was successfully performed. In applying this technology, the pressures at the wellhead and the bottom were carefully controlled to prevent lost circulation and well kick from occurring. The well cementing job was safely performed while the job quality was enhanced. This technology has been successfully applied in cementing the well Shunnan-6 and the well Shunnan-7. This technology is of great importance in cementing wells penetrating pressure-sensitive formations, and is worth applying widely.
Abstract: To improve the job quality of cementing the borehole penetrating thick salt and gypsum formations, an over-saturated potassium chloride solution (contains 38% KCl) was used in formulating a cement slurry, in an effort to avoid rock salt dissolution during well cementing. The over-saturated KCl cement slurry formulated was treated with a salt-resistant filter loss reducer CG80S, an enhanced anti-channeling agent GS12L, and a non-penetrating agent BX-80. Laboratory evaluation showed that the over-saturated KCl cement slurry had controllable thickening time and filter loss. The compressive strength of the set cement, after aging for 24 h at 68℃, was greater than 15 MPa. When contaminated by 5% gypsum, Glauber's salt or shale cuttings, the properties of the cement slurry did not change noticeably. Laboratory experiments also showed that the bond of the cement slurry and the salt formations improved remarkably, indicating that the quality of the bond between the cement sheath and the casing string, and the bond between the cement sheath and the formations can both be guaranteed.
Abstract: Wells drilled with oil base drilling fluid always have poor cementing job quality because of the contamination to the cement slurry by the oil base drilling fluid. Studies on the cement slurries that are resistant to contamination have been conducted using experimental method and theoretical analysis. In laboratory experiments with artificial cores, the effects of oil base drilling fluid on the cementing job quality, especially the effects of oil base drilling fluid to the bonding of the cement sheath and the borehole wall, have been proved. Anti-P (main component being alkylphenolpolyethoxylate), an anti-contamination agent for cement slurry was developed by studying the change of the properties of base cement slurry before and after being contaminated with oil base drilling fluid. Laboratory studies showed that cement slurry treated with Anti-P can stand the contamination by oil base drilling fluid of less than 10%, the properties of the cement slurry was not affected, and the cementing job quality satisfied the requirements. The application of Anti-P in several wells has gotten good results. This technology has filled the gap of anti-contamination cement slurry and is well worth further study and application.
Abstract: Wells drilled in the Block SN have high bottom hole temperature under static conditions, and the gas zones are very active. Prevention of well kick and lost circulation during drilling is quite difficult. Latex anti-channeling cement slurry alone has been used in the past in well cementing, but it didn't work well. Liquid silica latex, as a nanometer anti-channeling agent, has active SiO2 that will take part in the hydration reaction of cement. It thus helps increase the strength, reduce the elastic modulus and permeability of set cement. By optimizing the amount of silica used and the ratio of coarse particle over fine particle silica, a high temperature antichanneling liquid silica latex cement slurry was developed. This cement slurry had filter loss less than 50 mL, a right-angle thickening curve, an SPN less than 1, good anti-channeling performance and settling stability. SEM and XRD analyses demonstrated that a dense set cement can be acquired. Tobermorite and xonotlite, instead of Ca(OH)2, were found in the hydrated cement, and this results in a stable strength of the set cement at elevated temperature. High pressure gas zones in wells drilled in Block SN have been effectively cemented with this anti-channeling liquid silica latex cement slurry.
Abstract: In cementing wells that lost circulation have ever occurred, or wells with long cementing section, loss of cement slurry into loss zones will result in a cement top that is lower than the designed depth, hence leaving the reservoir sections uncemented. To deal with these problems, a polymer gel lost circulation material (LCM), CPA, was developed through water solution graft copolymerization. The copolymerization used sodium acrylate (PAANa) and chitosan (CTS) in optimized ratio as raw materials, potassium persulphate (KPS) as initiator, N, N-methylene-bis-acrylamide (NMBA) as cross linking agent, and calcium carbonate (CaCO3) as enhancer. The optimum reaction conditions were as follows:CTS:PAANa=1:7, initiator concentration=3.3%, concentration of cross linking agent=2.1%, reaction temperature=60℃, concentration of CaCO3=1%. The synthesized product was characterized with IR spectroscopy, and was studied for its water adsorptivity in different salt solutions, temperatures, and pH values. The evaluation indicated that CPA had good salt tolerance, and its water adsorptivity in different salt solutions were in the order NaCl > MgCl2 > CaCl2. CPA had higher water adsorption rates at higher temperatures, while the maximum water adsorption scale factor remained almost the same. At pH value of 5-9, CPA had the maximum water adsorptivity.
Abstract: A set of well cementing technologies, such as oil-displacing prepad fluid, toughness-enhanced anti-channeling cement slurries, and the evaluation of the integrity of cement sheath, was developed to improve the job quality of cementing horizontal wells (in which multistage fracturing will be performed) in Yumen Oilfield. These technologies, special for cementing horizontal wells drilled in Yumen Oilfield,were aimed at establishing long-termzonal isolation, and were developed based on the studies on cementing materials, the failure of cement sheath, and cementing techniques. These technologies have been applied on seven horizontal wells in Yumen since 2015, and the cementing job quality of each well was satisfactory at the first try, and four wells out of the seven wells had excellent cementing job quality. Each of three wells that have been cemented with these technologies and have put into production has average water cut that is less than 30% after fracturing, lower than the water cut of the wells drilled in the same block. These technologies have also been applied on eight wells with small annular spaces, and 75% of the cementing job was excellent. These technologies are promising and have gained good results in horizontal well cementing.
Re-fracturing diverting has been planned in the well Zheng-x in Zhengzhuang CBM gas field with fuzzy ball temporary plugging fluid. This job was to be done in an effort to increase the gas production by generating new fractures in the reservoir formations, without disturbing the production of the existing fractures. In laboratory studies, a fuzzy ball fluid was used to temporarily plug the artificial fractures on a 33 mm (diameter) coal plug, then an activated water was used to test the pressure bearing of the temporary plugging; it was 20 MPa, exceeding the fracturing pressure of the formation, which is 18 MPa. The percent recovery of the permeability of the coal plug previously flushed with the fuzzy ball fluid was 85%, satisfying the needs for the production of the existing fractures. In field applications, a fracturing blender truck and a water tank were used for the circulation of the fracturing fluid. A fuzzy ball fluid, with density between 0.94 g/cm3 and 0.98 g/cm3, apparent viscosity between 30 mPa·s and 34 mPa·s, was prepared through a shear funnel. After checking the existence of fractures with activated water, 60 m3 of fuzzy ball fluid was injected into the formation at 3.0-3.5 m3/h. The tubing pressure was stabilized at 12 MPa while stopping pumping for 30 min, indicating that the plugging of existing fractures with the fuzzy ball fluid was successful. The formation was then fractured with activated water when the tubing pressure was increased to 18 MPa. The azimuth of the new fractures was N13°W, as measured with microseism, meaning that 55° of diverting was realized compared with the N42°E azimuth of the existing fractures. A gas production of 200 m3 in 2 h after fracturing was achieved, doubling the gas production rate before the fracturing job. Microseism monitoring and the gas production rates before and after the fracturing job indicated that the fuzzy ball forced the fracturing fluid to divert to generate new fractures, while the production of the existing fractures was not affected. This technology is suitable for the re-fracturing of old CBM wells to generate new fractures, while the production of the existing fractures was not affected. This technology is suitable for the re-fracturing of old CBM wells.
The quality of water from the backflow fluid of guar gum fracturing fluids is determined through analyses of the backflow fluid from multiple wells. The effects of pH, reducing ions, hardness, salinity, oil contents and contents suspended matters on the performance of the guar gum fracturing fluids were studied based on the aforesaid analyses. To recycle the backflow fluid, the water quality should be controlled as follows:pH between 6.5 and 7.5, Fe2+ less than 5 mg/L, S2+ less than 2 mg/L, Ca2+ less than 500 mg/L, salinity less than 100,000 mg/L, and suspended matter less than 300 mg/L. These data provide a basis for the recycling of the backflow fluids of fracturing fluids.
A hydrophobically associating quadripolymer, AAMS-1, was synthesized through reverse emulsion polymerization, using AM, AMPS, hydrophobic monomer M (2-Dimethyl hexadecaneaminomethacrylate chloride)/rigid monomer S (4-acrolylamino sodium benzenesulfonate). The synthesized AAMS-1 was characterized with IR spectrum. Thermogravimetric analysis showed that AAMS-1 was chemically stable at 250℃. The synthesized AAMS-1 emulsion had particle sizes around 2,500 nm, with critical associating concentration of 0.15%. The network structure of AAMS-1 in fracturing fluids can be clearly seen using with an SEM. Fracturing fluids formulated with AAMS-1 have good viscoelasticity, sand carrying capacity, and permeability protection performance. Water solution of 0.6% AAMS-1 sheared at 150℃ and 170 s-1 for 2 h had residue viscosity not less than 50 mPa·s, indicating that AAMS-1 had satisfactory shearing stability and high temperature stability.
A new hydrophobically associating polymer, LP-3A was synthesized through inverse emulsion polymerization, using AM, AMPS and monomers with hydrophobic chains and polyoxyalkylene groups as raw material, and benzoperoxide (BPO) as initiator. The polymerization conditions such as the optimum ratios of monomers, reaction time, temperature and initiator concentration etc. were determined through one-factor-at-a-time method. The molecular structure of LP-3A, a viscosifier used in fracturing fluids, was characterized, and the properties of LP-3A, such as temperature stability, shearing stability, recovery performance after shearing, viscoelasticity and thixotropy were studied. The study demonstrated that LP-3A had good high temperature stability and shearing performance. After being sheared under 150℃ and 170 s-1 for 2 h, LP-3A still had residue viscosity of 200 mPa·s. After being sheared for 20 min at 500 s-1 and 1,000 s-1, respectively, shearing was stopped, and 90% of the viscosity of the LP-3A solution can be recovered. Compared with guar gum, energy needed to destroy the network structure of LP-3A was higher, and time needed for the recovery of the structure was longer. In the LP-3A fracturing fluids, elasticity prevails, and the viscoelasticity of LP-3A fracturing fluids is superior to guar gum fracturing fluids.
Abstract: A thixotropic expandable high strength water shutoff agent and a technology of staged injection of the shutoff agent have been developed to satisfy the needs of water shutoff operation in horizontal wells. Laboratory evaluation showed that the water shutoff agent had good thixotropy and yield point of 10-15 kPa. It was suitable for use at temperatures between 30℃ and 120℃. The compressive strength of the water shutoff agent was greater than 13 MPa, and the thickening time was longer than 6 h. The volume of the water shutoff agent after solidification expanded by 1.0%-1.5%. As a high strength water shutoff agent, it increases the efficiency of water shutoff, prolongs the life of water shutoff, and overcomes the problems often encountered in horizontal section such as the mixing of cement water shutoff agent and kill mud, and poor application safety of other water shutoff agents commonly available. A self-degradable sol was developed to protect the water shutoff agent plug from being mixed with kill mud during injection. Tools for staged injection of water shutoff agent were selected for the staged shutoff of the water producing sections. This technology has been successfully applied on 5 wells in Dagang Oilfield and Qinghai Oilfield, with oil and gas production increased by 5 849 t and 1.4 ×104 m3 in total, respectively, demonstrating the reliability and long-term safety of the technology.
Competent Authorities：China National Petroleum Corporation Ltd
Sponsored by：CNPC Bohai Drilling Engineering Co. LtdPetroChina Huabei Oilfield Company
Address： Editorial Department of Drilling Fluid and Completion Fluid, Bohai Drilling Engineering Institute, Yanshan South Road, Renqiu City, Hebei Province