Abstract: A device was designed to produce energized foam drilling fluid which can be used to replace conventional foam drilling fluids easily to be defoamed by pressure. The energized foam mud was formulated with energized foams made at high pressure being mixed with common drilling fluids, and was thus quite different from conventional foam muds. Study indicated that the energized foam mud produced by the device had (bubble) core pressures of 0.1-20 MPa, capable of withstanding higher pressure. In annular spaces with high pressures, this energized foam mud still maintained low density, and hence low static pressure on the bottom hole.
Abstract: Two water base drilling fluids were formulated with CaCl2 and polymers highly resistant to calcium contamination. Compared with other water drilling fluids, the CaCl2/polymer drilling fluids had better performance;the inhibitive capacity and lubricity of the drilling fluids were greatly improved. After hot rolling 16 hours at 120℃, the first percent recovery and secondary percent recovery of shale samples were both 100%. Friction coefficient of the drilling fluid was as low as 0.038, almost the same as that of oil base drilling fluid. This drilling fluid was cost effective, pollution-free, and easy to use.
Abstract: Nano SiO2 (silicon dioxide) is proposed to plug the nano sized pore throats in shale formation to retard invasion of filtrate into the formation in contact with drilling fluid, thus avoiding tight hole and borehole collapse. Effect of nano SiO2 on the improvement of drilling fluid properties was evaluated by measuring the viscosity, filter loss of drilling fluid and shale swelling. The results showed that to improve the performance of the drilling fluid, the nano SiO2 used should be resistant to salt contamination. Treatment of the drilling fluid with 1%-5% nano SiO2 increased the viscosity of the fluid by increasing inter-particle friction. On the other hand, the nano SiO2 was sensitive to the concentration of salt. Laboratory experiments at room temperature showed that by adding 3% nano SiO2 into the drilling fluid, it will have the capacity of tolerating salt commination to 12%. Particles of the nano SiO2 can deposite into the filter cake, reducing the filter loss of the drilling fluid (percent reduction of filter loss volume as high as 40.2%). By retarding the invasion of filtrate, nano SiO2 improved the inhibitive capacity of the saltwater drilling fluid. Nano SiO2 remarkably reduced the volume of filter loss of saltwater drilling fluid (salt concentration less than 8%).
Abstract: An organophilic clay was developed using octadecyl benzyl dimethyl ammonium chloride, a polymer ENVAMOD-95 and a purified sodium montmorillonite, and analyzed with X-ray and simultaneous thermal analyzer DSC-TGA. A water in oil mud was prepared with the organophilic clay, and was tested for its properties against a mud sample taken from a well. The analyses showed that octadecyl benzyl dimethyl ammonium chloride and ENVAMOD-95 can both enter into the space between the layers of montmorillonite to form organophilic clay. ENVAMOD-95 actually enhanced the thermal stability of the organophilic clay. In laboratory experiment, the viscosity and gel strength of the mud first increased and then decreased with temperature. The prepared water in oil mud retained its properties after hot-rolling 16 hours at 210℃, showing that organophilic clay made from ENVAMOD-95 had better thermal stability than other two polymer samples tested. Water in oil mud prepared with this organophilic clay at rig-site retained good properties after hot-rolling at 150℃, showing its potential for field use in HTHP wells.
Abstract: A new emulsifier was developed to mitigate the problems of oil base drilling fluid such as high viscosity and low gel strength which are negative to the suspension and carrying of drilled cuttings. An oil base drilling fluid was formulated with this new emulsifier. The properties of this mud were as follows: density 1.0-1.7 g/cm3, plastic viscosity≤40 mPa·s, ratio of yield point to plastic viscosity 0.35-0.50 Pa/mPa·s, and electric stability≥800 V. This mud had good rheology and was tolerant to contamination by water to 15%, and drilled cuttings to 10%. This mud had been successfully used in Well Jiaoye54-1HF.
Abstract: An oil base drilling fluid filter loss reducer, FCL, was developed by hydrogenation of an oleophylic polymer which was synthesized with α-olefin and styrene through emulsion polymerization and sulfonation by acetic anhydride and concentrated sulfuric acid. Treatment of 1.5% FCL in white oil base drilling fluid reduced HTHP (180℃) filter loss to 8.4 mL, without evidently affecting the rheology. Compared with other similar oil base mud filter loss reducers, FCL performs much better in filtration control. FCL does not obviously affect the rheology of oil base drilling fluids with density less than 1.5 g/cm3. In oil base drilling fluids with higher densities, FCL increases the viscosity while decreases their gel strengths.
Abstract: A high performance foam LCM mud, CLPA-1, was developed for use in the Block Lengjia where lost circulation posed difficulties to drilling the old, fractured formations. Lost circulation did not occur in four wells in this area drilled with CLPA-1, and in another three wells lost circulations were stopped first time when they occurred, with no subsequent lost circulation happened. Field application proved that the CLPA-1 foam mud was effective in lost circulation control in the area, where mud losses into fractured formations had long been common.
Abstract: Settling of barite has long been a problem in deviated well and extended reach well drilling. A cost effective method for preventing barite settling is developed by combining the methods for barite particle size measurement and sedimentation stability testing. Experiments showed that by adding a certain amount of ultra-fine barite into commonly used drilling fluid barite improved the sedimentation stability, especially the dynamic sedimentation, of the barite, the dynamic density difference decreased from 0.436 g/cm3 for conventional barite only, to 0.011 g/cm3 for the mixed barite, greatly improving the sedimentation stability of barite.
Abstract: In coal-bed methane (CBM) drilling and coal bed fracturing operations, coal powder generated, if deposited on the bottom of the hole, imposes severe negative effect on the productivity of the CBM well. A coal powder suspending agent, FYXF-3, was developed aimed at solving this problem. FYXF-3 at concentrations not less than 0.3% can suspend coal powders in good stability, ensuring their flow to the surface along with production fluid. FYXF-3 had the ability to reduce surface tension of liquid, enhancing the production efficiency and minimizing formation damage. Based on these studies and the characteristics of the coal bed in Hancheng area, a reasonable fracturing program was designed and applied successfully in field operations.
Abstract: Well KMJ-1-4HF is a bi-lateral horizontal well located in the No.1 Hade Structure of the Hadexun tectonic zone in the north of Manjiaer trap in the Tarim Basin. High friction between drill string and borehole wall caused difficulties exerting weight on bit and pipe sticking. An anti-wear friction reducer KMJ-1 was used to solve these problems. KMJ-1 formed a tough lubricating film on both the surface of the borehole wall and drill string to reduce the frictions between them. KMJ-1 functioned at low concentration in drilling fluid, and greatly reduced drag and resistance to the moving of drilling strings and pipe sticking.
Abstract: A new vegetable lubricant was developed by reacting waste vegetable oils with low molecular weight alcohols to form long chain fatty acid ester being treated with surfactants and other treatments to render it high temperature stability. At room temperature, 6% bentonite slurry treated with 1% vegetable lubricant had extreme pressure friction coefficient reduced by 85.5%-88.6%, and coefficient of adhesion reduced by 80.0%-86.7%. This lubricant remained its lubricating capacity at 140℃, and tolerated contamination by 15% salt. It had fluorescence level of 3 and EC50 of over 50,000 mg/L, and was well compatible with polymers and sulfonates commonly used in water base drilling fluid. In field application in the Well Zhuang23, crude oil previously used as lubricant was reduced at least by 50%. Experimental wells drilled with drilling fluid containing this vegetable lubricant, 3900m in depth, had average well construction time reduced from 33.55 d to 29.11 d. Furthermore, the use of waste oil from manufacturing this vegetable lubricant was also beneficial to environment protection.
Abstract: Depleted fractured Ordovician carbonate formations in Tahe Oilfield were buried at 6,000 m, with formation temperature of about 130℃. When lost circulation occurred, mud circulation can be re-gained with bottom hole pressure exceeding 10 MPa.These fractured formations had high channel connectivity and high salinity formation water. A downhole crosslinking solidification technology was developed to deal with lost circulation in these formations. In laboratory experiment, the crosslinking gelling agent SF-1 had its viscosity soared to above 10,000 mPa·s at high temperature (130℃) and high calcium environment, and stayed in place long enough for the mud loss to be stopped. HDL-1, a lost circulation material followed SF-1 reacted with SF-1 in the hole to form a dense plug being able to stand pressures up to 15 MPa, ensuring the efficiency of lost circulation control. This technology was successfully applied in the Well TH12179CH in Tahe Oilfield, where severe lost circulation always occurred.
Abstract: Mud losses were frequently encountered when drilling the Pabdeh, a low strength dolomite formation in the south edge of the HOS, Block Y in a country. Many mud loss zones are present and irregularly distributed, with lost circulation continually lasting for a long time. Rates of mud losses are sensitive to mud weight. To control the mud losses which had been difficult to stop during drilling operation, a bridge LCM formulation was developed through experiment on a DL-A HTHP LCM tester. This LCM formulation is suitable for controlling mud losses into 2 mm wide fractures. By analyzing the mud loss behavior in whole well drilling operation, it is recommended that when drilling the top formation, more attention should be paid to mud loss prevention, and use LCM mud to stop them if mud losses do occur. In the upper middle section of the well, low density should be used to drill through the thief zones. In the lower middle and lower section of the well, a combination of "control mud losses while drilling" and "control mud losses under pressure" techniques can be applied to stop mud losses or mitigate the negative effect of mud losses on drilling operation. These practices have been proved successful in the drilling operation of the Well S25.
Abstract: Lost circulation borehole collapse and pipe sticking were encountered in the Kurdish Oilfield, leading to prolonged drilling time and high drilling cost. Hydrogen sulfide in the reservoir formations poses threats to human life. The Well SN-2 was drilled with drilling fluid optimized for each interval to solve the problems mentioned above. A 2.2 g/cm3 undersaturated saltwater drilling fluid was used to drill the salt and gypsum formations and to deal with hydrogen sulfide. Time spent drilling the Well SN-2 was 65 days less than the adjacent wells.
Abstract: Complex formation in the Kuche piedmont structure in Tarim Basin had led to frequent lost circulation, which in turn resulted in poor well cementing job. Factors affecting lost circulation are analyzed, including drilling fluid property, clearance between casing string and borehole wall, running speed of drill string and casing string and pump rate, all factors affecting surge pressure. The clearance between drill string/casing string and borehole wall should not be less than 20 mm. Decrease in the yield point of drilling fluid reduces the surge pressure produced when gel structure of the drilling fluid is broken. A better model is presented for better determination of the running speed of drill string/casing string. A concept of increasing the frequency of pump rate is presented together with the control method. By improving the rheology of the drilling fluid, friction in running drill string/casing string can be reduced. The technology presented in this paper provides a guidance to the lost circulation control design for wells drilled in the piedmont structure in Kuche Country, Xinjiang.
Abstract: Effects of several rice husk ashes prepared under different incineration conditions on the compressive strength and engineering performance of cement slurry is studied. The study shows that incineration, concentration of the rice husk ash, aging temperature and alkaline activator all affect the compressive strength of set cement. In field application, husk rice ash prepared under low temperature is preferred, and the optimum treatment is about 10%. The use of alkaline activator increases the compressive strength of the set cement. RHA-1, a cement slurry treated with 10% rice husk ash has very good engineering performance, satisfying the needs for well cementing.
Abstract: Abstract Two modified carbon nanotubes, TNIMH4(—OH) and TNIMC6(—COOH) were selected to satisfy the needs of natural gas storage and high pressure oil and gas well for better mechanical performance of set cement. Laboratory experiments showed that cement slurry treated with 0.01% TNIMH4 had its compressive strength increased by 4.32%, cement slurry with 0.07% TNIMC6 had its compressive strength increased by 19.18%. At the same treatment, the compressive strength of cement slurry treated with TNIMC6 was greater than that of cement slurry treated with TNIMH4. Tri-axial compressive strength experiments showed that the tri-axial compressive strength of the cement slurry treated with TNIMC6 was 41.21% greater than that of the blank cement slurry., and the elastic modulus of the cement slurry was increased from 3,692.5 MPa to 4,366.5 MPa. SEM observation showed that the nanotubes at low concentrations were dispersed evenly in the set cement, and began to agglomerate at increasing concentrations, which in turn aggravated the heterogeneity of, and hence weakened the strength of the set cement.
Abstract: Drilling fluid composition directly affects the composition and property of filter cakes, which in turn affect the mechanical performance of the filter cakes at interlayer interface. Shear strengths of several clay samples, such as pure bentonite, bentonitehematite manipulated clay, and bentonite-quartz powder manipulated clay were measured to study the effect of three solids (clay, weighting agent and drill cutting) on the shear strength of filter cakes at the interlayer interface. The study showed that, at certain water content and compaction condition, the angle of internal friction and cohesive strength of filter cake linearly decreased with an increase of hematite content in filter cake. When mass ratio of quartz powder in filter cake was less than 10%, same result as hematite was obtained. When mass ratio of quartz powder in filter cake exceeded 10%, the angle of internal friction and cohesive strength of filter cake remained almost constant. Cohesive strength of filter cake increased with an increase of bentonite content in filter cake at a certain range.
Abstract: High bottom hole temperature and formation pressure of deep and ultra-deep wells easily give rise to poor cementation of cement sheath caused by fluid channeling. A high density flushing fluid, XM-1 was developed to tackle this problem. In laboratory study, a vegetable gum X-P was used as the suspending agent of the flushing fluid, CTK-1 as the weighting agent, and KZ-1 as the interface strength enhancing additive. XM-1 had good compatibility with oil base drilling fluid, and cleared mud cakes thoroughly. Cementation strengths between cement sheaths were increased by more than 50%.
Abstract: In the Well NP-36-3804 drilled in the Xinpu Gu-2 platform, 4,714 m of production casing was required to be cemented in on cementing operation. Conventional cement slurry was unable to meet the requirement of cementing such a long casing string because of low slurry density and big differential temperature. Success of the cementing job required the low density cement slurry to have lower density, to be less affected by temperature difference, and to become set more quickly at normal temperatures. Two high density low density cement slurries, having densities of 1.35 g/cm3 and 1.50 g/cm3 respectively, were formulated by selecting competent lightweight materials, developing high performance anti-gas migration agent, and selecting the best close packing calculation model. It was found in field application that the two slurries had no free water. The cement slurries were stable and had good rheology at operational conditions. API filter loss and thickening performance all met the requirement of field application. The low temperature early strength and the compressive strength of set cement were all satisfactory.
Abstract: When a lost circulation material is used to temporarily plugging the a fracture, new fractures will be forced to propagate in non-fractured zones. This is the so-called "non-damaging to original fractures while fracturing" technology. In the application of this technology, the liquid conductance of the original fractures is not affected while new fractures are being generated. In laboratory studies, a temporarily plugging fluid containing chorionic vesicles increased the flow resistance of artificial core fractures to 25 MPa. When treated with this temporarily plugging fluid, artificial cores (permeabilities 17.5×10-3 μm2 and 164.9×10-3 μm2, respectively) had permeability recovery (to crude oil) of 90.9% in 0.7 hour and 84.7% in 0.6 hour, respectively. When using chorionic vesicle in the operation of the Well LH1, pump pressure was held up at 22.0 MPa for 10 minutes. The daily production rates of liquid and oil 60 days after re-fracturing were increased by 48.0% and 119.2%, respectively, compared with those 30 days before re-fracturing, and the average water cut was reduced by 7.5%. These facts showed the good performance of chorionic vesicle in temporarily plugging fluid in fracturing operation.
Abstract: N, N-dimethyl oleamide propyl amine oxide was synthesized with raw materials such as oleic acid, dimethyl aminopropylamine and hydrogen peroxide. At 170℃ with sodium hydroxide (NaOH) as catalyst, oleic acid reacted with dimethyl aminopropylamine to form the intermediate, which in turn reacted at 55℃ with 30% hydrogen peroxide to produce N, N-dimethyl oleamide propyl amine oxide, gross percent conversion of which being 97%. A clear fracturing fluid was prepared with 1.5%-3% (mass ratio) of N, N-dimethyl oleamide propyl amine oxide and other additives, having viscosity in a range of 50-150 mPa·s after shearing for 1 hour at 170 s-1 and 80℃. Clear fracturing fluid containing 3% (mass ratio) N, N-dimethyl oleamide propyl amine oxide had viscosity of 30 mPa·s after shearing for 1 hour at 170 s-1 and 100℃. The N—O bonds in the molecules of N, N-dimethyl oleamide propyl amine oxide rendered it ability of strong viscosifying capacity. In laboratory experiment, clear fracturing fluids containing 2% N, N-dimethyl oleamide propyl amine oxide and 2% hydroxyl propyl guar gum, respectively, gave birth to permeability damage to artificial fractures of 13% and 90%, respectively, after flowing 10 PV of fracturing fluids, indicating that N, N-dimethyl oleamide propyl amine oxide is better than hydroxyl propyl guar gum in terms of reservoir protection. The clear fracturing fluid, when mixed with kerosene at 10:1 mass ratio, was allowed for the gel to break at 40℃ for 0.5 hour, and the viscosity of the fluid after gel breaking was 2.71 mPa·s, meaning that the gel was completely broken up.
Abstract: Fracturing waste fluid samples from a horizontal well in Changqing Oilfield were analyzed for their compositions at different times during fracturing operation. Inorganic ions, solid particles and residue additives were studied for their influences on the recycling of the fracturing waste fluid. In the fracturing fluid samples, the content of Ca2+ and Mg2+ ions are low, and will pose no negative effect on the reuse of the waster fluid. The Fe2+ and Fe3+ ions, rich in the waste fluid, can be removed through "oxidization-flocculation to precipitate-filtration". The presence of residue crosslinking agent in the waste fluid made the re-produced fracturing fluid highly viscous, and was thus masked with a solution containing triethanolamine and glucose (triethanolamine:glucose=1:9). To avoid the effect of gel breaker on the stability of the re-produced fracturing fluid at elevated temperatures, the gel breaker is suggested to be used in modest concentrations in the original fracturing fluid. Through these steps, the fracturing waste fluid can be recycled.
Abstract: Study on the property of clear fracturing fluid formulated by amphoteric surfactant LQ-FJ showed that LQ-FJ dissolved completely in water in 4 minutes and made the water viscosified into a clear fracturing fluid. At 2% of LQ-FJ, no counter-ionic salts were needed for the preparation of a clear fracturing fluid which had temperature stability up to 110℃. Viscosity-temperature curves of the fracturing fluid demonstrated that the 2% LQ-FJ fracturing fluid had thermal-thickening and thermal-thinning properties. Rheology study showed that the 2% LQ-FJ fracturing fluid had a temperature hysteresis loop and shear thinning property. Jeffrey's co-rotational constitutive equation can be used to characterize the flow curve of the fracturing fluid. Gel breaking experiment indicated that kerosene and ionic surfactant J1 all can be used as gel breaker for the 2% LQ-FJ fracturing fluid, and the gel-broken fluid had viscosity at room temperature of less than 1.5 mPa·s.
Abstract: Slick-water fracturing is becoming more widely accepted in shale gas well operation, and friction reducer is the critical additive in formulating this fracturing fluid. To quantitatively evaluate the performance of friction reducer in slick-water fracturing fluid, an evaluation device and a set of operational procedure need to be established. The JHFR-I evaluation system is such a system that has the advantage of HTHP operation over conventional evaluation systems. The highly automated JHFR-I is a full-function efficient system, which in rheological study can be used in simulating HTHP pipe flow at different shear rates. JHFR-I is highly helpful in the study and production of friction reducer.
Abstract: Block Xuwen is located in Beibu Gulf Basin, composed of Weixinan Sag, Wushi Sag, Fushan Sag and Leidong Sag. The deeper formations are mainly hard and brittle fractured shales with high collapsing pressures and are easy to collapse. Compound organic salt drilling fluid had been chosen to drill the unstable shale formations to prevent the borehole from collapsing. Compared with offset wells, three wells drilled with organic salt drilling fluid had rate of penetration increased by 44%, drilling time reduced by 26 days (average), and rate of hole enlargement reduced by 50%, indicating that borehole instability was greatly mitigated. Wireline logging, because of improved borehole stability, was performed with higher rate of success.
Abstract: A new drilling fluid was formulated incorporating potassium-polymer-sulfonate drilling fluid technology, silicone-base inhibitive drilling fluid technology and anti-balling technology, which was aimed at reducing mud weight and increasing drilling rate in the mid-Sichuan area. Laboratory study showed that this drilling fluid formulation is tolerant of salt contamination and reduces the potential of bit balling. Percent recovery of shale samples tested with this drilling fluid formulation was 95.0%, while shale core swelling test gave a percent reduction of swelling of 96.8%, both of which were better than polymer mud and polymer-sulfonate mud, but inferior to oil base mud. In field application in mid-Sichuan basin, average ROP was increased by 48.66%, time spend in reaming was reduced by 74.9%, and average percent hole enlargement was reduced by 18.14% in wells drilled with the said drilling fluid formulation.
Abstract: Geological condition of the formations in Sulige Gasfield allows the use of drilling fluids with same formulation and properties, making possible the recycling of drilling fluid in multiple-well drilling. GWSSL is such a drilling fluid that can be reused in this area. Samples of drill-in fluids in horizontal drilling from 3 wells at different times and fresh drilling fluid made in laboratory were tested for their property changes over a period of 15 days. The test results showed that, given enough treatment of the drilling fluids with necessary additives, in 15 days, which was mandatory for the drilling fluid to be stored, transported, and reused, the samples had properties that were almost the same as that of the drilling fluid at well completion. Most of the drill-in fluid can be reused, some of them may need slight treatment, for example, dilution. It is estimated that recycling of 1 m3 drilling fluid would save 300 RMB Yuan. Using solids-control equipment to remove the unwanted solids, combined with treatment of the drilling fluids with high molecular weight flocculant, such as KPAM, the properties of the recycled drilling fluids will be easy to control.
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