Abstract: A low clay content and low solids ultra-high temperature water base drilling fluid was engineered using optimized polymer viscosifier SDKP, high temperature filter loss reducer, oil-soluble plugging agent, lubricant, high temperature protective agent and water block preventer, based on an analysis of the characteristics of the reservoir in Nanpu, Jidong. Laboratory experiments showed that after 16 hours of aging at 165℃, 1% SDKP water solution still retained 20% of its original viscosity. A combination of two filter loss reducers, SD-101 and SD-201, remarkably reduce the filter loss of a 1.0% bentonite slurry. HQ-10, an oil-soluble plugging agent, can remarkably reduce the HTHP filter loss of drilling fluid. This drilling fluid remained stable at 235℃. At 200℃, the plastic viscosity was 15 mPa.s, satisfying the needs for carrying drilled cuttings. The drilling fluid maintained good rheology even contaminated with 10% NaCl, 2% CaCl2, or 10% inert clays. In inhibition test, the percent reduction in core swelling was 78%, and the percent recovery of cores increased from 8.24% to 84.45%. The application of this drilling fluid in the exploration well Nanpu3-82 showed that, at 220℃ (bottom hole temperature), the rheology of the fluid was stable the API filter loss remained unchanged, good carrying capacity of the fluid was realized. Well Nanpu3-82 was successfully drilled to 6,037 m, and had a liquid production of 43.20 m3/d.
Abstract: Sloughing of shale in the lower Dongying Formation and Shahejie Formation caused serious downhole troubles in the Block KL3-2. Laboratory study of the drilled cuttings with X-ray, SEM, pore size distribution, physic-chemical property analysis etc. showed that brittle mineral content in the cuttings sample taken from the formation of interest was more than 60%. Swelling clay content was relatively low. Micro fissures, fractures and beddings were quite developed in the samples studied, showing that the formations are hard and brittle shale. When in contact with drilling fluids, mud filtrates infiltrate along the bedding plane into the formation under the action of capillary force and differential pressure, causing the micro fissures and micro fractures to expand, thus resulting in borehole sloughing. To control this kind of borehole instability, HSM, a micro nano plugging agent, and HAS, an amino silanol shale inhibitor, were selected to formulate an inhibitive drilling fluid, which can effectively plug micro fissures, micro fractures in shales and retard the transmission of pressure in formation. In field use, HSM remarkably improved the quality of the filter cake and reduced filter loss of the mud. The application of this inhibitive drilling fluid helped in controlling borehole wall instability and minimizing downhole troubles related to the hard brittle shales.
Abstract: A new weak gel water base drilling fluid was formulated with a new developed weak gel agent as the main additive and other additives such as filter loss reducer, shale inhibitor and sealing and plugging agent selected through experiment. Laboratory experiment shows that this drilling fluid has unique rheological behavior, i.e., it has high viscosity at low shear rates, and weak gel is formed quickly within the fluid. This drilling fluid has very good filtration property and superior performance in shale inhibition. The properties of this drilling fluid remain stable at 150℃ or when contaminated by calcium of 4 000 mg/L. Study with SEM and Zeiss microscope shows that sol particles are encapsulated and embedded at the nodal points of a 3D network developed within the drilling fluid. This drilling fluid can form dense sealing layers with good compressibility in formations full of micro fractures or fissures, preventing water from entering into the formations, thus inhibiting the hydration and swelling of shale or formations with high content of clays.
Abstract: The "zero potential" theory was used to optimize the formulation of drilling fluid used in deep well and ultra-deep well drilling in Tarim Basin to overcome shale swelling and pipe sticking in top formations and difficulties in mud property maintenance in lower deep formations. Using optimized cationic polymers, a "zero potential" water base drilling fluid was formulated. This drilling fluid had high concentration of cations, and clay particles of high zeta potential, almost equal to or slightly higher than the zeta potential of the "in-situ" drilled cuttings, meaning that the potential difference between the formation and the drilling fluid is "zero", hence greatly mitigating the possibility of borehole wall instability caused by frequent migration of electric charges between formation and drilling fluid. This drilling fluid also had good rheology and filtration property, and was resistant to contaminations from the introduction of salt, calcium and clays, especially at high temperatures in deep and ultra-deep wells. The "zero potential" drilling fluid had been used in 20 wells in Tarim Basin. Compared with conventional water base drilling fluids, total time spent in dealing with drilling fluid-related downhole troubles was reduced by 10.2%, ROP increased by 14.9%, and drilling time reduced by 9.8%. The successful application of the "zero potential" drilling fluid in Tarim Basin provides a means of fast, safe and efficient drilling deep wells, and enriches and further develops the idea of "zero potential" drilling fluid.
Abstract: A starch copolymer was developed through draft copolymerization of starch and newly prepared alkene monomer. In laboratory experiments, this starch copolymer (modified starch) showed good filtration control performance in fresh water base mud, saltwater base mud, saturated saltwater base mud, seawater base mud, compound saltwater base mud, and calcium chloride mud. It also showed good stability at high temperature (130℃) and good tolerance to salt and calcium contamination to saturation. Filter loss of a mud treated with this modified starch was decreasing with an increased salt and calcium contamination. Introduction of cationic groups into the molecules of the modified starch rendered it good inhibitive capacity.
Abstract: Two sets of solids-free workover fluids were formulated with natural mineral sulfide scavenger. The adsorption rates of sulfide hydrogen of the workover fluids were as high as 237.33 mg/L. They also had low alkalinity, low corrosivity, did not form scale and were compatible with calcium and magnesium ions, and formation waters. Being solids-free, they posed no damage to reservoirs. Pilot application of the workover fluids in five wells in Dagang Oilfield was successful, average restoration period of these wells was 2 days, and the reservoir formation was proved not damaged by the workover fluids.
Abstract: Xanthan gum was hydrophobically modified using NA, an alkylated organometallic compound, as modifying agent, and absolute ethanol as dispersion medium under acidic condition. The prepared dispersible instant xanthan gum, DIXG, was evaluated for its dispersing capacity, dissolubility and rheology. Experiment results showed that DIXG has dispersing capacity and dissolubility that are better than dispersible xanthan gum produced in China, with its rheology being the same as other samples.
Abstract: Two commonly used sulfonated phenolic resins, SMP-Ⅱ and SMP-Ⅲ, were tested for their molecular structures, saltresistance, molecular weights, and their capacities in rheology control. SMP-Ⅲ can control the HTHP filter loss of drilling fluid to 17.5 mL, while SMP-Ⅱ, when used with SMC, a sulfonated lignite, can control the HTHP filter loss to 20 mL. High temperature and high salinity push forward the modest crosslinking of SMP-Ⅱ or SMP-Ⅲ itself, or the crosslinking of SMP-Ⅱ(or SMP-Ⅲ) and SMC, producing high molecular weight copolymers that are effective in rheology control. The copolymers, by adsorbing onto the surfaces of clay particles, improve the quality of filter cakes, reducing filtration of drilling fluid. The optimum treatment of SMP-Ⅱ or SMP-Ⅲ is determined to be about 5%.
Abstract: A high temperature water base drilling fluid filter loss reducer, BZ-HTF, was developed for use in Block Niudong, Qinghai. BZ-HTF was synthesized with monomers AM, AMPS and IA in a mass ratio of 42:40:18, and initiator concentration of 0.10%. Total concentration of the monomers was 30%. The reaction lasted for 4 hours at 55℃. BZ-HTF has a degree of hydrolysis of 30%, and remains effective at temperatures as high as 200℃. It has good filtration control capacity in fresh water base mud, brine mud and saturated saltwater mud, and does not greatly increase the viscosity and gel strengths of the muds. BZ-HTF has filtration control capacity comparable to Drispac D, while its cost is only one fourth of the latter.
Abstract: A quadripolymer filter loss reducer was synthesized using acrylamide (AM), 2-acrylamide-2-methyl propane sulfonic acid (AMPS), acrylic acid (AA) and dimethylaminoethyl methacrylatemethyl chloride (DMC) as raw materials through redox polymerization. The mass ratio of the four monomers is AM:AMPS:AA:DMC=55:30:10:5, the concentration of initiator 0.3% (taking the concentration of all monomers as 1), total concentration of monomers 20% (mass ratio), reaction temperature 50℃, pH of the solution 7, and reaction time 4 hours. Characterization of the molecular structure of the copolymer showed that the molecular structure was the same as design. Treatment of API standard water base mud with 0.7% copolymer reduced the API filter loss to 6.0 mL. After aging at 180℃, filter loss at 0.7 MPa was 8.2 mL, and 11.6 mL at 3.5 MPa. In hot rolling test, shale cuttings recovery of 99.4% was attained at copolymer concentration of 1.0%. These laboratory tests showed that the synthesized copolymer had good filter loss control capability, thermal stability and inhibitive capacity.
Abstract: Nano calcium carbonate was modified for better hydrophobicity. The modified calcium carbonate was then used to formulate a temporary plugging drilling fluid. At temperatures below 140℃, the fluid had stable filtration property, and was resistant to contamination caused by 2.5% CaCl2, or 9.0% mono valence salts, or 14.0% clay. It also had good shale inhibitive capacity. The film strength under extreme pressure was 190 MPa, indicating good lubricity of the drilling fluid. Percent recovery of permeability of cores with initial permeability ranging from 50×10-3 μm2 to 1,000×10-3 μm2 was greater than 90% for all these cores tested. It was also environmentally friendly.
Abstract: Shale gas well drilling imposes strict limits to the performance of drilling fluid used because of the shale formation and technical features. A water base drilling fluid formulated with nano material was recently developed in an effort to replace oil base drilling fluid commonly used in shale gas drilling. In this drilling fluid, the nano particles plug the pore throats of shale formation, and the sulfonated asphalt is used to stabilize shale formation. In laboratory study, this drilling fluid showed better shale inhibitive capacity than poly glycol drilling fluids. The friction coefficient of the drilling fluid was 0.21, and that of the filter cake 0.0497. At 120℃, this drilling fluid still retained its good property. Low surface tension of this drilling fluid mitigated reservoir damage. This drilling fluid can also be used in shale drilling.
Abstract: No instrument is available currently for the evaluation of the primary properties of gel lost circulation material (LCM), a novel additive for lost circulation control. To accurately measure the performance of this kind of LCM, an instrument system is developed. This paper introduces the composition, working mechanism and application of the system. The system acquires test pressure automatically and has working temperature ranging from room temperature to 200℃. The smartscreen of the instrument can monitor test pressure, maximum workload, change of workload vs. time, time in which the gel LCM can stop the mud loss, and backpressure, all shown in curves and printed on papers. With this system, the evaluation test can be performed accurately and conveniently, with testing results directly viewed. This heavy-duty system is made with high quality components and can be used in long-time testing.
Abstract: Lost circulation was frequently encountered in the complex formations in Misan Oilfield in Misan Province of Iraq. Lost circulation, especially those occurred in the reservoir formations, cannot be stopped using conventional techniques. When drilled the Well AGCS27 to 2,932 m, lost circulation occurred, and was not able to be completely controlled after trying various lost circulation materials (LCM) for 20 times. Finally, a casing barrel was used to transfer the large particle, long fiber LCM to the thief zones, and the lost circulation was successfully stopped. As an economic and practical method of lost circulation control, this technology is worth trying in drilling deep wells with fracture-induced lost circulation.
Abstract: The Cretaceous, Triassic, Permian and Carboniferous systems are thick hard and brittle shales full of fractures in Tazhong area. Bore hole cave-in and collapse were frequently encountered in these formations during drilling. In drilling the Well Zhonggu431-H4, a special plugging and collapse prevention technology had to be used to avoid down hole troubles. Several special plugging agents with "synergistic effect", and a special plugging technology were adopted seal the borehole wall, preventing it against erosion and water penetration. No downhole problems were encountered after 55.3 days of exposure of borehole wall to drilling fluid, 5 times of whole tripping and 3 times short tripping. The special plugging and collapse prevention technology successfully solved the downhole problems caused by the characteristics of formation penetrated, effectively reduced drilling cost and NPT.
Abstract: Cement slurry of different densities were prepared and studied on their pumpability, mechanical properties, contamination tolerance, bonding strength and cleaning at different temperatures. Compound set cement with densities ranging from 0.8 g/cm3 to 1.80 g/cm3 can be made by adding light weight agent or weighting agent and epoxy, combined with settling preventer. Using solidifying agents such as aromatic amines of different activity, and solidification accelerator to treat cement slurry, the cement slurry can be pumped at 45-125℃. The compound set cement has mechanical property much better than that of the elastic tough set cement modified with rubber powders. The compound set cement is resistant to oil base mud contamination, and has higher bonding strength. The residue compound cement slurry can be readily cleaned with 20% alcohol.
Abstract: The reaction mechanism of the hydration process of oil well cement in induction period, and the effect of an oil well cement retarder, BH, (a long branched chain carbonic acid, sulfonic acid) on the induction period were studied through a series of laboratory experiments. Ca(OH)2 content in the cement clinker at the early hydration stage was about 2%, and went up to 45% at the end of the induction period. This indicates that the induction period is controlled by the concentration of Ca(OH)2 in the liquid phase. BH can be adsorbed fast on the surface of cement particles to form a wrapping layer, retarding further hydration of cement. The complexion of Ca2+ by BH increased the super-saturation solubility of Ca(OH)2 to 1.97 g/mL, inhibiting the formation of Ca(OH)2 crystal nucleus and prolonging the induction period of the cement slurry. SEM charts show that BH changed the appearance of the Ca(OH)2 crystals and inhibited its growth, further prolonging the thickening time, and retarding the hydration of cement.
Abstract: False filter cake on borehole wall has great influence on the job quality of well cementing, often causing the cementation of the interface between cement sheath and borehole wall to become deteriorated, and resulting in fluid channeling. The shear stress on the borehole wall caused by cement slurry in eccentric annular space is analyzed. With the help of river sediment flow dynamics in hydraulic engineering, the critical starting shear stress necessary for the removal of filter cake is calculated. By comparing these two shear stresses in annular space, the erodability of false filter cake in the whole annular space can be determined. It is shown that the particle size distribution and the thickness of filter cake greatly affect the erodability of the filter cake, and the eccentricity of casing string also plays a role in this aspect.
Abstract: A new high temperature polymer retarder, GWH-1, was synthesized through free radical polymerization in water solution. GWH-1 was used to deal with the slow setting of the top cement in cementing long open hole with big temperature difference. Laboratory evaluation showed that GWH-1 can stand high temperature to 200℃, and was resistant to contamination from saturated salt solution. The thickening time of the cement slurry can be adjusted by changing the concentration of GWH-1. A low density (1.30 g/cm3) cement slurry treated with GWH-1 had thickening time of 386 min, after aging at 130℃. After aging at 30℃ for 72 h, the set cement had compressive strength of 3.5 MPa. No free liquid was found for the cement slurry at high temperature, and the density difference between the top and the bottom of the set cement was less than 0.02 g/cm3. GWH-1 was successfully used in the cementing job of well RP7008 in Tarim Basin.
Abstract: Excellent mechanical performance of set cement is required in cementing wells of 6000m and deeper using one-stage cementing technology. Improvement of mechanical performance of set cement plays an important role in maintaining the integrity of cemented hole. Comparison of polypropylene fiber and basalt fiber in in improving the mechanical performance of set cement was conducted by analyzing the changes in compressive strength, tensile strength, breaking strength and elastic modulus of set cement. It showed that at low concentrations basalt fiber has little effect on the flow properties of cement slurry, and, like the polypropylene, it remarkably reduces the API filtration rate and free water content of cement slurry. Cement slurry treated with basalt fiber gives set cement of enhanced compressive, tensile and breaking strengths. At a concentration of 0.5%, the tensile strength of set cement is increased by 50%, with an obvious decrease in the elastic modulus of the set cement. As an economical cement slurry additive, basalt will find wider application in oil and gas wells cementing.
Abstract: A new diverter acid was developed through precipitation reaction between the hydrolysis product of acid chemicals and calcium ions. Laboratory study on the diverter acid showed that this diverter acid had better retarding performance and lower corrosivity than hydrochloric acid. Testing of the diverter acid on medium to low permeability carbonate rock samples showed a diverting capacity of 15%, five times that of hydrochloric acid; the viscosity of the residue diverter acid was almost equal to that of clear water, and the oil-water interfacial tension was less than 10 mN/m, meaning that the diverter acid can be easily removed by backflow. Experiment on the diverter acid with SEM and XRD showed that the diverter acid produced some calcium sulphate (CaSO4·2H2O), which retarded the reaction between acid and rocks, thus pushed the flow of the acid to low permeability area. The use of in-situ authigenic sealing diverter acid makes an even distribution of the acid fluid.
Abstract: Formation waters of different salinities were studied for use in the preparation of fracturing fluids for the sake of environment protection and cost control in gas fields, west Sichuan. The guar gum fracturing fluid prepared with formation water had viscosity of 100 mPa·s after shearing 90 min at 45℃, surface tension of 27.66 mN/m, rate of swelling reduction of 87.5%, rate of permeability impairment of only 26.5%. Using salt-resistant friction reducer, the slick water prepared with formation water reduced flow friction by 69%-71%. The formation water fracturing fluid has been used in the Well SF38-2 and the Well SF38-4 with good results. The slick water was successfully used in the SRV fracturing operation in the Well X502, a nonconventional gas well.
Abstract: The Changxing Formation in Jianxing Gas Field has two sedimentary types, bioclastic beach and biogenic reef, and different minerals in the reservoir formations react differently with acids. Lack of understanding of the reaction patterns of rocks and acids resulted in poor stimulation job quality. Laboratory study on rock samples showed that composition and maturity of crystal grain of the rocks greatly affected the reaction rate of rocks and acids, the reaction rate of bioclastic limestone and gelled acid was 1.3 times that of biolithite, 1.4 times that of limy-dolomite, and 1.9 times that of common limestone. The four rock samples, after reaction with acids, all produced non-uniform corrosion on their surfaces. Dolomite with erosion pores, after reaction with acids, will experience further permeability impairment because of compaction and particle migration. After reaction with acids, the calcite fillings of biolithite and bioclastic limestone reacted much easily with gelled acid, with erosion first formed in the inter-crystalline pores and inter-crystalline cracks, but acid wormholes were rarely seen.
Abstract: The well Guping 28-21 is a horizontal well having the longest horizontal length (2,006 m) in Changqing Oilfield. It has a ratio of horizontal displacement to vertical depth of 1.7. The reservoir is of low porosity, ultra-low permeability, low electric resistance and high shale content. A CQSP-2 compound salts drill-in fluid was formulated to drill the reservoir section. CQSP-2 helped stabilize borehole wall in horizontal section of the well which is 418 m in length, having 20.84% of mudstone and carbonaceous mudstone penetrated along the hole. A gauge hole was obtained, with maximum hole enlargement of 1.61%, minimum of 0.05%, and an average of 0.63%. Friction coefficient in the horizontal drilling was kept at 0.03-0.05, showing good lubricity for the drilling. Hole cleaning performance was satisfactory, with no downhole troubles arising with hole cleaning. Good reservoir protection was achieved as selfflow was found when the well was initially put into production, giving a daily production of 83.6 t, seven times of the average daily production of other wells in Block Heshui.
Abstract: The Nanpu #3 Structure in Jidong Oilfield has big reserves which are deeply buried. Deep and ultra-deep wells have been drilled in this area with high bottom hole temperatures and large horizontal displacements. A high temperature KCl drilling fluid, BH-KSM, was formulated for use in this area. BH-KSM remains stable at temperature up to 200℃, and has excellent inhibitive and sealing capacity, and tolerance to CO2 contamination, essential for dealing with borehole instability, creep of formation at elevated temperatures, and contamination to drilling fluid by formation fluid in Nanpu #3 Structure. Technology for field application of the BH-KSM was engineered for maximum functioning of the mud. Field application of BH-KSM in 10 wells in the Nanpu #3 Structure showed that percent hole enlargement in the Dongying Formation, known for its being water sensitive and prone to collapse, was less than 7%, and the minimum of which being only 3.98%. The mud had stable rheology during drilling. HTHP filter loss can be kept under 12 mL. Cuttings over shale shakers were hard and had good integrity, illustrating good inhibition of the BH-KSM. Good carrying capacity of the mud resulted in satisfactory hole cleaning and increasing rate of penetration.
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