2021 Vol. 38, No. 1

CONTENT
2021, 38(1)
Abstract:
FORUM
Research Progress of Inhibition Mechanism of Shale Inhibitors
ZHANG Weidong, HAN Lei, WANG Fuhua, LAN Qiang, ZHU Haitao, YANG Hairong, ZHAO Qingyuan
2021, 38(1): 1-8. doi: 10.3969/j.issn.1001-5620.2021.01.001
Abstract:
From the perspective of amine shale inhibitors, ionic liquid shale inhibitors, nanocomposites, and other new shale inhibitors (biomacromolecules, polysaccharides, polyalcohols, et al) The mechanism of action of various inhibitors was analyzed, and the current evaluation methods of inhibitory effects were summarized. And on this basis, prospect the future development trend of shale inhibitors.
Ionic Liquids and Their Application in Drilling Fluids
JIAO Xiaoguang, LI Shujiao, ZUO Jingjie, ZHANG Xin, YAO Rugang, FENG Yanlin
2021, 38(1): 9-13. doi: 10.3969/j.issn.1001-5620.2021.01.002
Abstract:
As a kind of completely new environmentally friendly media and soft functional materials, ionic liquids have captured wide attention in drilling fluid industry. This paper summarizes the basic concepts and unique physical properties of ionic fluids, and their many industrial applications, it also covers the status quo and progresses made of ionic liquids in the upstream of petroleum industry, especially in drilling fluid domain. The feasibility of ionic liquids as shale inhibitors in drilling fluids is analyzed, and other potential application of ionic liquids presented. Ionic liquids can interact with clay particles through cation exchange and electrostatic adsorption, showing themselves excellent inhibitive capacity; they also improve cuttings carrying capacity of drilling fluids at elevated temperatures.
DRILLING FLUID
A Temperature Sensitive Polymer Flow Pattern Modifier for Water Base Drilling Fluids for Deep Water Drilling
LYU Kaihe, WANG Zhongyi, HUANG Xianbin, WANG Jintang, YANG Zheng, WANG Ren, SHAO Zihua
2021, 38(1): 14-20. doi: 10.3969/j.issn.1001-5620.2021.01.003
Abstract:
A flow pattern modifier PNAAM was developed to satisfy the needs of rheology control of water base drilling fluids at low temperatures in deep water drilling. PNAAM was synthesized with N-isopropyl acrylamide (NIPAM) and acrylamide monomers based on the fact that temperature sensitive polymers, when responding to the changes of temperature, show remarkable changes in their hydrodynamic volumes and molecular conformation. In laboratory study, the functional groups of the product of the synthesis reaction were characterized using FT-IR, and thermogravimetric analysis showed that the initial thermal decomposition temperature of the synthesis product was 300 ℃. Turbidity analysis of the synthesis product showed that the molar ratio of the monomers and salt concentration affect the LCST of the synthesis product by affecting the strength of the hydrogen bonds between the hydrophilic groups in the molecules of the synthesis product and the water molecules. The ratios of rheological parameters of PNAAM at 4 ℃, 25 ℃ and 65 ℃ in drilling fluids were: AV4 ℃AV25 ℃AV65 ℃= 1.75∶1.22∶1, PV4 ℃PV25 ℃PV65 ℃= 1.8∶1.4∶1 and YP4 ℃YP25 ℃YP65 ℃= 1.8∶1∶1.09. Analysis of the mechanisms shows that before the LCST is reached, the hydrophilic amide groups in the molecular chains of PNAAM are dominating the solution and PNAAM is soluble in water, hence there is no measurable hydrodynamic radius for PNAAM. When the environment temperature is greater than LCST, the hydrophobic groups in the molecular chains of PNAAM are dominating the solution and the hydrophobic associating action among the molecular chains of PNAAM is becoming stronger, thereby forming a 3-D network structure in the solution, which increases the viscosity of the solution and the particle sizes of the polymers, and makes the bentonite particles in the mud cakes more dense and more orderly arranged.
Preparation of Microsphere β-cyclodextrin Polymer Filter Loss Reducer for Drilling Fluids
GAO Xin, ZHONG Hanyi, QIU Zhengsong, JIN Junbin, LI Daqi, LI Jia
2021, 38(1): 21-26. doi: 10.3969/j.issn.1001-5620.2021.01.004
Abstract:
Aiming at the problem of the failure of the environmental-friendly filtration agent at high-temperature, β-cyclodextrin polymer microspheres with β-cyclodextrin as raw materials and ECH as cross-linker were synthesized by inverse emulsion polymerization. Infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, particle distribution and other test methods were used to characterize the structure of the product and evaluate the high-temperature filtration performance. It showed that β-cyclodextrin polymer microspheres have a uniform particle size and good sphericity, with an average particle size of 42.88 μm, and thermal stability is significantly better than β-cyclodextrin. After hot rolling at 180 and 200 ℃, it can effectively reduce the filtration loss of bentonite base slurry, which is better than the typical high-temperature filtration agent. After 200 ℃ hot rolling, the high-temperature and high-pressure filtration loss effect is outstanding. In addition, β-cyclodextrin polymer microspheres have little effect on the rheological properties of drilling fluids. β-cyclodextrin polymer microspheres can absorb a large number of water molecules to form deformable elastic microspheres, reduce the free water of the system, and improve the compressibility of mud cakes. More importantly, β-cyclodextrin polymer microspheres are partial degraded at high temperatures, generating nanoparticles, plugging mud cake pores, and effectively reduce filtration loss. β-cyclodextrin polymer microspheres have excellent high-temperature filtration loss performance, unique mechanism, and show good application prospects.
The Development of a Modified Starch through Inverse Phase Emulsion Copolymerization and its Performance as a Filter Loss Reducer
ZHU Wenxi, ZHENG Xiuhua
2021, 38(1): 27-34. doi: 10.3969/j.issn.1001-5620.2021.01.005
Abstract:
To overcome the gelling problem encountered in synthesizing modified starch filter loss reducer through aqueous free-radical polymerization, inverse emulsion polymerization was used to graph copolymerize starch with AM, AMPS and NVP whose molecules contain amide group, sulfonic acid group and benzene ring, respectively. The product of the copolymerization is a new filter loss reducer ESt-g-NAA with high temperature and salt and calcium resistance. The optimum synthetic conditions of the ESt-g-NAA were determined through orthogonal test: reaction temperature 60 ℃, molar ratio of the monomers nNVPnAMnAMPS= 1∶2 ∶3, and the HLB value = 5. A 3% bentonite base mud treated with 3% ESt-g-NAA had filter loss between 7.6-15.2 mL after being aged at 100-180 ℃ for 16 h, the high temperature filter loss of the ESt-g-NAA treated mud was always less than the high temperature filter loss of the WSt-g-NAA (an aqueous polymerization product) treated mud with the concentrations of ESt-g-NAA and WSt-g-NAA in the base mud being the same. The ESt-g-NAA in the experiments showed excellent salt and calcium resistant capacities; a saturated salt water drilling fluid treated with ESt-g-NAA had filter loss of only 5 mL after being aged at 150 ℃ for 16 h. A drilling fluid containing 0.5%-20% CaCl2 had filter loss between 5.0-15.5 mL after being aged at 150 ℃. If aged at 170 ℃, the drilling fluid was able to resist the contamination by 10% CaCl2; aging at 180 ℃ greatly impaired the calcium resistance of the drilling fluid. The filtration control mechanisms of ESt-g-NAA were revealed by analyzing the effects of ESt-g-NAA on the size distribution of the clay particles in the base mud and by observing the mud cakes under microscope.
Mechanisms of Borehole Wall Destabilization in Que’er’Que’ke Formation in Shunbei Oil and Gas Field and Measures Dealing with the Borehole Wall Collapse
CHEN Xiuping, GAO Leiyu, LIU Jingtao, HU Yunlei, LI Jiaxue, SHI Xiangchao
2021, 38(1): 35-41. doi: 10.3969/j.issn.1001-5620.2021.01.006
Abstract:
Frequent occurrence of borehole wall collapse in drilling the Que’er’Que’ke formation in Shunbei block in Tarim Basin has seriously affected the progress of the drilling operation. Laboratory experiments, such as rock disintegration test, point load experiment, X-ray diffraction, and SEM, were performed to find out the mechanisms of borehole wall collapse in drilling the well X in Shunbei block. It was found that the rock sample taken from the Que’er’Que’ke formation has high content of clays, of which 60% is illite and 10%-30% is illite/montmorillonite mixed layer. The rock sample has low percent water absorption (2%) and high ratio of disintegration (5%), and is a typical hard and brittle calcareous claystone. In laboratory experiment, the rock sample in fresh water and water base mud showed strong heterogeneity and reduced strengths (uniaxial strength of the rock sample in fresh water and water base mud was reduced by 10-40 MPa.) In oil base mud, the strength of the rock sample was almost not weakened. Furthermore, oil base mud can even seal the micro fractures in the rock. When drilling with water base drilling fluids, collapse of the borehole wall resulted from water absorption by the clay content in the formation and hydraulic wedging of the micro fractures developed in the formation. Water absorption by the clay content in the formation decreases the strength of the formation rocks, and the rocks can thus not be supported by their strengths. Hydraulic wedging accelerates the disintegration of the rocks. When drilling with oil base muds, the emulsifiers and wetting agents in the muds can effectively seal off the micro fractures in the rocks, thereby stabilizing the borehole wall through weakening of the hydration of the rocks and mitigation of hydraulic wedging. In the third sidetrack of the well, a water base mud was first used and severe borehole wall collapse happened. Then oil base mud was substituted for the water base mud, and the well was finally successfully completed with borehole wall collapse brought under control.
Laboratory Study on New Water Base Drilling Fluid for Extended Reach Wells
CHEN Bin, ZHOU Shanshan, ZHAO Yuanyuan, QIN Jianyu, RAO Zhihua, DI Mingli, ZUO Kun
2021, 38(1): 42-46. doi: 10.3969/j.issn.1001-5620.2021.01.007
Abstract:
A new water base drilling fluid was formulated to satisfy the needs of extended well drilling. Optimization was done to the lubricity, friction, torque and the control of the equivalent density of the drilling fluid. By adding a multi-function base fluid MBF into the drilling fluid, the lubricity of the drilling fluid can be improved to a level that is equivalent to oil base drilling fluids. Comparison of the new water base drilling fluid with conventional water base drilling fluids and oil base drilling fluids showed that the friction coefficient of the new drilling fluid treated with 30% MBF was 0.064, lower than the friction coefficient of conventional KCl polymer drilling fluid, which was 0.123, and close to the friction coefficient of an oil base drilling fluid, which was 0.056. This new drilling fluid is able to effectively inhibit the yield of clays, and has better filtration control capacity; its low HTHP filtration rate is close to that of oil base drilling fluids. The new water base drilling fluid formulated can be used to replace oil base drilling fluids in drilling extended wells.
Study on the Relationship Between Molecular Structure of Polymer for Drilling Fluids and Performance of Environmental Protection
ZHAI Kejun, GAO Wei, LI Wenxia, LYU Kaihe, XU Zhe
2021, 38(1): 47-53. doi: 10.3969/j.issn.1001-5620.2021.01.008
Abstract:
A series of drilling fluid polymers were synthesized to investigate the relationship between the molecular structure and environmental friendliness of drilling fluid polymers. Using the luminescent bacteria method (EC50) and BOD5/CODCr ratio method, the effects of the type of functional groups, the backbone structure of molecules and molecular weight on the biotoxicity and biodegradability of a polymer was studied. It was found that functional groups and backbone structures of a molecule play the major role in the magnitude of biotoxicity and biodegradability, the molecular weight of a polymer, on the other hand, has minor impacts on its biotoxicity and major impacts on its biodegradability.
A New Method of Measuring Rheological Properties of Drilling Fluids with Marsh Funnel Viscometer
LI Zhaochuan, ZHENG Lihui, WU Tong, HUANG Weian
2021, 38(1): 54-61,67. doi: 10.3969/j.issn.1001-5620.2021.01.009
Abstract:
The Marsh funnel viscometer is now used as a rheometer to measure the rheology of drilling fluids. The mathematical model obtained from the use of Marsh funnel viscometer, which has tedious calculation process and poor precision, is unable to satisfy the needs of measuring the rheological properties of the drilling fluids at rig site. This paper discusses the optimization of the mathematical models of flow coefficient, shear rate and shear stress prevailing at the borehole wall, and rheological curve for Newtonian and non-Newtonian fluids. Based on the study a new mathematical model for calculating the Newtonian viscosity, apparent viscosity, plastic viscosity and yield point was obtained. It was found that there is a strong positive correlation between the rheological curves obtained from the model for mineral oils, synthetic oil, fuel oil, follicle flushing fluid and formate drilling fluid, and the rheological curves of these fluids obtained on HAAKE MARS Model III rheometer. The errors between the Newtonian viscosity, apparent viscosity, plastic viscosity and yield point of five fluids obtained with the new model and those obtained with ZNN-6 rotational viscometer are 1.40%, 4.29%, 2.78% and 10.13%, respectively, indicating that the new model as a simple way can be used to reliably measure the rheological properties of drilling fluids and gives results that satisfy the needs of rheological design at the rig site.
Low Friction Potassium Silicate Drilling Fluid System For Shale Gas Horizontal Wells
LEI Zhengyong, XU Mingbiao, YOU Fuchang, GUO Yuanyao, ZHOU Wen
2021, 38(1): 62-67. doi: 10.3969/j.issn.1001-5620.2021.01.010
Abstract:
At present, with the increasingly severe environmental protection pressure, it is more and more urgent for drilling fluid practitioners to develop a set of water-based drilling fluid system that can replace oil-based to solve a series of problems such as friction, wellbore stability and borehole cleaning in the process of shale gas horizontal drilling. In this study, a potent water-based lubricant with synergistic plugging ability was developed and introduced on the basis of potassium silicate drilling fluid’s features such strong inhibition, strong plugging and easy film-forming.Finally, the low friction potassium silicate drilling fluid was constructed through a series of screening and evaluation experiments. Its lubrication coefficient is about 0.08, and the weight of anti-wear weight reaches 10 kg, which is comparable to oil-based lubrication and anti-wear performance; at the same time, it has a low filtration rate (FLHTHP < 6 mL); in addition, the system has strong inhibition and anti pollution ability, and its rheology is easy to control, which can fully meet the development needs of shale oil and gas reservoirs.
Study and Application of the Method for Evaluating Damage to Shallow Unconsolidated Sandstone Gas Formations
MA Yongxin, ZHANG Liquan, YANG Zhonghan, XU Fabin, XIANG Xiong, YANG Honglie, LIU Xiliang
2021, 38(1): 68-73. doi: 10.3969/j.issn.1001-5620.2021.01.011
Abstract:
Columnar cores are generally difficult to be obtained from unconsolidated sandstone formations because of poor formation cementation. Conventional methods for evaluating the damage of unconsolidated sandstone oil and gas reservoirs cannot be used to evaluate the degree of damage to the unconsolidated sandstone oil and gas reservoirs. A method for evaluating the damage to unconsolidated sandstone gas reservoirs has been presented based on the fabric characteristics of cores from unconsolidated sandstone gas reservoirs. Evaluation of the drilling fluids used in gas field A and gas field B in the west of South China Sea showed that the results of the new method coincided with the field well test results, indicating that the new method can be used to simulate field operation with high accuracy.
Control Mud Losses in Well Shunbei-5-9 with ZYSD High Fluid Loss Solidifying Slurry
FANG Junwei, JIA Xiaobin, LIU Wentang, YUE Ming
2021, 38(1): 74-78. doi: 10.3969/j.issn.1001-5620.2021.01.012
Abstract:
The Well Shunbei-5-9 is an appraisal well drilled in the potential area of the low uplift Shuntuoguole north margin. The Silurian system penetrated by this well has low pressure bearing capacity and plenty of induced fractures which are easy to widen and extend when pressure surge is applied, and mud losses are thus occurring. When using bridging lost circulation materials (LCM) to control mud losses, it is difficult to have suitable particle size distribution of the LCMs, and the LCMs deposited on the surface of the wellbore has pressure bearing capacity that is not sufficient to resist mud losses again. Furthermore, there are high pressure saltwater zones developed in the Silurian system, making the mud loss control more difficult. Several wells drilled nearby experienced severe mud losses, borehole wall collapse and even well abandonment. To overcome the difficulties encountered in controlling mud losses in the Silurian system, a ZYSD high fluid loss LCM was used. ZYSD is able to seal off the mud loss channels in 30 s, and the formation plugged with ZYSD has pressure bearing capacity of at least 18 MPa. This technique has been used 7 times in field operation and were all successful. Time spent dealing with mud losses was reduced by 81%. Mud loss zones treated with ZYSD had pressure bearing capacity of 8.5 MPa. Equivalent circulation density of mud when drilled into the Silurian system was 1.51 g/cm3. The application of the ZYSD technique successfully solved mud losses and water kick problems encountered in drilling the Well Shunbei-5-9.
A Solidifying Mud Loss Control Slurry for Well Drilling in Coal Mine Goafs
LI Chenxin
2021, 38(1): 79-84. doi: 10.3969/j.issn.1001-5620.2021.01.013
Abstract:
A new solidifying mud loss control slurry has been developed for use in well drilling in coal mine goafs where severe mud losses were frequently encountered. The mud loss control slurry is formulated with slag as the solidifying agent, and other additives such as activator and suspending agent etc. This mud loss control slurry has the ability to satisfy the needs of plugging and solidifying when drilling in coal mine goafs characteristic of low density and low temperature. The hydrational mechanism of the mud loss control slurry was verified through laboratory evaluation and micro-structure examination. Under the action of the activator, the vitreous structure of the solidifying agent is broken down, producing various hydrational products. Part of the calcium-rich phase leaves the original structure and fills in the pores of the hydrational products. On the other hand, as the silica-rich phase continues to become hydrated, the hydrational products are filling in the pores of the hydrational product of the calcium-rich phase, thereby making the hydrational products denser and denser. The hydrational products are mainly C—S—H and C—A—S—H gels, rendering the solidified product high compressive strength. Data from simulation tests and field tests have proved that the solidifying mud loss control fluid is able to satisfy the needs of mud loss control in coal mine goafs, and the goal of studying on the mud loss control in coal mine goafs is achieved.
Study on Optimization of Method for Measuring the Content of Potassium Salt of Polyacrylamide in Drilling Fluids
CHEN Leixu, HOU Yong, ZHAO Fei, LIU Cuiwei, SHI Ye
2021, 38(1): 85-88. doi: 10.3969/j.issn.1001-5620.2021.01.014
Abstract:
The potassium salt of polyacrylamide (PAM) is a widely used anionic polymer. In examining the quality of this polymer in accordance with the standard SY/T 5946—2002, several factors affect the final results, for example, the purity of the polymer is affected by inorganic salts existed in the process of examination, sodium nitrate used to measure the intrinsic viscosity is a kind of easy-to-explode substance and requires high level of control, and there is a big error in the determined chloride ions concentration. The procedure of examining the quality of the potassium salt of PAM was modified in our laboratory experiment. In measuring the purity of the polymer in laboratory, ethanol and hydrochloric acid as the washing liquid. The temperature and time for residue ignition were optimized. Sodium chloride was used to replace the sodium nitrate in measuring the intrinsic viscosity. In measuring the chloride ions content, the treatment of the sample was optimized and the pH of the sample was measured with titration method. All these measures helped improve the accuracy of the examination. It was found in the experiment that by adding 1.5% hydrochloric acid in the pure washing liquid, the solubility of the inorganic salt in the sample was increased, and the parting rate of the purity of the sample was thus increased by 40%. The residue of the sample was ignited at 800 ℃ for 3 hours, in so doing the real effective content of the sample can be measured. When using NaCl to replace NaNO3 in the measurement of the intrinsic viscosity, the range of variation of the results was (00.40)/100 mL/g. In the measurement of chloride ions concentration, the sample was ignited at elevated temperatures and the pH value of the titration solution was adjusted, thus the variation of the results between parallel measurements was reduced from 1.02% - 1.73% to 0.0018%. These optimization measures help improve the accuracy and precision of the measurement, providing an effective base for examining the product quality of the potassium salt of PAM.
Application of a Self-Solidifying Lost Circulation Material in Well G21X3 in Jidong Oilfield
XU Jing, WANG Zaiming, ZHANG Yixin, HOU Yi
2021, 38(1): 89-92. doi: 10.3969/j.issn.1001-5620.2021.01.015
Abstract:
The Well G21X3 is a key exploratory well drilled at the upper part of the Gao-21 fault in Gaonan slope. The designed completion depth of this well is 4,392m. When drilled to 2,670 m, the bit drilled into caves and the mud lost return. In drilling the Dongying-1 member and Dongying-2 member, totally four times of mud losses occurred and eight times of mud loss control jobs were performed. Totally, 250 m3 of mud was lost into the formation. To deal with the mud losses in the future, a new technology was presented based on the analyses of the deficiencies of the mud loss control techniques previously used. The new technology involves the use of a self-solidifying lost circulation material (LCM). Laboratory evaluation of the self-solidifying LCM was performed on its morphological feature, solidifying state at different temperatures and the pressure bearing capacity of the formation plugged with the self-solidified LCM. The mechanism of the self-solidifying LCM is to coat LCMs such as mica, fiber, nutshell and silica with a layer of resin, and these LCMs are then pumped into the loss channel, depositing there. The resin on the surface of the LCMs then condenses at the temperature prevailing in the loss zone and solidifies into hard lumps, thereby increasing the strength and stability of the LCMs. This technology has been successfully used in controlling mud losses occurred in the Well G21X3. The procedure of using the selfsolidifying LCM is the same as that of the compound LCMs, and is easy to operate. This technology is widely applicable, and has broad prospects of application.
CEMENTING FLUID
Preparation Properties and Structure of High Heat Conduction and Low Density Cementing Materials for Geothermal Wells
YANG Yu, XU Shuanhai, ZHANG Hao, HAN Yongliang, ZHANG Weidong, LI Yongqiang
2021, 38(1): 93-101. doi: 10.3969/j.issn.1001-5620.2021.01.016
Abstract:
High heat conduction and low density cementing material (HLC) can effectively solve the cementing problem of deep and easy to leak geothermal wells, and can effectively improve the underground heat transfer efficiency of geothermal wells. Through orthogonal test, based on analytic hierarchy process (AHP) and matrix analysis, and considering four indexes of thermal conductivity, 48 h compressive strength, density and cost, the HLC which can be used for cementing of deep geothermal well was prepared. The performance indexes of cementing materials were tested by experiments. The microstructure of HLC was observed by SEM, XRD and MIP, and the mechanism of heat conduction was analyzed. The results show that the HLC formula is: 0.78 water solid ratio, 55% cement, 9% graphite, 25% quartz powder, 2% fly ash, 2% silica fume, 2% fluid loss additive, 3% stabilizer, 1.5% expansion agent and 0.5% retarder; its performance indexes meet the requirements of relevant specifications; the addition of graphite improves the microstructure and pore size distribution of HLC; the heat conduction mechanism conforms to the heat conduction path theory. It can be used for reference for cementing construction and preparation of similar materials in deep geothermal wells.
Application and Analysis of the Synergy between Oil Well Cement Expanding Agents and Oil Well Cement Tougheners
LI Yunjie, LI Qian, XU Jianjun
2021, 38(1): 102-108. doi: 10.3969/j.issn.1001-5620.2021.01.017
Abstract:
Two expanding agents and two tougheners were selected to explore the synergy between oil well cement toughener and expanding agent. The expanding agents selected were a lattice expanding agent and a gas expanding agent, the tougheners selected were a fiber and a carbon nanotube (CNT). A cement slurry was treated with these agents whose synergy was investigated. Laboratory study was performed on the expansion performance, mechanical properties, pore structure and regular performance of the cement slurry, and the operating conditions of different combinations of the tougheners and expanding agents were analyzed. It was found from the study that under the condition of free expansion, the toughener and the gas expanding agent had higher synergistic expansion rate. The combination of CNTs and the expanding agents had better contraction inhibition effect at high temperature and high pressure. When CNTs were combined with the lattice expanding agent, the increase in the strength of the set cement was the greatest, the porosity of the cement matrix was the lowest and the pores were mainly micro ones. When the fiber was combined with the gas expanding agent, the crack residue strength was the highest. Combination of the expanding agents and the tougheners to some extent improved the filter loss and the settling stability of the cement slurry and retarded the thickening time of the cement slurry. Of the combination of the four agents studied, the combination of CNTs and the two expanding agents rendered the cement slurry higher yield point and stronger thixotropy. The study can be used as a reference and a guidance for the design of cement slurries used at different work conditions.
Low-density and Strength Cement Slurry for Fractured Formation
CHEN Xiaohua, DI Wei
2021, 38(1): 109-115. doi: 10.3969/j.issn.1001-5620.2021.01.018
Abstract:
The Yanchang formation in the E’nan block is the naturally fractured pay zone into which losses of cement slurry and hence the contamination of the reservoir often took place. To solve this problem, a low-density high strength high toughness cement slurry was formulated, based on the principle of low density, loss prevention and toughness improvement, to effectively seal the reservoir formation. An innovative epoxy-nanometer liquid silica cement slurry with low density high strength high toughness cement slurry was formulated with the synergy of several additives; a self-developed light-weight agent, a waterborne epoxy emulsion and a nanometer liquid silica that were carefully selected. The density of the cement slurry is 1.65 g/cm3. Performance evaluation of the cement slurry showed that the filter loss of the cement slurry can be controlled within 40 mL/30 min, the thickening time of the cement slurry has reasonable time range. The set cement has high compressive strength, the elastic modulus of the set cement is less than 7.0 GPa. The set cement has good elastic and plastic mechanical properties, and low contamination to the reservoir. Using this technology, low density, high strength and toughness enhancement were achieved. Later stage reservoir fracturing of wells cemented with this cement slurry can be easily performed. The application of this technology has ensured the successful exploration and development of the Paleozoic natural gas in E’nan area.
Laboratory Study on an HTHP Ultra-High Density Cement Slurry
SONG He, YANG Wei, TANG Junfeng, LIU Cuiwei, WANG Jingpeng, LIN Zhiwei
2021, 38(1): 116-121. doi: 10.3969/j.issn.1001-5620.2021.01.019
Abstract:
The well Tianwan-1 is an ultra-deep exploration well located in the middle of the Junggar Basin, with depth of 7,500 m, bottom hole pressure of 170 MPa and bottom hole temperature of 160 ℃. A high temperature high pressure ultra-high density cement slurry was developed in laboratory to overcome the high temperature and high pressure, as well as the other problems related to ultrahigh density cement slurries, such as poor fluidity, poor settling stability, high dynamic fluid loss, and over-retarding of the strength of the top set cement under big temperature differences, etc. The highest density of the cement slurry was 2.55 g/cm3. The cement slurry was developed with a new weighting agent, micronized silica, a high temperature stabilizer, powdered silica passing through 600-mesh screen, a new micronized manganese powder, a suspending agent, a high temperature retarder, a high temperature filter loss reducer and a high temperature friction reducer. Laboratory experimental results showed that the cement slurry had fluidity of 32 cm, good settling stability, high strength of top set cement and strong capacity of anti-channeling. The thickening time of the cement slurry is linearly adjustable at 160 ℃ and 170 MPa. Dynamic filter loss of the cement slurry was 40 mL. The cement slurry can be used in a wide range of downhole conditions; by changing the concentrations of the different additives, the cement slurry can satisfy the needs of cementing operation at different downhole temperatures (hence different depths) in the well Tianwan-1.
Study and Experiment on Radial Expansion and Contraction of Cement Sheath
WANG Fuyun, ZHANG Huali, ZHENG Youzhi, SONG Wenhao, HE Yu, HUANG Juan
2021, 38(1): 122-126. doi: 10.3969/j.issn.1001-5620.2021.01.020
Abstract:
The radial expansion and contraction of cement sheath in oil and gas wells is one of the key factors affecting the bonding quality of the interfaces between casing string, cement sheath and borehole wall. To overcome the technical difficulties in testing the expansion and contraction characteristics of cement sheath in working conditions, the autoclave of the tester was modified and restructured to make the tester capable of measuring both axial (conventional tester) and radial expansion and contraction of the set cement. Using this new equipment, the tough anti-channeling cement slurry and the flexible self-stressing cement slurry presently in use in the Chuan-Yu area were evaluated for their expansion-contraction characteristics. The volumetric change characteristics of the cement slurry was found using the new tester and the evaluation procedure. The critical points of expansion and contraction of the cement slurry at different temperatures and pressures can be measured and used as important experimental data for selecting different cement slurries for different sections of the well. The new equipment and the data obtained with it have provided a reference for ensuring the job quality of well cementing in the Chuan-Yu area.
FRACTURING FLUID & ACIDIZING FLUID
A Drag Reducer: It’s Interaction with Water, Synthesis and Performance Evaluation
JING Xianwu, LIU Youquan, XU Yuan, KANG Zhiqin, DAI Shanshan
2021, 38(1): 127-132. doi: 10.3969/j.issn.1001-5620.2021.01.021
Abstract:
The interaction energy of three polymers with water was compared using molecular dynamics method. From the radial distribution functions it was found that the hydrogen bond between the oxygen atoms in the polymer molecules and the hydrogen atoms in the water molecules is mainly responsible for the interaction between the polymer and water. In laboratory experiments, which were done to verify the radial distribution functions, a ternary hydrophobic association polyacrylamide (P(AM-AA-MPEG)), which was a copolymer made from a nonionic surfactant hydrophobic monomer, acrylamide and acrylate, was used as a drag reducer. HNMR spectroscopy of the ternary hydrophobic association polyacrylamide molecules indicates that the copolymerization was successful. The molecular weight of the ternary hydrophobic association polyacrylamide measured with light scattering method is 2.83×106 g/mol. The friction of fresh water flowing in a pipe was used as a blank friction data group to calculate the rate of drag reduction. The maximum rate of drag reduction at polyacrylamide (PAM) concentration of 0.025% is only 40%, while the maximum rate of drag reduction at P(AM-AA-MPEG) concentration of 0.025% can be as high as 65%. Polymers having higher interaction energy with water have better drag reduction performance. The network structure formed by the molecules of a polymer in water solution is the direct cause of drag reduction, the long side chains of a polymer also help improve the rate of drag reduction.