2023 Vol. 40, No. 5

DRILLING FLUID
Effect of Weighting Materials on the Properties of Synthetic-Based Drilling Fluids
REN Liangliang, CHEN Chen, LI Chao, HE Zhuoxin, HU Yueyue, XU Botao, LUO Jiansheng, GAO Erhu
2023, 40(5): 551-555. doi: 10.12358/j.issn.1001-5620.2023.05.001
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Abstract:
The influence of different weighting agent on the performance of synthetic drilling fluid system (SBM) were studied in this work. Based on the MODRILL drilling fluid system of China Oilfield Services Co., LTD., the variation of SBM performance with 2.04 g/cm3 were investigated with different weighting agent of 4.3 g/cm3 Barite, 4.4 g/cm3 Barite and 4.8 g/cm3 Trimanganese tetra oxide with the ratio of 10∶0∶0、0∶10∶0、5∶0∶5、6∶0∶4、7∶0∶3、8∶0∶2、5∶5∶0. The results showed that the rheological property, emulsion-breaking voltage and high temperature and pressure filtration are affected by the different weighting agent. The apparent viscosity and the plastic viscosity would be decreased and the yield point and 6 rpm reading would be increased with the increasing trimanganese tetra oxide. The emulsion-breaking voltage would be decreased with the increasing trimanganese tetra oxide. The high temperature and high pressure filtration would be substantially increased when adding the increasing trimanganese tetra oxide. The above conclusions were verified in the filed test by studying the effect of weighting agent on the performance of synthetic drilling fluids.
Drilling Fluid Technology for Plugging and Strengthening the Borehole Wall of Wells Penetrating the Faulted Fractured Reservoirs in West Sichuan
GAO Shuyang, TANG Zhichuan, SONG Bitao, LI Kaixian, LIU Zuocai
2023, 40(5): 556-562. doi: 10.12358/j.issn.1001-5620.2023.05.002
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Abstract:
Drilling the broken formations in the faulted fractured reservoirs in west Sichuan has been encountered with frequent drill pipe sticking and a well is very difficult to be drilled in accordance with the designed parameters. Geological characteristics analyses and laboratory evaluation results have shown that the rocks in the faulted fractured broken formations are weakly bonded and are developed with microfractures. When a liquid invades into the microfractures, the microfractures extend and the integrity and mechanical property of the rocks are damaged, which in turn changes the status of the effective stresses of the rocks around the borehole and results in borehole collapse. Based on this conclusion, a high temperature chemical borehole wall strengthening agent was developed and a high efficiency plugging agent selected to formulate a drilling fluid with the capacity of plugging and strengthening the borehole walls in the faulted and fractured formations. This drilling fluid, with an enhanced plugging and strengthening capacity, has been successfully used in drilling several wells, including the well M6, and the walls of the borehole penetrating the broken faulted fractured formations were maintained stable during drilling. This drilling fluid will have a good application prospect.
ECD Sensitivity Analyses and Prediction Based on Interpretable Machine Learning
MA Lei, ZHOU Bo, ZHANG Ningjun, YANG Heng, CAI Xinshu, LIU Zheng, XU Tongtai
2023, 40(5): 563-570. doi: 10.12358/j.issn.1001-5620.2023.05.003
Abstract:
The calculation of equivalent circulation density (ECD) of drilling fluids is very cumbersome and time-consuming, and the pattern of sensitivity of the ECD has not been quite understood yet. To solve this problem, 1928 data from the Block Keshen were acquired and analyzed using the ProHydraulic software to calculate the theoretical ECD. Based on the calculation some characteristic parameters were determined. Key factors affecting the sensitivity of the ECDs of a drilling fluid, such as mud properties, drilling parameters and sizes of the annular spaces are analyzed using interpretable machine learning technology. Using linear regression, an empirical equation for calculating the ECDs of drilling fluids in the Block Keshen, which covers 12 main characteristic parameters, is constructed. ECD calculation with the model shows that the model gives results that fit the practical values with excellence. The coefficient of determination of the testing set is 0.963, and the average absolute error is only 0.04, indicating that this empirical equation is simple and efficient in ECD calculation in practical engineering application.
Research on a New Method for Simulation of Fractured Plugging Based on 3D Scanning and Printing Technology
WANG Tao, YE Yan, ZHU Jinzhi, ZHANG Zhen, LU Haiying, LI Chengli, SUN Zhenwei
2023, 40(5): 571-577. doi: 10.12358/j.issn.1001-5620.2023.05.004
Abstract:
The frequent leakage and large loss of drilling fluid during drilling in Bozi area of Tarim Oilfield have caused huge economic losses, which is a major difficulty in exploration and development in this area at present. The existing traditional fracture plugging simulation method is difficult to simulate the downhole fracture conditions, resulting in a large difference between the indoor experimental results and the field application. Taking the Bozi area as an example, through the analysis of its reservoir characteristics, it is clear that the reservoir leakage is caused by natural fracture leakage and weak formation fracture; Based on 3D scanning and printing technology, a simulation fracture plate with real fracture characteristics of the reservoir is made, and a new method of fracture plugging simulation is established with this as the core. The evaluation experiment of plugging formula under different fracture widths is carried out using self-developed plugging instrument. The experimental results show that the new method of fracture plugging simulation is applicable to the simulation and evaluation of the plugging formula in multi-scale fractured formations, and can provide strong support for the on-site testing of the plugging formula for fracture loss.
Adsorption of Polar Fragments of Amide Lubricants on Iron Surface
LIU Chao, LU Fuwei, WANG Wei, ZHANG Shuncong, TANG Yuhua, WANG Tengfei, GUO Tingting
2023, 40(5): 578-585. doi: 10.12358/j.issn.1001-5620.2023.05.005
Abstract:
DFT simulation was used to investigate the bonding effects of different polar segments on iron (001) surface. These polar segments were intercepted from the hydrophilic chain segments of oleic acid amide lubricants, include primary amine, secondary amine, amide, and hydroxyl. Results indicated that amide group, primary amine group, and hydroxyl group generated the most stable adsorption at the bridge site of Fe (001) surface, and secondary amino group generated the most stable adsorption on the top site of Fe (001) surface. The adsorption energy in descending order were primary amine group, secondary amino group, hydroxyl group, and amide group. Results of population analysis indicated that the orbital population of four polar groups changed during the process and obtained electrons from Fe (001) surface. Among them, secondary amino group obtained 0.16e electrons, primary amino and amide group obtained 0.09e electrons, and hydroxyl group obtained the lowest number of electrons at 0.08e. Results of DOS analysis showed that there exist DOS overlap between 2p orbitals of N and 3p、4s orbitals of iron, with chemical bonding effect. In the extreme pressure lubrication test and four ball friction test results, the lubrication coefficient reduction rate of oleic acid Diethylenetriamine is 83.6%, higher than 78.2% of oleic acid diethanolamide, and the wear scar radius is 287.184 μ m. The wear radius is lower than that of oleic acid diethanolamide. The experimental results indicate that surfactants containing amine and amide groups have better lubrication performance than surfactants containing hydroxyl groups.
Experimental Study on Mud Intrusion in Tarim Tightly Fractured Reservoirs
LI Ming, GUO Jianchun, LIU Yuxuan, LIU Wenhui
2023, 40(5): 586-593. doi: 10.12358/j.issn.1001-5620.2023.05.006
Abstract:
In recent years, the problem of tight sandstone reservoir damage and protection has attracted the attention of scholars. Due to the existence of natural fracture channel communication, the fluids can easily enter the reservoir along the fractures during the development of fractured tight reservoirs and cause serious damage to the reservoir. In order to investigate the degree and mechanism of mud damage to fractured reservoirs, this paper conducts mud intrusion damage experiments with fractured tight sandstone reservoirs in Tarim Kucha Piedmont block as the research object. The experimental results show that the mud intrusion process can be divided into four stages according to the formation process of mud cake, namely, no mud cake stage, mud cake rapid generation stage, mud cake dynamic equilibrium stage and formation of sealing stage; the mud intrusion rate is affected by the reservoir permeability, mud cake permeability, fluid properties and specific gravity, and when the reservoir permeability is higher than the critical permeability, the intrusion rate is mainly determined by the filter cake permeability; by Scanning electron microscope results show that the blockage state of mud solid phase particles in core pore throat is divided into three kinds: blockage, adhesion and filling, and different blockage states have different degrees of damage to reservoir permeability. The mud dynamic damage analysis and solid-phase particle intrusion study obtained in this paper can help improve the complex reservoir simulator, which has certain guiding significance for the field construction operation and mud optimization.
Study on Technology for Protecting Loose Sandstone Reservoir in Bayan Oilfield
CHENG Zhi, LUO Yucai, LIU Rongqing, OUYANG Wei, PENG Song, TAN Tianyu, WANG Tao, YU Haitao
2023, 40(5): 594-601. doi: 10.12358/j.issn.1001-5620.2023.05.007
Abstract:
The reservoirs in the Bayan oilfield are weakly cemented sandstone reservoirs with medium and low permeability. Those reservoir formations are buried deep and are strongly water sensitive. Fresh water based drilling fluids have long been used to drill the wells, and because of the poor inhibitive capacity of the drilling fluids, the reservoirs are contaminated by the change in the salinity of the formation waters. Oilfields with the same buried depth and the similar reservoir physical properties in China are rarely seen, and a new micrometer sized reservoir protection additive is needed for drilling the loose sandstone reservoirs. Based on the analyses of the factors related to the reservoir damage in the Bayan oilfield, a micrometer sized emulsion reservoir protection agent with both filming and clay swelling inhibitive capacity was developed. The capacity of the reservoir protection agent to plug fractures with wide size distribution and the synergistic effect of the reservoir protection agent is verified using laser particle size analyzer, sand-bed plugging tester, PPA plugging filtration tester and SEM. The particle size of the reservoir protection agent D50 is ≤ 2.17 μm, and the D90 is ≤ 7.05 μm. The percent reduction of the linear swelling of cores tested with the reservoir protection agent is 51.35%. Compatibility of the reservoir protection agent with the drilling fluids in which it is used is satisfactory. The reservoir protection agent, combined with acid soluble materials, forms an integrated reservoir protection fluid capable of protecting reservoirs with various properties. Laboratory experimental results show that using this technology, percent permeability recovery of cores made with rock samples from weakly cemented reservoir sandstones can be 90% or higher. In field supplication, skin factor measurement and well production data all demonstrate the good reservoir protection capacity of this technology.
Low Damage Highly Inhibitive Water Based Drilling Fluid for Drilling Shale Oil Reservoir
AI Lei, GAO Yunwen, OUYANG Yong, XIN Qingqing, ZHOU Yu
2023, 40(5): 602-610. doi: 10.12358/j.issn.1001-5620.2023.05.008
Abstract:
Chang 73 reservoirs have the characteristics of micron-nano crack development and low strength of formation rocks. It can lead to the intrusion of drilling fluid filtrate into the reservoir causing borehole collapse and reservoir damage. We clarified the destabilization mechanism of Chang 73 shale and the technical difficulties of drilling fluids. Then the multi-stage particle size distribution intervals with broad spectrum was constructed by introducing rigid and deformable plugging materials, which was based on the "1/3 and 2/3 bridging rule". Next, using the instantaneous water loss as the evaluation index, the optimal ratio was optimized by surface response modeling, and the combination of anti-collapse inhibitor was preferred in the room. Based on which a low damage and anti-collapse water-based drilling fluid was developed. The results of the evaluation indicated that the drilling fluid can effectively balance the formation collapse stress, and the rheological properties remain satisfactory after aging for 72 h. It also reduced shale linear swell by 16.74% and 13.61% compared to clear water environments and in the field drilling fluids respectively. Due to its remarkable plugging properties, the instantaneous filtration loss of the drilling fluid was only 1mL and the plugging rate of the core was as high as 93.5%. Based on the reservoir protection capability of the drilling fluid, there was no pore throat plugging in the core slab after mud cake removal and the permeability recovery value of the core was as high as 95.2%. It was important that the lubricity of the drilling fluid was moderate and the friction coefficient remain around 0.08 before and after the drilling fluid ages. The average diameter expansion rate of the horizontal section in the field test was only 4.27%, and the average mechanical drilling speed could reach 18.4m/h. There were no complicated downhole accidents in the horizontal section during the drilling period, and all the performances could meet the needs of horizontal wells in the Chang 73 reservoirs.
Study on Solids Distribution and Control in Water Based Drilling Fluids-Take Gas Wells in Western Sulige as Example
LI Minghui, WANG Kai, WANG Qingchen
2023, 40(5): 611-616. doi: 10.12358/j.issn.1001-5620.2023.05.009
Abstract:
This paper discusses the studies on factors affecting solids control of a drilling fluid, such as changes in the solids content of the drilling fluid during drilling, particle size distribution of the drilling fluid, sand content of the drilling fluid as well as the efficiency of the solids control equipment, taking the water based drilling fluids from two gas wells drilled in the eastern Sulige area as examples. The purpose of the studies is to push forward the precise control of field drilling fluids and hence further improve the safe and efficient drilling operation. The results of the studies show that during drilling from the Yanchang formation down to the Majiagou formation, the solids content of the drilling fluid increased from 4%-7% to 9%-13%, accompanied with an increase in mud density. The content of the solids with particle sizes > 109 μm (140 mesh) decreased from 63.05% to 35.5%, the content of the solids with particle sizes < 74 μm increased from 3.98% to 12.73%, and the solids content cannot be reduced to a lower level anymore. The sand content of the drilling fluid was controlled at less than 0.5%. Before and after mud system conversion, the highest efficiencies of solids removal of the sand trap and the shale shakers are reached, which are 43.31%-51.47% and 45.38%-53.98%, respectively. At the same time, the solids removal efficiency of the mud cleaner (desander and desilter) is at the lowest level, which is 5.31%-11.76%. These studies can be used as a reference to the efficient solids control and precise optimization of water based drilling fluids in field operation.
Application of Gravity Displacement Drilling Fluid and Low Friction Drilling Fluid in ST2-4 Well
ZHU Xuefei, YANG Kun, XU Sixu, SUN Jun, FENG Yong, XI Yunfei, HUANG Nianyi
2023, 40(5): 617-621. doi: 10.12358/j.issn.1001-5620.2023.05.010
Abstract:
Well ST2.4 in 152.4 mm hole 4350~4800 m interval well deviation 0°-61.1°, in the process of the middle-completion direct-push memory logging, the electric logging tool got stuck, the non-water hole channel of the 50.95 m electric logging tool could not set up a cycle, and the conventional unstuck fluid did not get unstuck after the first immersion, for the second time, the formula of the conventional unblocking agent was upgraded to an improved unblocking agent. Firstly, the clean water of the unblocking agent was replaced with 10% CaCl2 salt water, and secondly, the concentration of the rapid penetrant fast T was increased to 30% , the third is to raise the density of the unblocking fluid to 0.5 g/cm3 above the mud density, and to replace the unblocking fluid to the bottom of the well by using the gravity replacement principle, thus successfully unblocking the electric measuring instrument, avoiding the loss of over ten million electric measuring instruments. The“Low viscosity, light slurry + heavy slurry slug” sand-carrying technology was used to keep the wellbore unblocked after the break-up, and the organic drag reducer YJJZ-1 was introduced to convert the conventional KCl polysulfonate system into the low friction drilling fluid to reduce the friction, through improving the quality of HTHP mud cake and strengthening the combination of anti-sloughing and inhibition of mud, the electric logging and casing running operations in the inclined section are completed.
Using RSM to Determine Electric Gel Breaking Conditions for Waste High Density Water Based Drilling Fluids
WANG Xiaohui, WANG Xudong, JIANG Chunli, SHI Haolin, XUE Jiawen, XU Jiafang
2023, 40(5): 622-628. doi: 10.12358/j.issn.1001-5620.2023.05.011
Abstract:
As oil and gas wells are drilled deeper and deeper, higher formation pressures need to be balanced with high density drilling fluids, and this leads to another problems: the treatment of more and more high density waste muds. Waste muds are generally treated with chemical flocculants and problems such as high treatment cost, poor universality and potential secondary pollution are the norm. In a study an electric field was applied to treat a high density waste mud. Based on the results of a single-factor experiment, the effects of three factors, i.e., current intensity, time of gel breaking and the distance between two electrodes, as well as the interaction of the three factors on the Zeta potential and particle size distribution of the drilling fluid were studied using response surface methodology (RSM). It was found that an optimum gel breaking can be obtained when the electric current intensity = 8 A, the time of gel breaking = 10 min, and the distance between two electrodes = 3 cm. After gel breaking, the Zeta potential of the drilling fluid was increased by 38.29%, reaching −26.2 mV, and the particle size distribution factor D90 reached 562.5 μm, indicating that the gel stability of the waste drilling fluid was broken, and this provided a powerful support to the subsequent recovery of the useful mud components as well as the treatment of the waste portion of the waste drilling fluid.
Compound and Efficient Blockage-Removal Agent for Polymer Flooding Oilfield
LIU Yilong, QI Ning, GAN Junchong, SHEN Yuyang, ZHANG Zhenjun, SHI Xiangke
2023, 40(5): 685-692. doi: 10.12358/j.issn.1001-5620.2023.05.020
Abstract:
Aiming at the problem of complex blockages in which polymers, inorganic scales and heavy oils are wrapped around each other after long-term polymer injection in the polymer flooding oilfield, resulting in serious blockage of the formation, a stable and efficient compound blockage-removal agent with 0.6% percarbonamide, 1% acetic acid, 0.3% OP-10, 1%DTPMP, and 1%HSJ-3 was prepared. And the properties of the compound blockage-removal agent were evaluated. The results showed that the agent can effectively degrade the simulated blockages under different temperature conditions. Under the condition of 80 ℃, the degradation rate of more than 90% can be reached in 4 h, with excellent degradation performance and temperature resistance. Placed at 80 ℃ for 1 h, the stability was maintained at 97%, with good stability performance and the corrosion rate was 0.9871 g·m−2·h−1, which met the industry-level standard. When prepared with 15×104 mg/L high salinity brine, the blockage-removal efficiency was basically not affected and the salinity resistance is excellent. The compound blockage removal agent can effectively solve the complex blockages formed in the process of polymer flooding through gradual stripping and continuous degradation. After injecting the composite blockage-removal agent, the core permeability increased from 0.244×10−3 μm2 to 6.391×10−3 μm2, and the permeability increased by a factor of 25.192. The compound block-removal agent can effectively solve the complex blockages.
CEMENTING FLUID
The Synthesis of ATP Loaded Heterocyclic Amphoteric Copolymer and Its Performance and Mechanisms of Reducing Filtration Rate under Ultra-High Temperatures
WANG Qike, LIU Wenming, LING Yong, XU Yixin, ZHANG Hang, DUAN Yungang, GUO Jintang
2023, 40(5): 629-636. doi: 10.12358/j.issn.1001-5620.2023.05.012
Abstract:
The AMPS copolymer filter loss reducers have obvious thinning effect which is detrimental to the ultra-high temperature settling stability cement slurries. To solve this problem, an ultra-high temperature cement slurry filter loss reducer ATP-FLA is developed for use at elevated temperatures to weaken the high temperature dispersion side-effect of pure copolymers. ATP-FLA is synthesized as an attapulgite (ATP) loaded heterocyclic amphoteric copolymer. Comparison of the copolymer with and without ATP loading shows that in a temperature range of 150-240 ℃, a cement slurry treated with 4.0%-6.0% ATP-FLA and 2.0%-4.0% suspending agent has API filtration rate of less than 40 mL and density difference from settlement of the cement slurry of not greater than 0.03 g/cm3. After aging at 240 ℃ and 120 MPa, the cement slurry has flow index of 0.897,6 as well as high thickness and shear resistance at high temperatures. To evaluate the compatibility of the filter loss reducer ATP-FLA, ultra-high temperature cement slurry samples were taken from several wellsites. The evaluation test results show that the ATP-FLA can control the filtration rate without affecting the other properties of the cement slurries. Study on the working mechanisms of ATP-FLA using molecular dynamics shows that ATP-FLA has advantages over conventional ionic copolymers in that the disturbances to the molecular chains of ATP-FLA from the “dehydration” effect of metal ions in the environment are weakened, and the ATP-FLA molecules are therefore resistant to the attack of the metal ions, and this is why, on the basis of mechanisms, the ATP-FLA filter loss reducer is more adaptable to the metal ion environment prevailing in cement slurries.
A Storable Liquid Cement Technology
SHA Linhao, XU Peng, TANG Shaobing, FENG Wangsheng, GUO Qiushi
2023, 40(5): 637-643. doi: 10.12358/j.issn.1001-5620.2023.05.013
Abstract:
This paper introduces a new cement slurry – a storable liquid cement. This is a cement that can be stably stored in liquid state, and can set and be made hardened when necessary. Using this technology, the cement slurry can be made in advance, thus solving the problem of large density fluctuation of conventional cement slurries, realizing the accurate control of the density of a cement slurry, and satisfying the requirements of cementing a well that is far away and with hard rig-site operation conditions. The composition, properties, technical features and applications of the storable liquid cement are described in detail. The cement has stable properties when in storage, and can be stored for a long time of more than 90 days, for instance. The liquid cement, after being activated, has properties that are quire close to the conventional cement slurries, and can meet the requirements of operation at 40 – 180 ℃. The cement slurry has short transitional time of static gel strengths, low SPN value, and good anti-channeling performance. This cement slurry can be formulated at the operation base and is not necessarily formulated at the rig-site. The properties of the slurry, after well formulated, can be “locked up”, that is, its properties will always be maintained at the levels when the cement slurry was formulated. When the cement slurry is pumped down the hole, it is activated and then becomes hardened.
The Performance of Set Aluminate Cement Modified by Micro Silica Compounded Sodium Hexametaphosphate under Condition of Shale Oil In-situ Conversion
WAN Xiangchen, ZHANG Jian, WANG Wenbin
2023, 40(5): 644-651. doi: 10.12358/j.issn.1001-5620.2023.05.014
Abstract:
In the in-situ conversion of low purity shale oils, extremely high temperature will result in strength retrogression of the set cement. To solve this problem, study was conducted on the macro-properties and microstructures of an aluminate cement before and after aging 650 ℃. The aluminate cement is a cement modified by micro silica compounded sodium hexametaphosphate. It is found that at 50 ℃, sodium hexametaphosphate can significantly reduce the permeability of a set aluminate cement, and the compressive strength of the set cement is significantly increased. After treatment at 650 ℃, the aluminate cement modified with 5.0% sodium hexametaphosphate has the highest compressive strength, which is 47.19 MPa, while the aluminate cement modified with micro silica compounded sodium hexametaphosphate has strengths that are declining. The hydrational products of the aluminate cement before and after treatment at 650 ℃ have experienced significant changes, from C3AH6 and AH3 to C12A7 and CA, respectively. Among these products, C3AH6 and AH3 are thermally degraded in temperatures between 180 ℃ and 400 ℃, and because of the changes of the crystal form, the permeability of the set cement is increased. Micro silica accelerates the formation of C2ASH8 by the set cement at 50 ℃, and this is beneficial to the improvement of the microstructure of the set cement. Since C2ASH8 will degrade after treatment at 650 ℃, the sizes of the pores in the set cement will also increase.
Optimization of Preparation of Amphiphilic Polymer as High Temperature Retarder and Intelligent Control of Thickening Time of Cement Slurry by Response Surface Methodology
WU Zhiqiang, XING Xuesong, ZHAO Yipeng
2023, 40(5): 652-657. doi: 10.12358/j.issn.1001-5620.2023.05.015
Abstract:
Cementing in long sealing section of deep well is faced with the problem of long thickening time in high temperature section and long solidification time in low temperature section. Based on the concept of molecular structure activity changes during the formation/dissociation of amphiphilic polymer self-assembly structure. AMPS, unsaturated carboxylic acid (PA) and cationic monomer (CM) are used to synthesis a temperature responsive intelligent retarder TRIR by RAFT polymerization. Response surface methodology was used to optimize the synthetic process conditions of the polymer. The optimal process conditions were determined as follows: monomer concentration 28.7%, initiator dosage 0.6%, synthesis temperature 50 ℃, and reaction pH 4.5. The structure and thermal stability of the polymer were characterized by infrared spectroscopy and thermogravimetric analysis, and its retarding performance was evaluated. The results show that TRIR has excellent temperature resistance, the thickening time at 200 ℃ can reach 356 min under 4.0% (liquid) dosage, and the retarding property is significantly enhanced with the temperature rise in the range of 120~180 ℃. The thermal response polymer proposed in this paper can provide a new idea for the development of intelligent polymer in the future petrochemical field.
Study and Application of a Tough Anti-Channeling Cement Slurry for Well Xingtan-1
FENG Ruige, LI Wei, MENG Renzhou, WANG Junjie
2023, 40(5): 658-664. doi: 10.12358/j.issn.1001-5620.2023.05.016
Abstract:
The well Xingtan-1 is a deep horizontal well drilled in the Shuangyang district of Changchun city by the Jilin Oilfield. This well has a total depth of 5,758 m and horizontal section of 2,015 m. Studies were conducted on two problems, which are mud losses and strict requirement for the impact resistance of the cement sheath to withstand the effects of large scale fracturing jobs. A toughness enhancing anti-channeling agent TA-1 is developed. TA-1 is a product with “core-shell” structure, and is used to formulate an anti-channeling cement slurry with good toughness. The molecules of TA-1 have elastic cores and flexible molecular chains, and are able to improve the toughness of the cement slurry and form films. Test results of the performance of the cement slurry show that the slurry has good stability, with thickening time adjustable between 150 min and 350 min. The SPN value of the cement slurry is 1.15, indicating the cement slurry has good anti-channeling capacity. TA-1 reduces the elastic modulus of the set cement by 29.5% and enhances the impact resistance of the set cement by 16.4%. A cement slurry treated with TA-1 has 24-hour strength of greater than 20 MPa. Well cementing with this anti-channeling cement slurry on the well Xingtan-1 is successful, helping solve the problems of gas channeling through the cement sheaths and cracking of set cement during fracturing operation.
A Preliminary Method for Identifying Xanthan Gum and Welan Gum
FU Junfang, ZHAO Zhiqiang, SUN Qiang, ZHAO Shengxu
2023, 40(5): 665-669. doi: 10.12358/j.issn.1001-5620.2023.05.017
Abstract:
Welan gum and xanthan gum are all anionic bio-saccharide, their water solutions all have pseudo-plastic fluid characteristics and similar appearance. Welan gum has properties that are superior to those of xanthan gum, and its price is much higher than that of xanthan gum, which render necessity and importance to regulate market application and identification of the two bio-saccharides. The characteristics of the two saccharides were compared by IR spectroscopy, viscosity change with temperature and their performance in cement slurries. The results of the experiments show that the two bio gums have generally similar IR spectra, a methyl group on the unique rhamnose ring of the welan gum molecular structure has a unique absorption peak around 2,978 ± 2 cm−1. At shear rate of 0.5 s−1, temperature between 25 ℃ and 180 ℃, and mass concentration of 0.4%, the viscosity – temperature curves of the two gums run against each other; the viscosity of xanthan gum decreases with temperature while the viscosity of welan gum increases with temperature. At 65 ℃, a cement slurry with water/cement ratio of 1.0 treated with 0.4% welan gum has stable properties, while the same cement slurry treated with 0.4% xanthan gum does not. Using these three differences shown by xanthan gum and welan gum together, preliminary identification of xanthan gum and welan gum can be made.
FRACTURING FLUID & ACIDIZING FLUID
Study on Solubilization Behavior of Molecular Simulation Cosolvent in Siloxane SC-CO2 Fracturing Fluid
CHEN Yufei, WU Tong, ZHANG Hui, LI Jun, ZHOU Yingcao, ZHANG Geng
2023, 40(5): 670-677. doi: 10.12358/j.issn.1001-5620.2023.05.018
Abstract:
Due to the low viscosity of supercritical carbon dioxide fracturing fluid system, the method of adding tackifier is generally used to overcome the problem of low sand carrying efficiency. Siloxane tackifiers are widely used due to their low cohesive energy and good tackifying effect, but it is necessary to add cosolvent to improve the dissolution effect. Therefore, in this paper, the widely used polydimethylsiloxane was selected as the research object, and the effect of the addition of cosolvents such as methanol, toluene and cyclohexane on the dissolution behavior of polydimethylsiloxane in SC-CO2 system was studied by molecular simulation. Based on the binding energy, cohesive energy density and radial distribution function of solvent-solvent and solvent-solute, the solubilization effect of polar cosolvent and non-polar cosolvent on polydimethylsiloxane in supercritical carbon dioxide fracturing fluid system was compared and analyzed. The molecular simulation results show that the solubility parameter difference between methanol and solvent system is less than 0.5 at the same cosolvent content, and the solubilization effect is better than that of toluene and cyclohexane. The conclusion is that the essence of using cosolvent to improve the solubility of PDMS in SC-CO2 is the balance of the intermolecular force between CO2 and PDMS polymer, the intermolecular force between CO2 and cosolvent, and the intermolecular force between PDMS polymer and cosolvent. Therefore, when the siloxane tackifier itself is a non-polar material, toluene is recommended as a cosolvent. When the siloxane material has a certain weak polarity, methanol is the most suitable.
Preparation and Properties of Viscosification and Drainage Integrated Polymer Dispersion
LIN Hai, ZHANG Chengjuan, ZHAO Wenkai, WAN Youyu, WANG Zhisheng, GUO Delong, WANG Jinran, JIA Wenfeng
2023, 40(5): 678-684. doi: 10.12358/j.issn.1001-5620.2023.05.019
Abstract:
Rapid dissolution and salt-tolerance polymers are the key products for effective utilization of highly mineralized formation water and backflow water. The integration of viscosification and drainage is the main research direction of thickeners. A weak hydrophobic association polymer was designed and synthesized, and an integrated dispersing fluid with the properties of viscosification and drainage was optimized. The overall performance of fracturing fluid was evaluated. The polymer dispersion can meet the online preparation requirements using 194 557.93 mg/L ultra-high mineralized water, and the viscosity can be adjusted from 2 to 106 mPa·s when the amount of salt-resistant thickener was 0.1-1.2%. The surface tension of breaking fluid was less than 27 mN/m when the amount of dispersion was greater than 0.4%.At 90 ℃, under shearing for 1h, the viscosity of the integrated fracturing fluid was greater than 50 mPa·s. The viscosity of 1.0% polymer dispersion was about 4 mPa·s under 80 ℃ water bath for 2 h. When the amount of polymer dispersion was 0.1%, the drag reduction rate of fracturing fluid was greater than 65%. The polymer dispersion can meet the requirements of mixing ultra-high salinity formation water and flowback fluid, realize the integration of online viscosity change and drainage, greatly reduce the cost of fracturing fluid, and simplify the on-site liquid mixing process, so it has a wide application prospect.