2019 Vol. 36, No. 4

Display Method:
2019, 36(4)
Progress in Applying and Studying Dendrimers in Drilling Fluids
ZHONG Hanyi, GAO Xin, QIU Zhengsong, GUO Baoyu, ZHAO Chong, SHEN Guangcheng
2019, 36(4): 397-406. doi: 10.3969/j.issn.1001-5620.2019.04.001
More and more complex formations are drilled presently to find more oil and gas. To satisfy the needs of modern drilling engineering for "safety, fast operation, environment protection and high efficiency", higher requirements are imposed on drilling fluid additives. Dendrimers with their unique molecular structures and superior properties, are finding more application in many fields. This paper introduces the characteristics of the molecular structure, the performance and main synthetic methods of dendrimers, summarizes the progresses made in the research work of applying dendrimers in drilling fluid, analyzes the potential of dendrimers applied in drilling fluid, and explains the vision of the authors for the development of dendrimers in drilling fluid industry in the future. This paper is aimed at providing new clues and new methods of developing novel high-performance drilling fluid additives.
Preparation of Nanoparticle Calcium Carbonate and Study of Its Use in Water Base Drilling Fluids
WU Yuanpeng, TIAN Yingpei, LUO Pingya, LIN Yuanhua
2019, 36(4): 407-413. doi: 10.3969/j.issn.1001-5620.2019.04.002
To improve the rheology and filtration property of water base drilling fluids, a nanoparticle calcium carbonate surface modified with anionic polyacrylamide (APAM), CaCO3/APAM, has been prepared through surface in-situ polymerization. The CaCO3/APAM was characterized using FTIR and SEM to determine its molecular structures. In laboratory experiment, a water base drilling fluid treated with CaCO3/APAM had increased viscosity at low shear rate, indicating that the addition of CaCO3/APAM is helpful in improving the shear-thinning property of water base drilling fluids. At 80℃, a water base drilling fluid treated with 1% CaCO3/APAM had flow index of 0.72, yield point of 0.45 Pa and filter loss of 22.2 mL, three properties that were better than those of the base fluid. Addition of 1% CaCO3/APAM in a water base drilling fluid containing 1% salt reduced the filter loss of the drilling fluid by 21.2%. Analysis of the micro-structure of the mud cake showed that the nanoparticles, by filling into the spaces among the particles forming the mud cakes, improved the compactness of the mud cakes, thereby reducing the filter loss of the mud.
Preparation and Performance Evaluation of a Drilling Fluid MicrosphereStarch Filter Loss Reducer
CHEN Siqi, QIU Zhengsong, ZHONG Hanyi, ZHANG Qian, YAN Feng, LIU Shujie
2019, 36(4): 414-419. doi: 10.3969/j.issn.1001-5620.2019.04.003
To address the poor temperature resistance of conventional starches, a novel environmentally friendly microspherestarch has been synthesized through emulsion polymerization using soluble starch as the raw material and N-hydroxysuccinimide (NHC) as the crosslinking agent. The microspherestarch was characterized with FT-IR, SEM, TGA and Nanobrook particle-zeta potential tester. The microspherestarch was evaluated for its filtration control performance and temperature resistance in fresh water drilling fluid, saltwater base drilling fluid and calcium chloride treated water base drilling fluid. It was found that the particles of the microsphere starch have uniform particle size distribution (ca. 50 nm) and are in a shape of sphere. It has good thermal stability; after hot rolled at 150℃, a 4% bentonite slurry, a 10% saltwater mud and a 1% CaCl2 mud treated with 1% microsphere starch respectively had their API filter loss reduced by 70%, 55% and 60% respectively. This microsphere starch has only minor effect on the rheology of a drilling fluid, it is superior to conventional starch in filtration control, high temperature resistance and salt resistance.
Research and Application of a Novel High Temperature Filter Loss Reducer
CHANG Xiaofeng, SUN Jinsheng, LYU Kaihe, ZHANG Fan
2019, 36(4): 420-426. doi: 10.3969/j.issn.1001-5620.2019.04.004
A novel filter loss reducer PDANV has been developed with monomers such as 4-vinyl pyridine (VP), N, N-dimethyl acrylamide (DMAA), 2-acrylamide-2-methyl propane sulfonic acid (AMPS) and n-vinyl caprolactam (NVCL) through radical polymerization. Ammonium persulfate-sodium bisulfite is used as the redox initiator. The synthesized filter loss reducer can be used at temperatures as high as 260℃. The optimum polymerization conditions as determined by orthogonal experiment are as follows:nDMAA:nAMPS:nNVCL:nVP=6:2:1:1, reaction temperature 60℃, reaction time 2 h, mass of initiator is 0.5% of the total mass of the monomers (20%). The molecular structure of the polymerization product is determined with FT-IR and 1HNMR. TGA result shows that PDANV degrades at 301℃, indicating that it has very good thermal stability. Evaluation of PDANV in a water base drilling fluid shows that, at 2% concentration of PDANV, the filter loss of the drilling fluids is only 4.4 mL, and 6.0 mL after aging the drilling fluid at 260℃. The HTHP filter loss of the same drilling fluid is 24 mL. PDANV is resistant to salt contamination to saturation and calcium contamination to 20,000 mg/L. Analysis clay particle distribution, SEM analysis, Zeta potential analysis, as well as adsorption quantities of PDANV at different concentrations on clay particles further reveal the mechanisms of filter loss reduction of PDANV in water base drilling fluids.
Study and Field Application of a Highly Inhibited Drilling Fluid
XIA Haiying, LAN Lin, YANG Li, HUANG Huang, ZHU Hongyu
2019, 36(4): 427-430. doi: 10.3969/j.issn.1001-5620.2019.04.005
Open hole completion of horizontal wells is an effective way of reducing development cost. Based on the analysis of clay hydration mechanisms, an inhibitor able to form a hydrophobic film on the surfaces of a core and to change the wettability of the surfaces of a reservoir has been selected to satisfy a higher requirement for borehole stabilization in open hole completion. The inhibitor was evaluated in laboratory for its ability to change wettability, its relative rate of inhibition and percent recovery of shale cuttings in hot rolling test. A drilling fluid formulated with this inhibitor was optimized. Laboratory experiment results showed that the inhibitor can effectively inhibit surface hydration of clays, and is well compatible with other drilling fluid additives. Percent recovery of cuttings in hot rolling test was increased from 73.2% to 92.42% after optimization. Field practice showed that the inhibitive capacity of the drilling fluid was remarkably improved, and the drilling fluid showed very good resistance to cutting contamination, all of which were beneficial to borehole stabilization and increasing of rate of penetration.
Technology for Enhancing Pressure Bearing Capacity of Fractured Silurian System in Well Shunbei 5-8
FAN Sheng, SONG Bitao, CHEN Zengwei, LI Daqi, LIU Jinhua, CHENG Zengshou
2019, 36(4): 431-436. doi: 10.3969/j.issn.1001-5620.2019.04.006
Lost circulation is a severe downhole trouble frequently encountered in Block Shunbei in Xinjiang because of fractures around the fault zones resulted from strong geological movement in the Paleozoic Silurian System, high pressure formation saltwater and narrow safe drilling windows. In this paper, the characteristics of the mud losses occurred at the fractured Silurian System are extensively analyzed. The sizes and connectivity of the channels in the lost circulation zones are analyzed using actual drilling data, wireline logging data and hydraulic data, and factors affecting the pressure bearing capacity of the formations are carefully analyzed. A high temperature lost circulation material (LCM) slurry for the main fractured formations to make them dense was developed and a lost circulation control procedure, that is, "plugging while drilling, gradually strengthening, enhancing pressure bearing capacity section by section, and drilling steadily ahead", was formulated. This LCM slurry and the procedure were applied in Well Shunbei 5-8 for 13 times, all succeeded, greatly improving the pressure bearing capacity of the fractured formations. Time spent dealing with lost circulation has been reduced by 60%.
Development and Application of the Environmentally Friendly HL-FFQH Water Base Drilling Fluid
ZHANG Yongqing, HU Jingdong, XU Pengchen, ZHENG Xiong, CAO Jiao, WANG Yongqiang
2019, 36(4): 437-441,448. doi: 10.3969/j.issn.1001-5620.2019.04.007
A new environmentally friendly water base drilling fluid HL-FFQH has been developed to address the problems encountered in using conventional environmentally friendly drilling fluids, such as poor engineering performance and high cost. This new drilling fluid was formulated with previously developed five additives which are nontoxic, easy-to-degrade and have heavy metal contents that meet the standard. The formula of the drilling fluid is:4% bentonite +0.3%HLBE-2 (encapsulator) + 2% HLJ-1 (filter loss reducer) + 3% HLGB-3 (borehole wall strengthening agent) + 1% HLFD-1 (plugging agent) + 2% HLR-2 (lubricant) + barite. This drilling fluid showed good rheology in laboratory evaluation. Length of expansion of shale core in 8 h was only 2.5 mm, indicating that this fluid had good inhibitive capacity. After contaminated with drilled cuttings, the change of the filter loss of the drilling fluid was less than 0.4 mL, indicating that the drilling fluid was resistant to cuttings contamination. After aging at 150℃ for 16 h, the drilling fluid had friction coefficient and mud cake friction coefficient of 0.10 and 0.08, respectively, proving that this drilling fluid had good lubricity. Biotoxicity, biodegradability and content of heavy metals all met the relevant standards. The waste drilling fluid was light-colored, and the mud cake and filtrates of the drilling fluid did not affect the growth and life of animals and plants. No damage to the reservoir and downhole troubles have been found using this drilling fluid. Compared with offset wells, the ROP was increased by 85.5%. The HLFFQH drilling fluid conforms to the requirements of environmental protection from formulating to waste fluid treatment.
Low Damage Low Density Drilling Fluid Used in Songnan Gas Filed for Lost Circulation Control while Drilling
LIU Yanxue
2019, 36(4): 442-448. doi: 10.3969/j.issn.1001-5620.2019.04.008
The igneous rock reservoir in Songnan gas field has low formation pressures and is rich in formation fractures. Time efficiency of drilling operation has been low in this area because of mud losses frequently encountered during drilling. To address this problem, a low solids low damage low density drilling fluid with the ability of controlling mud losses while drilling was formulated based on laboratory experiment. To improve the cuttings carrying capacity of the drilling fluid, a hydrophobic associative amphoteric polymer PAADDC was selected based on the geology and drilling requirement of the gas field. By evaluating the water loss and wall building capacity, as well as pressure penetration property of the drilling fluid, a plugging additive mixed with PB-1 and ultra-fine calcium carbonate of different particle sizes was prepared. A lost circulation material used while drilling was formulated with hollow elastic rubber beads, calcium carbonate particles and hollow elastic micro beads. Evaluation of the drilling fluid shows that this drilling fluid has good rheology, plugging capacity, anti-sloughing ability and capabilities of controlling and preventing mud losses. Use of calcium carbonate makes it easy to minimize formation damage by acidizing job. When used in drilling the Well Yaoping-16, the mud showed stable properties. Mud losses in drilling the low-pressure igneous rocks, which negatively affected drilling time efficiency previously, was successfully resolved. Requirements of drilling operations and reservoir protection were satisfied with this drilling fluid.
Ultra-high Temperature Polyamine Organic Salt Drilling Fluid for Deepened Well Kun-2
HAO Shaojun, XU Zhenyan, GUO Zifeng, AN Xiaoxu, ZHANG Yun, WANG Bo, JIANG Lin
2019, 36(4): 449-453. doi: 10.3969/j.issn.1001-5620.2019.04.009
As the wells drilled in the Qaidam Basin are becoming deeper and deeper lately, much more attention has been drawn to the performance of high temperature and ultra-high temperature drilling fluids. Laboratory studies have been conducted on the stability, rheology and filtration properties of drilling fluids at ultra-high temperatures. A polyamine organic salt drilling fluid previously formulated was optimized with newly selected high temperature filter loss reducer and shale inhibitor to form a drilling fluid for use in drilling the ultra-high temperature deepened well Kun-2. After aging for 42 h, this new organic salt drilling fluid had HTHP filter loss less than 10 mL. The lithology of the formations penetrated by the well Kun-2 is mainly mudstones and is water sensitive and easy to swell and disperse. Combination of KCl, organic salt and polyamine greatly improved the performance of the drilling fluid, and the percent expansion of mudstone core tested in the drilling fluid was reduced by 93.33%. During drilling, mud losses took place between 6934 m and 6995 m. By adding 5% inert bridging agent ZYD, 3% ultra-fine calcium carbonate QS-4 and 2% gel particles into the drilling fluid, the weathered rock matrix was strengthened after several times of treatment to withstand the pressure exerted by a column of mud of 2.0 g/cm3, a key role in stabilizing the borehole wall and controlling mud losses in an ultra-deep well. With the use of this polyamine organic salt drilling fluid, the deepest well Kun-2 with the highest bottom-hole temperature in Qaidam Basin, was drilled successfully.
Technology for Safe Drilling of an Offshore Well with Long Horizontal Section through Depleted Gas Reservoir
ZHANG Wandong, YANG Yuhao, YANG Qianliang, HAN Cheng, ZHANG Ke, XIE Lu
2019, 36(4): 454-458. doi: 10.3969/j.issn.1001-5620.2019.04.010
Extended reach horizontal drilling is used in developing the shallow gas reservoir buried in the 2nd segment of the Yinggehai Formation. The Y platform, where the horizontal wells were drilled, is located in an offshore gas field in the east of the Western South China Sea. The buried depth of the gas reservoir is about 1,300 m, the maximum horizontal length of the well is 3,783 m, with the maximum horizontal vertical length ratio of 2.73. After decades of production, the reservoir became depleted to some extent. The horizontal section of the wells drilled on the Y platform penetrated a fault zone, and the risk of mud losses during drilling existed. Mud losses in previous development well drilling have been encountered. A temporary plugging solids free drilling fluid was modified to address the mud loss problem based on the analyses of difficulties previously encountered and the characteristics of the formations around the Y platform. The temporary plugging solids free drilling fluid plus the technique of annular ECD real-time monitoring and precise controlling, successfully resolved the mud loss difficulty. Drilling efficiency of 5 wells drilled on the Y platform was obviously increased, the average rate of penetration (ROP) in drilling the φ215.9 mm horizontal section was 77.27 m/h, created a new record in extended reach horizontal shallow well drilling in the same area. The gas reservoir was well protected; the production rate tested was 25% higher than predetermined.
Laboratory Evaluation and Application of A Raw Bentonite Drilling Fluid
SHU Yiyong, ZHOU Huaan, SUN Jun, YAN Zhihang, XU Sixu, SHAO Ping
2019, 36(4): 459-462,467. doi: 10.3969/j.issn.1001-5620.2019.04.011
Wells drilled in the Dabei block in Tarim Basin have big hole sizes and the top formations have gravels in them, making it difficult for the drilling fluids to carry out drilled cuttings. Pipe sticking by settled cuttings and differential pipe sticking may be encountered because of the big hole sizes and gravels. The OCMA bentonite (conforms to OCMA standard or API standard) presently in use has limited viscosifying effect in KCl polymer drilling fluids; drilling fluids formulated with OCMA bentonite have low viscosity and gel strength, and high filtration rate, and are thus not suitable for use in Dabei block where big holes are drilled in the piedmont structure. To address this problem, raw bentonite is used to replace the OCMA bentonite in formulating drilling fluid. The causes of OCMA bentonite losing its viscosity are analyzed, and the drilling fluids formulated with raw bentonite are evaluated for their rheology, wall building ability, compatibility and saltwater contamination resistance. The particle size distribution and specific surface area of the raw bentonite are studied. Field application shows that drilling fluids formulated with raw bentonite have better viscosifying effect and lower filtration rate than drilling fluids formulated with OCMA bentonite. Use the raw bentonite formulated drilling fluids, downhole conditions are much safer, sand carrying requirement by large hole drilling can be satisfied, and gage hole can be obtained. Field application of the raw bentonite drilling fluids indicates that they are worth spreading.
Problems Existed in Executing the Standard “GB/T 16783.1-2014/ISO 10414: 2008” and Suggestions for Correction
CAI Lishan
2019, 36(4): 463-467. doi: 10.3969/j.issn.1001-5620.2019.04.012
Liquid phase measurement and analysis is one of the important measures to ensure safe drilling operations. It was found in field practices that in the measurement of Ca2+, Mg2+ and K+ using the standard "GB/T 16783.1-2014/ISO 10414:2018" is unable to perform or the measurement results are quite different than the actual situation because of lack of clearly defined titration endpoint and inevitable manmade errors in reading the amount of centrifuged precipitates. To eliminate these problems and to improve the precision of measurement, it is suggested that the standard "GB/T 16783.1-2014/ISO 10414:2018" be corrected using the data collected from filed practice and laboratory experiment. Laboratory experiment results show that, after correction, the cumulative errors in the measurement is effectively minimized and the measurement precision improved. K+ ion concentration data from 5 wells show that after replacing the "C-V method" with "C-m method", the measured K+ concentration matches the actual K+ concentration. Compared with the "C-V method", the "C-m method" has better operability and completely eliminates manmade errors of measurement. It is thus concluded that the "C-m method" is a method that can be used to get accurate measurement results.
Influence of Waste Drilling Fluids in Loess Area on Yield and Quality of Alfalfa
ZHAI Wenxi, HAO Mingde, WANG Zhe, ZHANG Rongyao, REN Peng
2019, 36(4): 468-472. doi: 10.3969/j.issn.1001-5620.2019.04.013
Taking the alfalfa grown on the wellsites with backfilled waste drilling fluids in Changqing Oilfield as the research object, the waste drilling fluids were studied for their influences on the yield, content of heavy metals, quality and amino acids of alfalfa. It is concluded that the contents of Pb, Cd, Cr, As, Hg and Cu in the alfalfa all meet the requirements as set in the standard of GB13078-2017. The waste drilling fluids have obvious effect in increasing the yield of the alfalfa which was increased by 730.20 kg/hm2, or 21.6%. The quality of the alfalfa also was also improved, the gross content of crude protein was increased by 24.87 kg/hm2, the gross content of crude fat increased by 3.34 kg/hm2, the gross content of starch increased by 9.61 kg/hm2, and the gross content of reducing sugar increased by 45.92 kg/hm2. The content of crude fiber, on the other hand, decreased a little bit. The gross content of amino acids was increased by 3.6%, the essential and the non-essential amino acids were increased by 1.2% and 2.3%, respectively.
Cementing Small Liner Strings with Narrow Clearance in Deep Wells in the Kuche Piedmont Structure in Tarim Basin
ZHANG Feng, LIU Zishuai, LI Ning, YU Yongjin, AI Zhengqing, ZHANG Chi
2019, 36(4): 473-479,485. doi: 10.3969/j.issn.1001-5620.2019.04.014
The Kuche Piedmont is an important oil production area of the Tarim oilfield. Well depths in this area are generally between 6,000 m and 7,000 m, and geological conditions are very complex. The maximum temperature encountered during drilling was 180℃ and the maximum gas reservoir pressure 150 MPa. Wells of five intervals were drilled to the Bashijiqike Formation, the target formation of only 200 m in thickness, and cased with liner string. In designing the thermal stability, rheology and mechanical property of the cement slurries, consideration has to be given to the challenges such as well depth, bottom hole temperatures (120-180℃), narrow clearance between borehole and the liner string, and the length of the liner string of only 200 m. Meanwhile, some of the wells were drilled with water base drilling fluids, leaving thick mud cakes on the borehole wall which were difficult to remove. This presented challenges to performing the cementing job with safety and high quality. To address these difficulties, cement slurries with high thermal stability and high strength as well as high temperature flushing spaces that are able to clean the mud cakes were selected for cementing the wells. A special cementing technique was engineered to use in combination with the cement slurries and spacers. Using this cementing technology, the efficiency of displacing annular space was greatly improved, and the strength of the cement slurries was developed quickly, which in turn improved the bonding quality of set cement and ensured the performing of late-stage channeling test at negative differential pressure. This technology has been applied in cementing the φ127 mm liner string in the well Dabei-1101, 97.2% of the cementing was qualified and 79.4% excellent. The cementing of the liner string passed the channeling test at 33 MPa negative differential pressure.
A Method for Evaluating the Thermal Stability of Cement Slurry Polymer Additives Based on Ubbelohde Viscometer Method
ZHENG Guanyi, LI Zaoyuan, ZHAO Jun, WANG Xiyong, LUO Deming, GUO Xiaoyang
2019, 36(4): 480-485. doi: 10.3969/j.issn.1001-5620.2019.04.015
An important cause for the quality of cementing high temperature and deep wells to be difficult to maintain is that the integrated performance of a cement slurry at elevated temperatures is difficult to maintain. Presently the high temperature performance is generally adjusted using cement additives, which are generally polymers. The settling stability and filtration rate of a cement slury at high temperatures are maintained with filter loss reducers, while the thickening time of a cement slurry is adjusted with retarding agents. As a well is drilling deeper and deeper, the downhole temperature and pressure are increasing, and it becomes more and more difficult to control the settling stability, filtration rate and thickening time of a cement slurry. Even so the methods of evaluating the performance of these polymer additives are rarely seen. A method is recommended for use in evaluating the thermal stability of polymer additives. This method is based on the mechanism of viscosity reduction of polymers at elevated temperatures and an Ubbelohde viscometer is used to measure the change of viscosity. By measuring the rate of change of molecular weight of additives before and after aging at a certain high temperature, △M, the thermal stability of a polymer can be measured; when △M is approaching zero, the thermal stability is good. This measurement can be used to guide the selection of high temperature cement slurry additives.
Investigation of Factors Affecting Cementing Job Quality in Wells Penetrating Low Pressure Permian Formations Having Mud Loss Tendency in Shunbei Oilfield
ZHANG Jun, YANG Mou, LI Shuanggui, LIU Yongjing, LU Feifei, HE Yingzhuang
2019, 36(4): 486-490. doi: 10.3969/j.issn.1001-5620.2019.04.016
The Permian System formation in Shunbei oilfield is developed with fractures and has low leaking pressures, resulting in 82% of the wells experiencing lost circulation during well cementing and 54.5% of the wells had to be re-cemented through reverse squeezing of cement slurry. Cementing job quality has been unsatisfactory in the past. The internal causes affecting the quality of well cementing in the area was systematically analyzed using the methods such as identification of pressure bearing capacity of the formation, evaluation of the eccentricity of casing string, performance evaluation of a flushing fluid at turbulent flow and calculation of the compatibility between different slurries. It was found that the leaking pressure of the Permian System formation is between 62 MPa and 67 MPa. Distance between two centralizers can be 55 m when the percent hole enlargement is 10% and hole angle less than 0.3°. This distance is reduced to 22 m when the quality of the borehole is poor. Poor well cementing generally results because of high viscosity of prepad fluid, incompatibility between the parameters of spacer and lead slurry which results in retention of spacer in the hole, as well as cementing slurry returning to the surface ahead of time. This study has provided a new clue for calculating the leaking pressure of a formation with low pressure during cementing, designing the placement of centralizers and optimizing cement slurries, and presented a key technical measure to the similar well cementing problems.
Reservoir Protection Technology Used in Cementing Horizontal Wells in Chenghai Xinqu, Bohai Bay
WANG Qiong, HU Jinjun, GENG Zhishan, GUO Qiushi
2019, 36(4): 491-494. doi: 10.3969/j.issn.1001-5620.2019.04.017
The Shahejie Formation sandstone is a proven shallow heavy oil reservoir located in the Chenghai Xinqu area, Bohai Bay. Eight horizontal wells have been planned to drill in this area and completed with screen pipes. The φ244.5 mm technical casing is used to case the horizontal section drilled into the Shahejie Formation. In early stage exploration, the sandstone reservoir was highly contaminated because of mud losses into the high porosity high permeability sandstone, invasion of cement slurry filtrates, and edgebottom water channeling caused by casing string eccentricity. To protect the reservoir from damaging, a low-density low filter loss nanoparticle cement slurry of 1.5 g/cm3 was used to cement the well. The cement slurry had no free water and no density difference between the top and the bottom. The strength of the set cement was at least 17.9 MPa after aging for 24 hours, and the filter loss of the cement slurry was 38 mL at most. These two parameters are 24% better than standard requirements for cement slurry. A new type of φ244.5 mm all-in-one elastic centralizer was used with casing. This all-in-one elastic centralizer has no stress weak point, and compared with conventional centralizers, this new type of centralizer has restoring force that is 25% higher, starting force that is 27% lower, the centrality of the casing string can be enhanced by at least 57%. These technologies have been proved suitable for use in cementing horizontal wells drilled in Chenghai Xinqu. Six wells have been cemented with these technologies and no slurry losses and water channeling have occurred during well cementing. High quality cement job and high oil production rate were obtained. These technologies are beneficial to the development of oil and gas resources in Chenghai Xinqu area.
Difficulties in Cementing Liners in Block Tambococha 43 and Corresponding Measures
PAN Yuqiang, TANG Kai
2019, 36(4): 495-499. doi: 10.3969/j.issn.1001-5620.2019.04.018
The daily production rate of a single well in the Block Tambococha in Ecuador is from 300 t to 1,100 t. The casing program is special because of special production requirements; the distance between the running depth of the φ177.8 mm liner and the top of the reservoir is less than 30 m. Caliper logging data acquired from LWD are seriously distorted, making it difficult to determine the amount of cement slurry, and a high risk of cementing the φ177.8 mm liner exists. Previous practice shows that the job quality of cementing cannot be ensured if wiper trip is not performed prior to running liners, or a high displacement efficiency in narrow annulus cannot be obtained, or the oil and water in the reservoir are active. A rotating liner cementing technology for use in bottom water reservoirs in Block Tambococha was developed through designing of a compound spacer, studying on micro-expansion latex cement slurry as well as studying on the rotating liner cementing techniques for annulus of narrow clearance. This technology is helpful to run liner to the designed depth, to accurately determine the annular volume of an open hole section and to improve the casing centrality. The flushing efficiency of the spacer is 93%, and the 12 h compressive strength of the set cement slurry is 36.4 MPa. Application of the technology on 15 wells gave a rate of excellent cementing job quality of 95%, providing a technical support to the success of cementing narrowannular-clearance highly deviated wells for strong bottom water reservoirs and resolving the problem of cementing wells with special casing profile in Block Tambococha in Ecuador.
Development of a Low Temperature Early Strength Cement Slurry with Low Exothermic Heat of Hydration
GUO Yongbin, LI Zhong, LIU Hexing, DONG Zhao, WU Zhiming, MA Chuanhua
2019, 36(4): 500-505. doi: 10.3969/j.issn.1001-5620.2019.04.019
In deep water drilling, special environment in formations containing hydrate-forming chemicals requires the cement slurry to have low exothermic heat of hydration and early strength at low temperatures. Most of the cement slurries presently in use do not have the low exothermic heat of hydration characteristics and the rate of low temperature hydration reaction is slow. A study plan has been presented to resolve these problems. The study has aimed at finding a cement slurry with low temperature early strength and low exothermic heat of hydration. This cement slurry is formulated with a mixture of aluminate cement and class G cement in a mass ratio of 1:1 followed by the treatment of other additives such as energy-storing micro spheres, light-weight agent, stabilizer and so on in carefully determined concentrations. The early strength additive used is triethanolamine at 0.06%, the filter loss reducer is 1% CML, a polyvinyl alcohol base filter loss reducer, the retarder is boric acid at 0.35%, and the dispersant is 1.5% SYJZ-1. Performance test of the cement slurry shows that after aging for 24 h at 4℃ the compressive strength of the set cement is 5.9 MPa. It can be found that this cement slurry has excellent early strength, low exothermic heat of hydration and density characteristics.
Methods of Predicting and Evaluating Effect of Acidizing Job of Water Injectors in Bohai Oilfield
LI Jin, WANG Kunjian, HAN Yaotu, ZHANG Qilong, JIA Lixin
2019, 36(4): 506-511. doi: 10.3969/j.issn.1001-5620.2019.04.020
A study has been conducted in an effort to address the problem of poor acidizing job performed in water projectors in Bohai oilfield. Typical Ⅱ stage projectors with poor acidizing job in Block SZ were selected for studying and data regarding the acidizing job were collected for more than 60 wells/times. Factors affecting the acidizing job quality of the injectors in Bohai oilfield and prediction and evaluation of the job quality were studied using Grey Relational Analysis.The study shows that the acidizing curves of the injectors in Bohai oilfield can be classified mainlyas S-type, double-step-shaped type, average type and rapid-declining type, most of which is the S-type curve. Injectors with S-type curve have the longest time in which the effect of acidizing job remains effective, and injectors with rapid-declining curve have the shortest time in which the effect of acidizing job remains effective. Several factors affecting the effects of augmented acid injection, such as the operational parameters, reservoir data and the blocking of flow channels in the formations, were studied for their importance of affecting the effects of augmented acid injection. The key factors affecting the effects of augmented acid injection were found to be the type of acid and its ability to eroding the blockage, the apparent water injectivity index before acidizing job, acidizing radius, the effective thickness of acidized formation, and the permeability and porosity of formations. A model has been established for predicting and evaluating the effective period of an acidizing job and the cumulative volume of acid solution injected. The study can be used to predict and evaluate the effect of acidizing job and is helpful to the optimization of acidizing program for injectors. By prolonging the effective period of an acidizing job and increasing the cumulative volume of acid solution injected, the effect of an acidizing job can be ensured, contributing to the realization of stabilizing petroleum production at 30 million tons per year in Bohai oilfield.
Study of Slick Water and Its Application in Spatial Fracturing Fractured Carbonate Formations
DUAN Guifu, HE Chunming, CAI Bo, ZHANG Hui, WU Gang, CHENG Xiaodong
2019, 36(4): 512-516,521. doi: 10.3969/j.issn.1001-5620.2019.04.021
Slickwater is a fracturing fluid widely used in fracturing unconventional petroleum reservoirs such as shale gas reservoirs and tight oil reservoirs. Slick water has low viscosity and high penetration performance which are helpful in enhancing the complexity of natural fractures. Generally speaking, deep fractured carbonate reservoirs have matrix rocks of poor physical properties and strong inhomogeneity, and fractures are the main spaces and channels for the petroleum to stay and flow through. Therefore, increasing the volume of rocks being fractured is the key to produce more petroleum, and this goal can be achieved by performing spatial fracturing with fracturing fluid composed of low viscosity slick water, gel and converting acid. Low viscosity and high injection flow rate help activate more natural fractures in rocks. In this paper the evaluation of a new slick water containing polymers is discussed. Laboratory study and numerical simulation were combined to ascertain the working mechanisms of slick water in spatial fracturing. It was found that:1) the new polymer slick water has good drag reducing property, and is able to reduce the fraction and drag acting on the pipe string, thereby realizing high flow arte injection and improving stimulation efficiency. 2)Complex fractures are generated with injection of slick water at high flow rates, and the connectivity of the fractures is enhanced by forming acid-etched wormholes by the injection of low-viscosity acids. Alternated injection of slick water (hydraulic fracturing) and low-viscosity acid (acid etching) gives birth to networked fine fractures. By applying these studying results in field operations, the well AT3x has acquired daily oil production rate of 35 m3 and daily gas production rate of 50.3×104 m3, providing a new technical reference for stimulating complex deep high temperature reservoirs in China.
Study and Performance Evaluation of an “Integrated” Insulation Test Fluid Using in Deep-water Well Test
LI Zhong, WU Zhiming, XIANG Xingjin, YAN Bangchuan, YU Yi, LIU Zhiqin
2019, 36(4): 517-521. doi: 10.3969/j.issn.1001-5620.2019.04.022
An "integrated" insulation test fluid has been formulated with a synthesized polyol and a reducing sugar alcohol to address problems encountered in testing deep-water wells with single-layered riser, such as poor heat insulation, connection of the annulus of the upper riser and the annulus of the lower production string, which affects well testing and pressure transmission, etc. The "integrated" insulation test fluid is a non-aqueous fluid with low heat conductivity. Laboratory evaluation on the heat conductance, density adjustability, pumpability and rheology of the test fluid shows that this test fluid has the following properties:temperature resistance of up to 150℃, heat conductivity of 0.2428-0.2866 W/(m·K), density adjustable between 1.05 g/cm3 and 1.50 g/cm3, settlement factor of 0.50 after standing still for 15 d, apparent viscosity at 25℃ of 70 mPa·s at most, gel strength at 4℃ of 3 Pa at most, good pressure transmission, average corrosion rate in 3 d at 150℃ of 0.0369-0.0690 mm/a, and percent core permeability recovery of at least 95%. Furthermore, this test fluid is environmentally friendly, and has no oil in it. It satisfies the Class 1 requirements of offshore application in accordance with the standard "Biological toxicity for pollutants from marine petroleum exploration and exploitation -Part 1:Grading". This test fluid can be recovered for reuse, greatly reducing operational cost. It can be used in testing deep water wells with single-layered riser.
Factors Affecting Loss of Kill Mud Used in Carbonate Rock Reservoirs
ZHU Fanghui, LI Mingxing, HE Bingcheng, LIU Wei, LI Qiongwei
2019, 36(4): 522-528. doi: 10.3969/j.issn.1001-5620.2019.04.023
The carbonate gas reservoir in Changqing oilfield isfull of fractures and vugs, different zones have quite different characteristics, andsevere inhomogeneity exists in the formations. Fracturing stimulation only makes the fractures in the reservoir much more complex. In the late period of development, workover operation performed on a well killed with a kill mud has always been facing with high volume of mud losses and factors of the mud losses are not well defined. To find out the affecting factors of the mud losses, numerical simulation of 5 factors has been conducted using the Warren-Root dual-permeability model by analyzing the geological data and production data of the typical wells and by fitting the water production rate, the gas production rate and the average formation pressure. The results of the numerical simulation show that the most important factors affecting mud losses are the positive differential pressure of the fluid column inside the well, the viscosity of the kill mud and the permeability of the fractures, of which only the differential pressure and the permeability are controllable. By moderately increasing the viscosity of the kill mud and decreasing the positive differential pressure of the fluid column inside a well, mud losses can be well controlled.The problem is that the high viscosity will result in difficulties in pumping the kill mud and formation damage from adsorption and detention of the kill mud. Viscosity increase of a kill mud can be achieved by increasing its viscoelasticity; this not only increases the resistance to the flow of kill mud into formations, it also renders the kill mud pressure bearing capacity. An idea of using elastic gel as the kill mud with temporary plugging capacity in Changqing is presented in this paper based on the research achievements.