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Real-time early warning of drilling overflow based on naive Bayes algorithm
YUAN Junliang, FAN Baitao, XING Xuesong, GENG Lijun, YIN Zhiming, WANG Yiwen
[Abstract](0) [FullText HTML](102) PDF 1012KB(12)
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If the overflow in the drilling process of high temperature and high pressure (HTHP) well isn’t identified in time, serious consequence will be caused. Existing overflow monitoring technology depends on downhole or surface tools, so it is time lagged to some extent. To solve this problem, this paper developed the real-time overflow early warning method based on naive Bayes and drilling big data. As for an area with a certain scale of drilled wells, the probabilistic relationships between the historical drilling overflow and the geological data, mud logging while drilling and wireline logging while drilling are analyzed, the prior probability calculation model of overflow and the condition probability calculation model containing six attributes of region, stratigraphy, lithology, torque, pumping pressure and rate of penetration (ROP) are established. The posterior probability of overflow is calculated based on Bayes theory. Thus, the function of real-time early warning is realized. It is indicated the overflow early warning method based on naive Bayes is more advantageous in terms of reliability, transmission efficiency and data accessibility. And its feasibility is verified based on actual cases.
Real-time ROP optimization technology based on big data and artificial intelligence
HUANG Xiaolong, LIU Dongtao, SONG Jiming, HAN Xueyin, QIAO Chunshang
[Abstract](1) [FullText HTML](78) PDF 1317KB(11)
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In view that the daily operation cost of offshore drilling is quite high, one of the important research subjects is how to make use of big data and artificial intelligence technologies to improve the rate of penetration (ROP), so as to shorten the operation cycle and reduce the operation cost. In this paper, the big data information at drilling sites was collected, and mud logging data, wireline logging data and drilling fluid property were put into the neural network to calculate the initial predicted ROP. Then, the real-time global optimal solution was calculated by means of the optimization algorithm, and the real-time ROP optimization model based on machine learning method and optimization algorithm was established. Finally, the model was embedded into the visual system to guide the field operation, so as to realize ROP improvement. This technology was applied to the real-time drilling process by taking Well A of South China Sea PY Oilfield as the test well. The practice shows that this technology can not only improve ROP effectively, but is of reference significance to the digital development of oil fields.
Risk assessment model of sustained casing pressure of gas well based on Bayesian network and its application analysis
FENG Xuezhang, SUN Yuduo, WANG Xiaolei, FENG Dianfang, HA Simu, SONG Wenrong
[Abstract](0) [FullText HTML](68) PDF 1132KB(134)
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Sustained casing pressure gets serious increasingly in the process of gas well production, which increases the risks of well integrity failure. To solve this problem, this paper assessed and studied the risks of sustained casing pressure. The early warning model of sustained casing pressure based on Bayesian network and actual production data was established. By virtue of the model, the influential factors of sustained casing pressure were divided into two units, i.e., tubing/casing leakage and cement sheath failure, and the main risk factors and risk failure probability of each unit were determined. In addition, the quantitative risk assessment indexes of sustained casing pressure were set and the risks were classified correspondingly. Thus, the risk assessment method of sustained casing pressure of gas well is developed. It was applied practically based on the statistical failure probability of 191 wells in No.1 Gas Production Plant of Xinjiang Oilfield Company. The case application indicates that this model can quantitatively calculate the potential risk of sustained casing pressure, deduce the reverse origins of main risk factors and provide decision making basis for sustained casing pressure prevention and control, which is conductive to reduce the occurrence probability of sustained casing pressure of gas well.
Rock breaking simulation of flexible PDC-impregnated diamond coupling bionic intelligent bit
WU Zebing, XI Kaikai, WANG Jie, LI Chao, CHENG Huan, YANG Chenjuan
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To cope with difficult lithology identification, serious wear of PDC bit, low rock breaking efficiency of impregnated diamond bit and bit balling in the process of drilling, this paper established the lithology identification model by means of BP neural network leaning algorithm. In addition, a novel flexible PDC-impregnated diamond coupling bionic intelligent bit was designed and then simulated in Matlab and ABAQUS, respectively. The simulation results show that the BP neural network model can identify lithology very accurately, which is beneficial to select bit type reasonably, adjust drilling parameters in time and improve drilling efficiency. Compared with conventional bits, the stress applied on rock surface by the bionic intelligent bit is much higher, so it can reach the rock breaking limit more easily and its drilling speed is improved. This design integrates intelligent lithology identification, high rock breaking efficiency, self-regeneration function and anti-balling function and provides a new idea for the design of petroleum bits in China.
Experimental law of well scaling in the production process of deepwater gas well
LIU Wenyuan, HU Jinqiu, YAO Tianfu, OUYANG Tiebing, LI Xiangfang
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Offshore gas wells are characterized by large depth, complex scale removing operation and high operation cost, so it is imperative to predict and control the scaling in the wells of deepwater gas wells. In this paper, laboratory experiment and theoretical calculation were combined to evaluate the scaling risks in the wells during the production of four typical deepwater gas wells in the South China Sea Gasfield, predict scaling velocities and scaling positions in the wells of gas wells in the process of production and analyze the scaling characteristics and laws. It is indicated that the scaling type of gas well is controlled by the compositions of formation water and the scaling velocity in the production process of gas well is mainly dependent on the deposition velocity of stable scale after the surface deposition period. The scaling difference at different well depths in the production process of deepwater gas well is mainly dominated by the temperature distribution along the well, and the scale control shall focus on the middle and lower parts of the well and the conditions of high gas production rate and high water/gas ratio. Compared with onshore gas wells, deepwater gas wells are affected more by the scaling in wells, so to keep the efficient and safe production of deepwater gas wells, it is quite important to take the scale control measures in time to prevent the formation of scale and control the scale deposition in the allowable range.
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2021, 43(3): 0-0.  
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2021, (3): 1-4.  
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DRILLING AND COMPLETION
Construction of “well-factory” drilling cost model and optimization of pad deployment scheme
YAN Wei, DING Xiaoping, LI Wenbo
2021, 43(3): 265-271.   doi:
[Abstract](1) [FullText HTML](701) PDF 1224KB(329)
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The operation mode of “well factory” achieves the benefit development of unconventional oil and gas. In this paper, the constituent elements of well-factory drilling cost were determined by analyzing the characteristics of the “well-factory” drilling of unconventional oil and gas, and these elements were quantitatively studied. Then, a well-factory drilling cost analysis model was established according to well-factory drilling process integration. The factors influencing well-factory drilling cost were determined and optimized. An optimization algorithm of well-factory drilling cost was developed. Several factors were mainly considered, including position and number of pads, drilling sequence, drilling learning efficiency, well type, wellbore trajectory, batch drilling sequence and drilling fluid recycling rate. Based on the practical drilling engineering in the tight oil reservoirs of Jiyang Depression, the Bohai Bay Basin, the model parameters were optimized. The optimal scheme was worked out by taking the cost minimization as the objective function, and the percentage of each drilling cost element in the optimal scheme was calculated. Rig cost (40.55%), casing cost (15.11%), drilling fluid cost (14.80%) and cementing cost (9.89%) are the top four cost elements, whose sum accounts more than 80% of total well-factory drilling cost. Finally, the credibility of the cost calculation model was evaluated by using the “cosine similarity” method, and its error is less than 2%. This research provide theoretical basis for the optimized design and cost estimate of well-factory drilling scheme of unconventional oil and gas.
Distribution characteristics and drilling engineering significance of Dongying Formation overflow facies in the gentle slope belt of Huanghekou Sag
DENG Jinhui, TAN Zhongjian, ZHANG Xiangqian, CAO Jun
2021, 43(3): 272-280.   doi:
[Abstract](1) [FullText HTML](400) PDF 3179KB(99)
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Igneous rocks dominated by basalt and tuff of overflow facies are widely developed in the Dongying Formation in the gentle slope belt of Huanghekou Sag. This type of rocks are relatively hard and tend to suffer low rate of penetration (ROP), circulation loss, hole collapse and other problems in the process of drilling, which have greater impact on drilling engineering. In this paper, the volcanic eruption cycles and stages in the first and second Members of Dongying Formation (Ed1 and Ed2) were identified and divided by using mud logging and wireline logging data comprehensively. And combined with seismic data, the volcanic overflow facies in BZ34-9 block was described precisely. It is indicated that the volcanic rocks in the study area are mainly distributed in the conjugate strike-slip fault zone of BZ34-9 and KL4-2 structure zones, where fissure type volcanic eruption is dominant. Six eruptive cycles and sixteen eruptive stages can be identified and divided in Ed1 and Ed2. The eruptive cycles in the early stage of lower Ed2 and the early and late stages of Ed1 are small sized while those in the late stage of lower Ed2 and the early and late stages of upper Ed2 are large sized, which reflects the growth process of volcanic activity from weak to strong and then weak gradually. Based on the construction of complex fault and formation model, combined with the simulation of tectonic stress field, geomechanically weak belts or fracture development characteristics can be predicted, which provide reliable basis for the trajectory optimization of development wells and the selection of drilling tools, drilling parameters and drilling fluids.
Dynamic evaluation method of anti-deflection characteristics of double-stabilizer pre-bending BHA
LIU Kerou, ZHANG Hui, WANG Xinrui, FU Hao, LIU Yuwan, LU Zongyu, SHI Jiangang
2021, 43(3): 281-288.   doi:
[Abstract](1) [FullText HTML](411) PDF 2336KB(74)
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Deviation control and fast drilling of vertical well has always been a difficult problem in the field of drilling. Pre-benting BHA technolog uses pre-bending structure to guide BHA deformation to produce large dynamic deflection reduction force, so as to realize the purpose of dynamic deviation prevention and fast drilling. However, the dynamic quantitative evaluation of deviation prevention characteristics of pre-bent BHA is still a difficult problem. Based on the dynamic model established by Jansen, the dynamic lateral force model at the bit is established. The eddy trajectory data of section A obtained from simulation is applied to the calculation of dynamic lateral force. Finally, the anti-deviation characteristics of this kind of drilling tools are evaluated quickly and intuitively through whirl trajectory diagram, dynamic lateral force distribution time history diagram and average dynamic lateral force. The simulation results show that: (1)With the increase of well deviation angle, the force of reducing inclination increases; (2)With the increase of rotating speed, the anti-deviation characteristics of drilling tools can be divided into three stages: stable, unstable and losing the ability of reducing deviation;(3) Under different inclination angles, the first and second critical speeds increase with the increase of well deviation angle. Through the study of the above models and laws, the mechanism of deviation prevention and declination of the pre bent BHA with double stabilizers is further revealed, which is of great significance to the application of pre bent BHA in the field.
Selection of extended reach well trajectory design scheme based on entropy weight method
WEI Longgui, WANG Zan, CHEN Liqiang, LI Lei, ZHANG Changchao
2021, 43(3): 295-301.   doi:
[Abstract](1) [FullText HTML](528) PDF 1147KB(79)
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The trajectory design of extended reach well is quite important for its safe and efficient drilling. The drilling of extended reach well faces several problems, such as poor wellbore stability in the long open hole section, high torque and drag, serious string buckling and difficult hole cleaning, so its trajectory design needs comprehensive analysis and evaluation. In this paper, a model for evaluating the trajectory design scheme of extended reach well was established based on the entropy weight method, in which the weights are calculated and the schemes are scored by making full use of the fluctuation of evaluation indexes, so that the trajectory design scheme of extended reach well is quantitatively evaluated. It has been successfully applied to the drilling of extended reach well in one certain oilfield. This research not only provides a new idea and a guidance method for the selection of trajectory design scheme of extended reach well, but also a technical reference for the subsequent drilling technology optimization and risk evaluation of extended reach well.
Study on the failure mechanism of large-size hole stabilizer joint of ultra-deep well
LI Shaoan, WANG Juhe, QIN Ken, WANG Wenchang, CHEN Feng, DI Qinfeng
2021, 43(3): 302-308.   doi:
[Abstract](1) [FullText HTML](351) PDF 1651KB(56)
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The 171/2"(Ø444.5mm) large size boreholes of Ultra-deep well in Shunbei block was a long section, there were not only the problems of speed raising and deviation control, but also the frequent failure of box end of stabilizer. Based on the analysis of pendulum bottom hole assembly(BHA) dynamics, this paper discussed the failure mechanism of box end of stabilizer in large size boreholes. Firstly, based on the dynamic finite element equation of drill string, the complex dynamic characteristics at the stabilizer of BHA in large-size borehole were studied, and the dynamic bending moment and vortex characteristics near the box end of stabilizer were determined. Secondly, a three-dimensional finite element model of the thread joint at the box end of the stabilizer is established, and the stress distribution characteristics of the thread joint under complex load were analyzed by using the explicit dynamic finite element method. Finally, the dynamic stress near the variable cross section position of the BHA stabilizer's box end was deeply analyzed by taken the failure of the box end of stabilizer in Shunbei XX well as an example. The results show that the axial and torsional vibration level of the box end of the stabilizer were low, but there was a strong high frequency vortex, and a high frequency additional dynamic bending moment(0~453.0 kN·m) aroused near the box end of the stabilizer. This bending moment produced a maximum stress of 799.1 MPa on the thread of the box, although the value was less than the stress (973.1 MPa) on the thread of the drill collar pin engaged with it, the amplitude of variation was large (465.0 MPa) and the frequency was high. This high frequency variation stress was one of the key reasons to cause the failure of the box end of the stabilizer. Hence, it is suggested to control the vortex and minimize the dynamic bending effect near the stabilizer when designing large-scale borehole BHA.
Influence of high-temperature dry combustion and water wet environment on the structure and property of set cement
XUE Guoqing, LIU Xu, TANG Mingguang, YU Chengchao, LUO Jiao, FU Qiang
2021, 43(3): 309-315.   doi:
[Abstract](3) [FullText HTML](582) PDF 1846KB(37)
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In order to evaluate the influence of alternating ultra-high temperature on the mechanical property and microstructure of set cement in a heavy oil thermal recovery well more accurately, this paper designed a set of ultra-high temperature water wet simulation curing device and method based on the actual downhole environment of set cement. And based on this, the change laws of the compression strength of set cement under dry combustion environment and water wet environment were studied. In addition, the influence of different curing environments on the physical composition, chemical structure, pore structure and micromorphology were explored by means of XRD, TG, nitrogen adsorption and SEM technology. It is experimentally indicated that after set cement is cured 7 rounds under alternating ultra-high temperature, its compression strength under the dry combustion environment decreases by 17.7% from 28.7 MPa to 23.62 MPa; but in the water wet environment, it decreases by 6.3% from 29.54 MPa to 27.68 MPa, which is 14.67% higher than the value in the dry combustion environment. Furthermore, the set cement in the water wet environment has high hydration product content, small pore diameter, low porosity and compact overall structure. The research results can provide technical support and theoretical guidance for the performance evaluation of set cement in heavy oil thermal recovery wells and is of great significance to enhance the safe and efficient development of heavy oil resources.
A key underwater piling technology for the installation of deepwater drilling conductors
WEI Hongshu, DENG Yuming, TONG Wujun, SUN Zigang, ZHAO Suwen, ZHAO Weiqing
2021, 43(3): 316-321.   doi:
[Abstract](1) [FullText HTML](909) PDF 921KB(89)
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As for the installation of deepwater drilling conductors, a foreign company in this industry put forward a new technology to realize batch installation of conductors by means of underwater piling recently, whose feasibility has be proved practically. In this paper, its characteristics, basic principles and operation process were analyzed by investigating and analyzing this technology. In addition, its key points were analyzed deeply, including the design & processing, drivability and stick-up stability of conductor, the type selection of deepwater pile hammer and the design & type selection of low-pressure wellhead housing. This technology has the advantages of reducing the operation risks and improving the controllability of driving accuracy, but its application is limited by the current equipment and technology level. Finally, based on domestic status of installation technologies for deepwater drilling conductors, the suggestions on the application of this technology in domestic deepwater development were proposed. The research results provide the references to deal with the difficulties in the domestic exploratory application of this technology and point out the research direction.
Study and application of setting-completion integrated technology
LIU Lian, LI Huihui, ZOU Wei, FAN Lingyun, CHEN Lifan
2021, 43(3): 322-327.   doi:
[Abstract](2) [FullText HTML](797) PDF 1560KB(69)
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Temporary plugging technology is an important protection to ensure well control safety during the modification of wellhead device, but it has the defects of low well completion efficiency, high tool cost and serious reservoir contamination by drilling fluid. To this end, this paper developed a two-setting packer and achieved a setting-completion integrated technology. Two-setting packer integrates mechanical setting and hydraulic setting together and both setting modes are independent, so after either of them is unset, the other mode can be started for the second setting. The setting-completion integrated technology can give full play to the advantage of the two-setting packer to conduct temporary plugging and production in one trip, so that well completion efficiency is improved greatly while wellbore integrity and well control safety are ensured in the process of well completion. The setting-completion integrated technology has been successfully tried out on site. And thanks to the simplicity, convenient operation and high reliability of its support tools, this technology has already been popularized and applied in Tahe Oilfield.
Application of low-frequency electromagnetic wireless transmission test technology in the complex fault block reservoirs of Abei sag
ZHANG Yufei, ZHAO Kun, WANG Pan, XUN Ruina, RUAN Xiaofei
2021, 43(3): 328-333.   doi:
[Abstract](0) [FullText HTML](730) PDF 1798KB(62)
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Abei sag is structurally complex and its hydrocarbon accumulation laws are not understood clearly, so the conventional test technologies fail to read bottom hole shut in or downhole data in real time, which makes it difficult to control data accuracy and shut in time. To this end, the low-frequency electromagnetic wireless transmission test technology was optimized and the existing problems were corrected so as to enhance the pertinence and reliability of test data. To deal with the unsuccessful downhole signal docking, the short-circuit position in the string structure was analyzed, and the test tool and the string structure were improved. The inner diameter (ID) of the metal shaft of the centralizer was increased from 76 mm to 80 mm, the metal centralizer at the topmost was replaced with a nylon centralizer, and the outer diameter (OD) of the body of the positioning sub was decreased from 102 mm to 62 mm. To solve the problems of weak electromagnetic signal and short transmission distance, the design of the signal amplifying line was optimized and the research of weak signal detection technology was enhanced. As a result, the downhole long-distance transmission of 40 m is realized. What’s more, the transmission structure of the signal receiver was modified to transform the single-point reception into the two-way reception of communication loop. This technology has been applied on site in Well X16 of Xinsumu structural belt. Perforation-well startup-shut in process and test curve radial flow data are monitored in real time, which ensures test success rate and well test result effectively and provides technical support for the following exploration deployment in Abei sag.
OIL AND GAS PRODUCTION
A simulation calculation method for the lift process parameters of sucker-rod pump under different liquid supplying conditions
YANG Yaozhong, BING Shaoqiang, SONG Qingxin, DUAN Hongjie, JING Ruilin, MA Chengjie, SUN Zhaolong
2021, 43(3): 334-340.   doi:
[Abstract](2) [FullText HTML](407) PDF 1409KB(75)
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The methods for calculating pump intake pressure and piston stress were determined respectively based on the differences of liquid supply capacity in the lift process of sucker-rod pump. After the static model was established, the method for calculating the damping factor in the process of well lift was modified according to the sucker-rod wave theory, and the dynamic model of the lift of sucker-rod pump was established. the numerical distribution of pressure and sucker rod string stress in the vertical space of well under different liquid supplying conditions was calculated under the constraint of surface dynamometer card, the pump intake pressure, dynamic liquid level, formation flow pressure and other parameters were simulation calculated, and the method for the continuous simulation calculation of the lift process parameters of sucker-rod pump under different liquid supplying conditions was established. The research results show that this method can meet the required calculation accuracy of dynamic liquid level in oil wells under the working conditions with insufficient liquid supply and provide theoretical basis for the analysis and working system optimization and adjustment of well lift.
Experimental study and model modification of downhole throttling pressure drop laws in the gas wells with foam drainage gas recovery process
WANG Zhibin, BAI Huifang, SUN Tianli, ZHU Guo, SHI Hongyan
2021, 43(3): 341-347.   doi:
[Abstract](1) [FullText HTML](436) PDF 1402KB(60)
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Downhole throttling in gas wells is one key technology for the low-cost development of gas fields, and under suitable conditions, “downhole throttling + foam drainage gas recovery” process can improve the liquid carrying capacity of gas well. When the traditional gas-liquid two-phase choke flow pressure drop model is used for the size design of the downhole throttling choke in the gas well with foam drainage gas recovery process, the requireed production proration of the gas well cannot be satisified. Testing the throttling pressure drop laws and establishing or improving the mathematical model is conducive to improve the design level of downhole throttling in the gas wells with foam drainage gas recovery process. Physical simulation experimental equipment was designed and established for the downhole throttling in the gas wells with foam drainage gas recovery process. Then, the throttling pressure drop laws at different mass fractions of foam drainage agent were tested by using the foam drainage agent UT-11. In addition, four common mechanism models of gas-liquid two-phase choke flow (Sachdeva model, Perkins model, Ashford model and slippage numerical model) were evaluated from the aspects of choke flow regime transition predicting capacity and mass velocity and pre-choke pressure predicting capacity by using the experimetnal data. Finally, a formula for calculating the slippage factor of foam flow was constructed based on the experimental data. In this way, the accuracy of the slippage numerical model is improved, the absolute percentage error of mass velocity is decreased from 13.7% to 7.69% and that of pre-choke pressure is decreased from 16.5% to 8.01%. In conclusion, the research results provide an important theoretical base for the size design and pre-choke pressure prediction of downhole choke in the gas wells with foam drainage gas recovery process.
Research status and discussion of horizontal well interference in shale oil and gas reservoirs
GUO Xuyang, JIN Yan, HUANG Lei, ZI Jingyu
2021, 43(3): 348-367.   doi:
[Abstract](3) [FullText HTML](529) PDF 1458KB(152)
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Low-permeability shale reservoirs can hardly form industrial oil and gas flow naturally, and their commercial production is commonly realized by using horizontal well and hydraulic fracturing to create hydraulic fracture networks. As large-scale infill well deployment and fracturing is conducted, however, horizontal well spacing gets short and stimulated reservoir volume (SRV) is increased, so interference induced by hydraulic fractures occurs between wells, which impacts the wellhead pressure and production rate of the neighboring well and even induces the problems of well control, casing damage and proppant invasion and seriously results in the abandonment of horizontal well, so as to impact the production efficiency greatly. In addition, the depletion of old wells can lead to the dynamic evolution of reservoir geostress on the basis of the in-situ geostress to form the complex geostress state, which will impact the reservoir stimulation effects of infill horizontal wells and refracturing wells and restrict the productivity performance of well pads. The development of the shale oil and gas resources in the Junggar Basin, the Sichuan Basin and the Ordos Basin of China has stepped into the stage of small well spacing and infill well deployment, so well interference has already impact the normal production obviously. Therefore, it is in urgent to carry out specific studies. In this paper, domestic and foreign well interference phenomena, mechanism studies and diagnosis methods of shale oil and gas were introduced in details, and the intervention countermeasures were proposed. It is indicated that accurate characterization and prediction of fractured horizontal well interference shall be carried out in the framework of geology and engineering integration. The accurate understanding of natural fractures, faults, in-situ geostress and reservoir rock mechanical characteristics is the prerequisite to evaluate well interference. The modeling and characterization of formation depletion induced dynamic geostress and complex hydraulic fracture network is the key means to quantitatively evaluate the interconnection of complex fracture network between wells, as well as the effective method to quantitatively predict the impact of well interference on the estimated ultimate reserve (EUR) of well pad. Well shutdown, liquid injection into old well, refracturing, well spacing optimization and fracturing optimization are the means to intervene or diminish well interference.
Horizontal-well subdivision cutting and volume fracturing technology for the deep tight sandstone gas reservoirs in the Shengbei Block
XIANG Hong, SUI Yang, WANG Jing, WANG Bo, YANG Xiong
2021, 43(3): 368-373.   doi:
[Abstract](1) [FullText HTML](685) PDF 1047KB(57)
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To cope with poor early vertical well fracturing effect and difficult effective reserve production in the deep tight sandstone gas reservoirs of the Shengbei Block, Tuha Oilfield began to research the horizontal-well volume fracturing technology based on the reservoir geological characteristics of this block in 2019, focusing on improving the stimulated reservoir volume, ensuring the fracture conductivity and reducing fracturing construction risk. As a result, several key fracturing technologies are developed, including subdivision cutting, multi-stage and multi-cluster, large-scale volume fracturing, high-temperature mixed fracturing fluid system, high-temperature soluble bridge plug, combined small particle size proppant and construction proppant concentration control. By February 2021, these technologies had been practically implemented in 3 wells and realized breakthrough in single-well production rate. The maximum oil and gas equivalent of Well Shengbei 503H after fracturing is as high as 100 t/d. The field practice proves that this technology is well adaptive to the deep tight gas reservoirs in the Shengbei Block and lays the foundation for the effective production of the tight gas reservoirs in this block.
Intrafracture temporary plugging and diversion fracturing technology suitable for tight reservoirs
XU Jianguo, LIU Guangyu, WANG Yanling
2021, 43(3): 374-378.   doi:
[Abstract](1) [FullText HTML](516) PDF 1090KB(76)
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As oil and gas exploration and development advances continuously, unconventional tight oil and gas reservoirs have already become the main objects for oilfields to realize reserve and production increase. This type of reservoir is characterized by low permeability (<0.1×10−3 µm2) and large bidirectional stress difference (> 10 MPa), so it is difficult to induce fracture network only based on the stimulation of large displacement and liquid rate. To this end, intrafracture temporary plugging and diversion fracturing technology is needed to increase the net pressure further and improve the fracture complexity. The type selection and dosage design of temporary plugging agent is the determinative key to the formation of complex fracture network and consequently influences the stimulation effect of fracturing wells. The water based temperature control dissolution type temporary plugging agent was selected, and the plugging thickness of temporary plugging agent, the height of dynamic fractures and the quantity and thickness of micro fractures were taken into consideration comprehensively to form the method for the dosage design of temporary plugging agent. It has been totally applied in 37 layers of 11 wells, among which, the pressure of 28 layers under the same displacement is increased by 0.5-7.0 MPa after the injection of temporary plugging agent and the efficiency is up to 75.7%. Thus, the goal of intrafracture temporary plugging and diversion fracturing network is reached. The research results provide theoretical basis for the later tight reservoir stimulation, so as to achieve the effective production of tight oil and gas reservoirs.
Experimental study on the development effect of flue gas-associated SAGD
ZHAO Qinghui
2021, 43(3): 379-383.   doi:
[Abstract](0) [FullText HTML](403) PDF 1173KB(49)
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Steam assisted gravity drainage (SAGD) is an effective technology to develop thick super heavy oil reservoirs, but there are serious steam overlay, great heat loss, low oil/steam ratio and other problems in the middle and late stages of the development, which impact the development effect. In this paper, the influences of flue gas on in-place oil properties and the heat loss of steam in the overlying strata, change laws of steam chamber and production characteristics after the injection of steam with flue gas were experimentally studied in the laboratory by using PVT analyzer and proportional physical simulation system. It is indicated that the injected flue gas can effectively reduce the in-place oil viscosity, improve the flow capacity of crude oil and increase the volume coefficient and the elastic energy. Compared with conventional SAGD, the flue gas-assisted SAGD speeds up the transverse expansion of steam chamber and slows down the longitudinal expansion, so as to effectively inhibit the phenomenon of steam overlay. The flue gas injected together with steam accumulates above the steam chamber to form a heat insulation layer, which reduces the heat loss of steam in the overlying cover, so as to improve the heat utilization efficiency. Steam injection with flue gas in the process of conventional SAGD can reduce the amount of steam injection to a certain degree, increase the oil/steam ratio and improve the development effect.
An efficient integration technology of separate-layer sand control and separate-layer water injection for offshore oilfields
SONG Huihui, REN Congkun, REN Zhaolin, ZHANG Futao, TIAN Jun, LIU Yanxia
2021, 43(3): 384-388.   doi:
[Abstract](0) [FullText HTML](369) PDF 1025KB(32)
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At present, offshore separate-layer sand control and separate-layer water injection face short validity, long construction period and high operation cost. To solve these problems, this paper researched a new efficient integration technology of separate-layer sand control and separate-layer water injection for offshore oilfields. Crossing-type suspension release packer can connect sand control pipe string and water injection pipe string simultaneously, and small-diameter hydraulic compression four-rubber separate-layer packer can realize the setting of separate-layer sand control packer and the later fine stratification of water injection pipe string. By virtue of this technology, sand control pipe string and water injection pipe string are run into the hole in one trip, which saves the construction time more than 50%. After the soluble release support sleeve of crossing-type suspension packer is dissolved, sand control pipe string and water injection pipe string can be maintained independently, which extends the service life of sand control pipe string and reduce the operation cost. This technology has been successfully applied 10 well times in Shengli offshore oilfield with maximum hole deviation angle 65 °, maximum tool setting depth 3 780 m, maximum working pressure difference 10 MPa, construction success ratio 100% and stratification qualification rate 100%, and it effectively improves the development degree of offshore water flooding oil reservoirs.
Application of molecular film/mixed organic acids combined blockage removal technology in under-injection wells of Jiyuan Oilfield
WANG Guocheng, ZHANG Daofa, ZHANG Jinke, JIN Jijun, GOU Lipeng, JU Jiangtao
2021, 43(3): 389-394.   doi:
[Abstract](3) [FullText HTML](299) PDF 977KB(39)
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In Jiyuan Oilfield, the problem of under-injection well is increasingly serious, and there are a variety of blockages. Conventional acidizing cannot remove various blockages simultaneously. To solve this problem, this paper researched and developed a molecular film/mixed organic acids combined blockage removal technology of wider applicability by analyzing blockages and blockage removal mechanisms firstly. This new technology includes mainly mixed organic acids, novel molecular film, depolymerizing agent and additive. Experimental result shows that this combined blockage removal system has strong blockage removal capacity. Its dissolution ratio of field fouling samples is generally over 80% and its viscosity reduction ratio of polymers is over 90%. It is applicable to in-depth blockage removal and can effectively avoid secondary precipitation. Field application effect shows that the molecular film/mixed organic acids combined blockage removal technology can effectively reduce water injection pressure and improve daily water injection and is applicable to the reservoir stimulation of most under-injection wells.
Profile control technology with high-strength plugging agent for straightly-connected fractures in Honghe Oilfield
WANG Hongshen, WANG Tianhui, HUANG Yongzhang
2021, 43(3): 395-399.   doi:
[Abstract](2) [FullText HTML](345) PDF 1157KB(33)
Abstract:
The oil reservoirs with developed natural fractures are faced with fast waterline advancing, easy water channeling and poor water flooding effect in the process of water flooding development. In order to solve these problems, Honghe Oilfield carried out researches and field tests on profile control technologies with gel plugging and gel plugging+particle/bentonite plugging. Due to the material mechanical performance of the gel system, however, the overall effect is not satisfactory. A series of investigation and analysis were carried out to select a set of high-strength plugging agent system of monomer polymerization. This system has the advantages of high viscosity, short gelation time, high strength and good thixotropy. Under the condition of 65 ℃, its gelation time is adjustable between 15 h, and the breakthrough pressure in the pipeline with length of 0.5 m and diameter of 3 mm is 7.0 MPa/m. In Honghe Oilfield, pilot tests are performed in four wells by five times and the effective rate is 100%. It can form high-strength plugging in fractures and effectively increases the plugging strength of the plugging agent in straightly-connected fractures. After profile control is implemented, average pressure is increased by 6.7 MPa, cumulative water injection is 5 643 m³ and cumulative oil increase is 2 723.1 t. In conclusion, this system can effectively solve the problem of fast water channeling in the oil reservoirs with developed natural fractures in the process of water flooding development in Honghe Oilfield.
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