Petroleum Exploration and Development

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Deposition of Yanchang Formation deep-water sandstone under the control of tectonic events, Ordos Basin

Yang Hua and Deng Xiuqin

, 2013, 40(5): 2170-0.

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A large area of deep-water sandstone was formed under the combined action of delta and gravity flow in the central Ordos Basin during the depositional period of the Ch6 and Ch7 oil-bearing formations of the Upper Triassic Yanchang Formation. According to U-Pb dating of zircons by the method of LA-ICP-MS, the ages of the tuff layers at the bottom and upper parts of Ch7 oil-bearing formation are 228.2± 2.0 Ma and 221.8±2.0 Ma, respectively. Based on the ages of the tuff layers, it is suggested that the gravity flow complexes at middle-upper Ch7 and lower-middle Ch6 oil-bearing formations were formed during 215-224 Ma. The depositional time of tuff and gravity flow is roughly the same as the time when tectonics are most active in the Qinling area, i.e. middle Indosinian period. The steadily widespread tuff at the bottom of the Ch7 oil-bearing formation and the extensive gravity flow sediments formed at early lake regression period are the direct outcomes of the tectonic event. Tuff layers are widely deposited at the bottom of Ch7 oil-bearing formation under the influence of the middle Indosinian tectonic events. Divided by the tuff layers, there is obvious difference in clastic composition between the lower and upper strata. The events control formation of large-area deep-water depressions, change of depositional system, migration of depositional center, and occurrence of gravity flow.

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Genesis and maturity identification of oil and gas in the Xihu Sag, East China Sea Basin

Su Ao; Chen Honghan; Wang Cunwu; Li Peijun; Zhang Hui; Xiong Wanlin and Lei Mingzhu

, 2013, 40(5): 2171-0.

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Based on the composition and stable carbon isotope ratios of condensate and natural gas in the Xihu Sag, East China Sea Basin, origin and maturity of the hydrocarbon gas, CO2, N2 and condensate are determined using multiple methods. The CO2, low content of N2, condensate and hydrocarbon gas are mainly derived from thermal pyrolysis of coal-bearing measures. The relatively high content of N2 is collectively controlled by the thermal degradation of kerogen, vertical migration of gas and microbiological deterioration. Considering “evaporation fractionation” effect, a modified relationship between heptane and isoheptane has been used to calculate maturity of the condensate, which is in consistence with the results of the Mango method, i.e., the condensate is from mature source rock. The “two-segments of methane stable carbon isotopic fractionation model” has been used to calculate the hydrocarbon gas maturities. There are two mature stages of gas: one is mature gas which is equivalent to the condensate in maturity; the other is high maturity gas.

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Quantitative analysis of the Mesozoic abnormal low pressure in Ordos Basin

Li Shixiang; Shi Zejin; Liu Xianyang; Yang Shiyu; Deng Xiuqin; Liu Guanglin and Li Jihong

, 2013, 40(5): 2172-0.

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Abnormally low pressure is characteristic of the Mesozoic reservoirs in the Ordos Basin. Based on the study of low pressure distribution, the formation mechanisms of abnormally low pressure were quantitatively analyzed from several aspects, such as tectonic uplift, stratum temperature decrease and dissolution-increased porosity. The Mesozoic reservoir pressure experienced two major evolutionary stages: the pressure rising to maximum pressure stage from the Late Triassic to the Early Cretaceous, the pressure decreasing to abnormally low pressure stage from the end of Early Cretaceous to now. Since the late Early Cretaceous, porosity rebound caused by tectonic uplift, stratum temperature decrease and dissolution caused pressure decrease of up to 20-25 MPa, the decrease ratio is about 54%-77%. The three factors are the main reason for the pressure decrease of the Mesozoic in the Ordos Basin, and among them stratum temperature decrease is the most important factor. Combined with other factors, they made the formation pressure reduced gradually and eventually formed the abnormally low pressure distribution pattern of 10-18 MPa.

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Vertical zonation of weathered crust ancient karst and the reservoir evaluation and prediction—A case study of M55-M51 sub-members of Majiagou Formation in gas fields, central Ordos Basin, NW China

He Jiang; Fang Shaoxian; Hou Fanghao; Yan Ronghui; Zhao Zhongjun; Yao Jian; Tang Xiujun and Wu Guorong

, 2013, 40(5): 2173-0.

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The M55-M51 sub-members of the Middle Ordovician Majiagou Formation in gas fields of central Ordos Basin were taken as a case to analyze the vertical zonation characteristics of weathered crust ancient karst and to evaluate and predict reservoirs through plenty of core and thin section observation, with geological background and petrological characteristics as main clue. According to detailed underground geological survey, description of typical karst section, systematic sampling, and laboratory test, there mainly developed karst formation rock and transformation rock in ancient weathered crust in the top of the Majiagou Formation, which were divided into surface karst zone, vertical vadose zone, horizontal underflow zone and deep slow flow zone from surface to subsurface. Karst intensity in each zone has great effect on the storage and flow capacity of reservoir. In the strong karstification subzone of the horizontal underflow zone with over strong karst, the parent rock was extensively damaged and formed karst caves filled with karst formation rock rarely with pores. In the deep slow flow zone with over weak karstification, there are sedimentary and filling activities. The medium karstification subzone of the horizontal underflow zone and the vertical seepage zone had a moderate karstification, which not only created storage and flow space but also prevented collapse, and were most beneficial to reservoir development.

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Hydrocarbon potential in the key basins in the East Coast of Africa

Zhou Zongying; Tao Ye; Li Shujun and Ding Wenlong

, 2013, 40(5): 2174-0.

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This paper analyzes the evolution and sedimentary filling characteristics of regional structures in the sedimentary basins in the east coast of Africa and discusses the different geological conditions of hydrocarbon accumulations (e.g. source rock, reservoir and cap-rock) and their exploration potential. These basins are superimposed basins developed on the Precambrian basement, they were successively filled with three sedimentary sequences, i.e. the late Carboniferous - early Jurassic intra-continental rifting continental sedimentary sequence, the mid/late Jurassic - early Cretaceous intra-continental weak rifting sedimentary sequence, and the late Cretaceous - Neogene passive margin marine sedimentary sequence, where different source-reservoir-caprock assemblages show good prospects for exploration. The comprehensive comparison and analysis has been conducted on such geological conditions in six key basins (Lamu, Somali, Tanzania, Rovuma, Mozambique and Morondava). It is considered that the Tanzania, Rovuma and Somali basins are highly potential for superior geological conditions, such as excellent source rocks and cap rocks, and good preservation later. The Mozambique basin is also favorable for exploration, but the Lamu and Morondava basins are unacceptable.

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Karstification of reef-bank facies carbonate rock and its control on pore distribution: A case study of Upper Ordovician Lianglitage Formation in eastern Tazhong area, Tarim Basin, NW China

Qu Haizhou; Wang Zhenyu; Yang Haijun; Zhang Yunfeng; Yu Hongfeng and Wang Xi

, 2013, 40(5): 2175-0.

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The karstification type and characteristics and its control on pore distribution in reef-bank carbonate rock in the Upper Ordovician Lianglitage Formation (O3l) in eastern Tazhong area were studied using cores, thin sections and well logging data. The area experienced two types of karstification: syndepositional karstification and early diagenetic karstification near surface. During the depositional stage of reef-bank complex, meteoric diagenetic lens with lots of selective dissolution pores were formed by the syndepositional karstification, they were developed in the middle and upper parts of reef-bank sedimentary cycles, and a single porous/cavity layer has a thickness of 10-30 m, increasing the absolute porosity by 3%-4%. After depositional stage, sediments were uplifted and exposed without experiencing burial diagenesis, the depositional topography was influenced by early diagenetic karstification near surface and turned into karst paleotopography and formed four karstification zones within 100 m below the top of the Upper Lianglitage Formation. The surface karstification zone and radial flow karsitifiction zone have favorable porous connectivity, increasing the absolute porosity by 4%-8%. These two types of karsitifiction are continuous in diagenesis stage and the formed porosity is successive in distribution. The favorable space-time coupling is the key reason for effective pores being largely developed in the O3l3-O3l1 members.

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Logging interpretation of coal petrologic parameters: A case study of Hancheng mining area

Shao Xianjie; Sun Yubo; Sun Jingmin; Tang Dazhen; Xu Hao; Dong Xinxiu and Lü Yumin

, 2013, 40(5): 2176-0.

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Aiming at a serious obstacle for building a logging interpretation model to accurately interpret density and sonic speed value of each coal component which cannot be measured directly in lab scale, a logging interpretation method of coal reservoir parameters was studied using the Hancheng mining area as an example. The enumeration method was used to calculate density and sonic speed value of fixed carbon, ash, and volatile according to experimental determination of industrial components, pore, gas content, density and sonic speed value of many coal samples in the Hancheng mining area. On the basis of the relationships of each coal component and its density and sonic speed value, logging response relationships between each component and its compensated density and acoustic travel-time differences were studied using numerical fitting. As fitted carbon content increases, ash content and density decrease and sonic speed difference increase. By combining statistical analysis method and theory model calculation method, interpretation models of industrial components, gas content and pore for coal reservoirs were built and a logging integrated interpretation software was programmed, which have got good effect in actual application.

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Pore structures evaluation of low permeability clastic reservoirs based on petrophysical facies: A case study on Chang 8 reservoir in the Jiyuan region, Ordos Basin

Lai Jin; Wang Guiwen; Chen Min; Wang Shunan; Chai Yu; Cai Chao; Zhang Yongchen and Li Jianlun

, 2013, 40(5): 2177-0.

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The sedimentary facies, diagenetic facies and fracture facies of the Upper Triassic Yanchang Formation Member 8 (Chang 8) reservoir in the Jiyuan region were studied using core observation, thin section, logging and drilling data. On this basis, the petrophysical faices of Chang 8 oil layers were examined to evaluate the pore structure by classification and predict zones with high porosity and permeability. The petrophysical facies were divided according to the superposition and combination of sedimentary facies, diagenetic facies and fracture facies. A number of petrophysical facies of Chang 8 oil layers such as underwater distributary channel, dissolution of unstable components, high-angle fracture, were identified in this way. Four main categories of petrophysical facies were summed up according to the constructive and destructive impact of sedimentary facies, diagenetic facies and fracture facies on the reservoir property and pore structure of Chang 8 oil layers. Since the reservoir quality index (RQI) is an optimal indicator for describing the reservoir micro-pore structure quantitatively, the value of RQI of different petrophysical facies was calculated respectively. So the classification and evaluation of Chang 8 reservoir pore structure in a single well were realized by the division of petrophysical facies combined with logging data. At last, the vertical and horizontal distribution of sedimentary micro-facies and diagenetic facies of each single layer of Chang 8 oil layers were mapped, the distribution of favorable petrophysical facies can be used to predict the zones with high porosity and permeability.

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Scientific issues on effective development of marine shale gas in southern China

Wang Hongyan; Liu Yuzhang; Dong Dazhong; Zhao Qun and Du Dong

, 2013, 40(5): 2178-0.

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Shale gas resources are abundant in China and have been discovered in some areas. They are widely distributed in the Cambrian, Ordovician and Silurian strata in Southern China, with technically recoverable resources accounting for 3/4 of the whole country. The Southern China will be the main area for shale gas development. Compared with North America, there are a lot of differences in shale gas exploration and development in Southern China which include intensive tectonic movements in marine shale, complex stress field, deep burial depth, special surface condition, etc. With those, it could be ineffective if the existing theories and techniques of shale gas developed in America are taken for granted. The effects of nano-pore formation on shale gas production are unclear; Prediction methods for shale gas production have not been established; In the process of drilling, the horizontal section collapses seriously and the drilling cycle is too long; Stimulation effect is not ideal, with low single well production. In order to effectively develop shale gas in Southern China, three scientific issues should be studied which include quantitative characterization of nano-pore formation and multi-scale storage space, mechanisms of nonlinear flow under multi-field coupling in complex medium, mechanical mechanisms of shale instability and fracture network formation.

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Physical simulation on gas percolation in tight sandstone

Hu Yong; Li Xizhe; Wan Yujin; Lu Jialiang; Zhu Huayin; Zhang Yufeng; Zhu Qiuying; Yang Min and Niu Liwei

, 2013, 40(5): 2179-0.

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Capillary pressure was tested on 40 matrix cores (in situ permeability: 0.002×10-3–100 ×10-3 μm2) in the Sulige gas field and the pore structure features of different type sands were described finely. Based on the research on the pore structure features, gas percolation experiments were designed under the conditions of homogeneous cores with different permeability, heterogeneous cores and different water saturation, to research the gas percolation laws in tight sand. Nanometer pore throats and microscopic capillary pore throats are the main flow channels for gas in tight sand. Percolation resistance of gas or gas-water in tight sand is far greater than that in conventional sand or medium-high permeability sand. Depletion experiments show that gas percolation resistance is bigger when permeability of dry sandstone is lower than 0.1×10-3 μm2 or permeability of water sand is lower than 1×10-3 μm2, so the starting pressure gradient exists. Water saturation has great effect on gas percolation in sandstones. When water saturation is higher, producing reserves are lower. The starting pressure gradient, calculated by monitoring the pressure values of all test points in depletion experiments of long cores, would be scientific and helpful for forecasting the oil drain radius and evaluating producing reserves.

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Productivity evaluation and influential factor analysis for Sarvak reservoir in South Azadegan oil field, Iran

Liu Hui; Guo Rui; Dong Junchang; Liu Li; Liu Yang and Yi Yingjie

, 2013, 40(5): 2180-0.

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Production pattern of oil wells and influential factors on productivity for the massive carbonate reservoir in the Middle East were researched by productivity evaluation on Sarvak and analysis of properties impact on production. Based on dynamic performance of Sarvak production test, the relationship between daily oil production, tubing pressure, cumulative oil production and choke size was analyzed and reasonable productivity prediction model was established by applying Poettman model, and the effect of physical properties and fluid parameters on productivity were analyzed further by numerical simulation. The study shows that daily oil production is linearly correlated with oil pressure under certain working regime, and daily oil production is power law correlated with choke sizes before and after working regime adjustment. The average designed single well productivity should be about 270 m3/d by depletion to ensure a three-year plateau period. Sarvak is a blocky carbonate reservoir, when developed with horizontal wells, interbeds distributed between layers and permeability property have the strongest impact on production of horizontal wells. So, highly deviated wells should be used to reduce the effect of interbeds and acidizing should be considered to improve the reservoir physical properties.

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Preliminary study on a depositional interface-based reservoir modeling method

Huang Jixin; Mu Longxin; Chen Heping; Yin Yanshu and Zhou Jiuning

, 2013, 40(5): 2181-0.

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According to the channel deposition process and response features, the reservoir modeling based on the depositional interface (DI) is extended from turbidite fans to fluvial sandstones, in order to reconstruct the deposition process and improve the architecture simulation of channel sands. The DI-based modeling of fluvial reservoir is conducted in four steps: (1) Use a simple harmonic oscillation (SHO) damping model with disturbance to generate river flow lines and then complete the beaded association of singe-genetic sands; (2) Identify the interfaces at ends of channels (point bars) to generate the point bar model; (3) Determine the superimposition template inside channel (point bar), and fit the interfaces with such functions as hyperboloid, paraboloid and polynomial; and (4) Take samples at random using the trigonometric function of key parameters for lateral accretion bedding, to complete characterization of point bar. It is concluded that the DI-based modeling method well reproduces the depositional process of fluvial sandstones and finely characterizes the architecture units therein.

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Exploitation mode oriented heavy oil-oil sand recoverable reserves calculation method

Ma Zhongzhen; Chen Heping; Xie Yinfu; Liu Yaming; Li Jia; Wang Dandan; Yang Xiaofa and Zhou Yubing

, 2013, 40(5): 2182-0.

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Based on special exploitation mode of heavy oil-oil sand, this paper established a recoverable reserves calculation method for heavy oil-oil sand. First, calculate recoverable reserves of single exploitation mode according to oil layer selection criterion including four parameters of buried depth, single layer thickness, porosity and oil saturation for different exploitation models. Second, calculate recoverable reserves for different exploitation model combination and the max recoverable reserves of the block; Last, set up heavy oil-oil sand recoverable reserves database. The method has great correlation with PRMS reserves evaluation system. The method has been used in the heavy oil classification evaluation for larger M of the J block in Venezuela heavy oil belt, the recoverable reserves are 4.06′108 t, 15.23′108 t and 7.40′108 t respectively by cold production, steam drive and steam-assisted gravity drainage, and the max recoverable reserves are 15.97′108 t, which provides reserves basement for block development.

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Waterless fracturing fluid with low carbon hydrocarbon as base fluid for unconventional reservoirs

Hou Xiangqian; Lu Yongjun; Fang Bo; Qiu Xiaohui and Cui Weixiang

, 2013, 40(5): 2183-0.

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As the conventional fracturing fluids are not good for stimulation of unconventional reservoirs and the conventional oil-based fracturing fluids crosslink slowly, a ferric-complex cross-linking agent that cross-links fast with dialkyl phosphate ester was prepared and the fracturing fluid systems for the unconventional reservoirs were obtained. The main influencing factors on the properties of the cross-linking agent were analyzed and optimized, and then the ferric-complex cross-linking agent was prepared based on the optimizing results and its performance was evaluated. The optimizing and evaluating results show that: The ferric-complex cross-linking agent with excellent performance can be obtained in the condition that the content of cross-linking promoting agent is 5%, the content of ethylene glycol is between 8% and 10%, and the complexing agent is L5 with content of 10%. The ferric-complex cross-linking agent has better performance than ferric sulfate and aluminium sulfate. It is found that the crosslinking slows down with the growth of carbon chain when using different base fluids. The fracturing fluid systems with low carbon hydrocarbon (such as LPG) as base fluid, dialkyl phosphate ester as gelling agent and ferric complex as cross-linking agent are developed, and all of them have excellent crosslinking performance and are suitable for unconventional reservoirs.

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Artificial lift technique of multistage sliding vane pump used in thermal production wells

Shen Zejun; Huang Xiaodong; Zhang Lixin; Hao Zhongxian; Lei Derong and Jin Jingwei

, 2013, 40(5): 2184-0.

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For low efficiency and poor high-temperature resistant performance of the conventional artificial lift systems, a new sliding vane pump and the matched lift system were designed, and the pump property study, field test and economy analysis were conducted. The redesign of flow direction reduces the pump’s radial size and the design of series connection makes higher pumping pressure possible with lower revolution speed. By building pump characteristics models and doing laboratory experiment, it is found that the pump has steady hydraulic and mechanical characteristics, good no-load and heavy-load characteristics, and high system and volume efficiencies. The artificial lift system, including oil tube, sucker rod, transmission cylinder and anchor, was designed in reference to the progressive cavity pump (PCP) artificial lift system. The pump was tested in five wells and compared with other common lift equipment in energy consumption, high-temperature resistant performance and investment. The new artificial lift technique features its high efficiency, high temperature resistance, low investment and good adaptability.

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A high temperature retarder HTR-300L used in long cementing interval

Guo Jintang; Xia Xiujian; Liu Shuoqiong; Jin Jianzhou; Yu Yongjin and Yu Qianfeng

, 2013, 40(5): 2185-0.

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With regard to slow development or super retarding happening at the top of cement slurry in deep and ultra-deep wells with long cementing intervals, a new type of retarder HTR-300L was developed and its properties were evaluated. Thickening property tests at different temperatures for slurries with HTR-300L and IR, DSC and TG analysis show that: HTR-300L has good temperature-resistance performance and stable molecular structure. It can be used at the bottom hole circulating temperature of 70 to 200 ℃. The thickening time of the slurry can be regulated effectively by adjusting the additive amount of HTR-300L. Thickening property tests for slurries with different salt contents show that HTR-300L has good salt-resistance performance and can be used in salty cement slurry. Strength development, thickening time, fluidity and API filtration of slurries with HTR-300L were studied at different top-bottom temperature differences. The results show that: The slurry with HTR-300L develops well in strength at large temperature difference and can overcome super retarding of the top of the slurry in long cementing interval. HTR-300L is applicable for large temperature range and can be used for slurries with both high and low densities. The slurry with HTR-300L has good overall performance, easy to regulate and control, and can satisfy cementing requirements for long cementing interval.

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Prediction model of casing annulus pressure for deepwater well drilling and completion operation

Yang jin; Tang Haixiong; Liu Zhengli; Yang Liping; Huang Xiaolong; Yan De and Tian Ruirui

, 2013, 40(5): 2186-0.

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Casing collapse and fracture may be caused by the rise of casing annulus temperature and pressure in the initial stage of production and testing of deepwater wells. Based on the casing program and wellbore heat transfer process, a pressure calculation model for casing annulus was established, which provides basis for annulus pressure control. With the annulus between testing string and production casing as an example, a casing annulus temperature calculation method was derived according to the principle of conservation of energy and wellbore heat transfer analysis. The casing annulus pressure prediction model was established for typical deepwater wells according to the volume change of casing annulus fluid with temperature and pressure, and in combination of the casing annulus PVT equation and annulus temperature equation. The casing annulus temperature and pressure calculation methods were successfully applied in the casing annulus temperature and pressure management operation in 7 deepwater wells in West Africa, and the predicted temperature and pressure were compared with the actual ones, which indicates that casing annulus temperature and pressure prediction methods have good accuracy, with the relative error below 10%.

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Semi-active drilling drawworks heave compensation system

Huang Lumeng; Zhang Yanting; Zhang Lei and Liu Meiying

, 2013, 40(5): 2187-0.

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In order to simplify the structure of the ocean drilling heave compensation system and reduce the energy consumption of active drawworks heave compensation system, a new type of semi-active drawworks heave compensation system was designed through structure design, system modeling and internal model PID robust displacement controller design. Then the feasibility of the system was verified by non-linear time domain simulation and experimental study. The structure design realizes decoupling control of heave compensation and automatic bit feed, reduces energy consumption of the system. The system is simplified to build simulation model by lumped mass method and energy conservation principle. The double control scheme of hook displacement closed loop in the outer loop and motor speed closed loop in the inner loop is put forward, the internal model PID robust displacement controller of outer loop is designed. The steady-state deviation of internal model control is zero when the model is matching or mismatching. The dynamic performance and resisting disturbance capacity of the internal model control is better when the filter time constant is smaller. The compensation rate is above 90% by simulation and experimental research results, the compensation effect is good and the system is feasible.

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A real-time borehole correction of electromagnetic wave resistivity logging while drilling

Yang Zhen; Yang Jinzhou and Han Laiju

, 2013, 40(5): 2188-0.

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The response of electromagnetic wave logging while drilling is influenced greatly by borehole and drilling fluid resistivity when the size of borehole is relatively large and drilling fluid resistivity is low. Borehole radius and drilling fluid resistivity were introduced to obtain more accurate transformed resistivity on the basis of the commonly used resistivity transformation model. The influence of borehole was considered in the newly established three dimensional transformation model, and a new borehole correction method was proposed. The resistivity transformation database can be established by calculation according to a certain instrument, and the true resistivity is obtained by three dimensional interpolation search technology of real-time correction in practical use. The results of numerical simulation and modeling verification show that the transformed resistivity by real-time correction coincides with the resistivity corrected by charts. The method can eliminate the borehole influence, reduce calculation dimension, and improve the inversion efficiency of highly deviated and horizontal wells logging data.

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Hierarchical nested simulation approach in reservoir architecture modeling

Li Yupeng and Wu Shenghe

, 2013, 40(5): 2189-0.

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A hierarchal nested reservoir architecture simulation methodology is proposed to meet the current challenges in reservoir heterogeneity modeling. It matches the architecture geological research principle which is shortened as “hierarchical constraint, pattern fitting and multi-dimension proof”. In this proposed methodology, different modeling approaches are adopted in different stages of architecture analysis, and the result from current architecture analysis is used as constraints and information for next level architecture analysis. The meandering river reservoir architecture modeling is used to illustrate the proposed methodology. The meandering river sand complex is the first modeling stage. The Fluvsim program is updated to characterize the bounding surface of single channel within the channel sand complex. In second stage, a new point bar simulation program, Barsim, is developed. The abandoned channel and the known point bars are assembled together according to the quantity fluvial reservoir architecture model. The spatial vector based program Ihssim is developed to characterize the inclined heterogeneity strata (IHS) inside the point bar sand at third level architecture study stage. Through such an integrated three modeling procedures, the heterogeneity characteristics of a reservoir which is represented by reservoir architecture elements in different scales and hierarchical levels are presented in the final reservoir model.

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Explosive fracturing simulation experiment for low permeability reservoirs and fractal characteristics of cracks produced by explosive fracturing

Xu Peng; Cheng Yuanfang; Liu Xinyun; Zhang Xiaochun and Shi Libao

, 2013, 40(5): 2190-0.

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Based on the explosive fracturing simulation experiment for low permeability reservoir, growths of the cracks produced by the explosive fracturing in the samples were analyzed. And associated with fractal geometry theory, the cracks fractal characteristics were studied and the influences of explosive quantity and confining pressure on the cracks fractal dimension were analyzed. Different explosive quantities and confining pressures under which the simulation experiment was carried out were designed. After the experiment, the fractal dimension of the cracks produced by explosive fracturing in different samples was got by the box dimension calculation method. The results show that: With the increase of explosive quantity, the amount, length and width of the cracks on the surface of the sample produced by explosive fracturing simulation experiment under the same confining pressure increase. The amount and length of the cracks produced by explosive fracturing under the same explosive quantity decrease with the increase of confining pressure. Under the same confining pressure, the cracks fractal dimension increases with the increase of explosive quantity, and the relationship between them is approximately linear when the confining pressure is relatively low and approximately nonlinear when the confining pressure is relatively high. Under the same explosive quantity, the cracks fractal dimension decreases with the increase of confining pressure. It is suggested that site operation should match the explosive quantity with the confining pressure, and the charge pattern of axial coupling and radial uncoupling should be applied.

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, Volume 40 Issue 5