【作者】 戴建全；

【导师】 刘宝珺；

【作者基本信息】 成都理工大学 ， 沉积学， 2010， 博士

【摘要】 龙门山逆掩冲断推覆带,系指四川盆地西部茂汶—汶川断裂带以东至关口-彰明断裂带所挟持的区域。在龙门山冲断滑脱构造亚带及前缘地区发现了中坝、邛西、平落坝气田以及鸭子河、金马、大邑、高家场、莲花山等含油气构造,关口断裂以西的构造复杂地区勘探程度很低。龙门山逆冲推覆带的研究已达数十年,著书立说层出不穷,特别是“十五”以来,中石化向该区投入了超亿元的勘探与研究经费。然而,时至今日,包括中石油在内均未在此带取得重大油气突破。究其原因,龙门山逆冲推覆带构造条件十分复杂,该区油气保存条件的研究十分薄弱。在断裂作用和破碎强烈地区,保存条件就更为重要。因此,保存条件正是龙门山复杂构造带重要的成藏要素。可是,迄今为止未系统开展过这方面系统、深入的专项研究。本论文通过野外地质调查分析、取样与室内研究(物理模拟、实验分析、综合研究)相结合进行研究。采用地质与地球物理、地球化学相结合、宏观与微观相结合、定性与定量相结合的研究方法,综合利用地表露头、岩心、地震、测井等资料,并结合油气水及盖层保存条件的研究,研究龙门山逆冲带形变破裂作用与油气保存条件的关系,侧重于区域构造单元划分和形变特征、断层特征与封堵性研究,取得了一系列新认识和新成果。龙门山造山带及前缘地区的构造单元划分为5个一级构造带。Ⅰ:松潘-甘孜褶皱带;Ⅱ:龙门后山逆冲推覆构造带;Ⅲ:龙门前山推覆滑脱构造带;Ⅳ:川西前陆盆地;Ⅴ:川中平缓构造带;其中川西前陆盆地构造带有可分为6个二级构造带。Ⅳ1:龙门山前缘构造带;Ⅳ2:龙门山山前低缓构造带;Ⅳ3:北部平缓构造带;Ⅳ4:中部近东西低缓构造带;Ⅳ5:南部平缓构造带;Ⅳ6:龙泉山-熊坡构造带。从北西到南东,构造变形由韧性较强到脆性较强,从高强度变形到低强度变形。构造样式含盖了几乎所有的常见样式,如纵弯褶皱、断层相关褶皱、叠瓦断层、双重构造、反冲构造、推覆构造等等。在北东向构造的大背景下,龙门山前山中段存在东西向褶皱与断层带,构造形态表现为直立褶皱、平卧褶皱、水平断层等。野外研究得到的中央断层、前山断层、前山原地系统、前山飞来峰等构造单元的构造期次、所受应力均显示从北西到南东变得简单些。中央断层有9期构造变形及应力,它们是:(1)NW-SE韧性逆冲;(2)NEE-SWW右旋(半脆性强化变形带);(3)NW-SE逆冲(劈理);(4)SN左旋正断(劈理);(5)左旋逆冲(节理);(6)WE右旋;(7)NW-SE伸展,正断;(8)左旋;(9)NW-SE逆冲。到了前山断层,构造期次减少,有些地段才显示1次运动。平衡剖面恢复揭示了前山带及前缘地区的构造构造样式主要是叠瓦推覆断层及相关的褶皱,构造缩短量很大;构造发展主要呈前展式。物理模拟实现了绝大多数构造样式的再现及前展式发展的再现。前山断层两盘系统采磷灰石样后的裂变径迹研究揭示了两盘白垩纪以来的差异隆升活动,结果显示南段白垩纪差异隆升明显。初步建立了构造变形强度指标与保存条件的半定量关系:地层缩短量(对区域而言)小于7.3%时保存条件好、褶皱系数为0.02-0.13时保存条件好、井下裂缝密度小于5条/m时保存条件好、断裂分数维D小于1.3时保存条件好。对白鹿鸭子河地区断层封堵性使用了断层面压力封堵性、泥岩涂抹系数封堵性、地层压力封堵性以及爱伦剖面封堵性4种方法计算,结果显示:关口断层对下盘基本封堵,对上盘不封堵。彭县断层基本不封堵。对安县香水断层的断层面压力封堵性计算显示一定深度后封堵。对大邑F1断层爱伦剖面封堵性的计算显示其封堵性好。通过评价研究认为,前山带和前缘带的局部构造保存条件都差;山前低缓构造带和东西构造带大部分局部构造保存条件好且变形强度适中;坳陷中平缓构造带保存条件好但变形强度弱。利用前面所建立的构造变形强度与保存条件的关系,评价了研究区有利的成藏区带。对不同层位考虑的因素侧重点有所不同。须家河组最有利区带是山前低缓构造带(Ⅳ2)的南段和北段以及东西向构造带(Ⅳ4)。雷口坡组最有利区带是山前低缓构造带(Ⅳ2)的北段和中段以及东西向构造带(Ⅳ4)。嘉陵江组最有利区带是山前低缓构造带(Ⅳ2)的北段和中段。更多还原

【Abstract】 The overthrust nappe thrust in Longmen mountain refers to the area from the east part of Maowen-Wenchuan thrust in western Sichuan to Guankou-Zhangming thrust. Three gas fields(Zhongba, Qiongxi and Pingluoba gas fields) and many gas-bearing structures, such as Yazihe, Jinma, Dayi, Gaojiachang and Lianhuashan gas-bearing structures were discovered in the area of sub-thrust belt detachment structure and the front edge. Those areas with complicated structures in the west part of Guankou were of low level of exploration.The overthrust belt in Longmen mountain has been studied for many years and many books and articles about it were published, especially since the period of the tenth-five years, Sinopec has investigated prospecting funds over thousand millions for exploration and research. However, whether Sinopec or CNPC has not achieved great breakthrough. Why? The complicated structure conditions and less research work about preserve conditions are the direct reasons. For those faulting and crushing areas, preservation conditions are very important. Therefore, preservation conditions are key factors of gas accumulation for complicated structures in Longmen mountain. However, till now, there are less systematically and deeply research work about the preservation conditions.This article focused on the relationship between deformation and rupture of thrust belt and preservation conditions in Longmen mountain through integrated studying on field geological survey analysis, sampling and laboratory research (physical simulation, experiment and comprehensive study), adopting the combination methods of geology, geophysical and geochemical, macro and micro, qualitative and quantitative, utilizing outcrop, core, seismic, logging data etc, combining the preservation conditions of oil-gas-water and seals. It achieved some new understanding and new results, especially on the research of regional tectonic units, deformation features, characteristics of faults and sealing.The tectonic units of orogenic belt and the front edge in Longmen mountain were divided into five one-grade structure belts:Ⅰ:Songpan-Ganzhi folded belt;Ⅱ:Overthrust belt in rear Longmen mountain;Ⅲ:Thrust detachment belt in front Longmen mountain;Ⅳ:Foreland basin in western Sichuan;Ⅴ:flat belt in middle Sichuan. The foreland basin in western Sichuan was further divided into six secondary structure belts:Ⅳ1:front edge belt;Ⅳ2:low and flat belt in the front of Longmen mountain;Ⅳ3:flat belt in the north part of Longmen mountain;Ⅳ4:low and flat belt near WE in the middle of Longmen mountain;Ⅳ5:flat belt in the south part of Longmen mountain;Ⅳ6:Longquan mountain-Xiongpo structure belt.From WN to ES, the level of structure deformation changed from strong toughness to brittleness, from high intensity to low intensity. All structural styles are included, such as vertical bend fold, fault related fold, imbricate fold, duplex structure, backthrust, nappe etc. Under the background of NE-trending structures, there were WE-trending folds and faults including vertical folds, flat folds and horizontal faults etc ., existed in the middle section of the front Longmen mountain.Based on the field research, it shows that the tectonic period and the stress level of central fault, front fault, front in-situ system, front klippen etc, became simpler and simpler from WN to ES. The central faults deformed nine times, such as (1) NW-SE ductile thrust; (2)NEE-SWW dextrorotation(enhanced semi-brittle deformation) (3)NW-SE thrust(cleavage) (4)SN levogyrational traction fracture cleavage; (5) levogyrational thrust(joint); (6)WE dextrorotation; (7)NW-SE stretch, traction fracture; (8)levogyration; (9)NW-SE thrust. The tectonic period of those faults in the front Longmen mountain became less, some of where experienced tectonic movement only one time. From the balanced cross section, it can be revealed that the tectonic style of front and foreland edge was mainly imbricate overthrust fault and related fold, with large reduction of fault and front expansion structure development. Physical simulation achieved reappearance of most tectonic style including front expansion ones.Based on the fission track study after sampling apatite in both hanging and foot walls in front Longmen mountain, it is proved that there existed different lift movement since Cretaceous period, the south one lifted apparently.The semi-quantitative relationship between deformation strength and preservation condition has been initially established. Only if one of the following conditions is achieved, the sealing can be preserved well, such as formation reduction amount(in terms of regional) is less than 7.3%,fold factor is 0.02-0.13,crack density is less than 5 per meter, rupture fractal dimension D is less than 1.3.Four methods to study fault sealing for Bailu Yazihe area have been adopted, such as pressure of fault plane, smear factor of mudstone, formation pressure and Allan profile. The study shows that Guankou fault sealed the foot wall, not hanging wall. Pengxian fault did not seal. Xiangshui fault in Anxian sealed when it entered certain depth. Dayi F1 fault sealed well.Through the above evaluation and studies, it can be concluded that part structures in the areas of front and foreland edge were of bad preservation condition; most low and flat structure belts and WE structures were of good preservation condition and proper strength; middle and flat structures were of good preservation condition and weak deformation.According to the above relationship between deformation strength and preservation condition, favorable gas accumulation area was evaluated in the research area. Different factors can be considered for the different layers. The south and north structures of front flat structure are the most favorable area in Xujiahe formation(Ⅳ2),north, middle and WE structures of front flat structure belt in Leikoupo formation(Ⅳ2),the north, middle structures of front flat structures(Ⅳ2)in Jialinjiang formation.更多还原