龙门山北段地下水动力特征及油气保存条件研究

【作者】 程建；

【导师】 王多义；

【作者基本信息】 成都理工大学 ， 矿产普查与勘探， 2010， 硕士

【摘要】 龙门山以北东—南西走向的茂县—汶川断裂,北川—映秀断裂,安县—灌县断裂为界,分为后山带、前山带和山前带。由西向东依次称为:松潘-甘孜褶皱带,茂县-汶川韧性剪切带,龙门山逆冲推覆构造带及川西前陆盆地。垂直区域构造线方向上,以绵竹汉旺镇,都江堰(灌县),雅安天全为界,由北向南分为龙门山北段、中段和南段。龙门山冲断带纵向上具有多层次的滑脱特征,存在多个滑脱面:①须三煤系地层;②雷口坡组上部的膏岩层;③飞仙关组及下二叠统泥质岩与泥灰岩层;④寒武系和泥盆系下部泥质岩与泥灰岩层。龙门山北段有良好的烃源岩条件,发育了多套有利的生储盖组合和构造圈闭。油气苗显示丰富,横向上分布广泛,纵向上从古生界志留系到中生界侏罗系都有油气显示。主要烃源岩层系为震旦系、下寒武统、下二叠统、上二叠统以及上三叠统。龙门山北段储集层以二叠系茅口组、长兴组生物碎屑灰岩;中、上三叠统嘉陵江组、雷口坡组白云岩及须家河组岩屑石英砂岩为最优。储集空间为裂缝—孔隙型。在诸如矿山梁、天井山、河湾场等地勘探的失败以及江油中坝的成功揭示了这一地区构造的复杂性。应用遥感技术、构造地质学、油气水文地质学等方法技术综合研究龙门山北段构造特征,认为构造条件和区域水动力条件决定了油气保存条件:(1)通过油田水水化学分析,选取划分油田水常用的Na+,Mg2+,Ca2+和Cl-,SO42-,HCO3-及其相互关系作为基本参数研究该地区油田水成因、类型,发现河湾场气田水呈现出低矿化度,高Na+/Cl-特征,属于典型渗入成因水。证明该区由于水文地质开启程度高,地下水自由交替的氧化环境不利于油气藏的保存。勘探事实也表明,在河湾场地区无工业性油气流而产出较多三叠系嘉陵江组、雷口坡组地热水。(2)广元西部龙门山前缘,岩层呈北东—南西向单斜展布,岩层高角度陡倾,往盆地则迅速变缓。遥感地质解译和野外地质调查发现,三叠系由于强烈构造作用出露地表,裂隙发育,嘉陵江组和雷口坡组灰岩溶蚀作用强烈,这为大气降水向下渗透提供了条件。由于没有区域性大断裂的阻隔作用,加之上下非透水性岩层的阻隔,大气降水将在重力作用下受迫迅速向纵深循环,由地形高差形成的渗入成因承压水水动力系统将打破地腹原始的沉积成因水水动力系统,渗入成因水逐渐取代岩石孔隙中的流体(包括水和油气),进而破坏河湾场背斜圈闭内的油气藏。(3)中坝地区西北部,龙门山山前发育走向北东-南西,倾向北西的阻水断层;中坝西南部,发育有走向北东-南西,倾向北西的彰明断层,同样具有封闭性。龙门山山前断层能有效阻隔断层上盘地表水向下盘及盆地内侵入。区内三叠系储集层深埋地腹,不能接受大气降水的渗入,与渗入成因水失去水力联系,因此该地区沉积成因水水动力系统与渗入成因水水动力系统相互独立,互不相干,油气藏不会遭受渗入成因承压水水动力的破坏,因而油气保存条件较好,形成了有效圈闭。再者,位于气田西南部的彰明断层具有封闭性,这为油气在背斜圈闭内聚集成藏提供了重要条件。(4)中坝气田水呈现出高矿化度,CaCl2和Na2SO4水型为基本特征,属于封闭的沉积成因水。封闭、地下水交替停滞的还原环境有利于油气的保存,油气得以聚集成藏。勘探远景区应在远离山前带的地区,勘探层位应以三叠统及上二叠统碳酸盐岩深盆气为主。更多还原

【Abstract】 Longmenshan divided by three major NE-trending faults, i. e, from west to east the Maoxian-Wenchuan fault, Beichuan-Yinxiu fault, Anxian-Guanxian fault into“back-mountain belt”,“front-mountain belt”and“piedmont belt”. They are Songpan-Ganzi fold-belt, Maoxian-Wenchuan ductile shear belt, Longmenshan over- thrust nappy belt and foreland basin of western Sichuan. On the vertical direction of structural-line, Longmenshan divided by HanWang, DuJiangyan (Guanxian), TianQuan.YaAn into“North section”,“Middle section”and“South section”from north to south. Longmenshan thrust belt has four major slip horizons on the longitudinal of it:①coal measure stratum of XuJiahe formation;②a nhydrock and salt beds of Upper LeiKoupo;③mud rock and muddy limestone of FeiXianguan formation and Lower Permian;④mud rock and muddy limestone of Cambrian and Lower Devonian. North section of Longmenshan has a good condition of hydrocarbon source rocks, rocks-reservoir-cap combinations and traps. A lot of oil and gas seepages have been discovered wildly. The hydrocarbon seepage distributed in the sedimentary rocks from Silurian (Paleozoic) to Jurassic (Mesozoic).The main hydrocarbon source rocks are Sinian, Lower Cambrian, Lower Permian, Upper Permian and Upper Triassic. The unsuccessful explorations: KuangShanliang, TianJingshan, HeWanchang and the successful explorations such as ZhongBa disclosed the complexities of stucture in the Longmenshan thrust belts. The most important reservoirs are bioclastic-limestone of MaoKou formation,ChangXing formation in Permian; dolostone of JiaLingjiang formation, LeiKoupo formation; lithic quartz sandstone of XuJiahe formation in Middle and Upper Triassic. The type of the reservoir is fracture-pore.On the basis of Remote Sensing, Structural Geological, Hydrogeological, in combination with the wild-field surveys, the structural characteristics of the north section of Longmenshan were studied systematically, the studied suggested that the hydrocarbon preservation condition is decided by the structure condition:(1):By the analysis of oil field water composition, this paper elected Na+, Mg2+,Ca2+ and Cl- ,S O42-,HCO3- as the essential index to researching the source of the oil field water in HeWanchang and ZhongBa. Results show that the water of HeWangchang gas field have a low salinity but high ratio of Na+/Cl- , it was typical infiltration water. Because of high opening degree of hydrogeology, underground water in HeWanchang was in a well-oxygenated environment that was a bad factor of petroleum. As the explorations has indicated that: there is no oil accumulation in HeWanchang but some geothermal water which produced from JiaLingjiang formation and LeiKoupo formation (Triassic).(2) In the west of Longmenshan thrust belt,HeWanchang, the beds are monocline which have trend of NE-SW, the dip angle of rock is very steep, and it becomes gentle near the basin rapidly. The Remote-Sensing and wild-field surveys indicated that rocks of Triassic are exposed as a result of strenuous tectonic movements, on the other hand, the crack of rocks is well-developed; the corrosion of carbonate rocks of Jialingjiang formation and Leikoupo formation is very intensive. This special geology character will make the ground water seep into ground directly. There is lack of water-tight faults and another important factor: the upper and lower rocks on the beds of Triassic are impermeable, so water can only fluid-though the layers of Triassic which have high permeability, by the huge difference of land height, water of infiltration could take the place of sedimentary-water and destroy the hydrocarbon pool in the traps which on the lower land.(3): In contrast, there are some NE-trending, NW-direction water-tight faults in northwest of ZhongaBa, this type of fault could prevent ground water infiltrating to the depth of the basin. The Triassic layers can not accept the atmospheric water or ground water as these stratum are buried in depth of basin, as a result of that, sedimentary-water system lost connection with infiltration water, these two difference type of hydrodynamic force system are separated by the huge water-tight faults located in the piedmont belt of Longmenshan. Finally, petroleum is saved from destruction that comes from the infiltration water like HeWanchang anticline. Moreover, ZhangMing fault, which located in the southwest of ZhongBa oil field also have fluid-closing ability, this will provide a important condition of accumulating of oil and gas.(4): Oil field water of ZhongBa has a wild difference to the water in HeWanchang: its salinity is high and the water type is sulfate-sodium type or chloride-calcium type. This type of oil field water is a typical sedimentary-water, it represent a reducing and closed environment. Underground water fluid slowly, even ceased in an environment like that, it was favorable for accumulating of oil and gas. The prospect of petroleum in this area will be the trap where far from the“piedmont belt”,the aim reservoirs must be carbonate rocks of Triassic and Upper Permian.更多还原