【作者】 刘迪；

【导师】 张哨楠；

【作者基本信息】 成都理工大学 ， 矿产普查与勘探， 2013， 博士

【摘要】 塔里木盆地广泛分布了寒武系的碳酸盐岩地层,随着近些年来勘探力度的加大,多口钻井钻遇或钻穿寒武系,对寒武系的了解和认识逐渐加深,已有的资料表明,寒武系具备良好的勘探前景。因此,对塔里木盆地寒武系储层特征、储层形成机理进行研究以及对塔里木盆地寒武系进行储层评价对盆地的深层油气勘探具有重大意义。本论文在广泛收集和消化资料的基础上,以碳酸盐岩沉积学入手,结合油层物理学、地质地球化学、储层地质学、成岩作用、测井地质学等相关理论为指导,通过宏观与微观相结合、地质与测井相结合的方法,借助阴极发光显微镜、扫描电镜、同位素分析、X-衍射分析、包裹体、荧光分析、电子探针、岩石物理性质分析、微量元素分析等先进技术手段,对塔里木盆地寒武系白云岩储层特征及成因机理进行了详细研究,取得了如下研究成果：(1)根据白云岩的结构特征,将塔里木盆地寒武系白云岩分为泥微晶白云岩,保留(残余)原始结构的白云岩和晶粒白云岩这三类。其中泥微晶白云岩在寒武系分布最为广泛；(残余)原始结构白云岩主要分布在塔河地区,特别是寒武系台地边缘建隆体上；晶粒自云岩构成了寒武系白云岩的主体,粉-细晶到中-粗晶均有出现,并且寒武系储层也多发育于各类晶粒白云岩中。(2)综合沉积、成岩以及地球化学特征综合分析,建立了塔里木盆地寒武系不同类型白云岩的成因模式：①(准)同生期白云石化作用,产物主要为泥微晶白云岩和(残余)颗粒白云岩,塔北地区和塔中-巴麦地区的准同生白云岩由于沉积环境、岩石类型以及白云石化流体动力学上的的差异,而使其同生期的白云石化模式各异,其中塔中-巴麦地区的白云石化作用多为蒸发泵白云岩化模式,而塔河地区寒武系准同生白云石化则以渗滤回流白云石化模式为主；②埋藏白云石化作用,产物主要为各类晶粒白云岩,不同晶粒大小和晶体形态可以形成于不同的埋藏阶段；白云石化作用有关的流体仍与残余的海水有关；形成模式上,浅埋藏阶段以隐伏回流白云石化作用为主,而中深埋藏阶段的白云化可能与海源孔隙水在地温梯度的作用下发生循环对流有关；③热液白云石化作用在寒武系地层中广泛发育；塔里木盆地的热液白云岩可能与海西晚期(早二叠世末)的伸展运动以及所引起的大量火山活动有关,同时热液白云石化作用受不同性质热液流体的控制而呈现出不同的特色,并深刻的影响着储集空间的发育和分布。(3)寒武系白云岩的成岩作用复杂,复杂的成岩作用对储集空间的发育和破坏也起着明显的控制作用,对储集空间发育有利的成岩作用主要为岩溶作用、白云石化作用和破裂作用以及热液溶蚀作用。胶结作用、压实压溶作用、过白云石化和自生矿物的形成及充填作用显然对储集空间的发育起破坏作用。详细讨论了有机酸溶蚀作用机理,对比碎屑岩储层次生孔隙的形成机理,认为寒武系碳酸盐岩储集空间的的发育和有机酸溶蚀作用没有关系。(4)寒武系白云岩的储集空间主要为晶间孔、晶间溶孔、裂缝和溶蚀孔洞等,目前仅在粉晶白云岩可见有残余晶间孔,而裂缝、溶蚀孔洞则是组成塔里木盆地寒武系不同类型白云岩的主要储集空间类型,相应的构成了以裂缝为主的裂缝型储层类型和以溶蚀孔洞为主的溶蚀孔洞型储层类型及裂缝+溶蚀孔(洞)复合型储层类型。(5)寒武系白云岩储集体的成因主要与溶蚀作用有关,一方面是表生期岩溶作用的影响；另一方面则是埋藏过程中与深部断裂有关的热液溶蚀作用。单纯的白云石化作用并不能形成寒武系白云岩现今的储层规模,因此各类溶蚀作用是白云岩储集体形成的关键。表生岩溶作用形成的储集体主要分布在天山南地区,岩溶作用影响的范围和深度主要受古地貌及断层控制；深部热液的溶蚀作用对未经历风化岩溶改造的白云岩地层具有重要意义,使原本已经逐步失去储集性能的岩石能够形成新的储集空间,热液活动对储层的改造与热流体的来源以及断裂的发育程度密切相关。通过地质和地球化学的综合研究,以及对白云石化成因理论的总结,结合塔里木盆地的地质演化特征,取得了以下创新认识：(1)建立了热液溶蚀和热液白云石同源沉淀的机理通过对寒武系白云岩的微量元素、氧碳同位素、锶同位素和包裹体温度的测试分析,对于热液白云石化的机理进行了详细的讨论,认为热液流体本身在塔北地区不可能引起石灰岩的白云石化,寒武系热液白云石化的物质来源可能就来源于已经存在的白云岩的溶蚀,遭受溶蚀的白云岩再次以异型白云石沉淀在溶蚀孔洞中,同位素和微量元素的演化趋势以及同源性证实了这一解释机理的存在。(2)确定了塔里木盆地两种热液流体来源通过详细的岩相学和地球化学分析发现,塔里木盆地寒武系白云岩中至少存在两种性质迥异的热液流体：一类属于壳源热液流体,热液矿物的O、C、Sr同位素以及微量元素与基质白云岩相差甚远,同时具有极强的侵蚀性,不仅可以形成大量热液交代成因的白云岩而且能够形成大量有效孔隙,对大部分寒武系白云岩储集性能的改善具有重要意义；另一类属于地层热液流体,其O、C、Sr同位素以及微量元素与基质白云岩具有一定相似性,而其流体包体中的均一温度要高于围岩,这类热液流体多与地热增温或是岩浆活动中的热传递有关,真正的深部流体并未混入其中,因此大部分流体仍以地层水为主,只是温度升高,但是侵蚀性较弱,并未能够形成大量新的储集空间。(3)指出了塔里木盆地寒武系有利储层发育的控制因素和勘探方向通过对寒武系储层储集空间发育特征以及储集空间的组合特征和控制因素的研究,指出了寒武系白云岩储层勘探的三个方向：一是天山南地区与岩溶作用的有关的储集体发育区,特别是古潜山发育部位,叠加了岩溶和热液溶蚀的影响,是寒武系白云岩储层最为发育的区域；二是受断裂控制的热液白云岩储层发育区,该类储层具有岩断裂分布的特点,塔河地区塔深1井附近、塔中地区Ⅰ、Ⅱ号断裂带夹持的区域以及巴楚隆起区西部一些断裂带均具有走滑断裂的性质,可以看作是这类储集体勘探的重点区域；三是寒武系台缘相地层以及巴楚隆起区寒武系中盐下碳酸盐岩由于与膏岩层具有良好的储盖匹配关系加之距离寒武系烃源岩较近,具有形成大型油气藏的基础。更多还原

【Abstract】 The Cambrian carbonate rocks are distributed extensively in the Tarim Basin. With the further exploration and several wells drilled across these sediments, more and more materials show the great exploration potential in the Cambrian succession. Understanding the characteristics and the formation mechanism of the reservoirs is, therefore of important significance for both reservoir assessment and petroleum exploration in the deep-burial Cambrian carbonate rocks.Based on the sedimentology, petrophysics, geochemistry, reservoir geology and latest theories about the carbonate diagenesis and well logging, this paper focuses on the features and origin of the Cambrian dolomites reservoirs in Tarim Basin. A number of advanced methods have been used for this study, including photomicrography of thin-section, cathodoluminescence, SEM and BSE, analyses of stable (oxygen/carbon) isotopes and radioactive (strontium) isotopes and trace elements, tests of homogenization temperature (Th) and final ice melting temperature (Tm) of fluid inclusion and physical properties. The following is the main results in this study:(1) Three types of matrix dolomite in Cambrian sediments can be identified based on the rock textures and fabrics:micrite dolomite, relict mimetic dolomite and crystalline dolomite. The micrite dolomite is the most widely distributed in the basin. The relict mimetic dolomite occurs in the carbonate platform margin (build-up) facies in the Tahe area. The crystalline dolomite can be divided into very fine to fine-crystalline dolomite and medium to coarse-crystalline dolomite. Most of the Cambrian carbonate reservoirs are developed in the crystalline dolomite in Tarim Basin.(2) According to the integrated analyses of the sedimentology, diagenesis and geochemistry, three dolomitization models have been established:①penecontemporaneous dolomitization is responsible for the micrite dolomite and relict mimetic dolomite. The dolomitization models between Tahe and Tazhong-Bamai area are different due to the distinctive depositional environments, dolomite types and hydrodynamic forces of dolomitizing fluids. The penecontemporaneous dolomitization in Tahe area is interpreted to the seepage-reflux of Cambrian evaporative seawater as the development of the platform margin. However, the dolomite in Tazhong-Bamai area may be associated with the evaporative pumping dolomitization;②burial dolomitization:the dolomites which are related to this process include various of crystalline dolomites with different crystalline size and shape. The formation of burial dolomite can be subdivided into latent reflux dolomitization during shallow-burial diagenetic stage and geothermal convection dolomitization during the deep-burial diagenetic stage.③hydrothermal dolomitization developed extensively in Cambrian dolomite in Tarim Basin. The hydrothermal activities are closely associated with the stretching tectonic movements and volcanism in the late stage of Early Permian. Meanwhile, different kinds of the hydrothermal fluids, which were first identified in this study, influence the development of the Cambrian dolomite reservoirs.(3) The complicated diagenesis of the Cambrian dolomite plays an important role in the formation and distribution of the reservoirs in study area. The diagenesis which improved the porosity includes the karstification, dolomitization, facturing and hydrothermal dissolution. On the other hand, compaction and pressure-solution, over-dolomitization, authigenic minerals decrease the reservoir space in the Cambrian dolomite. Moreover, the dissolution of organic acid fluid in the dolomite reservoirs can be ruled out due to the detailed research on the mechanism of the organic acid reaction and the comparison with the development of secondary porosity in sandstone.(4) The pore types of the Cambrian dolomite reservoir are composed of intercrystalline, vuggy, facture (channel) and cavity pores. The intercrytalline pores are only discovered in the very fine-crystalline dolomite. In contrast, the vuggy and facture pores are considered as the most important pore types in Cambrian strata. In addition, the main types of the reservoirs also are related to the facture type, vuggy type and complex type reservoirs.(5) The origin of the Cambrian dolomite reservoirs are closely associated with the dissolution, including the karstification during the epidiagentic stages and the hydrothermal dissolution cause by the tectonic activities during burial. The dolomitization is the one of the factors improving the porosity development, but the other dissolutions are more important for the formation of the reservoir space. The karstification mainly occurred in the Tianshannan area. The influence range of the erosion was controlled by the features of paleo-geomorphology and faults in this region. On the other hand, the hydrothermal dissolution was subjected to the sources and degree of saturation of the hot water as well as the attributes and the extent of the faults in study area.The creative points in this doctoral dissertation are summarized as follows:(1) Setting up the mechanism of the hydrothermal dissolution and consanguineous precipitation of the hydrothermal dolomite.Based on the analyses of the trace elements, O/C isotopes, strontium isotopes and homogenization temperature, the detailed formation mechanism of the hydrothermal dolomite has been investigated. Because the hydrothermal fluid was not able to result in the dolomite replacement of limestone, the material source of the hydrothermal dolomitization in Tabei area probably came from the dissolution of the precursor dolomite in the Cambrian successions, in turns the previously dissolved dolomite re-precipitated from the hydrothermal fluid in the vuggy and/or facture pores. Meanwhile, it also could be proved by the similar tendencies of the isotopes and trace elements between the matrix dolomite and saddle dolomite.(2) The sources of the two kinds of hydrothermal fluids have been determined.Two distinctive kinds of hydrothermal fluids has been identified through the specifically petrographic and geochemical study. One is the crustal-source hydrothermal with the different C/O, Sr isotopes and trace elements to the matrix dolomite, and highly undersaturated with the dolomite. This fluid was not only responsible for the origin of saddle dolomite but also for the development of the dissolved pores. It is pretty important for the modification of the deep-burial dolomite reservoirs. The other hydrothermal fluid is associated with the formation water. The geochemical features are similar to the matrix dolomite except for the homogenization temperature in the fluid inclusion. This phenomenon can be interpreted as the thermal transmission during the volcanism, without the influx of hydrothermal fluids. Therefore, the dissolution ability of this hydrothermal fluid was weak and unable to form new porosity in the Cambrian dolomite.(3) The advantageous controlling factors and the new exploration targets of the Cambrian reservoirs have been pointed out.There are three exploration targets of the Cambrian dolomite reservoirs in Tarim Basin:①the reservoirs which are associated with the karstification, especially are influenced by both karst and hydrothermal dissolution in Tianshannan area, are the most vital target of the Cambrian reservoirs in the entire Tarim Basin.②the reservoirs which are developed with the fault-controlled hydrothermal dissolution can be considered as the second beneficial objective for the Cambrian exploration. Because the reservoirs are obviously influenced by the faults, especially the strike-slip and wrench faults, the TS1well region, the area between the Tazhong No.1fault belt and No.2fault belt and the western portion of the Bachu Uplift show greater importance than other areas.③the third target is the dolomite reservoirs located in the Bachu area, because they are near to the Cambrian source rock and the evaporative rocks, which can form the good cap, develop extensively in this region.更多还原