南海西沙石岛西科1井岩心矿物学特征及成岩作用分析

发布时间：2018-08-04 08:25

【摘要】：2012年中海石油（中国）有限公司湛江分公司在西沙石岛设计钻探了“西科1井”，设计钻井深度1350m，至2013年底钻取岩心长度为748m，取芯率78.4%。本文依托国家科技重大专项中“新近纪以来古气候与古环境的地球化学示踪”专题，以南海西沙石岛“西科1井”钻井为主要研究对象，通过对钻井岩心的矿物相分析、主量元素、微量元素的地球化学特征分析，，结合已有的4口钻井岩心研究成果，划分各井地层及沉积相；利用获得的沉积相、地球化学等数据对西沙生物礁岩心的成岩作用进行分析，重点讨论后期白云石化作用成因模式；结合南海古海洋事件，探讨生物礁形成演化对古环境的响应，为南海生物礁碳酸盐层油气资源评价与开发提供科学依据，并取得以下主要结论或认识。西科1井全新-更新统、上新统、上中新统底界分别为216m、373m和577m，结合矿物学特征变化并与西沙邻近生物礁钻井对比认为井深35.4m处附近是更新世与全新世的分界。钻井岩心主要以生物礁灰岩、生物碎屑灰岩、生物碎屑白云岩、生物礁白云岩等为主；识别出生物礁格架相、生物碎屑滩相、泻湖相、灰沙岛相和礁坪相；结构组分包括生物格架、泥晶、亮晶、粒屑（颗粒）；常见结构类型有生物格架结构、粘结结构、障积结构等。西科1井岩心矿物相类型主要有低镁方解石相（即方解石相）、高镁方解石相、文石相、白云石相和粘土矿物相；文石、高镁方解石主要分布钻井顶部位置；181.25m井深处开始出现白云石；366.6m及387m附近发现粘土矿物。定量分析结果显示，西科1井发育5套白云岩层。分别为上上新统白云岩（层5）、上中新统白云岩（层2、3和4）和中中新统白云岩（层1）。碳酸盐岩钻井岩心Ca、Mg、Sr、P等元素含量具明显的分段性，Ca、Mg元素含量在个别层段相关性较好；P主要来自鸟粪层，在表层出现明显富集，以尖峰的形式出现的P2O5高含量，指示灰砂岛相沉积；Sr元素含量在顶部及中部出现文石矿物层段波动较大，随着埋藏深度增加，在白云岩层段稳定在100~200μg/g之间；Ga、Ba、Hf、Zr四个元素分布特征相似，并未出现在白云石段的富集现象。西沙生物礁碳酸盐岩矿物的形成主要受生物礁发育及演化时所处海洋环境条件控制，如形成时的压力和温度、所处海水中的地球化学特征（如Sr、Mg和Ca元素含量等）、后期的埋深成岩作用等。古海平面的下降，使西沙生物礁易发育暴露风化剥蚀面，导致矿物相之间的进一步相互转化。结合邻近钻井岩心的对比分析可知，上新世北极冰盖的形成、晚中新世米辛尼亚（Messinian）事件和中中新世南极冰盖扩展事件所造成的海平面变化均对礁体的发育产生了影响。生物礁碳酸盐岩的白云石化作用，主要有蒸发泻湖渗透回流作用模式、混合水模式和埋藏压实条件下的成岩作用三种形式。
[Abstract]:In 2012, CNOOC (China) Co., Ltd. Zhanjiang Branch designed and drilled "Xico 1 well" in Xisha Shidao. The designed drilling depth was 1350m. By the end of 2013, the length of core drilled was 748m, and the core extraction rate was 78.4m. Based on the special topic of "Geochemical tracing of paleoclimate and paleoenvironment since Neogene" in the major national scientific and technological project, this paper takes the drilling of Xice-1 well in Xisha Island, South China Sea, as the main research object, and analyzes the mineral facies of the drilling core. The geochemical characteristics of principal elements and trace elements are analyzed, combined with the existing research results of four drilling cores, the strata and sedimentary facies of each well are divided, and the obtained sedimentary facies are used. The diagenesis of Xisha reef core is analyzed by geochemical data, and the genetic model of dolomitization in the late stage is discussed, and the response of reef formation and evolution to the paleoenvironment is discussed in the light of the South China Sea paleoceanic events. It provides a scientific basis for the evaluation and development of hydrocarbon resources in the carbonate beds of the reefs in the South China Sea, and obtains the following main conclusions or understandings. Xice-1 well is brand-new Pleistocene, the bottom boundary of Pliocene is 216mg ~ 373m and Pliocene is 577m, respectively. Combined with mineralogical change and contrast with Xisha adjacent reef drilling, it is concluded that the boundary between Pleistocene and Holocene is near the depth of well 35.4 m. The core of drilling is mainly composed of reef limestone, bioclastic dolomite, reef dolomite and so on, and the reef framework facies, bioclastic beach facies, lagoon facies, ash sand island facies and reef flat facies are identified. The structural components include biological lattice, mud crystal, bright crystal, particle (particle), and the common structural types are biological lattice structure, bond structure, barrier structure and so on. The core mineral facies of well Xice1 are mainly composed of low magnesium calcite facies (i.e. calcite facies), high magnesium calcite facies, dolomite facies and clay mineral facies, dolomite, high magnesium calcite mainly distributed at the top of drilling. Clay minerals began to appear in the depth of 181.25m in the vicinity of dolomite 366.6m and 387m. The quantitative analysis results show that 5 sets of dolomite formations are developed in Xice1 well. They are Pliocene dolomite (layer 5), Pliocene dolomite (layer 2, 3 and 4) and Miocene dolomite (layer 1), respectively. In carbonate drilling cores, the contents of Ca, mg, Sr, P and other elements in the core of carbonate drilling have obvious piecewise correlation. The correlation of mg content in some layers is good. The content of P2O5 is high in the form of spikes, and mainly comes from the guano layer, which is enriched obviously in the surface layer, and appears in the form of peak. The results indicate that the content of Sr elements in the silt island sedimentary facies fluctuates greatly in the top and middle part of the sedimentary facies. With the increase of burial depth, the distribution characteristics of the four elements in the dolomite formation are similar between 100 ~ 200 渭 g / g and 100 ~ 200 渭 g / g, respectively, and the distribution characteristics of the four elements are similar. There is no enrichment in dolomite section. The formation of carbonate rock minerals in Xisha reefs is mainly controlled by the marine environmental conditions in which the reefs are developed and evolved, such as the pressure and temperature at the time of formation. The geochemical characteristics of the sea water (such as the contents of Sr, mg and Ca), the late buried diagenesis and so on. The decline of paleo sea level makes Xisha reef easy to be exposed to weathering and denudation, which leads to further mutual transformation of mineral facies. Based on the comparative analysis of adjacent drilling cores, it can be seen that the formation of Pliocene Arctic ice sheet, the late Miocene Mihinia (Messinian) event and the Miocene Antarctic ice sheet extension event all have an effect on the reef development. The dolomitization of reef carbonate rocks mainly consists of three types: evaporative lagoon permeation reflux model mixed water model and diagenesis under buried compaction.
【学位授予单位】：中国海洋大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：P736.3;P585

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