【摘要】：2012年中海石油（中國）有限公司湛江分公司在西沙石島設(shè)計鉆探了“西科1井”，設(shè)計鉆井深度1350m，至2013年底鉆取巖心長度為748m，取芯率78.4%。本文依托國家科技重大專項(xiàng)中“新近紀(jì)以來古氣候與古環(huán)境的地球化學(xué)示蹤”專題，以南海西沙石島“西科1井”鉆井為主要研究對象，通過對鉆井巖心的礦物相分析、主量元素、微量元素的地球化學(xué)特征分析，，結(jié)合已有的4口鉆井巖心研究成果，劃分各井地層及沉積相；利用獲得的沉積相、地球化學(xué)等數(shù)據(jù)對西沙生物礁巖心的成巖作用進(jìn)行分析，重點(diǎn)討論后期白云石化作用成因模式；結(jié)合南海古海洋事件，探討生物礁形成演化對古環(huán)境的響應(yīng)，為南海生物礁碳酸鹽層油氣資源評價與開發(fā)提供科學(xué)依據(jù)，并取得以下主要結(jié)論或認(rèn)識。 西科1井全新-更新統(tǒng)、上新統(tǒng)、上中新統(tǒng)底界分別為216m、373m和577m，結(jié)合礦物學(xué)特征變化并與西沙鄰近生物礁鉆井對比認(rèn)為井深35.4m處附近是更新世與全新世的分界。鉆井巖心主要以生物礁灰?guī)r、生物碎屑灰?guī)r、生物碎屑白云巖、生物礁白云巖等為主；識別出生物礁格架相、生物碎屑灘相、瀉湖相、灰沙島相和礁坪相；結(jié)構(gòu)組分包括生物格架、泥晶、亮晶、粒屑（顆粒）；常見結(jié)構(gòu)類型有生物格架結(jié)構(gòu)、粘結(jié)結(jié)構(gòu)、障積結(jié)構(gòu)等。 西科1井巖心礦物相類型主要有低鎂方解石相（即方解石相）、高鎂方解石相、文石相、白云石相和粘土礦物相；文石、高鎂方解石主要分布鉆井頂部位置；181.25m井深處開始出現(xiàn)白云石；366.6m及387m附近發(fā)現(xiàn)粘土礦物。定量分析結(jié)果顯示，西科1井發(fā)育5套白云巖層。分別為上上新統(tǒng)白云巖（層5）、上中新統(tǒng)白云巖（層2、3和4）和中中新統(tǒng)白云巖（層1）。 碳酸鹽巖鉆井巖心Ca、Mg、Sr、P等元素含量具明顯的分段性，Ca、Mg元素含量在個別層段相關(guān)性較好；P主要來自鳥糞層，在表層出現(xiàn)明顯富集，以尖峰的形式出現(xiàn)的P2O5高含量，指示灰砂島相沉積；Sr元素含量在頂部及中部出現(xiàn)文石礦物層段波動較大，隨著埋藏深度增加，在白云巖層段穩(wěn)定在100~200μg/g之間；Ga、Ba、Hf、Zr四個元素分布特征相似，并未出現(xiàn)在白云石段的富集現(xiàn)象。 西沙生物礁碳酸鹽巖礦物的形成主要受生物礁發(fā)育及演化時所處海洋環(huán)境條件控制，如形成時的壓力和溫度、所處海水中的地球化學(xué)特征（如Sr、Mg和Ca元素含量等）、后期的埋深成巖作用等。古海平面的下降，使西沙生物礁易發(fā)育暴露風(fēng)化剝蝕面，導(dǎo)致礦物相之間的進(jìn)一步相互轉(zhuǎn)化。結(jié)合鄰近鉆井巖心的對比分析可知，上新世北極冰蓋的形成、晚中新世米辛尼亞（Messinian）事件和中中新世南極冰蓋擴(kuò)展事件所造成的海平面變化均對礁體的發(fā)育產(chǎn)生了影響。生物礁碳酸鹽巖的白云石化作用，主要有蒸發(fā)瀉湖滲透回流作用模式、混合水模式和埋藏壓實(shí)條件下的成巖作用三種形式。
[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.
【學(xué)位授予單位】：中國海洋大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2014
【分類號】：P736.3;P585

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