【作者】 翟普强；

【导师】 陈红汉；

【作者基本信息】 中国地质大学 ， 矿产普查与勘探， 2013， 博士

【摘要】 琼东南盆地是南海北部陆缘的富油气盆地,同时也是一个典型的高温高压盆地。早期多幕的裂陷活动叠加晚期的快速沉积和沉降,造成了该盆地独特的温压环境和埋藏条件,油气的运移聚集过程非常复杂。该盆地自从在环崖南凹陷地区发现YC13-1、YC13-4和YC13-6气田以来,虽然陆续在其周缘和盆地东部地区发现了一些气藏和含气构造,但至今尚未有新的重大突破,其根本原因可能在于对该盆地超压环境下的油气富集规律,尤其是超压系统分布与油气聚集的关系还了解得不够。异常超压的发育不仅会造成盖层的水力破裂,致使早期聚集的油气发生散失,还会引起天然气运移相态和动力的改变,主要表现为天然气以水溶相运移致使盖层水力封闭失效而无法成藏,因此水溶气只有析出为游离气才能聚集成藏。由此可见,超压系统边缘或内部地层压力释放带,即泄压带,是油气聚集的有利场所。本文即是从泄压带发育的微观与宏观地质特征入手,根据泄压带的微观成岩响应特征和宏观测井响应特征来识别和划分泄压带,并综合运用地震速度超压预测和盆地模拟技术,研究泄压带的宏观分布和演化特征,在此基础上进一步探讨泄压带发育与天然气成藏的耦合关系,建立一个考虑了水溶气离溶聚集成藏的天然气成藏模式。本文的主要研究内容和取得的认识有以下几点：(1)根据储层砂岩中成岩作用所揭示的微观流体活动信息来识别泄压带。通过薄片观察和阴极发光观察,发现崖城地区硅质胶结现象非常普遍,可能发生多期胶结,主要为裂纹充填胶结和石英加大,且石英加大更加明显,在YC13-1部位主要分布于陵水组和崖城组内,在YC35-1部位则主要位于黄流组二段底部,且发育石英加大段的储层厚度基本在200m以上。沿2号断裂分布的钻井中虽然也发现了大量石英加大现象,但相对于西部而言,石英加大发育的层段都比较薄,主要位于陵水组和三亚组内。石英加大发育的层段,储层物性(孔隙度和渗透率)普遍很好,并且西部地区要优于东部地区,镜下观察到该现象主要是由碎屑颗粒发生溶蚀造成的。大量的石英加大和溶蚀孔隙发育,反映该部位曾发生过大规模的酸性热流体运移,同时也指示了泄压带的所在,即水溶气大量离溶的区带。另外,在西部地区较深部位的石英加大发育层段,常见有钾长石的钠长石化现象,交代的钠长石呈加大边状分布,可以指示有关高温流体运移的信息。粘土矿物异常转变的深度与泄压带的流体排放作用有着密切联系,也可指示泄压带的存在。应用有机质成熟度指标还可以识别泄压带附近的短期热异常。(2)琼东南盆地的压力系统结构可划分为三种类型：常压,传导型超压和复合型超压,相应地可识别出四种泄压带类型。常压型压力系统又可分为正常压实常压段和速度稳定常压段,后者又主要分布于3号断裂以南陆架区的莺黄组底部～梅山组,其厚度向陆坡方向呈减薄趋势。传导型超压系统在盆地西部主要沿1号断裂带分布,在中央坳陷区主要分布在超压系统边缘；复合型超压系统在中央坳陷广泛存在。Ⅰ型泄压带仅在盆地西部边缘沿1号断裂带分布,一般位于莺黄组底部,非有利油气聚集部位。Ⅱ型泄压带也是沿1号断裂带分布,是环崖南地区最为发育的类型,储层砂岩中发育大量的硅质胶结,指示其为有利的油气聚集部位。Ⅲ型泄压带处在深部复合型超压系统顶面,而Ⅳ型泄压带则处于深部超压系统的内部,发育大量石英次生加大说明其也是有利的油气运移部位。(3)应用地震层速度资料预测了全区超压系统的分布,该方法需考虑崖南地区普遍存在的速度稳定段对压力预测结果的影响,研究中采取分区分段建立正常压实趋势的方法对其进行了校正。预测结果显示,中央坳陷带深部沿陆坡带发育有多个成“串珠状”分布的超压中心,但相互之间并不孤立,而是逐渐过渡并连成一片,反映中央坳陷带地区整体发育一个超压系统。超压发育具有陆坡区强陆架区弱、西部强东部弱和向东传递趋势,反映盆地晚期加速沉降阶段陆坡体系快速向南推进和莺歌海盆地的超压传递对该盆地的压力分布格局有重要影响。超压顶面埋深在乐东—陵水凹陷主要位于2250～2500m(莺歌海组内)以下,在松南凹陷位于2500m(黄流组内)以下,在宝岛凹陷位于3500m(梅山—三亚组)以下,在长昌凹陷主要位于4500m(三亚组)以下。(4)应用盆地模拟方法研究了全区古压力场的演化特征,该方法需进行大量的模型调研和参数统计,数值模拟结果可用现今超压预测结果进行约束。模拟结果表明,中央坳陷带在崖城组晚期就已形成了乐东、陵水、宝岛和长吕四个强超压中心,且各具一定的孤立性,裂陷期内可大致分为东部和西部西个超压系统；陵二段至陵一段末期超压整体发育较强,之后经历了儿轮增压～泄压旋回,大约10.5Ma以来逐渐演变为西部一个超压系统,形成以乐东凹陷为最强超压中心并呈自西向东传递的趋势。盆地西部地区大致经历了三个半压力旋回,现今超压是地质历史时期最强的且仍呈增压趋势：盆地东部地区大致经历了三个压力旋回,现今整体仍呈泄压趋势。盆地经历的最早泄压发生在崖城组末期至陵三段末期,且西部更明显；第二次泄压发生在陵一段末期至三亚二段末期,泄压较强；第三次泄压发生在梅山组末期,为大幅泄压：第四次泄压发生在黄流组时期,为小幅泄压,并且盆地东部的泄压趋势一直维持至今。(5)根据现今超压预测和压力场演化模拟的结果,分析了泄压带的时空分布特征。现今中央坳陷带的超压顶面总体向南北斜坡带不断加深,且向北坡(陆坡带)方向发生偏移,说明北坡发育的断裂-砂体输导系统的泄压性能更好,因而北坡的油气聚集条件更优,是天然气运移的优势方向。模拟结果显示,在超压系统演化的过程中,松涛凸起的南坡、陵水低凸起、松南低凸起、陵南低凸起东部和北碓凸起等部位始终位于超压系统边缘或内部相对低势区,即要泄压带分布地区,且松涛凸起的南坡、陵水低凸起和松南低凸起的成藏条件更优。(6)根据中央坳陷带主力烃源岩的成熟史和生排烃史模拟,结合流体包裹体充注史分析,确定大然气的主成藏期。由于10.5Ma处在中央坳陷带斜坡区陵水组烃源岩大量生烃时期,此时崖城组烃源岩仍在大量生烃,深部的地层水在高温环境下可溶解大量的大然气；又该时期处在晚期泄压阶段,超压系统能量的释放必然伴随大量的物质迁移和温度降低,深部的水溶气沿泄压带运移到浅部并发生析离,从而在有利部位聚集成藏。所以10.5Ma以来应该是天然气的主成藏期,该时期比流体包裹体方法确定的充注时期稍早,是比较可信的。(7)分析泄压带演化与天然气成藏的耦合关系。泄压带内的天然气离溶成藏主要取决于压力、温度和溶解气量,必须满足两个条件：溶解气量足够多,溶解度变化量足够大。有利的泄压带应该是既能沟通深部水溶气和浅部储层,又能造成温压条件显著变化的区带。相对而言,Ⅱ型泄压带成藏条件最优,既有断裂沟通深部水溶气和浅部储层,又有温压条件的显著变化,因而流体运移最活跃。Ⅲ型泄压带次之,但分布最广。由于盆地西部10.5Ma以来处于不断增压的环境,泄压带在平面上变化比较宽缓,相同深度处甲烷溶解度变化很小,不利于水溶气离溶成藏,并且压力不断增强还会导致水溶气析出深度变浅。相对而言,盆地东部10.5Ma以来处于持续泄压的环境,在凸起边缘的断裂和砂体连通部位,压力梯度变化较大,相同深度处甲烷溶解度保持一定差值或差值不断增大,这对水溶气析出比较有利。更多还原

【Abstract】 Qiongdongnan basin is rich in petroleum resources which located in northern South China Sea and typically characterized by high temperature and high pressure. The Superposition of the multi-episodic rifting events occured in the early stage and the rapid deposition and structural subsidence took place at the later stage led to a unique environment of temperature and pressure, and so the burial history. The processes of petroleum migration and accumulation are quite complicated. There has been no breakthroughs for a long time in the exploration of Qiongdongnan basin since the findings of YC13-1gas feild, YC13-4and YC13-6gas reservoir around the Yanan depression, although some gas beddings and gas-bearing structures were found around the Yanan depression or in the eastern basin. The primary cause may be the less understanding of the law of petroleum accumulation under overpressureed environment, especially the relationship between the distribution of hydrocarbon and the overpressure system. The development of overpressure would not only cause hydraulic ruptures in the cap rocks which leading to the loss of oil and gas accumulated in the early stage, but also change the migration phases and dynamics of the natural gas. Under high pressure and high temperature conditions, the gas would migrate in water-soluble phase and come to the failure of hydraulic sealing in caprocks. Thus, only by degasification can the water-soluble gas accumulate.Thus it can be seen, the zones with rapid pressure decreasing which is also called pressure discharging zones, locating at the edge or inside of the overpressure system, were the favourable sites for hydrocarbon accumulation. This study began with the microcosmic and macroscopic geology characteristics of the pressure discharging zone, distinguished and divided the discharging zone based on the diagenetic features and logging response, studied the macroscopic distribution and evolution by integrated application of overpressure prediction and basin modeling technology, furtherly discussed the coupling relationship between pressure discharging zone and hydrocarbon accumulation, then established a petroleum accumulation model which considered the degassing and accumulation of water-soluble gas and with a certain predictive feature. The main research contents and realizations achieved in this article are as follows:(1) Identify the pressure discharging zone according to the microscope information of fluid activities revealed by the diagenesis occured in the sandstone reservoir. By observation of thin sections and cathdoluminescence, it was found that the siliceous cementation phenomenon were very common in the Yacheng area and there may exist two stage of cementation, the first stage was mainly the cementation fillings in cracks, the second stage was mainly the quartz overgrowth which was more obvious than the first stage. The observed quartz overgrowth at the YC13-1structure was mainly in the Lingshui and Yacheng formations while at the YC35-1structure it mainly located at the bottom of the second member of Huangliu formation, the thickness of reservoir sections with quartz overgrowth were usually more than200m. Though the phenomenon of quartz overgrowth were also found in the wells distributed along the No.2fault, the setions were much thinner than that in west areas and mainly situated in the Lingshui and Sanya formation. The sections with quartz overgrowth phenomenon usually had good reservoir physical property (porosity and permeability) and were more common in western areas. By observation under microscope, we can see that the high porosity was mainly caused by the dissolution of detrital grains. Massive development of the quartz overgrowth and the dissolution pore usually means massive hot acid fluid flow and indicates the pressure discharging zone where the gas degassing occurred and large amount of water-soluble gas accumulated.In addition, the albitization of K-feldspar were also observed to frequently happen in the quartz overgrowth sections in the deeper layers, and the albite formed by metasomatism usually take a shape of thick overgrowth around the K-feldspar. Because this phenomenon was suggested only appear in the late stage of diagenesis, it may indicate the migration of high temperature fluid. The abnormal changes of clay minerals can also indicate the pressure discharging zone, it was usually caused by fluid flow near the pressure discharging zone. The maturity indictors of organic mater can also be used to identify the short-term thermal anomaly near the pressure discharging zone.(2) The structure of pressure system in Qiongdongnan basin can be divided into three types: normal pressure, transmission overpressure and compound overpressure, accordingly, four types of pressure discharging zones were indentified. The normal pressure system can be subdivided into a normal compaction section and a stable velocity section, the latter one mainly distributed from the bottom of Yinggehai-huangliu formation to the Meishan formation in the shelf area from the northen of No.3fault, thinning in the direction of continental slope. The transmission overpressure system distributed along the No.1fault zone in the western area and around the overpressure system in the central depression zone. The compound overpressure system exists widely in the central depression. The type I pressure discharging zone distributed only along the No.1fault zone and generally located in the bottom of the Ying-huang formaion, this type was not suitable for hydrocarbon accumulation for its bad conditions. The type Ⅱ pressure discharging zone also distributed along the No.1fault zone, and acted as the most important one among the four types around the Yanan area. Large amount of siliceous cementation were found in the reservoir sandstone, indicating that type Ⅱ was more favorable for petroleum accumulation. The type Ⅲ pressure discharging zone which located on top of the deep compound overpressure system was very common in the central depression. The type Ⅳ pressure discharging zone was located inside the deep overpressure system, great amount of quartz overgrowth developed locally in some sections inside the overpressure system, indicating that this type was also favorable for petroleum accumulation but not a primary type.(3) The distribution of the overpressure system in Qiongdongnan basin was predicted by integrated application of the seismic velocity data and pressure measurements, on the basis of logging analysis. The influence of the stable velocity section which widely developed in the Yanan area should first be calibrated. According to the calculation, many beaded overpressure centers along the continental slope had developed in the deep Central depression, they were not isolated but gradually transited into a huge overpressure system. The overpressure system were stronger along the continental slope and weaker on the continental shelf, and were stronger in the west than in the east, this may suggest that the quickly southward movement of the continental slope during the late accelerated deposition stage and the overpressure transmitting from the Yinggehai basin had significant influence on the present overpressure pattern and its evolution. The top of overpressure system in the Ledong-Lingshui sags were mainly below the depth of2250～2500m (within Yinggehai formation), while in the Songnan sag it was mainly below2500m (within Huangliu formation), in the Baodao sag it was mainly below2500m (within Meishan and Sanya formation), and in the Changchang sag it was mainly below4500m (within Sanya formation).(4) The evolution characteristics of the paleo-pressure field were studied by the application of numerical simulation methods. A lot of work referring to the model research and parametric statistics should be taken first. According to modeled results, the overpressre system in the central depression zone had already formed at the late stage of Yacheng formation, there were four overpressure centers located in the Ledong, Lingshui, Baodao and Changchang sags, with a certain isolation from each other. The overpressure systems got much strong during the stage of the second member and the first member of Lingshui Formation, then after several cycles of pressure evolution, a huge overpressure system much stronger than ever gradually formed in the west basin, with a strongest overpressure center in the Ledong sag and a trend transmitting from the west to the east. The earliest pressure discharging event occurred during the late stage of Yacheng formation and the late stage of the third member of Lingshui formation, and it’s more obvious in west. The second pressure discharging event, which was much stronger, happened during the late stage of the first member of Lingshui formation and the late stage of the second member of Sanya formation. The third pressure discharging event, much stronger than ever, took place in late stage of Meishan formation. The fourth pressure discharging event, which was much weaker, happened during the stage of Huangliu formation, and continued to the current time in the eastern. (5) The spatial and temporal distribution of the pressure discharging zones were analyzed based on the prediction of current overpressure system and the modeled evolution of paleao geopressure field. According to the prediction results, the top surface of current overpressure system in the central depression just deepens toward both the northern and southern slopes, and the overpressure changes much faster in northern slope, indicating that pressure discharging condition in the north slope was much better, as well as the petroleum accumulation condition. This should be related to the contribution of fault-sand transmitting systems developed on the northern slop. According to the modeling results, several sites remained at the edge of the overpressure system during the evolution of overpressure system, they were Songnan low uplift, Beidiao uplift, the easterm of Lingnan low uplift, the southern of Yabei area and the southern slope of Songtao uplift, these sites should be the potential pressure discharging zones.(6) The primary stage of natural gas accumulation could be synthetically determined by modeling of the maturation history of organic matter, the hydrocarbon generation and expulsion histories of main source rocks, combined with the charging events revealed by fluid inclusion, it’s concluded that the primary gas accumulation stage should since from10.5Ma. On the one hand,10.5Ma was during the peak gas generation stage of the source rocks in Lingshui formation on the slops of the Central Depression Zone, while the source rocks in Yacheng formation still generated massive hydrocarbon, thus massive gas could dissolved in the deep formation water in the high temperatures and high pressure environment. On the other hand,10.5Ma was at the beginning of the forth pressure discharging event, energy release of the overpressure system should cause a large number of mass transfer and temperature decreases, this was propitious to the segregations of deep water soluble gas migrating along the pressure discharging zone. In addition,10.5Ma was a little earlier than the hydrocarbon charging period determined by the fluid inclusion, which seems reasonable.(7) Analyze the coupling realationship between the evolution of pressure discharging zones and the gas accumulation. Accumulation of water soluble gas in the pressure discharging zones was totally determined by pressure, temperature and the amount of dissolved gas, whether enough amount of dissolved gas and enough changes in solubility were very important. The favorable discharging zones should be those not only link the deep water soluble gas and the shallow reservoir, but also cause significant changes in the temperature and pressure conditions. Relatively, the accumulation conditions of type II discharging zone was optimal, thus had more active fluid activity. The favorable sites of type III discharging zone were those near the Lingshui low uplift and the northern slop of Baodao sag, along the boundary faults and close to the normal pressure zone.更多还原