海洋地质与环境重点实验室知识库

白云凹陷位于南海北部的珠江口盆地，是我国天然气水合物研究的重点区域。该地区的天然气水合物与世界典型区域发现的水合物之间存在一定相似规律，但是相比较而言其差异性更为显著。受地质构造、沉积环境等方面的影响，白云凹陷神狐海域峡谷富集区钻遇的水合物样品多分布在细粒泥质、粉砂质沉积物中，其饱和度值与国际典型水合物分布区相比较低。根据已有的研究表明，钻探区不同站位发现的水合物气源特征、饱和度与分布、水合物层厚度均存在差异性。研究区不同成因类型水合物形成机制、成藏富集规律还不明确。开展生烃数值模拟工作，不仅能够对水合物饱和度及分布进行有效预测，还能够进一步探讨复杂成因类型的天然气水合物赋存成藏模式，并对今后无井地区的天然气水合物研究具有一定的指示意义。

本文以不同类型烃源岩生烃和天然气水合物饱和度及其分布研究为核心内容，借鉴前人水合物生烃数值模拟研究经验，结合地震数据资料、水合物钻井和油气钻井的岩心及测井数据、区域地质构造演化及热演化、烃源岩分布及地化指标等前人基础研究资料，建立研究区二维地质模型、温度模型、生烃模型，通过对不同烃源岩分布、不同流体运移方式、不同气源类型、不同饱和度分布的水合物形成机制开展模拟研究工作，并总结概况了研究区现今水合物成藏模式。

现今地层温度场模拟结果表明，白云凹陷神狐海域现今地层温度分布范围在0- 400 ℃，并且在W19、W17站位附近存在高温度异常，可能与深部流体活动性有关。烃源岩有机质成熟度、生烃率等模拟结果表明文昌组、恩平组、珠海组地层成熟度较高，均属于热生烃地层。而珠江组以上地层有机质成熟度较低，属于生物生烃地层。结合模拟计算的温度剖面以及生烃率剖面，进一步划分出生物生烃地层深度范围在海底以下1500 m的范围内，热生烃地层深度范围在2300 -6000 mbsf之间。此外，烃源岩生烃量的模拟计算研究表明，由于有机质丰度较小，生物生烃与热生烃产气量相比，存在数十倍差异。烃源岩产气量在横向展布也存在变化，推测原因是剖面西南侧靠近白云主洼沉降中心，其有机质丰度大于东北侧。

流体运移模拟结果表明，在神狐海域存在多种流体运移方式，沿低渗透率地层运移的Darcy Path运移方式分布最为广泛，珠海组地层存在局部沿高渗透率地层侧向运移的Flow Path运移方式，而Breakthrough和断层两种运移方式控制着深部流体向上运移。生物成因气靠浮力和扩散等作用沿峡谷侧壁在浅层运移；热成因气受基底隆起导致的倾斜地层和砂质储层分布的影响，主要在深部侧向运移至LW3油气田附近，少部分通过断层和背斜、穹窿等构造垂向运移至水合物稳定带底界下方。

水合物稳定带模拟结果表明，模拟计算的水合物稳定带底界位置与其它方法计算的稳定带底界位置基本吻合。SH2处模拟的稳定带厚度约为225 m，SH5处模拟的稳定带厚度约为180 m，W19处模拟的稳定带厚度约为168 m，W17处模拟的稳定带厚度约为241 m，与前人研究结果吻合。

水合物饱和度及分布模拟结果表明，神狐海域稳定带上方、分布不连续的水合物层，其形成主要与有机质丰度相对较低的生物生烃有关，并且饱和度值相对较低。当热成因气对水合物形成具有一定贡献时，才会形成相对高饱和度水合物富集，而且较长的烃类气体释放时间对形成高饱和度水合物富集具有重要意义。不同峡谷条带上水合物气源类型也存在差异性，SH2站位水合物的形成主要受生物成因气的影响，而W19、W17站位水合物形成与混合气有关，且热成因气贡献很大。

对研究区复杂成因类型的天然气水合物形成机制及成藏模式探讨表明，水合物富集成藏受构造活动、地层沉降、温度分布、烃源岩生烃、流体运移、水合物生成等因素共同影响。研究区在新世纪以前所处湖相沉积环境，新世纪以来所处半深海环境，沉积物多为细粒沉积物。在这种低渗透率地层中，生物成因气靠浮力、扩散等作用在浅层运移，而热成因气受基底隆起导致的地层倾斜以及珠海组局部高渗透率地层展布的影响，在深部侧向运移。同时受构造活动，以及深部背斜、穹窿处存在气体超压的影响，深部热成因气可以向上运移至稳定带底界下方。神狐海域峡谷富集区水合物分布多样性与不同成因类型的气体供应有关，峡谷西南侧靠近白云主洼，生物成因气丰度大，但构造活动较少，深部热成因气贡献有限，因此西南侧的水合物成因类型为生物成因。而峡谷东北侧远离白云主洼，生物成因气丰度较小，受基底隆起影响，断裂体系发育，深部热成因气对水合物的形成影响显著，因此东北侧的水合物成因类型为热成因气具有一定贡献的混合成因。

Baiyun sag is located in the northern margin of the South China Sea, which is the key area of gas hydrate research in China. The natural gas hydrate in this area is similar to that found in typical regions of the world, but the difference is more significant. Due to the influence of geological structure and sedimentary environment, most of the hydrate samples drilled in Shenhu sea area of Baiyun sag are distributed in fine-grained muddy and silty sediments, and their saturation value is lower than that of typical hydrate distribution areas in the world. According to the existing research, the hydrate gas source characteristics, saturation and distribution, hydrate layer thickness found at different stations in the drilling area are different. The formation mechanism and accumulation rule of hydrate of different genetic types in the study area are not clear. Carrying out hydrocarbon generation numerical simulation can not only effectively predict hydrate saturation and distribution, but also further explore the occurrence and accumulation mode of complex genetic types of natural gas hydrate, and provide some help for the future study of natural gas hydrate in the area without wells.

This paper focuses on the study of hydrocarbon generation and gas hydrate saturation and distribution of different types of source rocks, and draws on the previous experience in numerical simulation of hydrate hydrocarbon generation. Combining with seismic data, core and logging data of hydrate drilling and oil-gas drilling, regional geological structure evolution and thermal evolution, source rock distribution and geochemical indicators and other previous basic research data. Established two-dimensional geological model, temperature model and hydrocarbon generation model in the study area. Based on the simulation of hydrate formation mechanism of different source rock distribution, different fluid migration mode, different gas source types and different saturation distribution, the current hydrate accumulation model in the study area is summarized.

    The simulation results of present formation temperature field show that the present formation temperature distribution range of Shenhu sea area in Baiyun Depression is 0-400 ℃, and there are high temperature anomalies near stations W19 and W17, which may be related to the deep fluid activity. The simulation results of organic matter maturity and hydrocarbon generation rate of source rocks show that the strata of Wenchang Formation, Enping formation and Zhuhai Formation are of high maturity and belong to thermal hydrocarbon generation strata. However, the maturity of organic matter above Zhujiang Formation is relatively low, which belongs to biogenic hydrocarbon generation formation. Combining with the simulated temperature profile and hydrocarbon generation rate profile, it is further divided that the depth range of biological hydrocarbon generation formation is within 1500 m below the sea floor, and the depth range of thermal hydrocarbon generation formation is between 2300-6000 mbsf. In addition, the simulation calculation of hydrocarbon generation amount of source rock shows that there are dozens of times differences between biogenic and thermal hydrocarbon generation due to the small abundance of organic matter. The gas production of the source rock also changes in the horizontal distribution, presumably because the southwest side of the profile is close to the settlement center of Baiyun main depression, and its organic matter abundance is greater than the northeast side.

The results of fluid migration simulation show that there are many kinds of fluid migration modes in Shenhu sea area, and the Darcy path migration mode along the low permeability stratum is the most widely distributed. There is a flow path migration mode along the high permeability stratum in Zhuhai Formation, while the breakthrough and fault migration modes control the upward migration of deep fluid. Biogenic gas migrates in the shallow layer along the side wall of the canyon by buoyancy and diffusion; thermal gas migrates to LW3 oil and gas field mainly in the deep side due to the influence of inclined stratum and sandy reservoir distribution caused by basement uplift, and a small part migrates vertically to the bottom of hydrate stable zone through faults, anticlines, domes and other structures.

    The simulation results of hydrate stability zone show that the bottom boundary of hydrate stability zone calculated by other methods is basically the same. The simulated thickness of the stable zone in SH2 is about 225 m, that in sh5 is about 180 m, that in W19 is about 168 m, and that in W17 is about 241 m, which is consistent with the previous research results.

The simulation results of hydrate saturation and distribution show that the formation of discontinuous hydrate layer above the stable zone in Shenhu sea area is mainly related to the biogenic hydrocarbon generation with relatively low organic matter abundance, and the saturation value is relatively low. When the thermogenic gas has a certain contribution to hydrate formation, it will form relatively high saturation hydrate enrichment, and the longer hydrocarbon gas release time is of great significance to the formation of high saturation hydrate enrichment. There are also differences in gas source types of hydrate in different Canyon strips. The formation of hydrate in SH2 station is mainly affected by biogenic gas, while the formation of hydrate in W19 and W17 stations is related to mixture gas, and the thermogenic gas plays an important role.

The formation mechanism and accumulation model of gas hydrate of complex genetic type in the study area show that the accumulation and accumulation of gas hydrate are affected by structural activity, stratigraphic subsidence, temperature distribution, hydrocarbon generation from source rock, fluid migration, hydrate generation and other factors. The study area is located in the lacustrine sedimentary environment before the new century, and in the semi deep sea sedimentary environment since the new century. Most of the sediments are fine-grained sediments. In this kind of low permeability stratum, biogenic gas migrates in shallow layer by buoyancy and diffusion, while thermal gas migrates laterally in deep layer under the influence of stratum tilt caused by basement uplift and local high permeability stratum distribution of Zhuhai Formation. At the same time, affected by the tectonic activity and the gas overpressure in the deep anticline and dome, the deep thermal gas can move up to the bottom of the stable zone. The diversity of Hydrate Distribution in the gorge enrichment area of Shenhu sea area is related to the gas supply of different genetic types. The southwest side of the gorge is close to the Baiyun main depression, with large biogenic gas abundance, but less structural activity and limited contribution of deep thermal gas. Therefore, the hydrate genetic type in the southwest side is biogenic. However, the northeast side of the canyon is far away from Baiyun main depression, and the abundance of biogenic gas is relatively small. Affected by basement uplift, the fault system is developed, and the deep thermal gas has a significant impact on the formation of hydrate. Therefore, the genetic type of hydrate in the northeast side of the canyon is the mixed gas.

摘  要 I

Abstract V

第1章  引言 1

1.1  研究背景 1

1.1.1  天然气水合物气源特征 1

1.2  天然气水合物成藏生烃数值模拟 3

1.2.1  国际典型海域天然气水合物成藏模拟研究 3

1.2.2  我国南海北部天然气水合物成藏模拟研究 7

1.3  研究意义 10

1.4  论文主要研究内容 10

第2章  区域地质概况与天然气水合物分布 12

2.1  地质演化特征 13

2.1.1  构造演化史 13

2.1.2  热演化史 14

2.2  层序地层与沉积演化特征 15

2.3  烃源岩分布及地球化学特征 18

2.4  白云凹陷天然气水合物分布特征 21

2.4.1  测井识别天然气水合物 21

2.4.2  地震识别天然气水合物 23

2.4.3  典型测线天然气水合物成藏模拟 29

第3章  生烃数值模拟原理及模型构建 30

3.1  生烃数值模拟原理 30

3.2  模型构建 37

3.2.1  地质模型构建 37

3.2.2  温度模型构建 41

3.2.3  生烃模型构建 41

第4章  白云凹陷生烃数值模拟 43

4.1  白云凹陷温度场模拟 43

4.2  白云凹陷有效烃源岩分布以及生烃模拟 44

4.3  白云凹陷烃类气体运移模拟 46

4.4  白云凹陷天然气水合物饱和度模拟 49

4.4.1 流体运移路径对天然气水合物饱和度的影响 50

4.4.2 烃源岩生烃对天然气水合物分布及饱和度的影响 51

4.5  白云凹陷天然气水合物成藏模式探讨 56

第5章  结论与下一步工作建议 57

5.1  结论 57

5.2  下一步工作建议 58

参考文献 61

致  谢 71

作者简历及攻读学位期间发表的学术论文与研究成果 73