海洋地质与环境重点实验室知识库

高饱和度天然气水合物成藏与储层及气源条件相关，其稳定条件受控于海底温度压力，会受海底沉积动力、热流体等活动影响，水合物系统会发生动态调整。与国际典型高饱和度砂质水合物储层不同，我国南海水合物主要赋存在泥质粉砂沉积物中，局部富含有孔虫的粉砂质储层水合物饱和度较高。在水合物研究中探寻砂质水合物储层，研究天然气水合物富集的地质控制因素，对提升水合物成藏认识，选取水合物勘探靶区等方面有重要的理论和工程意义。

本文从国际上发现的高饱和度砂质水合物富集区入手，系统分析砂质水合物藏发育测井及地震地球物理响应特征，构造与沉积环境。发现高饱和度水合物多发育在浊积水道-天然堤-海底扇沉积体系中，储层岩性以砂为主，与被动大陆边缘环境适宜的温压条件及充足气源条件相匹配。高电阻率（3-200ohm-m）、高纵波速度（1700-3000m/s）及低伽马是高饱和度水合物层典型的测井响应特征，而似海底反射（BSR）、强振幅、高波阻抗等反射特征为高饱和度水合物层的地震响应特征。在神狐海域W11和W17站位，水合物层厚度高达70多米，平均饱和度约40%，呈明显的层状分布，相邻峡谷脊部的W18和W19站位，发现饱和度超过70%水合物层，厚度从14-30m不等，两个研究区水合物呈明显不均匀分布特征。对两个地区伽马与阻抗和孔隙度测井特征交汇分析对比，发现水合物发育在相对较低伽马异常层，主要由富有孔虫浊积砂组成，表明岩性有利于水合物富集。但对SC-02站位进一步分析发现水合物并非发育在水合物稳定带上部低伽马地层，而是位于水合物稳定带附近，表明并不是岩性单一控制着水合物富集，水合物富集还受其它关键因素的影响。

研究区测井分析及前人研究表明II型水合物可能广泛发育，指示研究区存在热成因气。高饱和度水合物站位的岩心孔隙水氯离子浓度出现异常高值，该异常值指示水合物形成时盐度异常未达到平衡，表明水合物系统可能近期形成，为研究该水合物系统活动特性，本文选取SC-02和W18站位，基于流体扩散置换原理，利用一维衰减模型对水合物形成时间进行模拟，结果显示水合物系统在1.9-2.9万年发生活动，尚未达到稳定状态。利用白云凹陷三维地震数据工作，识别多个水合物异常区，通过与含油气构造叠合发现，水合物异常区均与白云凹陷油气富集区高度重合。同时基于三维地震地层属性及“源-渠-汇”沉积体系分析揭示，峡谷内部局部发育富砂沉积，同时在峡谷末端叠置扇体是砂质储层的有利富集区，该区域具备高饱和度水合物成藏储层条件。白云凹陷大量油气钻井及压力模拟研究揭示深部地层白云凹陷中央出现超压现象，断层及气烟囱体系在水合物富集区下部大量发育，为流体从白云主洼运移到凹陷周边局部隆起带提供动力和疏导条件。结合天然气水合物在白云凹陷分布，流体横向运移也是研究区流体运移的一种重要方式，提出长距离流体运移与流体垂向运移控制水合物成藏，深部流体幕式供给可能是稳定带上方高饱和度近期活动及II型水合物发育主要机制。

海底峡谷沉积侵蚀作用是导致水合物系统动态调整重要机制，通过对三个不同规模海底峡谷与连续BSR，不连续BSR及古BSR发育特征分析，归纳总结了峡谷侵蚀及BSR演化阶段。利用相干及蚂蚁追踪地震属性刻画发现BSR下部大量正断层发育，为流体从深部地层向浅部水合物稳定带内运移提供通道。海底侵蚀作用导致地层变冷，进而水合物稳定带底界向深部地层调整，该过程伴随水合物分解及甲烷气体通过陆坡峡谷体系释放。

本研究认为天然气水合物广泛发育于珠江口盆地深水区，但水合物非均质性分布明显，白云凹陷发育有利高饱和度水合物富集有利储层，深部超压热流体活动为近期活动及高饱和度水合物富集重要原因，海底峡谷侵蚀作用为水合物系统动态调整重要机制之一。

The occurrence of high concentrated gas hydrate is related to the sand-rich reservoirs and gas sources. The gas hydrate stability zone (GHSZ) is controlled by the temperature and pressure in the subsurface sediments. Affected by the variations of submarine sedimentary dynamics and deeper thermogenic fluid migrations, gas hydrate system will be active and adjustment. In contrast to the sand-rich units for high saturated gas hydrate accumulation in worldly marine settings, gas hydrate mainly accumulate in the fine-grained sediments (clayey silty) in the Pearl River Mouth Basin, South China Sea. The search of sand-rich reservoirs and further study of geological controls on the gas hydrate accumulation have theoretical and engineering significance for improving the understanding of gas hydrate accumulation and exploration of the gas hydrate target area.

The systematical summaries of the geological setting, the depositional systems, features of well log and seismic data have been used to confirm the occurrence of high concentrated gas hydrate in marine setting. In previous study, the high concentrated gas hydrates accumulate in deep-water turbidite channel-levee-fans depositional systems where sand-rich reservoirs generally exist. The high concentrated gas hydrate characterized by high resistivity (3-200 ohm-m), high P-wave velocity (2200-3000 m/s) and low gamma ray values seen from well log data, and bottom simulation reflectors (BSRs), high amplitudes, high impedance and bright spots in seismic data. In the Shenhu area, a sediment layer with high thickness (>70 m) and average saturation (about 40%) has been found in the study area of sites W11 and W17, showing multiple gas hydrate layers in the seismic profile. In the adjacent ridge, the gas hydrate-bearing sediments with 30 m-thick and high saturation (>70%) are identified at sites W18 and W19 in the study area, which are related to the buried trough occurred near the base of gas hydrate stability zone (BGHSZ). The low gamma ray units caused by local foraminifer-rich sand are mainly reservoirs for gas hydrate accumulation. The crossplots of gamma-ray, acoustic impedance (P-impedance) and porosity show that turbidite-sand layers near the bottom canyons sediments significantly improve the reservoir quality for gas hydrate accumulation. The structure II hydrates have been identified in the study area, indicating thermogenic gas from deeper sediments contributed to the gas hydrate system.

A striking increase in pore-water chlorinity values has been identified from recently acquired logging-while-drilling (LWD) data and core samples, indicating an active or recently-active system. A one-dimensional (1D) diffusion model is used to estimate the time when the gas hydrate formed based on the saturation, thickness, and porosity of gas hydrate-bearing units at sites W18 and SC-02. The results show that gas hydrates at sites SC-02 and W18 respectively formed 19-29 ka ago. Two new gas hydrate study area have been identified from the three-dimensional seismic data covering the whole Baiyun sag. The distributions of gas hydrate study area overlapped with the deeper gas-bearing structure suggest the genetic relationship. The analysis of architecture elements and core data in canyon-terminal overlap fans indicate that canyon lag deposits, canyon confined sheets and terminal overlap fans are potential occurrence of high concentrated gas hydrate in the Baiyun sag. The analyses of drill log and simulated results indicate overpressured hydrocarbon in the deeper sediments supplies the motive force, and the normal faults and gas chimneys provide the migration pathways for fluid migration. Therefore, a model of long-distance fluid migration laterally has been presented for the occurrence of recently active gas hydrate system and structure II gas hydrate.

New acquired and reprocessed three-dimensional (3D) seismic data are used to delineate the distribution and characterization of bottom simulating reflections in the Chaoshan Sag. Three submarine canyons with different scales display three stages of canyon development and are related to the occurrence of multiples-BSRs. Abundant faults are identified from the coherence and ant-tracing attributions extracted from 3D seismic data, which provide the evidence for fluid migration from deeper sediments to the GHSZ. The seafloor erosion causes the cooling of the subsurface sediments and the deepening of the base of GHSZ, which is attributed to the presence of paleo-BSRs and BSRs downward shift in the study area. By seafloor erosions, methane gas from gas hydrate dissolution and free gas trapped below BSRs may be released trough submarine canyons.

Gas hydrate is widely occurred in the deep water area of the Pearl River Mouth Basin, showing the heterogeneous distribution. The local foraminifer-rich sands in canyonized area and terminal overlap fans are potential occurrence of high concentrated gas hydrate in the Shenhu area. The occurrence of overpressured hydrocarbon and fluid migrations from the deeper sediments are attributed to the occurrence of recently active and high concentrated gas hydrate system. The erosive submarine canyon is also an important mechanism for dynamical adjustment of gas hydrate system.

目  录

第1章  引言 1

1.1  研究背景及意义 1

1.1.1 研究背景 1

1.1.2 研究意义 2

1.2  国内外研究现状 5

1.2.1  国际有利盆地构造背景-被动陆缘 5

1.2.2  国际典型水合物地球物理识别特征 9

1.2.3  国际典型水合物发育区储层条件 11

1.2.4  神狐海域水合物成藏规律 13

1.3  存在问题 14

1.4  研究内容与论文创新点 15

1.4.1  研究内容 15

1.4.2  论文创新点 16

第2章  区域地质背景及数据 17

2.1  白云凹陷区域地质背景 17

2.2  潮汕坳陷区域地质背景 20

2.3  数据与关键方法 22

第3章  白云凹陷水合物识别及分布 24

3.1  白云凹陷水合物区域分布 24

3.2  水合物异常区分布 26

3.2.1  LW3及其南部水合物异常区 26

3.2.3  LW13及其东部水合物异常区 29

3.3  典型站位水合物分布 31

3.3.1  测井特征 31

3.3.2  地震特征 34

3.3.3  地震属性分析 36

3.4  II型天然气水合物发育 38

3.4.1  前人研究 38

3.4.2  W18和W19研究区II型水合物发育 40

3.5  近期活动水合物系统 40

3.5.1 一维衰减模型模拟水合物系统形成时间 40

3.5.2  水合物形成时间 41

3.5.2  近期活动水合物系统讨论 43

第4章  白云凹陷水合物成藏控制因素 46

4.1  水合物储层条件分析 46

4.1.1  交汇分析 46

4.1.2  埋藏凹槽发育 48

4.1.3  地震反演 51

4.1.4  沉积环境分析 54

4.1.5  有利砂体分布 57

4.2  气源研究 63

4.2.1  岩心气体组分统计分析 63

4.1.2  与深部油气构造匹配 64

4.3  断层分析 66

4.3.1  断层分类 66

4.3.2  断层平面展布特征 67

4.3.3  LW3水合物异常区断层分析 68

第5章  揭阳凹陷水合物识别及分布 72

5.1  构造运动及地层发育 72

5.2  BSR类型 75

5.3  海底峡谷发育及其特征 77

5.4  断层体系分析 78

第6章  水合物成藏模式分析 81

6.1 长距离流体运移控制活动水合物系统富集-白云凹陷 81

6.1.1  流体运移机制 81

6.1.2  流体运移成藏模式 83

6.2  侵蚀峡谷控制下BSR演化模式-揭阳凹陷 87

6.2.1  侵蚀控制BSR下移机制 87

6.2.2  BSR随峡谷演化发育阶段 88

第7章  结论及下一步工作建议 90

7.1  结论 90

7.2  下一步工作建议 91

参考文献 92

致  谢 105

作者简历及攻读学位期间发表的学术论文 107