琼东南盆地双似海底反射层成因及其与天然气水合物动态成藏关系研究

The double bottom simulating reflector(DBSR),which is important for the accumulation mechanism, distribution and enrichment characteristics ,and drilling and exploition site optimization of natural gas hydrate, has become a new international research hotspot ,however, little research on the genetic mechanism of DBSR and its relationship with the dynamic migration and accumulation of natural gas hydrate has been made around the world, which is constraining the progress of the reservoiring theory of gas hydrate; This project will focus on the DBSR that was a newfound phenomenon in Qiongdongnan Basin, and try to recognize and depict geological and geophysical characteristics of the DBSR based on the post-stack seismic attribute analysis, impedance inversion, velocity structures and AVO analysis. We will try to ascertain genetic mechanism and controlling factors of the DBSR by establishing the temperature-pressure stability phase diagram models using temperature-pressure data and geochemical testing data of the gas hydrate dissociation gas samples as well as pore water samples obtained from “Haima Cold Seep”. We also plan to demonstrate the distribution features of the gas hydrate-free gas system in the DBSR developing areas, moreover, the spatio-temporal coupling relationship between the gas source of gas hydrate, migration pathways including faults, mud diapirs and gas chimneys, and gas hydrate stability zones in shallow strata will be investigated. Finally, we will illuminate the relationship between the DBSR and the dynamic migration and accumulation of gas hydrate and establish the dynamic evolution models of the gas hydrate-free gas system. The results from the project can provide important scientific basis for the intense research of the genetic mechanism, distribution regularities and geological evolution of the DBSR and gas hydrate. The research of reservioring theories, and exploration and development of gas hydrate can also get a certain reference value from the project study.

双BSR已成为国际水合物研究的新热点，其在水合物成藏机制、分布富集规律及水合物钻采站位优选等方面有着重要意义，然而双BSR成因机制及其与水合物动态成藏关系等方面的研究薄弱，制约了水合物成藏地质理论研究的进步；本课题以琼东南盆地新发现的双BSR为研究对象，通过地震资料叠后属性分析及波阻抗反演、速度结构及AVO分析，识别双BSR并刻画其地质地球物理特征；利用“海马冷泉”区水合物分解气、孔隙水地化测试及温压等数据建立水合物稳定域相图模型，探究双BSR的成因机制及影响因素;查明双BSR发育区水合物-天然气体系分布规律及水合物气源与断层、底辟和气烟囱等通道及温压稳定域时空耦合关系。阐明双BSR与水合物动态成藏关系并建立动态演化的水合物-天然气体系模式，为深入研究双BSR及水合物成因机制、分布规律及其地质历史中的演变提供重要的科学依据，亦对水合物成藏理论研究，水合物勘探开发等具有参考价值。

研究双似海底反射层（双BSRs）的成因及其与天然气水合物系统的关系，对海洋天然气水合物勘探具有重要意义。本项目以琼东南盆地深水区新发现的双BSRs及相关天然气水合物地质地球物理响应特征为研究对象，利用高分辨率地震资料、识别和精细刻画双BSRs地震相特点，基于地层速度结构及叠后属性、波阻抗等特征，揭示双BSRs发育演化特点及其垂向和平面分布特征。综合利用已有温、盐、深(CTD)等勘查基础资料、2D/3D地震资料、水合物分解气、地层孔隙水地球化学分析资料，探究双BSRs成因机制及影响因素。. 基于研究区含油气系统特征及双BSRs地质地球物理特点，提出了三种可能引起双BSRs形成的原因：海底峡谷水道侵蚀和再沉积作用、热解气和生物气双重供给、古BSR的残留。查明了双BSRs与水合物稳定域顶界和底界关系，查清了双BSRs与水合物、水合物+游离气、游离气分布特征，建立水合物成藏序列，明确了双BSRs动态演化及其与水合物动态成藏的关系，DBSRs的出现也指示研究区水合物及游离气动态变化的过程，在陆坡峡谷水道下切侵蚀和再沉积作用下，水合物稳定域的变迁导致水合物出现差异分布的特征。BSR1应当是研究区现行的SI型水合物稳定域底界。DBSRs发育区可能存在SI型水合物与SII型水合物共存特征。BSR1之下和BSR2之间可能存在SII型水合物或者SII型水合物与游离气共存。在BSR2之下普遍分布游离气。据此研究，我们建立了与DBSRs发育演化相关的天然气水合物运移聚集模式，可为深水天然气水合物勘探提供地质参考。