A Study On The Characteristics Of The Assemblages Of The Source-reservoir-cap Rocks Of Mesozoic Strata, East And Central Guangdong

Since several decades, a large number of geophysical surveys and related comprehensive researches in the Bohai Sea, Yellow Sea, East China Sea and South China Sea have been carrying out by our Chinese scientists, resulting in obtaining a great deal of first-hand data. In particular, they had identified and confirmed that there exists Mesozoic strata in the northern part of South China Sea through combination of geological and geophysical studies, identified and found source rocks in the eastern Guangdong, hydrocarbon show and commercial oil and gas flow in the marine Mesozoic strata of the West Taiwan, successively. So far, only China National Offshore Oil Corporate and Guangzhou Marine Geology Survey have done a few surveys for the geology and mineral resources in the northern of South China Sea, no relative surveys for the oil and gas resources has been conducted, therefore, the understandings of the fundamental petroleum geology conditions are still very limited, questions such as whether any potential commercial accumulation developed are not clear. Generally speaking, researches on the marine region are still in low level and the relative data is very limited. At present, most scholars agree that the northern part of South China Sea belongs to Paleotethys environment during the Mesozoic Era, two transgression events occurred during Later Triassic-Early Jurassic and Early Cretaceous, respectively. Thus, considering that the sedimentary sequences of continent and marine could be well-compared, we can apply the thinking of from land-to-sea to study the petroleum resource potential in the northern part of South China Sea.This paper is based on the State Special Program entitled "The Studies on the Petroleum Resources Potential and Strategic Area Selection in the Northern Part of South China Sea" (the key work is focus on the aspect of continent in 2007), first, 52 source samples, 133 reservoir samples, 424 photos were obtained through investigating 8 Mesozoic outcrop profiles in the East and Central Guangdong. Then, indoor sample test analysis have been conducted, including 20 samples have been tested in the aspects of porosity, permeability, mercury penetration, 78 common thin sections and 20 casting thin sections have been prepared and identified, 10 samples have been done rock mechanical tests, two samples which are suspected as bitumen have been conducted fluorometric analysis. At last, a comprehensive evaluation map on the assemblages of the source-reservoir-cap rocks of Mesozoic strata, East and Central Guangdong, was compiled.Based on the above-mentioned studies, main understandings are as follows:1) As far as the Mesozoic strata is concerned, the potential reservoir are mainly sandstones occurred in Jurassic, including the Jinji Formation, Shanglongshui Formation, Changpu Formation, and Qiaoyuan Formation.2) Based on the observation and analysis of thin-sections, the major 3 types of reservoir spaces are solution cavities, fractures, and intergranular pore, among which the intergranular solution cavity is the major reservoir space; and the types of rock are coarse-fine quartz sandstone, feldspar quartz sandstone, debris feldspar quartz sandstone, feldspar quartz rubblestone.3) According to the field survey, reservoir property parameter test, observation under microscope and mercury penetration analysis, in the East and Central Guangdong Province, 4 sets of type II and type III reservoir are developed, respectively.4) Three source-reservoir-cap rock assemblages developed in the continental margin of South China, i.e. the first assemblage consists of the Xiaoshui Formation (T₃xsh) as source rock and the Toumuchong Formation (T₃t)-Shanglongshui Formation (J₁sh)-Changpu Formation (J₁ch) as reservoir rock -Jishuimen Formation(J₁jsh) as cap rock; the second assemblage is the potential of self-generation and self-accumulation within the Qiaoyuan Formation; the third one comprises the upper part of the Tangxia Formation as source rock and the Heshui Formation of Lower Cretaceous as reservoir and cap rock.In a word, the Yinpingshan-Shanglongshui-Changpu-Jishuimen Formations of the Lower Jurassic, East and Central Guangdong, developed moderate-poor source rocks, sandstone reservoir occurred within the Jinji, Shanglongshui, Changpu, Qiaoyuan Formations of the Jurassic. Thus, the Mesozoic strata in East and Central Guangdong possess some potential resources. This work can provide further study of land-to-sea with correlation data for the petroleum resources potential of the Mesozoic strata in the northern part of South China Sea.