The Distribution Study Of The Middle-deep Sandstone In The Southwest Margin Of Baiyun Depression, South China Sea

With the daily increasement of human demand for oil-gas resources and the rapid advancement of the oil-gas exploration and development technology, The marine oil-gas exploration and development especially in deep water has become a global research hot spot in the field. So far, the marine oil-gas resources have been largely exhausted in the shallow layer after several decades. Facing the serious situation of the strong demand for energy, we must have to pay attention to the high quality reservoir in deep or super-deep area(below 3500m). It indicates that the distribution of superior sandstone reservoir in deep or super-deep layer is predictable and recognizable, which has been constantly discovered in China and abroad.The research area of this paper is in the southwest of Baiyun Depression; the research content is the distributional regularities of middle-deep area sandstone and the research horizon is ZHSQ2(30-28.4 Ma) which in the under section of Zhuhai Formation. The study zone is the second sedimentary sequence after the expansion of the South China Sea movement, and there is abundant and wide distribution sandstone in it. But because of the large buried depth, the physical properties of this sandstone reservoir are affected by a lot of factors such as the sedimentary environment, temperature and buried tine, diagenesis(dissolution and cementation), tectonic effect and so on. Therefore, the physical properties of middle-deep sandstone reservoir will generally worse than that in shallow layer, but there is still high quality reservoir having good porosity and permeability. To find the high-quality sandstone richment is a precondition for exploration.So, in order to solve this problem, we make full use of the existing research results and the drilling or seismic data. To realize the seismic characteristics and establish seismic identification of typical sandstone and its combination with surrounding rock mass by using velocity analysis, wave impedance analysis and waveform analysis. We launch to resume the basin prototype and determine the sedimentary environment relying on the method of seismic line; furtherly we analyze the internal structure of the strata sequence, defining its internal parasequence set(sand body) in the sequence stratigraphic framework. Referring to the Seismic amplitude attribute(RMS, maximum, minimum, average amplitude attribute, arc length attribute), we make to delineate the sandstone on the RMS attributes figure, and combined with the corresponding sedimentary environment, water system, establish sedimentary system between the delta and deep-water fan. After the above research work, we achieved the following recognition:1) To establish relevant curve between sandstone and mudstone and summed up three kinds of different sandstones, namely: the?sandstone with good Physical properties, which speed is less than that of mudstone; the?sandstone with the same speed with mudstone; the ? sandstone; which speed is greater than that of mudstone and having poor physical properties, after counting and analyzing the different lithology speed in the study area.2) According to the results of seismic forward modeling analysis, summing up the different seismic response characteristics of sandstone and its combination with surrounding rock mass(waveform analysis, 14). Among them, the waveform characteristics of the gas-bearing sandstone and high pore- permeability sandstone have been used in the actual oil-gas exploration.3) To complete the sedimentary prototype and internal structure analysis of the typical seismic profile in the research area in the direction of Inline and Crossline, and identify the sedimentary environment, such as delta, shallow sea shelf, slope, by the method of seismic line. To confirm the FRST-LST-TST combination and sand body in ZHSQ2 strata sequence.4) By conducting the depict of plane distribution of sand body, we know that the southern study area is the main accumulation zone of sandstone, which has Characteristics of the higher abundance, wide distribution, coarse grain size and good lateral continuity, that provides the favorable conditions to form high quality sandstone reservoirs. However, in the north, the sandstone particle size is fine and scattered distribution. On the whole, the sand body shows the tendency of the developing distribution from north west to south east in the study area. In combination with the sedimentary environment and water flow system analysis, dividing into different sedimentary facies, namely, the delta plain, delta front, shallow sea shelf, slope and basin floor.