| Gypsum-salt rock and salt tectonic as reservoirs efficient preservation condition are always the focus in petroleum geology. Commonly, the development of large marine oil- and gas-bearing gas fields (such as Puguang gas field) is related closely to gypsum-salt rocks. Cambrian gypsum-salt rocks develop extensively in Sichuan basin. However, the distribution of gypsum-salt rocks, the sealing property and its implication for the underlain strata have not been studied thoroughly by now. Therefore it is of great significance to study the halite developmental characteristics, closed mode of Cambrian in Sichuan basin and its effects on the underlain reservoir.The aim of this thesis is to study the Cambrian salt in Sichuan basin. It mainly focus on the Gypsum-salt rock closed mode and its impacts on the underlain reservoir. The distribution, lithology assembleges and the controlling factors of the Gypsum-salt rocks were analyzed in detail as well. Based on the typical anatomy, the author established the halite block effectiveness mode and carried out the research on the underlain accumulation condition. The author also predicted the favorable hydrocarbon exploration zones. This thesis obtained the following findings.(1) BY analyzing more than 20 drillings and 3 sections of the lower-middle Cambrian in Sichuan basin, we found out that the sections containing gypsum-salt rocks consist mainly of carbonates (dolostone, calcareous dolostone, muddy dolostone, mudstone, marlstone, dolomitic marlstone etc.), sulphate (gypsum, dolomitic gypsum etc.) and so on, and they are interbeded with fine grained stones like mudstones, silty mudstones and so on. Gypsum-salt rocks occurrence in carbonate-sulphate buildings. According to the characteristics of the basic composition and structure of the sections that containing gypsum-salt rock in different places, the section of the lower-middle Cambrian in Sichuan basin could be divided into four categories:①Dingshan pattern, in the lower part of this pattern, grey oolitic limestone, microcrystalline dolostone, muddy dolostone and gypsum constitute a cycle.②Gongshen pattern, this pattern consists of grey marlstone, limestone in the lower part, microcrystalline dolostone in the middle part, gypseous dolostone in the upper-middle part and gypsum-rock in the top and they form a cycle.③Jianshen pattern, this pattern consists sandy dolostone in the bottom, huge thick layer of gypsum-rock in the middle part, and calcareous dolostone in the top.④Fandian pattern, characterized by the development of salt dissolved breccia.(2) With gypsum, dolomite and clay mineral as three end members, gypsum-salt rock could be divided into three divisions of muddy dolomitic gypsum rock, gypseous dolostone and gypseous sandstone and ten subdivisions of gypsum-salt rock; they have three kinds of compositions and six kinds of structures, and with the different components they have different sealing capacities; gypsum-rocks all developed in the climate that the cycle turning dry and shallow upward.(3) There are four centers in the distributions of gypsum-salt rock of Cambrian regionally, and they present'bovine eye'style, the evaporation lagoon facies of'bovine eye'style that distributed as girdle band is the most favorable development zone for gypsum-salt rocks. By researching, we found out the regional distributions, lithology composition partitionings and variations of thickness of the Cambrian gypsum-salt rock, of which gypsum is located southwest in Sichuan, WeiYuan and southeast in Sichuan, of the east-west oriented spread; gypseous dolostone and dolostone containing gypsum are located in southeast in Sichuan and Jianshen 1 well, of north-east oriented spread; macroscopic view shows that pure and thick gypsum has stonger sealing capacity.(4) Anatomy of the Weiyuan gas field indicates that the Cambrian gypsum rock caprock plays a more important role. Predecessors consider that the lower Cambrian shale is the key caprock, we find that gypsum is more important; based on drilling/ logging, testing and dynamic analysis, we proved that the middle and lower Cambrian gypsum rock have the closer height between the pinch point of the north and the spill point, which means the sealing of gypsum rock is more effective. We could get 3 conclusions by anatomy:①Although the sedimentory thickness of gypsum is thin and influenced by faults, but the gypsum rock sealing is more effectively;②The ancient uplift formed earlier, the trap matched more favorable;③intraplatform should be multi-layer, secondary holes seam reservoir produced by deep bury diagenism should have more sets.(5) Discussed the sealing efficiency of gypsum rock at the different blocks, and found that the sealing models are different. Gypsum rock sealing played a more important role in Central Sichuan uplift, although in Weiyuan region the sedimentary thickness of gypsum is thin and influenced by faults the caprock is more effective. On the west side of the southeastern Sichuan basin, the sealing of gypsum rock is effective, however, the easter part is intensely influenced by the tectonic reworking in later period and in flank the stratum was exposed and cut through by the Tiantong fault, as a result the east side of exploration area the sealing of the gypsum rock failed. In contrast, on the east side of the southwestern Sichuan Basin the caprock of gypsum rock is more effective.(6) Studies suggest that the lower Paleozoic geological conditions of accumulation is favorable in the Sichuan Basin, and hydrocarbon source rocks and reservoir rocks all have the conditions of forming large and medium gas fields. Through comprehensive study, we suggest that the potential areas for favorable exploration are the tidal beach-bar in southwest of Sichuan basin, intraplatform shoal and karst areas in Southeast of Sichuan Basin. The southeastern Sichuan Basin has excellent conditions of accumulation, abundant resources, the proven level of resources is only 0.6%; caprocks of gypsum rock distribute contiguous, and have multi-layers, the thickest layer of gypsum rock is 14m, and have good storage conditions; however, the slope of the southeastern Sichuan basin was caused by tectonic reasons, and the caprock formed late (Yanshanian Period, finalized in the Himalayan period), and did not match with the peak of hydrocarbon generation in∈1n,S1l, and have little meaning of accumulation. Therefore, the key of the oil-gas exploration in southeastern of Sichuan is to predicting the favorable reservoir and seeking the lithologic caprock in the tectonic high point. Another favorable exploration potential area is in southwest of Sichuan basin, the east side of this area is thickness center of gypsum rock, and have excellent preservation conditions; The tidal beach-bar distribute as radial pattern; This area also have no slope and sedimentary paleo-uplift, thus the direction of oil and gas exploration is to find the local tectonic high points of lithologic caprocks.
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