| The word “karst” was proposed in 1960 s, it has been nearly 50 years. Since our country found Renqiu Oil buried hill reservoir in 1975, geologists started to research ancient karst and reservoir. Recently years, exploration of palaeokarst has developed rapidly. Many basins have discovered a great deal of palaeokarst oil and gas reservoir, such as Tarim Basin, Ordos Basin, Sichuan Basin, and Qaidam Basin. And have built mid-large oil and gas fields like Tarim, Changqing, Weiyuan and Lunnan. Therefore, researching palaeokarst reservoir has significantly influence on the development of Oil and Gas exploration theory.The southeastern area of Sichuan Basin has well conditions of oil and gas’ s oil-generating strata 、 reservoir and capping formation. It also has exploration foundation of oil and gas. Thus, becoming favorable exploration replaced block of Sichuan Basin. However, with the speed up of oil and gas exploration and decrease of shallow layer’s exploration area, nowadays, the most important issue has become drilling gas in Palaeozoic Erathem layer and deep layer. That’s for the sake of achieving a major breakthrough of exploration in the southeastern area of Sichuan Basin. The thesis mainly research Permian system Maokou Formation and Sinian System Dengying Formation of Qijiang block, southeast Sichuan. From the view of palaeokarst reservoir’s exploration, combined with Sedimentology, Reservoir Petrology, Isotope Geochemistry, geophysics and Karst Geology. On the basis of geology data, drilling data, seismic data and test analysis data, using the combination of macroscopic and microscopic characteristic to describe the forming process and mechanization of lower assemblage karst reservoir carefully, summarizing the development characteristics, periods and types of palaeokarst, analyzing the pore types of karst reservoir, distribution pattern of accumulation space and controlling factors. Applying geochemical methods such as carbon and oxygen isotope, strontium isotope, test of trace elements, homogenization temperature data and cathodoluminescence characteristics to identify and distinguish types of palaeokarst, thus provide important theoretical basis for the study of palaeokarst reservoir. Finally, on the basis of combing geological condition and accumulation result of oil and gas, united normal and abnormal oil and gas reservoir exploration theory, giving exploration advice on lower assemblage’s favorable exploration range of Qijiang block, southeast Sichuan.The limestone of Maokou Formation have built various types of palaeokarst after weathering denudation and tectonic movement, mainly develops four types of palaeokarst: depositional karst、exogenous karst、burial karst and folding period karst. Exogenous karst and folding period karst develop large scale; they are key point of Maokou Formation’s oil and gas exploration. Owing to interaction and reconstruction of various karst types, recognizing different kinds of karst can’t only depends on field observation. Through the combination of macro and micro geochemistry method, we can classify different kinds of karst. And Maokou Formation karst’s develop mainly controlled by karst palaeogeomorpholog and structure.Maokou formation ancient karst reservoir has four kinds of abnormal reflection, they represent different karst: inclined karst; strong parallel karst; weak parallel karst; longitudinal stack and podiform karst. Inclined karst’s oblique highlight develops on karst highland and paleoslope, the trend is from palaeogeomorphology highland to lowland; karst develops along poor intensity of rock on the basis of fault. Strong parallel karst develops on paleoslope and the slope peripheral partly old high focus. Weak parallel karst develops on karst highland and palaeohigh ramp region. Longitudinal stack and podiform karst develops on the slope of palaeotectonics, presents lumpy and point distribution.Dengying formation reservoir mainly develops in algae dolomite, grain dolomite and powder crystal-macrocrystalline dolomite. In dolomite, denudation is widespread, different types of erosion present different geochemistry characteristics; it can be used in identification of different erosion, such as: exogenous erosion, buried erosion and hydrothermal fluid erosion. Dengying formation reservoir is controlled by diagenesis and tectogenesis.The abnormal reflection of Dengying formation mainly develops on palaeogeomorphology highland, it also develops on paleoslope. Karst highland and paleoslope are located in strong geologic stress area, the development of ancient karst provide convenient condition for vertical fracture, meanwhile, its position can be influenced by weathering and erosion action.Combing abnormal reflection characteristics,reservoir forecast and cave-cleft bodies examination, we get the achievements that in Maokou Formation, karst slope and partly high focus with the peripheral of karst highland are class Ⅰexploration area, karst highland is class exploration area; Define five exploration targets; the first Ⅱchoice is karst slope and partly ancient high peripheral of karst highland. According to the results of comprehensive evaluation, classified upper Dengying formation into three category four favorable reservoir area,lower Dengying formation into three category five favorable reservoir area; Combing seismic anomalous body and karst forecast anomaly outcome, finally determine two exploration targets. |
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