Characteristics Of Depositional System And Petroleum Geology In Paleozoic Period Of Rub'Al Khali Basin

Rub'Al Khali Basin is one of the important oil-bearing basins. Because of the lack of the knowledge of basin development, characteristics of depositional system and reservoir, the basic petroleum geology has to be done for further oil and natural gas exploration in the basin. This thesis mainly deals with the basin development, depositional system, reservoir characteristics, diagenesis of sandstone and carbonate based on synthetic analysis of filed work, core description , identification of thin section, wire line logging, seismic data reprocessing and interpretation. The five well data has been used in the research, three wells located in the research area, the other two wells are adjacent area. Almost 2000km seismic data have been reprocessed and reinterpreted to determine the distribution of reservoir. Thin sections and SEM analysis has been proceeded to evaluate the history of diagenesis of reservoir rocks. The achievements has been gained mainly as follows:1. According to the study of seismic data, the evoluation of Rub'Al Khali basin could be classified into six stages: rifting and depressing stage (Pre-Cambrian to Silurain); folding, faulting and tilting stage (Devonin to Pre-Unayzah); stable deposition and vertical uplift-depress stage (Early Permain to Early Craticeous); squeezing-folding stage; basin tilting stage; basin shrinkage stage.2. The depositional system of exploration target has been studied in detail. The depositional systems have been classified into glacial sedimentary system; playa sedimentary system; continental shelf system ad carbonate platform system depending on the data analysis of field profiles, core descriptions. The assemblages of rocks both in field profile and cores show clearly the sedimentary environments. The reservoir rock developed in glacial system is controlled by the dynamics of glacier melting and continental waves in Sarah Formation. The reservoir rock in playa system is controlled by the distribution of eolian sand dune and ephemeral braided river channel bars in Unayzah Formation. The quartz sandstone developed in continental shelf is the most favorite reservoir rock due to the very good sorting and uniform grain size and porosity in Haradh Formation. Massive dolomitized dolostone is the only reservoir rock in carbonate platform environment in Khuff formatin.3. Reprocessing and interpretation of seismic data exhibit the characteristics of each strata in the basin. Depending on the analysis of frequency and seismic attributes and impedence inversion with well restrict as well, the thickness and distribution of reservoir rocks have been predicted. The results of reservoir simulation revealed main frequency of reservoir which is the most useful methods for predicting the distribution of reservoir, especially in the region of oil and gas exploration with minor geologic data and rare research of geology background.4. Using wire line logging data and the data of testing temperature and gradient of geo-temperature adjacent area, temperature gradient has been studied, which shows the trend of temperature higher in the northeastern part and lower in southwestern part of the basin. The average temperature gradient is between 2.8℃/100m and 2.4℃/100m in well Mksr-1, well Tkman-2 and well Fydah-1. Qusaiba Formation has experienced the highest temperature before the starting of tectonics during lower Tertiary. The highest temperature is near 198℃. This result confidences the optimistic to the gas and condensate oil exploration in Rub'Al Khali Basin.5. The study of burial history of source rock clearly shows that the "Hot shale" of Qusaiba Formation has entered to the gas generating peak stage in deep depression of the basin. The range of gas generating is gradually expending along with the maturity increase of source rock. The productivity of gas generating is now approaching the highest.6. The characteristics of logging data is also summarized for recognizing and assessment the quality of reservoir rocks. Based on the correlation of the results of mud logging and wire line logging data interpretation, the gas reservoir has been recognized. Summarizing the history of basin evolution, development of source rock, geo-temperature, characteristics of reservoir rocks, depositional system, and reprocessing of seismic data, the oil-bearing system of Rub'Al Khali Basin has been discussed.