Characteristic Of Source Rock In Fulongquan Fault Depression, Songliao Basin

Source rock is a kind of rock not only rich in organic matter but also could supply oil and gas which has commercial value. Identification and evaluation of effective source rock is the foundation of researching the gas and oil system and hydrocarbon accumulation. The degree of understanding the source rock affects the discovery of the commercial oil and gas reservoir in exploration. How to study the effective source rock in a reasonable and effective in the early exploration has a very important theory and practical significance in understanding the spatial and temporal distribution of oil and gas, analysis and forecast of oil and gas prospect and direct petroleum exploration.Songliao basin is an important continental sedimentary basin in our country, which is rich in oil and gas resources. Fulongquan fault depression is in the south of Songliao basin. The source rock developed in Yingchang Formation and Shahezi Formation of Cretaceous. Up to now, no systemic study of resource rock has been done in Fulongquan area. This article bases on the material of well drilling, oil well logging and earthquake, combined with Sedimentary Facies, by the comprehensive research of geologic history, geologic thermal history and organic geochemistry and so on, mastering the geochemical characteristic and evolution law of the source rock of Fulongquan fault depression; Based on this, we put forward the identification criteria of effective source rock in Fulongquan fault depression area, south of Songliao basin, which has a low degree of exploitation, by comparison with the area which has an deep research in source rock. Provide evidence for the distribution of effective source rock in Fulongquan area and also direct the oil and gas exploitation in Fulongquan area.In the low exploitation area, we study the potential source rock first, and then study the effective source rock. The research of predecessor confirmed that source rocks are usually dark mudstone, muddy limestone, limestone and coal seam. These dark fine sediments are rich in organic matter, and have more organic matter which could generate hydrocarbon. In this research, we define dark fine sediment which has ability of generate hydrocarbon as potential source rock. The potential source rock in Fulongquan area including black, grey black and grey mudstone. The hydrocarbon could migrate and accumulate into reservoir if it has enough organic matter and in the stage of generating hydrocarbon. These source rocks define. The effective source rock must be in these dark fine sediments. Then determine initially the scope of source rock (potential source rock) when iriss out the distribution (area, thickness) of dark fine sediments without considering the organically geochemical parameter may. In this foundation, using organically geochemical parameter and referring to the sedimentary facies, iriss out the source rock which can satisfy the organic carbon content and the maturity standard. This source rock is the effective source rock.The potential source rocks can be identified by drilling data, based on lithology and color, and can statistic the thickness. In conventional methods, when seek thickness, generally extrapolates thickness between the well points by well point in thickness. However, the study area is large, the wells are on the other hand few, the wells drilling or drilling out Yingcheng Group and Shahezi Group is fewer, and the extrapolated thickness access of the lower accuracy. Given this situation, with a view to minimizing the use of existing information and obtain better results, therefore adopts the following methods:The development of source rocks and the depositional environment are closely related, seeking potential source rock thickness and the stratum depth correspond the section of various sedimentary facies (subfacies) which based on the deposition phase diagram of every wells in the study area, and obtaining potential source rock percentage which corresponds to each sedimentary facies (subfacies) (potential source rock percentage = potential source rock thickness/stratum depth). Statistics the percentage of all the wells in the study area which correspondence different sedimentary facies, and establishes a sedimentary facies and the potential source rock of the relationship. This may transform the stratum depth as the potential source rock thickness in the region between wells through the potential source rock percentage assignment to the sedimentary facies (subfacies) according to the sedimentary facies type. From this can obtain potential source rock isopach map of Yingcheng Group and Shahezi Group in the area of Fulongquan. The potential source rock isopach map selectes initially the scope of potential source rock, is the foundation of effective potential source rock research for the next step.Effective source rocks are the rocks that can produce and discharge hydrocarbon, and the discharged hydrocarbon can assemble and form commerce oil and gas pool. The effective source rock's definition emphasis it had already formed the commercial character oil gas pool after the oil source contrast proof, namely, had the commercial character oil gas pool to inquire into again which source rock position this oil gas did stem from. The reservoir have been found in the area of Fulongquan, but in order to obtain oil-gas exploration the breakthroughs, the deeper research of effective source rock is also imperative. Therefore we according to the situation of source rock of Fulongquan faut depression, comparing with Changling fault depression and Xujiaweizi fault depression where the effective source rock research is more deeper, and firstly determined the evaluation criteria at this stage of effective source rocks it the area of Fulongquan, then in accordance with the evaluation criteria for identification of the effective source rocks, and may know its distributed rule finally.Generally, the geochemistry characters research of source rock through the research of three aspects which are organic matter abundance, organic matter type and organic matter maturity. For a long time, has taken the organic matter abundance as the evaluation criteria of effective source rocks, while the majority researchers take the organic carbon content as the evaluating indicator. The evaluation criteria of mudstone organic carbon content is relative unity, it is generally believed that organic carbon content> 0.5% of the mudstone as a effective source rocks. The lower limit of organic matter abundance of Carbonate rock will greatly controversy, but domestic and foreign already verified can form the commercial oil deposit the carbonate rocks source rock organic carbon abundance is generally above 0.5%. According to the concrete situation of study area and the research results, this article uses the organic matter abundance and the organic matter maturity target in the discussion of evaluation criteria of effective source rock, namely uses the data of organic carbon content (TOC), vitrinite reflectance (Ro) and the rock thermal decomposition peak temperature (Tmax) as the evaluate parameter. Therefore, the evaluation criteria of study area is TOC>0.6%, Ro>1.0%, Tmax>430℃, namely the effective source rock of Fulongquan area is the source rock which satisfies TOC>0.6%, Ro>1.0%, Tmax>430℃.In order to research the thermal history, restore the denudation firstly. In Fulongquan Area, restoration denudation method are"the interval transit time method"and"formation material balance method", and then calculate the beginning of the erosion and eventually research the burial history and tectonic descent history.After restoration the burial history and tectonic descent history, we can complete the diagram of the Paleogeotemperature history and the maturity history. Analyze the period of producing hydrocarbon and evolvement phase of source rocks in Fulongquan area, combining the Paleogeotemperature, maturity history and burial history. Presently, the type of Cretaceous source rocks of Yingcheng Group and Shahezi Group are mainly type III in Fulongquan area, as part of type I and type II1, has entered the hydrocarbon threshold, starts forming gas, and at the stage of maturity– high maturity.In summary, based on the data of well drilling, well logging and seismic, through the comprehensive research of sedimentary facies, the geohistory, the thermal history and the organic geochemistry, has mastered the characteristic of distribution and geochemistry of source rock in complex geohistory situation in the area of lower degree of exploration, proposes the identified standard of the effective source rock, and has grasped the effective source rock distribution initially, to continue the deeper research effective source rock and instruct the exploration activity of the Fulongquan area has provided a important basis.