Formation Characteristics And Development Model Of High Quality Permian Source Rocks In Santanghu Basin

Permian Lucaogou formation and Tiaohu Formation are two main sets of source rocks in Santanghu Basin.At present,the lack of systematic research on the development characteristics and distribution of these two sets of high quality source rocks restricts the understanding of the development of these high quality source rocks and the selection of favorable exploration targets.In this paper,core observation,X-ray diffraction,thin section identification and logging data analyzation are used to identify the types of hydrocarbon source rocks and lithologic combination.The organic and inorganic geochemical index are used to evaluate hydrocarbon source rocks and to determine the distribution of high quality hydrocarbon source rocks.The forming environment of high-quality hydrocarbon source rocks and control factors are determined to establish the developmental patterning of the high-quality hydrocarbon source rocks.The results show that the lithologic assemblage of Lucaogou Formation is complex and the rock types can be divided into tuff,dolomite,dolomitic tuff and tuffaceous dolomite,but the is complex.The abundance of organic matter in tuff and dolomitic tuff is higher than tuffaceous dolostone and dolostone.The organic matter can be classified intoⅠ-II₁ kerogen,which is in low mature-mature stage.The potential source rocks in Tiaohu Formation are mudstone,tuffaceous mudstone and tuff,and the lithologic assemblage is relatively simple.Among them,the abundance of organic matter in mudstone is high,while the abundance of organic matter in tuffaceous mudstone is low,and the organic matter type is mainly II-III.As an oil reservoir,the abundance of sedimentary organic matter in tuff,is generally low.The source rocks of the Tiaohu Formation is in the stage of low mature without high quality source rocks.Oil-source correlation results show that the oil discovered in permian-Mesozoic is mainly generated from the source rocks Lucaogou Formation,which further confirms that the high quality Permian source rocks in Santanghu Basin are mainly developed in Lucaogou Formation.Comprehensive analysis further shows that the criterion of high quality source rocks in Lucaogou Formation is TOC>4%and S₁+S₂>30mg/g,and four sets of high quality source rocks are developed vertically in Lucaogou Formation,mainly located in the second Member of Lucaogou Formation.The development of high-quality source rocks is controlled by volcanic activity,sedimentary environment and preservation conditions of organic matter.The source rocks of Lucaogou Formation were formed in a moderate depth of brackish water in a reducing environment with dry hot climate,and organic matter was mainly derived from algae.The source rocks of Tiaohu Formation were formed in the water of moderate to deep depth with a humid climate,and the source rocks of Tiaohu Formation were mainly from a mixed source of organic matter.High salinity,dry-hot climate,reducing environment,medium depth of water and high paleo-productivity are favorable conditions for the development of high-quality source rocks.Lucaogou Formation develops four high quality source rock thickness centers in the west,southwest and southwest of Malang Sag,respectively.The source rock thickness of the western margin of Ma 9,Mazhong sag and southeast of Malang Sag is larger on the whole.