Qianjiang Formation Sedimentary System And Lithologic Trap Predictions Of Qianjiang Depression Strata

Qianjiang formation in Qianjiang depression is unique inland salt lake sedimentary with high salinity sodium chloride in China as well as the most important depression and layer with abundance hydrocarbon of Jianghan basin. In this paper,based on geological structure, tectonic evolution, depositional systems of Qianjiang depression and sedimentary paleogeomorphology also drilling sedimentary microfacies, seismic phase, seismic reservoir prediction, composite phase control sand body forecast in addition, lithologic trap identification technology combined with geological and earthquake, static and dynamic make a research on tectonic evolution paleogeomorphology restoration, depositional systems and lithologic trap predictions of Qianjiang depression which has improtant theory value and practical significance for research on depositional systems and lithologic trap predictions.Firstly, based on the big profile structure interpretation to analyze detailed fault structure characteristics, movement period and plane combination characteristic which contorl strata sedimentary in northern Qianjiang and Haokou area and put forward northern Qianjing fault complexity and their subsection:the western part developed branch faults, accompanying syntropy adjusted borken order; the eastern part grew number II faults controlled hollow(Qianjiang formation);the middle fault controlled strata sedimentary bellow the Eq4is singleness asssuming characteristics of the growth fault.The fault in the northern Qianjiang are independent from the fourth section to second one.At the end of Paleogene sedimentary period,the previous goose column type fault was extrude and uplifted to the same one by the persistent structures of the end of Qianjiang formation and then sliped and twisted; The basin margin paleotectonic patterns and northern Qianjiang fault tectonic transition zone controlled the one-way source supply system and scale in the north Qianjiang formation. The north Qianjiang fault developed three structural adjustment belt as the main provenance channel during the sedimentary period of Qianjiang formaion which respectively located between Yonglong river upheaval and Hanjaing river depression, Hanjiang river depression and Lexianguan horst, the eastern part and western of Jingmen depression;Through research on large number of drilling stratum thickness statistics, seismic section interpretation and erosion thickness restoration, compaction correction, combined with drilling lithology lithofacies analysis to draw up modern and ancient strata isopach map of the aim layer and then combine with drilling lithology lithofacies characteristic to restore focal sand micro paleogeomorphology of Qianjiang formation in Qianjiang depression which will affirm the control function for the exhibition of the sedimentary system.The deposition system is a three-dimensional rock deposited in the same depositional environment, which directly determines the reservoir spatial distribution law and control function of geometric shape depositional system distribution. Basin sedimentary filling and development of depositional systems distribution were controlled by ancient tectonic appearance, material source, paleoclimate.Meanwhile, ancient tectonic appearance further controlled material source entrance and distribution direction of depositional system whereas ancient climate, material sources controlled water condition and the sedimentary system scale. It was dry or wet frequently alternate controlled by the northern one-way matrial sourse and affected by the north-low and south-high paleotopography as well as the solt lake caused the sand thinned even wedeged out to the middle-south section to present "half basin of sand". Based on research on sedimentary paleogeomorphology and combined with zircon tracer, heavy mineral, sand contrast technology this paper made clear the matrial sourse direction of Qianjiang formation. According form drilling, well logging, seismic and analysis assay material,using lithofacies paleogeography and sedimentary body analysis techniques take focal sand groups Eq332、341、421、432and lower segment of Eq4as element to study further the material source entrance location and sedimentary system features. To identify sedimentary system distribution characteristics and law,this paper put forward that topography, sedimentary paleoclimate, water depth and water medium conditions controlled salt lake sedimentary system mode and the spatial distribution law.Through application of sequence stratigraphy theory and continental basin sedimentary filling principle, sedimentary system types and features of Qianjiang salt lake are summarized. To observe rock and indoor analyze, Qianjiang formation deposition period is main considered as shallow water environment and water became shallow in the fourth section and third one reflecting shallow water salt lake delta fresh-half salt water lake-salt lake sedimentary system where mainly developed micro-facies such as delta front underwater branch river, debouch ba、littoral and shallow lake dam、shallow water gypsum rock beach. Delta front facies and salt lake facies distribution range appears alternate. The lake basin gradually became shallow from below to the up in the vertical section. The sand body developed little by little was affected by material sources supply and water medium conditions so that each group sedimentary is cyclicity to influence sandstone development degree.It was salt lake sedimentary during the Qianjiang formation deposition period which provided favorable geological conditions for lithologic trap development. The ancient and modern tectonic pattern of Qianjiang depression have changed a lot and sand body has good configuration with ancient and modern tectonic to form multiple types of lithologic trap in Qianjiang formation. In addition,the lithologic trap distributed widely with multiple types and different types of them appeared zonal distribution. Because lithology and lithofacies changed much with thin reservoir and complex lithology, it is much difficult to identify the lithologic trap. Based on the drilling phase combined with seismic phase to form seismic geological composite sedimentary micro-facies and then carry out facies controlled sand body prediction to comprehensively identify lithologic trap. At last this paper put forward four lithologic traps developmental favorable regions:distributary channel finger-like sand of Mussels lake syncline southeast slope locality updip pinchout, the sheet sands of Zhanggang beach bar regional updip pinchout and branch river finger-like sand fault-lithology regional updip pinchout of Haogou-Zhoufan area as well as tectonic-lithology of Zhongshi area.