Research On Well Logging Sequence Stratigraphy In The Upper Palaeozoic In The Northeastern Part Of Ordos Basin

Ordos Basin is known located at the stable North China Craton, and there are relatively faint tectonic events in the inner of the Basin, the exploration of nature gas depends on the research on sedimentary, well logging and high resolution sequence stratigraphy. Therefore , there are a lot of research work on sedimentary, well logging and high resolution sequence stratigraphy in the Upper Paleozoic in the Northeastern part of Ordos Basin in this paper.On the basis of the analyses of peripheral ancient land, light and heavy mineral associations, the cathodoluminescence color of quartzes, the typomorphic characteristics of various debris and directions of palaeoflow, it is considered that detrital material of terrigenous origin of the Upper Palaeozoic in this area come from north provenance, Yimeng uplift in the northern part of Ordos Basin. Based on the synthetic research of field outcrops, drilling section and well logging, combined with analyses of geological background, sedimentary texture, sedimentary structure, geochemical and palaeobiological features, the researched area in the Upper Palaeozoic can be divided into six kinds of sedimentary fades, such as stream, lake, braided delta, delta, barrier coast and continental shelf. There are some obvious different main sedimentary fades in the different period. In the stage of Benxi, the deposits from east to west are respectively shallow-sea continental shelf, barrier island, lagoon and tidal flat in the area. Most areas in Taiyuan stage are distributed by shallow-sea continental shelf in the southern and eastern part, but in the northern and western part are scattered by clastic tidal flat and carbonate tidal. The deposits in Shanxi stage are, from north to south, braided stream, meandering stream, delta plain, delta front and littoral sediments. During the early stage of middle Permian, the studied area is dominant, from north to south, of braided stream, braided delta plain, braided delta front and littoral deposits, while the extension of sedimentary facies belts in the middle and the late stage of middle Permian is as the same as that of Shanxi Stage.Sequence stratigraphy for Upper Palaeozoic strata of the area is also discussed on this paper. The sedimentary formation can be summarized as epicontinental sea filling sequence, offshore debris lake basin sequence and inner continental lake basin sequence etc. 3 supersequence and 18 sequence. A framework of sequence stratigraphy for the Upper Palaeozoic strata is established in the area. Sequence 1 to 4 are correspond with Benxi formation and Taiyuan formation in this area, they are the epicontinental sea sedimentary sequence admixtured between carbonate rock and clastic rock. Sequence 5 to 15 are correspond with Shanxi formation and Shihezi formation, they are offshore debris lake basin sedimentary sequence. Sequence 16 to 18 are correspond with Shiqianfeng formation, they are inner continental lake basin sedimentary sequence.In analysis of sequence, the well logging curve can provide the dependable information of identifying the datum plane gyration, and resolve the analysis of high resolution sequence stratigraphy that problem because of lacking the heart well data. In the stream-delta sedimentary system, the curve of RSHSA described quantificationally to decide the mode of strata sedimentary and accept the space and sediment supply the velocity to compare on the abstract concept and variation. The variation not only can be use to divide the high resolution sequence automatically, but also can be use the important parameter of the strata imitation. The curve of RSHSA can make dividing stratum datum plane and sequence stratigraphy computerized, and raise highly the accuracy and efficiency of the strata demarcation.There is a relationship between sedimentary sequence and natural gas. Sequence can contrail the association of source beds, reservoir and cap beds, and affect the distribution and function of reservoir. Sequence 1-6 have good source rocks, they are the main source rocks in the Upper Palaeozoic in this area. Sequence 5-11 are the offshore debris lake basin sedimentary sequences and main reservoir in the Ordos Basin. Sequence 16-18 are inner continental lake basin clastic sediment sequence. Therefore, there are good association of source beds, reservoir and cap beds in the Upper Paleozoic of this area.