DISTRIBUTION OF LITHOFACIES AND THE CONTROL CHARACTERISTICS OF STRUCTURAL BASINS OF WUFENG-LONGMAXI FORMATION SHALE IN UPPER YANGTZEAREA CHINA

摘要

In this study, we perform the systematic analy-sis of graptolite biostratigraphy, lithofacies strata, logging response, geochemistry, element geochem-istry and other characteristics of 14 evaluation wells or pilot wells in the Wufeng Formation-Longmaxi Formation in the Weiyuan area. The development of the Wufeng Formation-Longmaxi Formation paleo-uplift in the remote area points out that the paleo-up-lift controls the thickness and lithofacies distribution of shale, clarifies that the distribution of high-quality shale is controlled by the paleo-uplift, and puts for-ward recommendations for the optimal deployment of horizontal wells. The main conclusions are as fol-lows:(1)For the first time, it is confirmed that there is an (underwater) paleo-uplift in the area of Well Z4-Z1-Weiye1-W5-WX from the aspects of biostra-tigraphy, lithologic stratum, electrical characteristics, and stratum thickness;(2)The stratum distribution and lithofacies in different periods are mainly con-trolled by the development of paleo-uplifts. The up-lift area and surrounding stratum are thin, the content of clay minerals or carbonate minerals is high. the deposition thickness of depression area is large, and the content of siliceous minerals is high. The source of the Wufeng Formation shale in the Weiyuan area during the sedimentary period is mostly from the an-cient land of central Sichuan. The early Rhuddania is dominated by biogenic quartz with less provenance. The source of the late Rhuddania maycome from the ancient land of central Guizhou in southern Sichuan. The source direction indicates the changes of the sedimentary system;(3) The quality of the early Rhuddania(LM1-LM3)stratigraphic reservoir is the best, the production is high, the plane distribution of the reservoir parameters is controlled by the uplift development, and the reservoir quality in the depres-sion area is the best. It is recommended to use the early Rhuddania strata as the target to implement horizontal wells and prioritize the deployment of horizontal wells in areas with large thicknesses in this interval, avoiding the uplift areas.