Study On Sedimentary System And Reservoir Characteristics In The Lower Part Of Yanchang Formation In Triassic System Of Ordos Basin

Based on the theories of sedimentary, logging geology and reservoir geology, sediment source, sedimentary facies and distributions, sand-body distribution, reservoir characteristics and distribution regularity of high-penetration reservoir about the lower of Yanchang formation of Chang9and Chang10oil layer group in Triassic system of Ordos Basin are researched. Chang10oil layer group is firstly divided into three parts, and Chang10|oil layer group is firstly divided into three parts too. Sedimentary facies and sandbodies distribution maps of the each part about the whole basin are protracted. Meanwhile, paleogeographic evolution of Chang9to Chang10of Ordos Basin was reconstructed. Reservoir of Chang1011oil layer group about in the whole Ordos Basin is researched firstly. Reservoir characteristics of Chang9and Chang1011in the indifferent region is classified and summarized firstly.Provenance of Chang9and Chang10which are comes from four systems including northeast, northwest, southwest and south is clearly put forward by study on paleocurrent direction, rock and mineral analysis, distribution of cathodoluminescencede, minor elements and sandbodies. Sedimentary system of Chang9and Chang10can be divided into four kinds of sedimentary systems such as lakes, deltas, rivers and alluvial fans which contain five kinds of sedimentary facies and thirteen kind of sedimentary subfacies by analysis of outcrop observation, core description and log facies. The conclusion that the main characteristics sedimentary facies about Chang10is rivers-deltas-shore shallow lake facie, but the sedimentary facies of Chang9has the features of "many of deltas around lake" has been drawn clearly. There are eleven relatively large scale deltas stone bodies of lake which form a series of water system, multi-source river and zonal pattern deltas in the period of Chang10to Chang9. Sedimentary system of Chang9and Chang10are different from the upper of Yanchang formation for the sand bodies of braided channel delta are more development than meandering river delta.Combining the laboratory data and oil production test data, the petrologic characteristics, pore types and structure, physical property characteristic and diagenesis of Chang9and Chang1011are studied. The results show that the sandstone is mainly composed by lithical arkose and arkose, interstitial material content is high (more than10%), chlorite is higher in the Chang9reservoir and laumontite is higher in Chang1011reservoir. It is mainly consist by fine-medium sand in Chang9reservoir, but medium sand in Chang1011reservoir. Porosity types of Chang9and Chang1011reservoir are mainly composed by predominantly intergranular pore, the secondly is solution pores of feldspar and laumontite. The main pore-throat type of Chang9is small pore and tiny throat, medium pore and tiny throat. The main pore-throat type of Chang1011is small pore and tiny throat, medium pore and fine throat. Constructive diagenesis includes chlorite cementation and solution. High-permeability reservoirs are mainly controlled by sedimentation environment and diagenesis. Sedimentary facies is the innate basis and diagenesis play important roles later.