Sedimentary System And Hydrocarbon Enrichment Of Yanchang Formation, Upper Triassic In Zibei Oilfield

Odors basin is located in the weste of Huabei area and intersection point of west and east structure domain, which is an important oil, gas and coal deposition in china. The Yanchang Formation of Upper Triassic in North Shaanxi is major terrigenous clastic system deposited in fluvial-latchstring environment, under the influence of the llocyclicity factor which include Indosinian tectonic, eustacy ,sedimentary supplies and the autocyclicity factor. In late Triassic, North Shaanxi was divided into two parts bounded by Zhidan-Ganquan-Yichuan demarcation line. The south part was slope and deep floor of the lake, and the north part was a broad shallow-water platform of the latchstring shore. In the north part, chang-6 and chang-7 oil-bearing beds of Yanchang Formation were typical shallow-water platform delta with an incomplete progradational sequence, in which the delta plain facies were well developed and the river-mouth bars were not developed.Chang-6 oil-bearing beds, one of the most important oil-bearing beds in Yanchang Formation, is a set of progradational deposits, which is formed by rivers pouring into the shallow-water platform of the lake after the greatest transgression in chang-7 Stage. Based on the analyses of outcrops, core, log data, agrochemical information, etc. Which can be recognized as delta sedimentary system in Zibei oilfield, Each sedimentary systematic characteristic and their genetic is analyzed carefully. The development of sedimentary environment of Yanchang formation be analyzed and discussed further.Based on the analyses of all kinds of sedimentary deposit .under the direction of the theory and methods of sequence stratigraphy, 4 type I sequence boundary could be recognized in the study area, according to the marked bed including plane of deflation, scour, the plane of lithological salutation, structural transformation, down cutting channel sheet sand and so on. type I sequence consists of low stand systems tract, transgressive systems tract and high stand systems tract. The relationship between sedimentary sequence and petroleum is analyzed further.The Process of diagenesis controlled partly by sedimentation, the evolution of pores influenced by it. The affection of origin ingredient and structure in sand to sediment and solution in gooey be exhibited. The activity area of sediment and solution in gooey is distributary river, which has gigantic water power, good degree of sorting and roundness, gruff grain .lower mud and mica content. So it has good porosity.The sand body distribution is under the control of sedimentary faces; source rock, reservoir rock and cap were affected by sedimentary sequence, porosity and permeability were affected by diagenesis, the three elements make the basis of petroleum system space-time unit distribution pattern.