Study On The Sedimentary Of Chang8₁Reservoir Of Yanchang Formation In Huaqing Area Of Ordos Basin

This article is a systematic study mainly about the sedimentary facies features of Chang81reservoir, which is located in HuaQing area of Ordos Basin.In this article, combined with the related research result, the sedimentary facies analysis theory and sedimentary facies research means and technology methods are used. At the same time, research respectively the study area about the stratigraphic division of the Chang81reservoir of the Yanchang formation and relevant indication parameter of the provenance characteristics and development characteristics of the sedimentary facies types and the main sandstone types. Based on those researches, we have a deeper understanding about the sedimentary system of the study area. The main research methods and conclusions include the following aspects:(1) Using the new logging data and seismic interpretation data, carries on the division and correlation of Chang81, and put the study area of Chang81into3layers.(2) In order to find the source of sedimentary, the palaeo-structure, flow ancient, distribution of the heavy minerals, the ZTR index, distribution of the light mineral, cuttings types were discussed in the article, and have a compare system research about the source conditions of the study area. The analysis results shows that there are three different sources from the west, southwest, northeast. The Baibao area which is located in the northeast of the study area was controlled by the northeast sources; the central region of the study area was controlled by the several sources; and the rest of the region was controlled by the west and southwest sources.(3) According to the analysis, we consider that the lithic feldspar sandstone is the main Sandstone type in the study area, and secondly is the feldspathic litharenite. And these sandstones are in good sorting and medium grinding roundness and high grade of maturity of rock structure and low grade of maturity of rock contents on the whole.(4) In order to find the developmental characteristics of sedimentary facies, the article based on the drilling core observation, sedimentary facies analysis, single well-log, sequence analysis and so on. Then the result is that:the one is that Chang81of Yanchang formation is composed of Lake system and Delta system. Another is that the study area is divided sedimentary identified into meandering delta front and braided delta front. The main microfacies types are sheet sand, underwater distributary channel, distributary gap and mouth bar, in some parts of the region develop the shallow lake mud microfacies. It should be pointed out that the sand body has these characters as follows:the distribution is concentrated with good lateral coalesced and the type is mainly medium-fine sandstone with large thickness and banded distribution in the underwater distributary channel microfacie. Because of the superimposed sand body in the underwater distributary channel microfacie, it is a pretty source reservoir cap assemblage, and then, it becomes a bebeficial reservoir exploration horizon.(5) In order to restor the complex evolution process, the lithofacies paleogeographic preliminary explaination on the second level of layer is based on the sedimentary facies of the profile of the contrast and the sedimentary facies analysis information of single wells.(6) There are four types of the cause of the sand body in the study area, they are underwater distributary channel sand body, mouth bar sand body, several underwater distributary channel superimposed sand body and superimposed composite sand body. The main lithology is the fine sandstone, is the main reservoir in the study area, and is the favorable block for oil and gas reservoir.(7)The discussion about the depositional model of the sedimentary facies in the study area, this article mainly relies on the palaeogeographic research and phase analysis as a basis for the preliminary analysis. And the conclusion is:the research area belongs to shallow water delta front subfacies depositional systems and is in Lake invasion development period with shallow lake subfacies and development. On the deposition it was a certain continuity.