Reservoir Characteristics And Evaluation Of Benxi Formation In YC Area,Southeast Of Ordos Basin

In this paper,the Carboniferous Benxi Formation of the YC area in Ordos Basin is taken as an object of study.A large number of core observations,logging data,castings,thin sheets,and mercury injections were analyzed and tested,a detailed analysis of the sub-layer division,sedimentary microfacies and sand body distribution characteristics,petrological characteristics,reservoir characteristics,etc.establish the effective reservoir division criteria for the Benxi Formation and evaluate the Benxi Formation reservoir in the YC area.The paper has obtained the following major understandings and achievements:?1?Two flag layers were identified in the stratum division of the study area:"8^#and 9^#coal seams"at the top and"iron-aluminum rock"at the bottom.According to the signature layer,taking into account the depositional cycle and the principle of sedimentary thickness,the Benxi Formation is divided into three intervals in the longitudinal direction.The Benxi Formation is relatively small in stratigraphic changes,with similar top and bottom boundary structures.with a single dip in the west and a low-width nose-like uplift extending in the east-west direction.?2?The Benxi Formation uses the barrier island sand dam as a skeleton sand body.The sedimentary microfacies mainly were barrier islands developed in the study area during this period of ben 3,while the distribution of lacustrine lakes was relatively limited;The development scope of barrier islands was relatively smaller than that of the ben 3 in the ben 2 period,and the lacustrine sediment scope was further expanded;In the ben 2 period,the distribution scope of barrier islands has further narrowed,and the sediment release range is relatively larger;Due to the cutting and strong transformation of the tidal channel during the ben 1 period,the distribution characteristics of the barrier islands were not obvious,and they were mainly isolated,showing the sedimentary characteristics of multiple isolated barrier sand bodies.?3?The reservoir of the Benxi Formation is dominated by quartz sandstone,followed by lithic quartz sandstone,The interstitials consist mainly of calcite,kaolin,and mud,and their content accounts for about 73.7%of the total content of interstitials.Sandstone sorting is generally better,roundness is better,and grain size is mainly medium-coarse grain.The physical properties of the reservoirs in the Benxi Formation are relatively poor,the average porosity is 3.06%to 7.83%,the average permeability is?0.45³.46?×10^-3?m²,and the porosity and permeability are positively correlated.The correlation coefficient?R²?)is 0.7045.?4?The heterogeneity of the reservoirs in the Benxi Formation of the study area is relatively strong,the plane heterogeneities of the small layers are strong,and the heterogeneity between the layers is weak.The reservoirs of the barrier island in the Benxi Formation are mainly distributed in the planes of Type II and Type III reservoirs.