Causes Of Densification And Predictions Of 'Deserts' Of Glutenite Reservoirs Of Shahezi Formation In Xujiaweizi Fault Depression

Shahezi Formation of Xujiaweizi Depression was used to be studied as the source rocks of overlying Yingcheng Formation.However,high-production industrial gas flow was achieved by deep horizontal wells when drilled Shahezi Formation,which showed the tight glutenite reservoirs of Shahezi Formation has great potential for exploration and development.In order to realize tight glutenite reservoirs'industrial exploitation value of Shahezi Formation,it is essential to predict distribution of‘deserts',and accurate understanding of the pore evolution during different diagenesis stages and the causes of densification are the basis of optimizing favorable‘dessert'area.Based on the former exploration,analyzed petrological characteristics of tight glutenite reservoirs of Shahezi Formation by logs,rock cores,sedimentary and structural data to conclude the lithofacies and lithological association.Based on the XRD,particle size analysis and property data to study the feature and vertical evolution law of property.Using data of casting thin section and SEM to analyze the pore types,diagenesis types and diagenetic evolution sequence.Based on the studies of reservoir and diagenesis characteristics,and the reservoir characteristics and diagenesis,quantitatively identified the degree of modification of the pore by different diagenesis,analyzing the reasons of dense of reservoirs.Summarized the main control factors and distribution rules of the‘deserts'of tight reservoir,predicted high quality reservoirs,which can provide practical guidance for future exploration and arrangement.The achieved results are as follow:(1)The main rock types were conglomerate,glutenite and coarse sand rock,which were poor sorting and low gridding,high content of debris and tuff fillings.The average porosity was less than 8%,and average permeability was less than 0.1mD,which means that Shahezi Formation was belong to extra low porosity and permeability reservoirs.The porosity and permeability of the reservoir in Shahezi Formation are gradually decreased with the increase of buried depth.There were three abnormal pore development zones in 3300m-3800m?3900m-4100m and 4500m-4600m respectively.The main pore types were dissolution pores and inter-crystal pores.(2)Shahezi reservoirs were in the B phase of middle diagenetic stage and the late diagenesis stage,Influenced by particles size and sorting,the diagenetic evolution sequence was classified into three types.They were dominated by dissolution,dissolution and cementation,cementation and compaction respectively.(3)On the background of low quartz grain content,high debris and matrix content,Shahezi Formation developed a low original porosity which lay a foundation of densification.Compaction was the main control factor of Shahezi Formation's densification,the average value of the porosity loss is 21.53%and the value of ementation was 8.33%,which was the intensification and key(4)The feature of desserts of glutenite reservoirs of Shahezi Formation was both developing residual primary pores and dissolution pores,and they was influenced by lithology,source storage formation allocation,migration pathway and early hydrocarbon charging.Coarse sandstone and sandy conglomerate are the material basis of forming desserts.The mutual layer distribution of glutenite and high quality source rock(TOC>1%)is the key,early effective oil and gas filling is the guarantee for the formation.At last,11‘deserts'were found out and the total area was 614km~2.