Sedimentary Facies And Sandstone Body Prediction Of Huagang Formation In Tianwaitian A Gas Field Of Xihu Depression

Xihu Sag is the largest and deepest sag in the East China Sea Shelf Basin which has a large area, big reservoir thickness and abundant petroleum resources. As the main oil-producing block of Xihu Sag, Tianwaitian A gas field should be studyed on sedimentary microfacies, the characteristics of plane distribution and the distribution of favorable sand body in this area. These researchs can not only have a certain guiding significance in the further oil and gas exploration in the study area, but also has realistic and far-reaching significance in expanding the exploration of oil and gas reservoirs in the whole sandstone reservoir of Xihu Sag.This paper which takes some theories such as the sedimentary theory and petroleum geology as the guidance, consider the Huagang Formation in Tianwaitian A gas field of Xihu Sag as the research target, is about several reaserchs such as the sedimentary microfacies, seismic attribution and inversion, distribution of favorable sand body and so on. All these research are based on the core observation, the well logging data interpretation, the logging data interpretation, the rock slices identification and the abundant sample analysis as well. Obtained are follows:First, based on meticulous core observation and description, according to lithofacies, sedimentary structures and sequence, the depositional facies of key sections of Huagang Formation in the study area were analyzed.Above reaserch suggest that, the meandering river facies, delta facies and lacustrine facies developed in Tianwaitian A gas field of Xihu Sag. Further these three types of sedimentary facies were divided into 6 types of subfacies,11 kinds of microfacies. The meandering river and delta facies are the most developed, mainly composed of meandering river channel, crevasse splay, levee, flood plains and other microfacies. Delta is divided of delta plain and delta front. Delta plain can be divided into branches of the river, the land natural levee, crevasse splay, swamps four kinds of micro-phase; Delta front can be divided into underwater distributary channel, between the Bay tributary mouth bar three kinds of micro-phase.Second, reveals the sedimentary microfacies plane distribution characteristics and its vertical evolution in the key sections of Huagang Formation of Tianwaitian A gas field through well and seismic attribute analysis.The H7b and H6b small sections of Huagang Formation of Tianwaitian A gas field is mainly developed meandering river deposit. The main river in the direction is from A to H to I to K bypass F well area distribution, sand content is between 40% to 90%. H5b small sections is delta plain deposit, the main river in the direction is from A to I to K bypass F and H well area distribution, sand conteng is between 30%to 90%. H3c and H1 samll sections is developed delta front deposit, the main river in the direction is from F to H to I to K well area distribution, and the sand content is between 30% to 70%. The Huagang Formation of study area were mainly through the process of rising lake level, the deposition of water gradually becomes deeper.Third, based on the above, by wave impedance inversion as a means, reveal the sand thickness of the gas reservoir section of the study area, and predicted the favorable reservoir sand body in the study area.Select the appropriate time window based on the model range impedance inversion results, fine dissected Tianwaitian A field containing sand gas reservoir section focuses thickness. The focus reservoirs containing gas reservoir sand distribution of Tianwaitian A gas field were analyzed. The sand body of Huagang Formation is relatively developed. The main sand body thickness range of H7b is 20-35m, H6b’s sand body thickness is between 15 to 30m, H5b’s sand body thickness is between 24 to 40m, H3c’s sand body thickness is between 15 to 25m, H1’s sand body thickness is between 50 to 80m.On the basis of all above research, combining with the seismic attribute extraction, sand thickness inversion, and the research of sedimentary microfacies in the sequence framework, it could be carried on the cumulative sand thickness of the key sections of Huagang Formation. Accumulate the five small formations’sand layer thickness. Through the contours line of 135m as the favorable sand boundary constraints to predict the favorable reservoir and body distribution area of the study area.