The Study Of Depositional Characteristics And The Prediction Of Oil And Gas Reservoirs In Bayanhua Group Of The Lower Cretaceous In Baiyinchagan Depression Of Erlian Basin

The Baiyinchagan depression, which is a secondary sedimentary units of Chuanjing depression, be located in north of Chuanjing depression which in westen of Erlian Basin in Inner Mongolia. We have achieved good success in higher structrual trap as the exploration and exploitation work outspreading. Looking for subtle reservoir in the lower and middle deprss becoming the main task while we brokethrouth in concealed reservoir in lower depression by drilling well Da24 and well Da39 succeeded, and this dissertation is openned out around it.We have established the stratum frame work of the whole basin by absorbing in the data of geology, crumn collecting, welllogs and seismology under the instruction of theory of sequence stratigraphy. Including sedimentary floor, eight formation boundary had been distinguished, along with seven sequence boundary, six third order sequence. The mode of sequence developing of formation of Duhongmu and Tenggeer group in Baiyinchagan depression. And it has believed that the region tectonic movement, characteristics of mother crumb and ancient climate are the main control facts in forming of the faomation.The structure and evolvement of the depression have been studied based on 3D seismic data. We considered that single-faulted structure overlaps the former twi-faulted structure, and single-faulted dustpan depression was formed. Erlian Basin could be divided into three phases in structure evoluation after Mesozoic period, that is the forming of Mongolia drape phase, rift developing phase and the attenuation and wither away of rift in late the Cretaceous period.It has been accepted by all that there are delta facies, shallow lake facies and deep lake and half-deep lake facies. Shallow lake sandbar has been recognized in southern slope belt, along with underwater embranchment riverway, mat sand, underwater fan microfacies near shore and turbidite fan in deep lake, and frontier of fan-delta, turbidite in deep lake had been found also. Combining with the plant dynamic data we have been certain of that shallow lake sandbar microface, frontier of fan-delta microface are the most favorable facies in characteristic of formation. Mat sand, turbidite fan in deep lake, underwater fan microfacies near shore stood the secondary stage in the basin. It has a fine relativity between porosity and permeability and oil saturation in good reservoir, along with high output wells.It has been approved by observing core slice that the holes between grain and holes in the grain be in the dominant stage, and microcrack, eroded hole and eroded crack are also found in the rocks. The influence on the characteristics of formation by diagenesis include two aspects: the first is structural impression which make the porosity decrease; the second are crack and cauterization which make the porosity increase.It has been believed that the main control fact of collecting of oil and gas are the structure pattern, distributing of microfacies, characteristics of formation, characeristics of reservoir, oil original formation and the development of the seals. The original formation, reservoirs and seals formed in the lower Cretaceous period bring the most favorite condition for the oilfield to be created. The distributing of oil and gas are controled by faults and reservoirs, and it distributed in layer and belt state. There are lower stage lithology reservoir, middle stage structure-lithology reservoir and high stage faulted reservoir in Baiyinchagan depression.