Comprehensive Evaluation Of The Oil And Gas Exploration Prospect In Dayangshu Basin

With the guidance of Oil & Gas exploration theory of rift-subsidence basin and basing on the distribution and characters of petrophysical property data in the whole area, the paper makes a comprehensive study in Dayangshu Basin after collecting existed data, analyzing all the samples carefully and applying each study fruits comprehensively. In order to evaluate the oil and gas exploration prospect of the basin comprehensively, the study, using joint inversion with gravity, magnetism, electrical survey and seismic exploration, solves mainly conditions of formation distribution, structure feature and source rocks development. Considering generally existing comprehensive geophysical survey data, we established a method using joint inversion with gravity, magnetism, electrical survey and seismic exploration and solved relating basic geological questions basing on the study of regional differences in density, magnetic and electronic property etc. and corresponding relations of major formations and lithological characters.According to the section features and plane distribution of compositive geophysical survey, we established suitable geological model and researched regional structure, sedimentary rocks distribution and petroleum exploration prospect. The research results show: 1. The structure of Dayangshu Basin presents the characters of two belts in east and west, two blocks in south and north, and stretching in NNE direction. Five first-order such as South Depression, South Uplift, Middle Depression, Middle Uplift and North Depression and sixteen second-order structural elements have been divided in the basin; 2. A large number of faults are developed in the basin and the stretching directions of most of them are close to SN and NNE, and only a few of faults are in NNW, NE and NEE directions. The maximum extending length of faults is near 200km and the maximum normal and horizontal throw can reach 3400.0m and 6.0km, respectively;3. The formations developed in Dayangshu Basin form bottom to top are Nanping, Longjiang, Jiufengshan and Ganhe. Among them, Longjiang, Jiufengshan and Ganhe formations are the principal ones and the area of Jiufengshan Formation is the biggest whereas Nanping Formation is distribution-limited. The maximum thickness of South Sag, Middle Sag and North Sag is 4300m, 3400m and 2400m, respectively;4. Dark mud rocks and coal beds are found in South Depression with source rocks in fault-depression belts. The source rocks become thinner form the center to the margin. The Dark mud rocks and coal beds account for 16.15 percent of the total sedimentary rocks, with 14.6 percent of dark mud rocks and 1.5 percent coal beds. The maximum thickness of source rocks of Longjiang-Nanping, Jiufengshan and Ganhe formation is over 60m, 160m and 70m, respectively.The normal sedimentary rocks and fine sedimentary facies are the main source rocks developed in Dayangshu Basin;5. TOC of source rocks in Dayangshu Basin is 1.14~3.14 percent and the total hydrocarbon content is 0.01~0.067 percent, H/C is 0.3~1.0 percent and O/C is 0.06~0.25percent. The main type of organic matter is humic type and the second is sapropel type, S1+S2 is 0.07~8.59mg/g, these mean that the source rocks in Dayangshu Basin is of some potential and material base for hydrocarbon generation;6. Five types of reservoirs have been proved to be existed in the basin, that is neutral-basic lava, acidic lava and coarse pyroclastic rocks with pores and cracks developed, and glutinite origin in alleviation and basement granite with pores. Longjiang, Jiufengshan and Ganhe formations develop tight volcanic lava, volcanic tuffaceous, mud stone and shaly siltstone, the composition of rocks is tight, and pores and cracks are rare, which make up the cap rocks of the basin; Being the rift-subsidence basin with multiphase volcanic extrusion, there are not only lots of structural traps but also volcanic and normal sedimentary rocks lithology traps developed in the Dayangshu Basin;7. The total gas amount generated in the Dayangshu Basin is 71502.3×108 cubic meters and the total oil amount is 279111.1×104 tons, the total gas amount expulsed 41404.07×108 cubic meters and the total oil amount expulsed is 100639.6×104 tons. The generated and expulsed amount of oil and gas from Jiufengshan Formation is the most. Referring to Songliao Basin and other peripheral basins and combining actual geological conditions of Dayangshu basin, the accumulative coefficient of oil and gas chosen in Dayangshu Basin is 10 and 1 per cent, respectively. The available accumulative oil and gas amount is 10063.96×104 tons and 414.0407×108 cubic meters, respectively. If reducing 1225 cubic meters gas to 1 ton oil, the total resource quantity in Dayangshu Basin is equal to 1.338×108 tons oil and the basin is of quite well exploration potency.8. The favorite petroleum exploration belts in South Depression in Dayangshu Basin are Baoshanchangjigang anticlinal belts and Geni fault-depression belts. Structures such as Liuhetun, Xinglongpu, Zhongxintun and Dongfude, having favorable reservoirs and cap rocks conditions and good trap types, developing multi formations and closing to oil-generating depression, are the first objectives for exploration activity in Dayangshu Basin.