Analysis On Lithology-Lithofacies Of Volcaniclastic And Sedimentary Rock Of Tongbomiao Formation-Damoguaihe Formation In Wuerxun-Beier Depressions Of Hailaer Basin

Hailaer basin is the biggest oil and gas basin on the periphery area of Songliao basin. Wuerxun and Beier, two bigger sub-fault depressions lie in the south of Beier Lake sag with the potential of exploration and development on oil and gas. So far, Wuerxun and Beier depressions have been in relative higher stage in prospecting, with more than 70 wells for exploration and more than 50 wells for development evaluation. However, the lithology of this region is very complex. There are some conflicts in identifying rocks. This has made the logging interpretation and the reconstruction of sedimentary environments difficult and uncertain, affecting the following exploration going on well. It is necessary to study the lithology and do systemic sedimentary research, to provide advantageous exploration belts and targets.1.MethoLogy of The ResearchBased on the description of well cores, the identification of the thin section and the grain size analysis, we got the lithologies of the research area and did the well sedimentary facies analysis. As a result, dependable analysis of core sedimentary facies had been obtained, while the description of sedimentary features and facies types had been done with the precision to microfacies. Further, with the analysis of map of sand content rate isoline, the preponderant facies was defined to realize the plane distribution feature of sedimentary facies and to analyze the features of sedimentary facies and the directions of provenances. On the above researches and the related data, some analysis of reservoir rocks were given through doing some statistics on the oil and gas shows in study well, to find out the relation between oil and gas shows and sedimentary facies, especially microfacies for the prediction of advantageous reservoir sands.2.Research on Types of RockThe lithology of Budate group- Damoguaihe formation in Wuerxun-Beier depressions of Hailaer Basin is a set of rocks between volcanic lava and normal sedimentary clastic rock, mainly of volcanic lava, pyroclastic rock , sed pyroclastic rock, pyroclastic sedimentary rock, normal sedimentary rock. The abundance of types of rocks reduces in turn according to the following: pyroclastic sedimentary rock, sedimentary rock, pyroclastic rock, sed pyroclastic rock, volcanic lava. Abundance of pyroclastic sedimentary occupies the absolutely superiority.3.Particularity in The Growth of Sedimentary Facies and The Types of Sedimentary FaciesThe research area in that time was located in a part of volcanism– deposition region and deposition region. There are seriously chaotic mélange of volcanic clasts and normal terrigenous clasts. Volcanic rock exists in forms of sedimentary microfacies in normal sedimentary belt. The special deposition of volcanic clast mainly displays in: volcanic clast channel, volcanic clast delta, volcanic ash in lacustrine environment, and so on.The target layers are sets of terrestrial deposits, including alluvial fan, braided stream, meandering river, fan delta, delta, nearshore subaqueous fan, turbidity current, subaqueous fan, coastal lake, shallow lake, half-deep lake. In the view of dispositional sequences, The episodic faulting is reflected in the depositional sequence (possibly exist conglomerate) of conglomerate - sandstone - mudstone–sandstone. With the participation of volcanic activity, it will take on the depositional sequence of conglomerate - pyroclastic rocks/sandstone - mudstone (possibly exist pyroclastic rocks) - sandstone (possibly exist conglomerate), also is the structure of deposition -volcano - deposition. This has reflected the control of structure - volcanism to the fills of the basin, corresponding to the divisions: faulting, faulting - volcanism and post faulting stage. This kind of depositional evolution not only may be reflected in the 4-5 rank of depositional cycle, but also reflected in the high ranks, like group or formation cycles.4.The Plane Distribution of Sedimentary FaciesWuerxun depression:The sedimentary facies belts of Tongbomiao formation distributed in north-east. There were alluvial fan, fan delta- nearshore subaqueous fan, fluvial facies, coastal-shallow lake, half-deep lake. Marginal facies grew very well, and provenances were from northwest and southeast. The sedimentary facies belts of the first member in Nantun formation still ditrbuted nearly north-east. There were alluvial fan, fan delta, shallow lake, half-deep lake facies. And shallow lake sediments were dominated. The provenances were from northwest and southeast. There were alluvial fan, fan delta, nearshore subaqueous fan, coastal lake, shallow lake, half-deep lake facies in the second member of Nantun formation. Half-deep lake sediments were dominated, and half -deep lake lay in the middle of the depression, took on nearly south-north in a shape of irregular ellipse. The provenances were from northwest, southwest and east. There were fan delta, shallow lake, half-deep lake facies in Damoguaihe formation. The sedimentary facies belts distributed in north-east. The provenances were from northwest and east.Beier depression:There were alluvial fan, fan delta, fluvial facies, shallow -half-deep lake facies in Tongbomiao formation. Marginal facies grew very well, the provenances were from west in the south, south, east in the south and east in the north. There were alluvial fan, braided stream, fan delta, delta, alluvial plain-coastal-shallow lake, shallow -half-deep lake facies in the first member of Nantun formation. Marginal facies grew very well, the provenances were from northwest, southwest, south and northeast. There were alluvial fan, braided stream, fan delta, shallow lake, half-deep lake facies in the second member of Nantun formation. Lake sediments were dominated, and there were two half-deep lake regions separately lying in south and north. The provenances were from west in the south and nearly southeast in the south. There were fluvial facies - delta, coastal lake, shallow lake facies in Damoguaihe formation. Shallow lake sediments were dominated. Provenance was from west.5. Distribution of Reservoir Rocks and The Prediction of Advantageous Sands in Research EareThe statistical result shows that, in the research area the oil and gas shows concentrates much on the first member of Nantun formation and the second member of Nantun formation, the second member of Damoguaihe formation is next, and the Tongbomiao formation is worst. The most advantageous accumulation facies belt is the fan delta, the next is nearshore subaqueous fan, turbidite fan, subaqueous fan. The most advantageous sedimentary microfacies are subaqueous, distributary mouth bar, distal bar and sand sheet of fan-delta front, channel sand of nearshore subaqueous fan, turbidite sand, subaqueous fan sand, and so on.