Study On Rock Types And Responses Of Well Logging In Urxun-Beier Depressions In Hailar Basin

Hailar basin located in suture zone of North China plate and Siberian plate, formed a fault basin of Mesozoic-Cenozoic in Hercynian. The area is 7048 km2 in total, and 44210 km2 in our country. The maximum depth of the buried sedimentary rock is about 6000 meters in Hailar basin. The Petroleum geological conditions varied greatly and the cases of hydrocarbon bearing were complex. It has been found several industry productions rich in oil and gas so far, which is considered to be the most favorable exploration area for oil and gas in Daqing.The study area is in Urxun and Beier depressions in Hailaer Basin. Urxun depression is a large unsymmetrical fault-depression with strike-slip in Mesozoic-Cenozoic,and Beier depression is an extensional depression in early Cretaceous which is early extension and later inversion. The strata in the study area consist of Budate Group, Xing'anling Group, Tongbomiao formation, Nantun formation, Damoguaihe formation, and Yimin formation. The aim of this paper is to clarify the type of the rock and use the borehole logging to found the relationship between the lithologic characters and electrical property.In this paper, many methods and techniques are utilized, such as well core descriptions, normal slice identification, crossplot and the logging technology.According to the core description of the 38 wells and the normal identification of 1282 slices in the Urxun-Beier depressions, It is indicated that there are five types of rock in Hailar baisn, including volcanic lava, volcaniclastic rock, pyroclastic sedimentary rock, sedimentary– volcaniclastic rock, sedimentary rock. Among these rock types, the proportion of the pyroclastic sedimentary rock is 43.35% being the most, the secondary is the sedimentary rock, its proportion is 26.84%. The proportions of the rest rock types are 17.68% for volcaniclastic rock, 10.02% for sedimentary– volcaniclastic rock, and 2.11% for volcanic lava. It is showed that pyroclastic sedimentary rock and the sedimentary rock are the mainly types in Hailar basin. According to the classification criteria of sandstone and the size of the tephra, the author subdivided tuff,ignimbrite and bedded tuff into coarse grain tuff/ ignimbrite/ bedded tuff,medium grain tuff/ ignimbrite/ bedded tuff,granule tuff/ ignimbrite/ bedded tuff and silt tuff/ ignimbrite/ bedded tuff. The main rock types or their association of the Budate Grop-Damoguaihe Formation in the research area are volcanic lava- sedimentary rock, pyroclastic sedimentary rock, sedimentary rock, pyroclastic sedimentary rock-sedimentary rock, pyroclastic sedimentary rock-sedimentary rock. Their distributions have some regularity. Taking Badate Grope for an example shows that its rock types have good zonality, and the lithologies from the southwest to the northeast are andesite,ignimbrite,tuff,bedded tuff and tuff sandstone in turn. There are two mudstone areas in the north of basin. From the distribution of the lithology, the author inferred there was a crater in the southwest, and the volcanism was intensity, the range of the volcanism exceeded the center of the basin. The farther distance from the crater, the fewer tephra is contained. The rock types change from andesite, ignimbrite and tuff which are near the crater to bedded tuff,tuff sandstone and mudstone which are far from the crater. So the volcanism effected the rock types.By the result of the core observation, It is showed that it is difficult to distinguish the polymictic conglomerate and tufaceous conglomerate,mudstone and tufaceous mudstone in core. In general occasions, compared to the tufaceous conglomerate, the gravel of the conglomerate has better rounding. Under the microscope, both of them can differentiate, presenting that the cements of the conglomerate are sands with different sizes and the cements of tufaceous conglomerate are tufaceous substances and tufaceous sands. The tufaceous mudstone and mudstone can be distinguished by crossplot or geochemical analysis.By the result of the slice identification, It is indicated that the chief post sedimentational changes of the oftufaceous substance are calcitic cementation,chloritization and devitrfication. Calcitic cementation was universal development in the tufaceous substance, it is manifested that calcitic cemented the tufaceous substances in the anaphase and calcium carbonate precipitated in the pores to form calcite, making the clastic particles jointed and consolidated. The rebuilding of the rock types was focused on the pyroclastic sedimentary rock, during which the calcium carbonate penetrated in the anaphase, replaced the original cements and matrices of the rock, most of which is the tufaceous substance. It had been three results:(1) A part of calcic replaced the remnant tufaceous substance, turning the rock into calcareous rock, such as calcic tuff sandstone/siltstone/mudstone or calcic replaced tuff.(2) All the tufaceous substances were re placed by calcic (the interstitial matters and some grains in the coarses clastic rock and the all in the fine clastic rocks were all replaced by calcic, still preserving the tufaceous structure, such as welded texture), turning the rock into calcareous sandstone/siltstone/mudstone(marlite).(3) Tufaceous substance is all replaced by calcic, and the tufaceous structure is not preserved, turning the rock into calcareous sandstone/siltstone/mudstone (marlite). In the cases of (2) and (3), it made tufaceous cemented rocks present out the characteristics of the normal sedimentary rocks. Chlorite is the outcome of clay alteration of the tufaceous substance and other related detritus, and it grew up by recrystallization. There are many phenomena of devitrification in this area showing the glassiness substance of tufaceous substance suffered alteration.In the study area, the rock type of such tephra-sedimentary rock is related to the volcanism. The types of the volcanism in the research region are catapult airfall, ejection airfall, base surge, pyroclastic flow and fine detrital air fall. The rock types by the the catapult airfall and ejection airfall are bedded tuff- tufaceous rock. The rock types by the hot pyroclatic flow are explosive breccia, tuff and bedded tuff. The rock types by the hot base surge are ignimbrite, changing to the feeble ignimbrite up and down. The rock types by the the fine detrital airfall are tuffsBy the research of the bore hole logging and crossplot, It is showed that it is not only to distinguish the less complicated rocks like sandstone and the conglomerate by useing of the borehole logging and crossplot, but also can recogonize the rocks of polymictic conglomerate and tufaceous conglomerate,tufaceous mudstone and mudstone which are easy confused. So using the well logging information and setting up lithology-logging response modes can recognize the strata of the losing core or without core.Through the evidences of the oil and gas analyses, the tufaceous sandstone of typeⅠhas the highest oiliness frequency, and it is the most effective reservoir in the research area. The other rocks such as medium tufaceous sandstone,fine tufaceous sandstone, medium sandstone and fine sandstone are also important for the effective reservoir and they need to be paid attention in oil explorations.