Study on reservoir physical properties of Nadanhada terrane

. The Nadanhada terrane is basically a large tectonic sedimentary hybrid, which is an accretionary complex belt formed by the subduction of the Pacific plate to the Eurasian plate. Through field geological survey, paleomagnetic analysis, paleontological analysis and microscopic observation of core slices, its structural and petrological characteristics were studied. The results show that the accretionary complex is mainly composed of 7 parts, including undeformed sedimentary rocks, shear deformed sedimentary rocks, shear deformed volcanic rocks, turbidites, deformed siliceous rocks, limestone blocks and basic ultrabasic rocks. Shear deformation structures of deformed sedimentary rocks and volcanic rocks are developed. The sediment grain size of the Lower Cretaceous reservoirs in each basin in the northern region is relatively coarse, the sorting is moderately deviated, and the rounding is poor, mainly secondary to angular. The grain size of the lower Cretaceous sediments of each basin in the southern region is relatively fine, with coarse, medium and fine sandstones, but mainly medium fine sandstones, with medium sorting preference and sub angular to sub round roundness.


Introduction
The Nadanhada (Wanda Mountain) terrain is located at the eastern edge of Heilongjiang Province.It starts from Dahe Town of Baoqing in the west, ends at the edge of the Wusuli River in the east, starts from Dongfanghong Town of Hulin County in the south, and ends at the edge of Heilongjiang in Fuyuan County in the north.It borders Russia in the east and north.The whole area is a strip about 80km wide from east to west and 240km long from south to north.The tectonic location is in the Nadanhada area east of the Yuejin Mountain fault and north of the Dunhua Mishan fault zone [1,2].In addition, marine Mesozoic strata are also developed in the eastern part of the Nadanhada region and the eastern part of Sikhot Alin in Russia, which can be compared with the Nadanhada terrane [3,4].

Nadanhada terrane structure
Paleolatitude data (Table 1): in the Middle Triassic (T2), the Nadanhada terrane was near the equator (8.0 °), and then gradually drifted northward.From the Middle Triassic (T2) to the Neogene (N), the Nadanhada terrane drifted northward, 37.8 ° (=45.8-8.0 °), about 4150km (110km × 37.8 °), the average drift speed is about 17.3km/Ma.The current position that has been drifting from the equator [5].The Nadanhada terrane is basically a large tectonic sedimentary hybrid, which is an accretive complex belt formed by the subduction of the Pacific plate to the Eurasian plate [6].In the process of field petroleum geological survey, it is found that the Wandashan accretionary complex is mainly composed of 7 parts, including undeformed sedimentary rocks, shear deformed sedimentary rocks, shear deformed volcanic rocks, turbidites, deformed siliceous rocks, limestone blocks and basic ultrabasic rocks.Undeformed sedimentary rocks are mainly composed of mudstone, siliceous rock and siltstone, and locally contain manganese.Pillow basalt formed by rapid condensation of submarine volcanic eruption is also developed, representing the deep-sea sedimentary environment (Figure 1).

Petrological characteristics 3.1 Mineral composition characteristics and sandstone composition classification
During the field petroleum geological survey of the basin groups in the north and east of Songliao Basin in Northeast China, a large number of reservoir samples were collected, thin sections were ground, and microscopic observations and identification were carried out.The lower Cretaceous reservoir is mainly lithic arkose (Fig. 3), followed by feldspathic sandstone (IV), feldspathic lithic sandstone (VI) and lithic sandstone (VII).Volcanic rocks are also developed in some areas of the Cretaceous system.

Sorting and rounding.
Generally speaking, sandstone with good roundness has good sorting property, even pore space size, many pore coordination numbers, wide throat connecting pores and good connectivity, and small pore throat ratio; The sandstone with poor roundness is also poor in sorting.The reservoir with good clastic particle sorting has large pore space and uniform distribution, single pore type, small pore throat ratio, few fillings in pores, good connectivity between pores, high porosity and permeability; On the contrary, for the reservoir with poor sorting, the particle size distribution is uneven, the fine particles occupy part of the pore space, the argillaceous matrix fills part of the pores, and blocks the throat of part of the pores, changing the geometric shape of the clastic rock in which the pore structure is determined by the skeleton particles, making the pore space of the reservoir complex, with large differences in pore space size, uneven distribution, and large pore throat ratio, The connectivity between pores is poor, and the porosity, permeability and reservoir capacity are poor.The clastic particles of the Lower Cretaceous reservoir in the study area are mainly medium to coarse, with medium sorting, and the roundness is mostly angular~sub round (Plate 4, Figure 5).On the whole, the sediment grain size of the Lower Cretaceous reservoirs in each basin in the northern region is relatively coarse, with medium deviation in sorting, poor roundness, and mainly secondary to angular.However, the structural maturity of the Lower Cretaceous reservoir in Boli Basin is relatively high, with good selection and sub prismatic to sub round roundness, which indicates that the sediments in the northern basin are mostly proximal sediments with short transport distance, and Boli Basin was the sedimentary center of the Dasanjiang Basin at that time.This research result is the same as that of sedimentary facies.The research on the survey and evaluation of the national oil and gas resources strategic selection area (2004)(2005)(2006)(2007)(2008)(2009) shows that during the sedimentary period of Chengzihe Formation and Muling Formation in the middle of Early Cretaceous, the northern part of the study area is a unified offshore basin (Dasanjiang Basin), and the sedimentary center is near the Boli Basin.The grain size of the lower Cretaceous sediments in each basin in the southern region is relatively fine, with coarse, medium and fine sandstones, but mainly medium fine sandstones, with medium sorting preference and sub angular to sub circular roundness.For example, the lower Cretaceous sediments in Hongmiaozi Basin and Tonghua Basin have fine grain size, good sorting and roundness, and parallel bedding is developed (Figure 6), which indicates that a large sedimentary basin (Daliuhe Basin) may be developed in the southern region at that time, Later, it was uplifted, denuded and disintegrated to form small and medium-sized residual basins.The coarse clastic rocks at the edge of the basin were denuded, and the fine clastic rocks at the center of the basin were preserved.According to the erosion amount calculated by Ro, the erosion amount of the Lower Cretaceous in Tonghua Basin at that time was more than 1800m [8].

Conclusion
The accretionary complex is mainly composed of 7 parts, including undeformed sedimentary rock, shear deformed sedimentary rock, shear deformed volcanic rock, turbidite, deformed siliceous rock, limestone block and basic ultrabasic rock.Shear deformation structures of deformed sedimentary rocks and volcanic rocks are developed.
The sediment grain size of the Lower Cretaceous reservoirs in each basin in the northern region is relatively coarse, the sorting is moderately deviated, and the rounding is poor, mainly secondary to angular.The grain size of the lower Cretaceous sediments of each basin in the southern region is relatively fine, with coarse, medium and fine sandstones, but mainly medium fine sandstones, with medium sorting preference and sub angular to sub round roundness.

Figure 1 .Figure 2 .
Figure 1.Evidence of accretionary complex in the Nadanhada terraneThe shear deformation structure of deformed sedimentary rocks and volcanic rocks is developed (Fig.2).It is preliminarily speculated that it may be related to the subduction of the ancient Pacific plate and is the main component of the accretion wedge.Turbidite is composed of medium thin fine siltstone and mudstone, mainly composed of A-B-C and B-C sections, and is the product of trench sedimentation.The deformed siliceous rocks are thin bedded, and fold structures are very developed.Sharp folds are formed in some areas, which may be related to the compression of the ancient Pacific plate from west to east.Limestone blocks occur in clastic rocks in blocks, with typical features of exotic rocks, and are the products of tectonic involvement in the process of oceanic crust subduction.The basic ultrabasic rocks are composed of peridotite, pyroxenite, cumulate gabbro, layered gabbro, diabase and pillow basalt, which have typical characteristics of ophiolite and represent oceanic crust fragments, while basalt, siliceous rock and limestone constitute oceanic island/seamount.