| Rang53 dense area is located in the middle of Changling Sag at Central Depressions in the South of Songliao Basin. It’s north and east is adjacent to two wells-structure, in the north west is Qian215 wells area and south west QianAn structure. It is a slope belt tilted toward the southwest in the regions, which is one of the key areas of dense oil and gas exploration and development in Jilin oilfield. The target strata of this study is the forth member of Quantou Formation i.e. the Fuyu oil layer, with the area of 260km2 and 52 wells. Along with the deeping exploratory development of oil field, more and more geological problems in the study area have become exposed gradually, such as reservoir characteristics unclear, main controling factors of reservoir unknown and so on. For the existing problems of the study area, in this paper, a fine isochronous stratigraphic framework is established with the theory of high resolution sequence stratigraphy as a guide, using the basic theories of sedimentology and petroleum geology etc. And the next is to deeply research the characteristics of sedimentary microfacies from point to line to surface, reling on the surrounding dense pattern information. It is same necessary to carry out the study of sedimentary microfacies flat and profile distribution features and spatial evolvement regularity with depositional system analysis. And then, in order to clear reservoir characteristics, something shoud be study, such as reservoir petrological characteristics, microscopic pore structure, diagenesis, reservoir influence factors and so on, combining with well logging and drilling and the core samples test data etc. The last is to evaluat the reservoir and reasonably predict favorable area with qualitative and quantitative methods, providing the secundum for effective reservoir distribution in the study area and fine reservoir valuation.Based on the integrated logging information interpretation and core observation, applying high-resolution sequence stratigraphy and lithostratigraphy, layers classification and correlation have been carried out with the start of standard wells research using the method of "point-line-surface" trinity, to establish a fine isochronous stratigraphy framework with 4 sand groups 13 small layers of 52 wells in the target strata, laying the foundation for subsequent reservoir study.Based on logging characteristics, core observations, grain size analysis and so on, combining with regional depositional setting, study on sedimentary microfacies has been carried out, reling on the surrounding dense pattern information. The results show that the main depositional environment of Quantou-4 member in the study area is a braided river delta, mainly coming from the southwest of Tongyu-Baokang river system with weak influence of southeast Huaide-Changchun water system. In this depositional systems, delta plain and delta front subfacies have mainly been developed. In delta plain, distributary channel deposit, interdistributary bay, overfall sand body and crevasse splay are the main sedimentary microfacies. There are four sedimentary microfacies, including subsea distributary channel, subsea interdistributary bay, sand sheet and mouth bar, having been recognized in delta front subfacies. The depositional environment in IV sand group is high-energy fluvial-dominated offshore shallow water delta plain; Ⅲ sand group is low-energy fluvial-dominated offshore shallow water delta plain; Ⅱ sand group is fluvial-dominated nearshore shallow water delta plain and I sand group for delta front.According to analysis and test data, including ordinary thin section, casting sections and SEM, reservoir petrology characteristics have been conducted from the side of composition and structure, as well as the reservoir diagenesis are analyzed in detail. Results show that, the main rock types of Quantou-4 member in the study area are feldspar-porphyry sandstone, feldspathic litharenite and syrosem feldspar-porphyry sandstone, with medium-good sorting, points-line contact relationship and subangular rounding mainly. The composition of matrix are mainly argillaceous and micritic limy, as well as the cements which mianly are porous cementation develop universally, including calcite, authigenic quartz and feldspar-increased. Quantou-4 member is in the middle diagenetic phase A period as a whole, going through a series of diagenesis, in which, compaction, cementation, and metasomatism reduce primary porosity of sandstone reservoir, leading to physical property worse. However, dissolution is helpful to develop secondary porosity, which is too weak to improve reservoir physical property.According to the analysis of casting sections, thin section and SEM, study shows that the pore types mianly include residual primary intergranular pore, intergranular dissolved pores, feldspar dissolved pore, lithic dissolved pore, mould pore and microfracture, in which, the most is intergranular dissolved pore. Combination of pore types are mainly intergranular-intragranular dissolved pore. Types of the throat in the area are shrinking pore-throat, sheet or bending sheet throat and microminiature throat. The latter two are the most developed.According to mercury penetration data, based on the analysis of the distribution of main pore structural parameters and the characteristics of capillary pressure curve, pore structure in the study area shoud be divided into four types:I class for low hole fine throat, on behalf of the good effective reservoir; II type class for low-lower hole micro-fine throat, on behalf of the general effective reservoir; III has low hole micro-fine throat, form industrial air flow after renovation; the type of IV which has lower-super low hole micro-fine throat is on behalf of the invalid reservoir. The reservoir in the area has complex pore structure, small median radius, the high expulsion pressure, relatively high displacement pressure, low efficiency of mercury withdrawal, high largest-into-mercury saturation degree, more slightly.coarse skewness, relatively good storage capacity, in which,the effective porosity proportion in the rock is little and seepage ability is poor.Research shows that the reservoir of Quantou-4 member in the study area has low-lower porosity and super low permeability. Grains components, types of depositional microfacies and cementation types are the main factors controlling reservoir physical property. Early full compaction and medium-term grains such as lithic argillation and silification into rock widely, greatly reduces the primary pore. Late, carbonate cement porous cementation further blocks the channel between pore and pore, reducing reservoir property. Dissolution is conducive to the development of secondary porosity, but it is so weak that has not great meaning. Therefore, the reservoir is overall densification.As to the comprehensive performance of reservoir, the study selects lithologic (grain size, composition, shale content), physical properties (porosity, permeability), pore structure (median pore throat radius, expulsion pressure), diagenetic facie, oil content (oil saturation), effective thickness and oil testing to conduct a comprehensive evaluation of the reservoir which is divided into four classes.The reservoir of Quantou-4 member in the study area is given priority to the fourth class, accounting for 34.21%; the third class is latter, accounted for 30.14%; the first class has a similar proportion to the second, which are 17.68% and 17.97% in order. On the whole, reservoir comprehensive type in Ⅱ and Ⅲ sand group is best, Ⅰ sand group second, and IV sand group worst. However, the first class of reservoir comprehensive evaluation is the most development in Ⅲ sand group, whose proportion is 19.10%; the second class, most in Ⅲ sand groups, with the proportion of 22.47%; the third class, most in Ⅰ sand group, with the proportion of 31.78%; the fourth class, most in Ⅳ sand group, with the proportion of 43.24%.Selecting favorable exploration with sedimentary characteristics, hydrocarbon accumulation regularity and reservoir comprehensive evaluation results in the study area. The benefit reservoirs are into three classes:the first is best, followed is the second, the third class is in general. |
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