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The Research Of Sedimentary Microfacies Features And The Influence Of Reservoir Fracturing Effect In Sabei Ⅲ Area In Songliao Basin

Posted on:2015-11-29Degree:DoctorType:Dissertation
Country:ChinaCandidate:L ZhangFull Text:PDF
GTID:1220330431495237Subject:Oil and Natural Gas Engineering
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This thesis uses sedimentology and high-resolution sequence stratigraphy as the theoretical basis and takes single sand body recognition technology as the guidance. Using the core data, well drilling data, logging data, analysis data and testing data of rocks, the thesis accomplishes the division and correlation of oil formations and sand sets in the study area with the partitioning method of "cycle comparison and hierarchical control". First of all, it establishes the tratigraphic framework, then carries on the division of oil formations, sand sets and oil layers step by step. We confirm division markers for each levels of formation and each subzone, then establish the division standard of the subzone.In the study area, eight primary standard layers and seven secondary standard layers are identified. As a result, we divide Saertu, Putaohua and Gaotaizi Oil Layers into67sedimentary units in the western part of Sabei Ⅲ Area. The thesis establishes sand body recognition technology of river-delta depositional system in flat terrains.Based on the study on a large number of previous research results, we confirm the study area is not only controlled by northern provenance, but also affected by the provenance from north-east. All these are based on the most comprehensive and detailed first-hand information. Through the observation and fine description6cores near the study area, the thesis analyzes the depositional environment combining lithology, fossils with single sand body shapes, logging curves. The above four general categories include colour, contexture, structure, lithology, cyclicity, composition, authigenic minerals and special-containing material, fossils, single sand body shapes and logging curves, in total of10indicators. Finally, we indentifies the study area belongs to river-delta sedimentary system including2kinds of phase,6kinds of subphases and18kinds of microfacies. The fluvial facies include channel microfacies, point bar microfacies, central bar microfacies, crevasse-splay microfacies, natural barrier microfacies, thin overbank sand microfacies, interchannel mud microfacies, abandoned channel microfacies, while the delta distributary plain includes distributary channel microfacies, abandoned channel microfacies, natural barrier microfacies, crevasse-splay microfacies, thin overbank sand microfacies, interchannel mud microfacies. The delta-front facies includes natural barrier microfacies, underwater interdistributary bay microfacies, sheet sand microfacies, distal bar microfacies. In addition, according to the distance between the reservoir sedimentary process and the lake shoreline in each sedimentary environment, the thesis divides reservoirs into Ⅰ、Ⅱ、Ⅲ in total of9depositional models. The type Ⅰ reservoir mainly has2depositional models-the sandy braided river and meandering river of the fluvial facies. The type Ⅱ reservoir mainly has3depositional models-the near-shore, far-shore and mid-shore distributary channel of delta distributary plain subfacies. The type Ⅲ reservoir mainly has4depositional models-the near-shore, far-shore and mid-shore underwater distributary channel of interior delta-front facies and sheet sand of exterior delta-front facies. There are three types of intercalations-shale intercalation, physical intercalation and calcium intercalation in the study area and shale intercalation is the main one. The interlayer heterogeneity is strong between each subzone and the permeability varies a lot in lateral. This research focus on the distribution features of interlayers in sand body, but their thickness have a big difference. The study shows that there are large numbers of interlayers developed in the sand body and they are thick, but some parts have fewer interlayers such as the central part of channel due to the effect of microfacies. So we find that interlayers are mainly developed at the channel edge, the border between different sand body and the joint within the sand body, for example, PI3subzone belongs to braided river sedimentary environment and its central bar have a big thickness. The variation laterally and vertically leads to rhythmic layering within sand body with many internal structure surfaces. By studying on the microfacies characteristics, reservoir heterogeneity and interlayers growth features in sand body, the thesis conducts a research on sand body in different microfacies and the structural surface of joints between different microfacies. We use structure fractal theory and divide the above into4types of sand body structural model both in lateral and vertical-single channel, superposition of multiple channel, mound shaped sand and sand sheet, which can accurately show the classification of inner structural features within the sand body. Moreover, it can depict the existence area of residual oil after water flooding during the high water cut stage in oilfields. Based on the study on microfacies characteristics, the reservoir heterogeneity and the distribution features of intercalations in the study area, the thesis carries on a comprehensive analysis on the effect of fracturing. We reach the conclusion that the dominant influences of fracturing are the effective thickness of sand body, the formation coefficient, the oil saturation and the formation pressure. Then we use these factors as the parameter estimation of one-factor variable model by the method of Marquardt. After that, we establish the iterative model of function by non-linear iterative method and the relationship between those single factors and oil increment. According to the above, the thesis finishes the calculation of technical threshold of single factors to oil increment. And the sand bodies are classified into4types based on sand body characteristics controlled by microfacies:the channel sand, the inter channel sand, the mound shaped sand and sheet sand. Meanwhile, we simulate and calculate the fracturing technical threshold of the4types of sand body:the effective thickness of channel sand is3.8m,the permeability is0.3D, the oil saturation is0.56and the total pressure differences is0.1MPa; the effective thickness of inter channel sand is4.3m,the permeability is0.1D, the oil saturation is0.3and the total pressure differences is0.2MPa; the effective thickness of mound shaped sand is3.9m,the permeability is0.13D, the oil saturation is0.42and the total pressure differences is0.2MPa; the effective thickness of sheet sand is4.3m,the permeability is0.11D, the oil saturation is0.39and the total pressure differences is-0.2MPa. Finally, a unified threshold of the fracturing model is established, that is only when the fracturing thickness is larger that4m, the formation coefficient reaches0.8D·m, the oil saturation eaches0.45and the total pressure differences reaches0.2MPa. the oil increment can reach5tons after the fracturing. By finishing the research on the microfacies, the reservoir classification, the reservoir heterogeneity features, intercalations in sand bodies and other factors, the thesis optimizes areas that are good for fracturing wells including macroscopic optimization and microscopic optimization. Macroscopic optimization means that we Optimize areas with good microfacies, well developed sand bodies, large effective thickness and high oil saturation. If all these factors are favorable, the reservoir will be defined as type I reservoir, which spread over sandy braided river and meandering river in fluvial facies. If the above factors are not good as type I reservoir, we classify them as type II reservoir, which are distributed in far-shore, near-shore, and the shore distributary channel of delta distributary plain subfacies. If the above factors are even not good as the type II reservoir, we define them as type III reservoir, which spread over the near-shore, far-shore and the mid-shore underwater distributary channel of interior delta-front facies and sheet sand of exterior delta-front facies. On the basis of macroscopic optimization, we should consider the optimization of the variation characteristics of different sand bodies in lateral and vertical and the internal structure characteristics of different sand body. At the areas that are less developed with sand bodies, we select those well blocks with more interlayers and those located in the border of different sand bodies because these areas are the rest of the development zones. Fracturing at these areas, the success rate of fracturing can be improved followed by increased crude oil recovery, which provides powerful theoretical evidence for increasing production in oilfields.
Keywords/Search Tags:Songliao Basin, Sabei Ⅲ area, sedimentary micro-facies, reservoirheterogeneity, fracturing effect
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