| Da’an oilfield is located in Da’an-Honggang Terrace, a secondary structural belt, of Central Depression in Songliao Basin. It is a nose structure controlled by Da’an thrust fault, there distributed many NW trending fractures in the central south. DG area is a small nose structure based on fault boundary in the south central of Da’an oilfield, and the fault is not developed. The Fuyu reservoir on the fourth member of Quantou formation in Cretacic and Yangdachengzi reservoir on the three member of Quantou formation are the target layers, which possess abundant oil and gas resources and have good exploration potential.The main focus of previous research on Da’an oilfield are sequence stratigraphy, depositional systems, reservoir evaluation and classification, oil and gas development and other aspects, and there is no precise study of each area. Affected by structure, lithology and sedimentary characteristics and other factors, genetic types and distribution characteristics of sedimentary microfacies in each area vary. Meanwhile, because of few core wells, and the uneven distribution and the lower accuracy of strata division, there is no further study on division and analysis of microfacies, which can not meet the needs of fine reservoir description. Aimed at the current geological research problems in this area, it is necessary to carry out the fine classification and correlation of the sublayers and sedimentary microfacies and sand body distribution system research. The research results will lay foundation for reservoir evaluation, hydrocarbon accumulation studies so as to improve the level of fine reservoir description.This paper is based on the research project of MI Energy Company, the Study of Fine Reservoir Description of reservoir DG area of Da’an oilfield. Fuyu reservoir has been chosen for the study object, and fine division and correlation of sublayers and the reservoir microfacies types in Fuyu reservoir have been studied.For the formation and development characteristics of Fuyu reservoir in DG area of Da’an Oilfield, on the basis of core, logging, well logging data interpretation, using the principle and method of sequence stratigraphy and petrostratigraphy for sublayer fine division and correlation, Fuyu reservoir has been divided into four sand zones and twelve units, and thus the skeleton unit section has been established.Based on the core observation, mudlogging, logging and test analysis,combined with regional sedimentary background, the provenance direction, sedimentary microfacies types and sedimentary evolution rules have been studied. It has been concluded that the source of Fuyu reservoir of the DG area, Da’an field mainly comes from Yingtai and Baicheng water system in the northwest, and Baokang and Tongyu water system in the southwest. Besides, most rocks of Fuyu reservoir are gray, purple, reddish brown and grayish brown, with locally grayish green and grayish black, reflecting the weak oxidation-weak reduction of the sedimentary environments. Feldspathic lithic sandstones with some lithic feldspathic sandstone predominate, which are fine-grained dominated by fine sand and silt. These sandstones are overall moderate in sorting, and sub-angular to sub-rounded. These sandstones are mainly represented by point-line contact, and pore-contact cementation, which show medium structure maturity. Probability cumulative curves of grain sizes are "typical two-stage","typical three-stage" and "three-stage transition", which reflect traction flow hydrodynamic mechanism. In addition, there is parallel bedding, wavy bedding, cross bedding and other sedimentary structures related to traction currents. According to the above sedimentary facies symbols and comprehensive analysis, it has been concluded that Fuyu reservoir in the study area was deposited in a shallow delta, composed of delta plain and delta front subfacies with the distributary channel, marsh, underwater distributary channel, intertributary,natural levee, crevasse splay, branch channel bar. |
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