Fluvial Reservoir Architecture Modeling and Remaining Oil Analysis

Abstract

Abstract Most of the mature oil fields in east China are in a stage of high water cut. For these oil fields, the reservoir characterization and remaining oil study need fine scale geological models. A study of reservoir architecture can provide such a fine model. In this paper, we focus on the architecture modeling of fluvial reservoir. Fluvial architecture contains hierarchical bounding surface and architecture elements. This architecture model provides information to analyze the reservoir heterogeneity caused by hierarchical bounding surfaces. Previous architecture studies were conducted on outcrop and modern river deposits. We use the 7th block of Gudong oil field in China as an example to analyze the subsurface reservoir architecture and distribution of remaining oil. Gudong oil field has been exploited for 30 years. A total of 1070 wells have been drilled and the well space is 150mx150m. Data are abundant and includes core data, horizontal wells, logging data, production data and surveillance data, all of which are used for the reservoir architecture study. We use the method of "fitting geological model" for the architecture study. Using results of outcrop and modern river deposit studies and paloe-environment analysis, we build the geological patterns of meandering and braided rivers. Based on our analysis, the geological pattern of internal point bar has the following characteristics: (1) parallel-inclined lateral accretion intercalation; (2) 200m width of single lateral accretion body; (3) 3~5 degree dig angle of lateral accretion surface. Our study also shows that the geological pattern of the internal mid-channel bar, which is confirmed by the production information and pair wells data, is asymmetrical intercalation and 2~5 degree dip angle of intercalation surface. Guided by geological patterns, we establish the internal architecture models of Ng522 layer and Ng64 layer in this study area. Using the internal point bar and mid-channel bar models, we analyze remaining oil and establish different remaining oil distribution patterns. Our analysis shows that the matching relationship between intercalations and perforated intervals is the main factor that influences remaining oil distribution of a sand body. This provides a new way to find remaining oil in a mature oil field.