Geomorphology Classification and Architecture Characterization of Braided River Reservoir: A Case Study From Guantao Upper Formation of Gudong Oilfield, Bohai Bay Basin, China.
Studies on the architecture of braided river reservoir have been carried out for decades. Whereas, some controversies still exist, including the depositional styles and architecture modelling of different braided rivers as well as their impact on reservoir heterogeneity. These difficulties in cognition and practice impede the high-efficient development for middle-late period of mature oilfield. The aim of this paper is to define the geomorphology classification of braided river and applying different types of quantitative prototype model to guide architecture characterization of braided river reservoir. In this study, braided rivers are divided into anabranched type and wandering type based on sedimentology and hydrology characteristics. From the perspective of fluvial geomorphology, anabranched braided channels are relatively fixed and present the appearance of alternation of single and multiple channels. While, a wandering braided river is not fixed due to rambling flow and its channels migrate frequently with interweaved appearance. The satellite photos of 6 large river systems from globe are captured, where 46 samples are selected based on different scales and drainage basins. After calculating and analyzing quantitative relationship and empirical formulas between different architecture elements, two types of quantitative prototype models of braided river are established, whose application to reservoir characterization are demonstrated with examples from Gudong Oilfield, Bohai Bay Basin, China. For anabrached river of Guantao upper formation, the average length-width ratio of braid bar is 3.2:1. For wandering river of this formation, the average length-width ratio of braid bar is 2.1:1 and the average width of single channel is 88m. There are three distribution types of interlayer inside braid bar: the extensive distribution pattern of sheet silting layer, the partly distribution pattern of sheet silting layer and the disperse distribution pattern of narrow banded cross-bar channel. The results of this study forward a step to the establishment of quantitative prototype models for two types of braided river. As a practical effect of this study, the architecture analysis of braided river reservoir has enabled a number of exploitation adjustment and improved oil recovery schemes to be considered.
AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017