Sandbody architecture analysis of braided river reservoirs and their significance for remaining oil distribution: A case study based on a new outcrop in the Songliao Basin, Northeast China

Dongsheng Zang,Li Zhang,Zhuolun Li,Xiting Xu,Min Li,Mingyang Wei,Ping Fu,Mingyi Li,Bo Niu,Zhidong Bao,Luxing Dou

doi:10.1177/0144598720951280

Abstract

The reservoir architecture analysis of braided rivers, especially falling-silt seam forms, has played a key role in predicting remaining oil distributions. However, no studies have used architecture analyses that document braided river outcrops and researched the tapping of the few remaining oil distributions based on outcrops in the Songliao basin, northeast China. In this paper, the architecture characteristics and remaining oil distribution of braided river reservoirs are studied using a combination of an outcrop, modern deposition and subsurface well data. The new 8–13 m thick Lower Cretaceous Quantou Formation outcrop of the Songliao basin is a braided fluvial succession arranged in one large fining-upward cycle. Eight facies (Gt, St, Sm, Sh, Sp, Sw, Fl and Fm), four architecture elements (CH, DA, LV, and FF), and three orders of bounding surfaces (third-, fourth-, and fifth-order) are recognized. A new distribution pattern of falling-silt seams and a braided river architecture model are presented according to the analysis of the outcrop. In the mid-channel bar, the falling-silt seams thin from the mid-bar to the bar tail following the flow direction. Each falling-silt seam is oriented tangentially to the basal surface of the mid-channel bar, and the upper falling-silt seam extends farther than the lower one. In a Daqing Oilfield exploitation block in the Songliao basin, while channels and bars are the main reservoir units, they have different remaining oil distribution patterns. For bars, water injection wells located at the mid-bar, zonal injection technology, the drilling of horizontal wells, and proper well patterns are proposed. Fourth-order bounding surfaces, single braided channels, stacking patterns, and the lateral blocking of levees and floodplains are the key factors affecting the remaining oil distribution in channels.

Highlights

Over the last three decades, many studies have described the sedimentary architecture of braided river deposits based on Maill’s theory (Miall, 1985, 1988, 1996)
Reservoirs formed in braided stream depositional environments are important worldwide, especially in the oilfields of the Songliao basin, northeast China, where braided river sandbodies play a key role, and detailed architecture analysis aids the prediction of remaining oil distribution (Falivene et al, 2006; Hou et al, 2008; Li et al, 2015; 2019; Niu et al, 2014; Xu et al, 2016)
The conglomerate, sandstone and claystone units in the outcrop were distinguished as eight lithofacies according to clasts size, sorting, and bedding types

Summary

Introduction

Over the last three decades, many studies have described the sedimentary architecture of braided river deposits based on Maill’s theory (Miall, 1985, 1988, 1996). A new distribution pattern of falling-silt seams and a braided river architecture model are presented according to the analysis of the outcrop. Keywords Reservoir architecture, remaining oil, braided river, mid-channel bar, Songliao basin

Results

Conclusion