Formation Mechanism and Sedimentary Pattern of Abandoned Channels

Abstract

Accurately identifying and quantitatively describing abandoned channels in meandering rivers are of great significance for improving hydrocarbon recovery. By using modern deposition analogy, field outcrop analysis, a dense well spacing, core observations and a review of the literature, this paper studied the formation process and space-time amalgamation of abandoned channels in meandering river. The results reveal that formation mechanisms of abandoned channels include chute cutoff patterns (shoal-cutting, ditch-scouring and embayment-eroding patterns) and neck cutoff patterns. The chute cutoff pattern forms a gradually abandoned channel, while the neck cutoff pattern forms a suddenly abandoned channel. From upstream to downstream, the sedimentary pattern of the abandoned channel transforms from a chute cutoff pattern to a neck cutoff pattern, where the main controlling factors transition from the grain size and gradient to the flow and vegetation. An abandoned channel formed by a chute cutoff pattern consists mainly of siltstone, fine sandstone and thin gravel layers, which form a lithological-physical barrier. The abandoned channel formed by a neck cutoff pattern consists mainly of mudstone and argillaceous siltstone, forming a lithological barrier. Based on the amalgamation and structure of the reservoir architectural elements, the abandoned channel can be divided into three planar sedimentary patterns (crescent, semilune and horseshoe) for a single channel and five vertical sedimentary patterns for composite channels.

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“…The tasks solved in the course of work:  To consider the geological structure of the deposit;  To review the development status  To develop a geological model for the selected objects to calculate geological reserves;  To offer development options and evaluate their cost-effectiveness. To compile the physical-lithological characteristics of productive sediment reservoirs [12], they used macro descriptions of the samples, the results of core analyses, petrographic descriptions of thin sections of Kudryashovsky and neighbouring deposits. The stratum A3 of the Verey horizon [13] is characterized by a wide distribution of terrigenous rocks in the sole and carbonate rocks in the roof.…”