Types and sedimentary genesis of barriers and interlayers in the composite turbidite sand bodies of a deep-water canyon: A case study of the Central Canyon in the Qiongdongnan Basin

Abstract

Deep-water oil and gas is currently the hot spot and difficulty of global oil and gas exploration, and the complex flow process inside the turbidite channels of deep-water canyons makes it difficult to characterize reservoir structures, identify barriers and interlayers and clarify the spatial distribution laws of reservoirs, which restricts the development of deep-water oil and gas. Taking the Central Canyon of the Qiongdongnan Basin as an example, this paper identifies and characterizes the barriers and interlayers of composite channel scale by means of seismic sedimentology, based on three-dimensional seismic and core data. Then, based on the turbidite filling process, barriers and interlayers are classified, and their genesis and control factors are analyzed. Finally, a development model of deep-water barriers and interlayers is established based on the quantitative analysis of sediment transportation system parameters. And the following research results are obtained. First, based on sedimentary genesis, barriers and interlayers are classified into four types, namely mudstone interlayers of lateral (aggradational) turbidite channel genesis (type A), mudstone interlayers of fine-grained turbidite channel genesis (type B), barriers of hemipelagic deep-water sediment genesis (type C), and calcareous petrophysical interlayers (type D). Second, based on the filling stage, barriers and interlayers are divided into four combination sequences, i.e., the initial canyon formation stage with strong sediment supply conditions (type A + type C and type B+ type C), the initial canyon formation stage with weak sediment supply conditions (type B + type C), the stable canyon development/late reworking stage with strong sediment supply conditions (types A + type D), and the stable canyon development/late reworking stage with weak sediment supply conditions (type D). Third, the development types and combination sequences of barriers and interlayers are controlled by the change of sediment transportation volume and terrain slope in the canyon. In the initial canyon formation stage, there is sufficient space for the development of turbidite, and the development of thin barriers and interlayers is controlled by sediment dischage volume, while the development of thick barriers and interlayers is controlled by terrain slope change. In the stable canyon development/late reworking stage, turbidite undergoes superimposed development and overbank. The sediment supply is the primary control factor of barrier and interlayer thickness, and the terrain slope change is the secondary factor. In conclusion, the development model of barriers and interlayers can be used to describe and predict the reservoir structure models under the same sedimentary background and provides a technical support for the exploration and development of deep-water oil and gas.