High-Resolution Sequence Stratigraphy and reservoir architecture of a strandplain Sandstone reservoir: Donghe Sandstone of early Carboniferous Formation in Tazhong 16 oilfield, Tarim basin, Western China

Recent hydrocarbon exploration targeting the early Carbonifeous Formation has renewed interest in Donghe sandstone of the Tazhong 16 oilfield, Tarim basin, Western China. A robust sequence stratigraphic framework of this... [ view full abstract ]

Recent hydrocarbon exploration targeting the early Carbonifeous Formation has renewed interest in Donghe sandstone of the Tazhong 16 oilfield, Tarim basin, Western China. A robust sequence stratigraphic framework of this siliciclastic system from early Carbonifeous time will have the potential to improve exploration strategies and provide new insight into the stratigraphic relationships across a third order sequences. It builds a high-resolution sequence stratigraphic framework based on sedimentology, complex structural, and reservoir heterogeneity analysis of the Donghe sandstone Formations. Sedimentological analysis was conducted using core, thin sections and outcrops to document the primary facies of the Donghe sandstone Formation, which composed of wave and tide influenced siliciclastic rocks interbedded with conglomeratic and mudstones. Detailed facies analysis suggests deposition in coastal and shallow marine environments. Vertical and lateral facies successions revealed that the Donghe sandstone Formation is composed of a 3rd order depositional sequences made of up higher frequency 4th and 5th order sequences and cycles.
The Donghe sandstone Formation has been differentiated into three system tracts. The Lowstand system tracts (LST) onlaps onto the Devonian system, its basal contact is marked by an angle unconformity, and entirely composed of unilaminar, single-scale conglomerates. The Trangressive system tracts (TST) overlies the LST, displays progradational-aggradational-retrogradational parasequence stacking patterns, and comprise single-storey strata with relatively small-scale homogenous sandstones. The Upper Donghe sandstone Formation displays aggradational to progradational parasequence stacking patterns (HST), and consists of multistory, large-scale sand stones with minor amount of small-scale single–storey conglomerates. Through the stratigraphy study, electrofacies are defined by well-log analysis and then matched with sedimentary facies defined by core analysis. Electrofacies associations and depositional enviroments are then inferred directly from well-logs on this basis. Three electrofacies characterizing the main sedimentary facies associations and depositional enviroments defined (sand bars, sags and mud flat). The lithology in this section includes greyish medium sandstone and fine sandstone with a little siltstone. Reactivation of basement structures appears to have strongly influenced accommodation during deposition of the Donghe sandstone Formation. Systems tracts, sequence boundaries and their correlative unconformities, maximum flooding surfaces, and forced regression surfaces were traced from shallow shelf to basinal settings.
Through the development of a fully high resolution sequence stratigraphic framework that incorporates surface and subsurface data, reservoir quality and distribution in the Donghe sandstone Formation can be evaluated away from sample control, and thus enhance the potential for future economic success of unconventional resource plays in this interval.