Sequence Stratigraphy in Paleogeomorphy Analysis: An Example from Tahe Oilfield

The development of sequence boundaries is usually associated with the eroding peneplaining, fluvial downcutting and tectonic uplifting processes which causes a great reforming of paleogeomorphy. By contrast, sequence patterns and the distributions of the sequences, their systems tracts and parasequences are influenced by paleogeomorphy, indicated by reflection characteristics such as truncation, lapout, progradation angle, regression scope on seismic sections. The sequence stratigraphy analysis here, therefore, provides a powerful tool to identify the paleogeomorphies. Based on the research on the sequence stratigraphy of the Carboniferous, Tahe oilfield, the marks of the onlap pinch-out lines of the first flooding surface and the maximum flooding surface, slope-break lines and folding shapes have been applied to identify the different paleogeomorphic units such as the uplifts, warps of differential compaction, moderately angled slopes, gently angled slopes and depressions during SQ1 and SQ3 sequence developments, firstly revealing an uplifting event caused by tectonic compression before SQ3 sequence. Meanwhile, the planar distribution of sand-bodies of the Ⅱ oil-unit has also been used to verify the results of paleogeomorphy. Through the synthetic analysis above, the authors have found that the sand bodies in lower systems tracts of SQ1 and SQ3 sequence are mainly distributed in the slopes and the depressions consist of the favorable sites of the lithologic trapping target.