Abstract:

Conventional characterization of meandering river reservoirs typically relies on data from densely-spaced vertical wells, but insufficient inter-well data results in unreliable planar combinations of architectural elements. Taking the SSF-AH horizontal well + large well group targeting the Permian Shanxi formation in Sulige gas field as an example, and by integrating horizontal and vertical well data, the lithofacies of the meandering river reservoirs were identified, and the reservoir architecture was analyzed. The results demonstrate that the lithofacies in the study area can be classified into four types. Type Ⅰ to Ⅳ shows a gradually decreasing hydrodynamic force during deposition. Types Ⅰ and Ⅱ constitute the main gas-bearing lithofacies, while Types Ⅲ and Ⅳ are generally non-productive. Three combination patterns of architectural elements of the meandering river reservoir are identified: transverse-spanning, longitudinal-spanning, and intercrossing. The sand bodies of the meandering river channels are 900-1 100 m wide; the sand bodies of point bars are 650-800 m long (avg. 720 m) and 800-1 000 m wide (avg. 910 m); and the width of abandoned channels are generally less than 100 m. The point bars are typically composed of 4-5 stages of lateral accretion sand bodies, with the thickness ranging from 0.4 to 1.5 m individually and the planar width ranging from 120 to 220 m. The lateral acceretion mudstones are 0.2-0.4 m thick, with a vertical density of 0.5-0.8 beds per meter and a planar density of 0.011 beds per meter. The integration of horizontal wells with large well groups can improve the accuracy of architecture characterization.

Key words: Ordos Basin, Sulige gas field, Shanxi formation, meandering river, lithofacies, architectural element, horizontal well