Architectural Characterization of Meandering River Reservoirs with Dense Well Patterns: Northern Block Zhong-2, Gudao Oilfield

The meandering river reservoirs of the Ng3–Ng4 members of the upper Guantao Formation in northern Middle Block 2, Gudao Oilfield, exhibit sand bodies with rapid lateral variation, complex contacts, and strong heterogeneity. Previous characterization using sparse well patterns showed deviations in depicting sand body boundaries and internal architecture with insufficient accuracy for optimizing development plans and tapping remaining oil. Additionally, small-scale lateral accretion mud interlayers within point bars—which are hard to trace between wells—limited fine characterization of point bar architecture. Using the high-resolution data and dense inter-well control of the study area’s dense well pattern, we traced 3–10 cm thick lateral accretion mud interlayers within point bars between wells, overcoming the challenge of characterizing thin interlayers with sparse well patterns, and dissected reservoir architecture. Results indicate the study area is dominated by meandering river deposits, with four architectural units: channels, abandoned channels, overbanks, and flood plains. Meander belts range in width from 450 to 1900 m with an average of 1420 m; point bars measure in length from 310.6 to 1754 m with an average of 1036.2 m and in width from 323.4 to 1586 m with an average of 1000.8 m. Lateral accretion mud interlayers show sub-oblique profiles, with dips of 3–6° and a thickness of 3–10 cm; individual lateral accretion bodies are 1.5–5.7 m thick and 32–255 m wide horizontally. Based on channel-point bar scale relationships, an empirical formula for quantitative characterization was established, enabling the prediction of single sand body scales in sparsely well-patterned areas to support well placement and remaining oil prediction. Combined with contact relationships of sand bodies across architectural hierarchies, the main architectural models of composite meander belts were developed. This study provides a reliable geological basis for dissecting meandering river reservoir architecture and tapping remaining oil under sparse well patterns.