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AAPG Bulletin, Preliminary version published online Ahead of Print 1 August 2023.

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Seismic sedimentology of a broad, low-relief carbonate platform: the Cambrian Longwangmiao Formation, Moxi-Gaoshiti area, Sichuan Basin, China

Wenzhi Zhao1 , Hongliu Zeng2 , Zhaohui Xu1 , Suyun Hu1 , and Qilong Fu2

1 PetroChina Research Institute of Petroleum Exploration and Development, Beijing, China
2 Bureau of Economic Geology, Jackson School of Geosciences, The University of Texas at Austin

Ahead of Print Abstract

Broad, low-relief carbonate platforms are commonly relatively flat bedded and show minimal topographic relief. These characteristics make the platforms difficult to interpret using seismic data. To systematically analyze these platforms for reservoirs, a seismic-sedimentological workflow was implemented to investigate the paleogeomorphology and reservoir quality of the Cambrian Longwangmiao Formation (LWM) in the Moxi-Gaoshiti area of the Sichuan Basin, China.
Conventional core and wireline-log data indicate that carbonate lithofacies are comprised of completely dolomitized grainstones, packstones, and wackestones to mudstones. Associated depositional environments were interpreted as shoal complex (shoal-crest, shoal-margin, and intershoal), lagoon, and deep shelf. The low (4-8%) porosity reservoirs are largely related to the shoal complex facies. Two third-order sequences were correlated throughout the field area, each demonstrating an upward-shallowing trend. The reservoir-quality rocks were formed in the highstand-system tracts in the sequences.
Lacking diagnostic shallow-water indicative seismic facies (e.g., the topset of clinoforms), seismic paleogeomorphology was assessed by restoring the paleostructure at the top of LWM and then evaluating gross thickness of LWM to establish the accumulation rate of sediments across the area. This approach demonstrated a fair correlation to measured reservoir-thickness data from wireline logs, indicating that the paleogeomorphology and depositional facies were largely controlled by a syndepositional, en echelon fault system that determined the distribution of shallow-water shoal complexes and deeper shelf areas across the field area. Seismic lithology determination by amplitude analysis of multiple frequency panels provided a quantitative assessment of reservoir distribution, supplementing the qualitative paleogeomorphologic maps for field development and reservoir modeling.

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Please cite this AAPG Bulletin Ahead of Print article as:

Wenzhi Zhao , Hongliu Zeng , Zhaohui Xu , Suyun Hu , Qilong Fu: Seismic sedimentology of a broad, low-relief carbonate platform: the Cambrian Longwangmiao Formation, Moxi-Gaoshiti area, Sichuan Basin, China, (in press; preliminary version published online Ahead of Print 01 August 2023: AAPG Bulletin, DOI:10.1306/02242318016.