Upscaling rock mechanical parameters of algal clotted dolomite in the Dengying Formation, Sichuan Basin
LI Minghao1, 2, LI Gao1, 2, FENG Jiaxin1, 2, SHANGGUAN Ziran1, 2, YANG Xu1, 2, LI Hongtao1, 2, YUAN Chenxu3
(1. State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, Sichuan 610500, China; 2. Underbalanced/Gas Drilling Laboratory, National Engineering Research Center of Oil and Gas Drilling and Completion Technology, Chengdu, Sichuan 610500, China; 3. College of Petroleum and Natural Gas Engineering, Southwest Petroleum University, Chengdu, Sichuan 610500, China)
Abstract：The algal clotted dolomite reservoirs in the Dengying Formation of the Sichuan Basin are characterized by well-developed pores and vugs exhibiting strong heterogeneity, which complicates the accurate determination of rock mechanical parameters through conventional experimental methods. This study integrates nanoindentation tests and micro-CT scanning to assess the meso-scale mechanical properties and pore-vug distribution characteristics of algal clotted dolomite, and establishes a digital rock model with realistic pore-vug distributions based on discrete element theory. Furthermore, by utilizing digital pore-vug extraction technology from outcrops, a rock block model containing large-scale defects was developed, facilitating the upscaling from nanometer to centimeter scales. This block model was employed to simulate multi-scale coring processes in the field, elucidating the conversion laws of rock mechanical parameters from laboratory to geological engineering scales. The results indicate that the algal clotted dolomite in the Dengying Formation displays significant vug development and algal framework structures with notable dissolution effects, characterized by poor pore-throat connectivity and heterogeneous distribution. The mineral elastic moduli conform to a Weibull distribution, with discrepancies of 1.2% for uniaxial compressive strength and 5% for elastic modulus between the digital rock model and experimental results, while demonstrating good agreement in failure patterns. The upscaled coring simulation reveals that both uniaxial compressive strength and elastic modulus initially decrease rapidly and subsequently stabilize as core size increases, indicating a gradual diminishment of size effects. Failure in the block model predominantly occurs around vugs, manifested as vug deformation under external loads, the initiation and propagation of microcracks along vug edges, and eventual connection through adjacent vugs to form cavities. Edge vugs, particularly those near free boundaries, facilitate crack initiation and propagation, with their influence diminishing as the distance between vugs and edges increases. The algal frameworks tend to experience relative slippage with surrounding minerals during stress transfer, thereby promoting the formation and propagation of shear cracks.
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2025, Vol. 44 
