Impact of pore structure on development performance in the LH-Y reef limestone field

Abstract The LH-Y oilfield in the South China Sea is a large reef limestone reservoir characterized by complex pore systems that vary laterally with sedimentary facies. This pore-scale heterogeneity contributes to rapid increases in water cut in development wells and a low recovery factor. To investigate the impact of pore structure on development performance, we analyzed core samples using scanning electron microscopy, thin sections, and geological vision resistivity logging. Three primary pore types were identified: intergranular pores, intragranular dissolved pores, and dissolution caves, along with three throat types: pore shrinkage, necking, and tortuous throats. Based on integrated core, imaging, and logging data, the reservoirs were classified into four structure types: relatively dense, dense fractured, pore fractured, and porous. Production data from more than 30 horizontal wells show a strong correspondence between the pore structure type and production dynamics. Reservoirs with high fracture density and large connected pores are prone to early water breakthrough and unstable performance. To address this, inflow control devices and continuous packers were deployed to isolate high-permeability channels and delay water coning. Field application of this strategy reduced water cut by approximately 10% and increased cumulative oil production by more than 50,000 m³. These results demonstrate that pore structure characterization is critical for guiding well completion and production optimization in fractured reef limestone reservoirs.