Rock-physics-model-based pore type characterization and its implication for porosity and permeability qualification in a deeply-buried carbonate reservoir, Changxing formation, Lower Permian, Sichuan Bain, China

In addition to porosity and mineral composition, pore type variation plays an important role in affecting permeability heterogeneity of carbonate reservoirs. Rock physics models that do not consider pore type diversity in carbonate reservoirs incompletely account for the relationship between rock acoustic properties and reservoir parameter. A new carbonate rock physics model that introduces the frame flexibility factor (γ) is deployed to characterize pore types and their structure variation. Calibrated by core data, our study on a deeply buried lower Permian carbonate reservoir shows: samples with frame flexibility factor (γ)<2.00 are dominated by round intraparticle moldic/oolitic pore type; samples with frame flexibility factor (γ)>7 have fracture dominated pore type; samples with frame flexibility factor (γ) 5-7 have either flat macro-interparticle pore type as its porosity is >5% or micro-intercrystalline pore type as its porosity is <5%; samples with a mixture of intraparticle and interparticle pore type generally have a frame flexibility factor (γ) between 2 and 5. Using the frame flexibility factor (γ), different porosity-impedance and porosity-permeability trends are classified with clear geological interpretation such as pore type variation, which improve porosity and permeability prediction accuracy. New porosity-permeability relationships with frame flexibility factor (γ) indication help delineate permeability heterogeneity in the study reservoir, and could be useful for other similar carbonate reservoirs studies.