Theoretical Investigation of Coupled Thermal-Hydraulic-Mechanical-Chemical Processes in Steam-Assisted Gravity Drainage Operations in Nigerian Heavy Oil Sands

Steam-assisted gravity drainage processes induce coupled thermal, hydraulic, mechanical, and chemical effects in heavy oil sands that govern the shape and growth dynamics of the steam chamber and the ultimate oil recovery achievable from the formation. A rigorous theoretical framework for the fully coupled THMC behaviour specific to Nigerian heavy oil sand properties does not exist, limiting the reliability of thermal EOR design calculations for Nigerian assets. This study develops a theoretical investigation of coupled THMC processes in SAGD operations applicable to Nigerian heavy oil sands in Delta State and Edo State. The theoretical framework is constructed by coupling the energy conservation equation with Biot's poroelastic consolidation equations, Darcy multiphase flow, and a reactive geomechanical model for clay swelling induced by steam condensate chemistry changes. Dimensional analysis is applied to identify the dominant dimensionless groups controlling steam chamber growth shape, leading to an original scaling relationship for Nigerian heavy oil sands expressing chamber growth rate as a function of sand dilation propensity, steam quality, and crude oil viscosity-temperature sensitivity. Numerical implementation in a purpose-built finite element code validated against analytical solutions for limiting cases confirms the theoretical scaling predictions. Application to an idealised Nigerian heavy oil sand section with geomechanical properties measured from Eriemu Field core samples demonstrates that dilation-enhanced permeability increases of 40 to 180 percent above initial values develop in the steam-swept zone during SAGD operations. Keywords: SAGD, coupled THMC, heavy oil sands, steam chamber, thermal recovery.