Abstract
Spontaneous imbibition(SI)is the principal production mechanism in naturally fractured reservoirs produced by waterflooding and is essential for fluid flow characterization to predict their future performance.As an alter-native to the expensive,time-consuming laboratory measurements,2D images render a different prospect to obtain SI capillary pressure curves,especially for tight reservoirs.This paper introduces a unique approach to infer SI capillary pressure curves from 2D images through integrating image analysis and fractal theory.Using pore-related information obtained from image analysis,we properly represent the pore structure as bundles of tortuous square and triangular tubes with sinusoidally varying radii to imitate cross-sectional variation between pore bodies and throats.Moreover,we simulate the piston-like and snap-off displacement mechanisms to derive an innovative fractal SI capillary pressure model.The developed model considers the contact angle hysteresis caused by surface roughness and heterogeneity of reservoir rocks.The Mayer-Stowe-Princen(MSP)approach is implemented to compute the entry capillary pressure of piston-like displacement.The laboratory-measured porosity and permeability are utilized to determine the model's 3D-related parameters that cannot be inferred from 2D images.The model reliability is verified with the good accuracy of the predicted capillary pressure curves versus laboratory-measured data of five samples from the Liushagang and Huangliu in the South China Sea.Finally,the fundamental parameters influencing the developed SI capillary pressure model are investigated with sensitivity analysis.
NSTL