Commun. Comput. Phys., 13 (2013), pp. 540-558. An Efficient Numerical Model for Immiscible Two-Phase Flow in Fractured Karst Reservoirs Zhao-Qin Huang 1, Jun Yao 1*, Yue-Ying Wang 11 School of Petroleum Engineering, China University of Petroleum, Qingdao 266555, Shandong, China. Received 16 July 2011; Accepted (in revised version) 24 February 2012 Available online 26 July 2012 doi:10.4208/cicp.160711.240212a Abstract Numerical simulation of two-phase flow in fractured karst reservoirs is still a challenging issue. The triple-porosity model is the major approach up to now. However, the triple-continuum assumption in this model is unacceptable for many cases. In the present work, an efficient numerical model has been developed for immiscible two-phase flow in fractured karst reservoirs based on the idea of equivalent continuum representation. First, based on the discrete fracture-vug model and homogenization theory, the effective absolute permeability tensors for each grid blocks are calculated. And then an analytical procedure to obtain a pseudo relative permeability curves for a grid block containing fractures and cavities has been successfully implemented. Next, a full-tensor simulator has been designed based on a hybrid numerical method (combining mixed finite element method and finite volume method). A simple fracture system has been used to demonstrate the validity of our method. At last, we have used the fracture and cavity statistics data from TAHE outcrops in west China, effective permeability values and other parameters from our code, and an equivalent continuum simulator to calculate the water flooding profiles for more realistic systems. AMS subject classifications: 35B27, 35Q30, 76S05 Notice: Undefined variable: pac in /var/www/html/issue/abstract/readabs.php on line 164 Key words: Fractured karst reservoirs, effective permeability tensor, discrete fracture-vug network model, two-phase flow, full-tensor simulator. *Corresponding author. Email: rcogfr_upc@126.com (J. Yao)