Predict the mud loss in natural fractured vuggy reservoir using discrete fracture and discrete vug network model

Abstract

In carbonate reservoirs, the leakage path is complex and the law of mud loss is not clear, which brings difficulties to the implementation of plugging measures. Carbonate reservoir is a naturally fractured vuggy media. One of the key scientific problems is that the fluid mass transfer among matrix pores, natural fractures and vugs is not well understood. In this paper, a discrete fracture and discrete vug model is presented to study the law of mud loss in the naturally fractured reservoir wherein natural fractures and vugs developed. The model solved the fluid flow in the discrete fracture and vug network, consisting of 1) Darcy flow in lowly permeable rock matrix and highly permeable natural fractures; 2) free flow in macro vugs. A physically-based boundary is applied to ensure the mass continuity on interfaces between vugs and matrix pores, vugs and natural fractures. A good agreement with analytical results for Poiseuille flow in a porous/free connected media is achieved. Two numerical examples using the commercial software COMSOL provide validation of the new model. When simulating the mud loss process, we find that as soon as vugs are connected to wellbore through natural fractures, total loss is observed. The size and number of vugs play prominent roles in increasing mud loss rate and accumulated mud loss. The numerical results show that the discrete fracture and discrete vug model provides a reliable way to model realistic fluid flow in fractured vuggy porous media. The model in this paper can not only simulate the mud loss process, but also the production process of carbonate reservoirs.