A multiple-continuum model for simulating single-phase and multiphase flow in naturally fractured vuggy reservoirs

a r t i c l e i n f o The existence of vugs or cavities in naturally fractured reservoirs has long been observed. Even though these vugs are known for their large attribution to reserves of oil, natural gas, or groundwater, few quantitative investigations of fractured vuggy reservoirs have been conducted. In this paper, a multiple-continuum conceptual model is presented, based on geological data and observations of core samples from carbonate formations in China, to investigate single-phase and multiphase flow behavior in such vuggy fractured reservoirs. The conceptual model has been implemented into a three-dimensional, three-phase reservoir simulator with a generalized multiple-continuum modeling approach. The conceptual model considers fractured vuggy rock as a triple-or multiple-continuum medium, consisting of (1) highly permeable and well-connected fractures, (2) low-permeability rock matrix, and (3) various-sized vugs. The matrix system may contain a large number of small or isolated cavities, whereas vugs are larger cavities, indirectly connected to fractures through small fractures, microfractures or matrix. Similar to the conventional double-porosity model, the fracture continuum is primarily responsible for the occurrence of global flow, while vuggy and matrix continua, providing storage space, are locally connected to each other and interacting with globally connecting fractures. In addition, flow in fractured vuggy reservoirs may be further complicated by occurrence of non-Darcy's and other nonlinear flow behavior, because of large pore space and high-permeability flow channels. To account for such complicated flow regime, our model formulation includes non-Darcy flow using the multiphase extension of the Forchheimer equation as well as flow according to parallel-wall fracture and tube models, based on solutions of flow through a parallel-wall, uniform fracture and Hagen–Poiseuille tube flow. Naturally fractured reservoirs exist throughout the world represent significant amount of the world oil and gas reserves, water and other natural resources. In the past half century, significant progress has been made towards understanding and modeling of flow processes in fractured rock (Barenblatt et al. However, most studies have focused primarily on naturally fractured reservoirs without taking into consideration of large cavities. Recently, characterizing vuggy fractured rock has received attention, because a number of fractured vuggy reservoirs have been found worldwide that can significantly contribute Among the commonly used conceptual models for analyzing flow through fractured rock, dual-continuum models, i.e., double-and multi-porosity, and dual-permeability, are perhaps the most popular approaches employed in fractured reservoir modeling studies. In addition to the traditional double-porosity concept, a number …