A new analytical model for flow in acidized fractured-vuggy porous media

Abstract

Acidizing is one of the widely used technologies that makes the development of naturally fractured-vuggy reservoirs effective. During the process of acidizing, carbonate minerals are dissolved by hydrochloric acid, which can create high conductivity channels and wormholes to connect fractures and pores. In this work, a new analytical model, incorporating the heterogeneity of the pore networks into acidizing region, is proposed to study the flow characteristics in acidized fractured-vuggy reservoirs. The model is coupled by an acidized inner region and a conceptualized outer region of common triple medium. The porosity and permeability of inner region, which are rather heterogeneous and disordered when observed at different length scales, can be well addressed by fractal theory. The properties of the outer region can be described with three basic parameters: the matrix block size L M , the space interval of fracture L F and the radius of the vug L v . Results show that the flow characteristic curves can be characterized by six flow stages (i.e. wellbore storage stage, radial flow stage in the interior region, fracture-vug inter-porosity flow stage, transition flow stage, fracture-matrix inter-porosity flow stage and external boundary response stage). It can be applied to estimate reservoir parameters for uncertainty reduction using inverse modeling.

A critical review on coupled geomechanics and fluid flow in naturally fractured reservoirs

“…In the past few decades, several mathematical modelling approaches have been developed and extended. They mainly depend on continuum approaches involving geometrical information for fracture and matrix formation systems, setting up the domain of the fracture matrix system for mass and energy conservation equations (Lei, Liao, and Zhang 2019;Wu, Liu, and Bodvarsson 2004). These approaches are followed by solving discrete nonlinear algebraic equations numerically which couple fluid flow phases with other physical processes (Warren and Root 1963;Wu 2016).…”

Numerical Modeling and Simulation of Fractured-Vuggy Reservoirs Based on Field Outcrops

“…Based on CT-scanning images, Fadlelmula et al [21] employed a multi-point geostatistical modeling technique to generate multiple fracturedvuggy realizations, which can be used for reservoir modeling prior to multi-phase fluid flow simulations. Lei et al [22] proposed a novel analytical model to explore the flow characteristics in acidized fractured-vuggy reservoirs, suggesting six flow stages (i.e., wellbore storage stage, radial flow stage, fractured-vuggy inter-porosity flow stage, transition flow stage, fracture-matrix inter-porosity flow stage, and external boundary To unveil the development mechanisms of fractured-vuggy reservoirs, many scholars analytically/numerically and experimentally investigate the impact of the coexistence of fractures and caves on oil recovery based on synthetic distributions of fractures and caves. Pioneering work in the field was performed by Neale and Nader [8], where they investigated how the caves influence the permeability of the porous media.…”

“…Based on CT-scanning images, Fadlelmula et al [21] employed a multi-point geostatistical modeling technique to generate multiple fracturedvuggy realizations, which can be used for reservoir modeling prior to multi-phase fluid flow simulations. Lei et al [22] proposed a novel analytical model to explore the flow characteristics in acidized fractured-vuggy reservoirs, suggesting six flow stages (i.e., wellbore storage stage, radial flow stage, fractured-vuggy inter-porosity flow stage, transition flow stage, fracture-matrix inter-porosity flow stage, and external boundary response stage). Limited by the scale issue, the combination of the CT-scanning method and multi-point geostatistics modeling is unable to deal with the case, containing a large-scale cave with tens of meters or larger.…”

A New Model for Predicting Flow in Fractured-Vuggy Carbonate Reservoirs under Pseudosteady State Condition

“…Taking China for example, according to the statistics of the Ministry of Natural Resources of China, in 2018, 7176 × 10 4 t of proved oil and gas reserves of Ordovician carbonate rocks (fractured-vuggy carbonate reservoirs) in Shunbei was reported [2]. As stated in the literature [3][4][5][6][7][8], in the near future, the resources of carbonate reservoirs will be one of the main battlefields for "increasing reserves and productivity" in China.…”

“…In general, influenced by a variety of geological processes, the carbonate reservoirs are heterogeneous, and the reservoir spaces are typically dual or triple porosity systems, which are different in size and complex in distribution. For fractured-vuggy carbonate reservoirs, the reservoirs can be classified as matrix system, fracture system, and vug system, in which the vug system is the main reservoir space, and fractures with larger permeability work as the main flow channels [5][6][7]. Physically speaking, during the developing process, formation permeability of each system in the reservoirs will decrease with the increasing effective stress [8].…”