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Simulation Of Acid Fracturing Including Acid Propagation In FormationNormal access

Authors: R.D. Kanevskaya and A.V. Novikov
Event name: ECMOR XVI - 16th European Conference on the Mathematics of Oil Recovery
Session: IOR/EOR
Publication date: 03 September 2018
DOI: 10.3997/2214-4609.201802256
Organisations: EAGE
Language: English
Info: Extended abstract, PDF ( 639.57Kb )
Price: € 20

Acid fracturing is a quite cheap and easy-to-use stimulation technique in carbonates. It differs from proppant fracturing in part of setting up a high conductivity channel. In the case of acid fracturing it is influenced by two processes: acid transfer along the fracture and dissolution of carbonate minerals in porous medium. The first process is critical for effective length of the channel, the second one regulates the initial channel conductivity. Conductivity prediction is one of the main issue of acid fracturing simulation. Modern simulators often assume infinite reaction rate at fracture surfaces while evaluation of acid fracture conductivity is based on various empirical correlations. In this study, we propose a model assumes strict evaluation of final porosity and permeability distributions in the affected area. The model includes calculation of two-phase multicomponent flow in porous media taking into account kinetics of acid-mineral interactions, porosity and absolute permeability changes, relative permeabilities modification. The water phase can contain acid, water, salt and carbon dioxide components. It is supposed that the last one is instantaneously dissolved in the water phase. Kozeny-Carman equation is used for an absolute permeability calculation but any other expression can be easily embedded. This model coupled with acid transfer model along the fracture that includes convection-diffusion problem, uses analytical expressions for velocity profile in the fracture and prescribed relation between fracture width and net pressure. One-dimensional and two-dimensional cases were considered. Such a model allows rather fast calculation of the size, porosity and permeability of affected area in order to estimate its effective parameters and use them in full-field flow simulation. It also provides an opportunity for various optimization and design of acid fracturing based on solution of mass balance equations in porous medium and fracture. Calculations were performed for a number of cases.

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