Phase behaviour modelling and compositional simulation of asphaltene precipitation in reservoirs.

摘要

Asphaltene are heavy hydrocarbon molecules that exist naturally in petroleum reservoir fluids. Asphaltene precipitation may occur during pressure depletion or during gas injection processes for Improved Oil Recovery (IOR). It is an important problem during oil production because it can result in formation damage and plugging of wellbore and surface facilities.;This dissertation describes methods for modelling (i) the phase behaviour of asphaltene precipitation, and (ii) the dynamic aspect of asphaltene deposition and plugging in reservoirs.;A thermodynamics approach is used for phase behaviour modelling. The precipitated asphaltene is represented by an improved solid model, while the oil and gas phases are modelled with an equation of state. A method for characterizing the asphaltene component in the oil phase is proposed. In this characterization method, the heaviest component is split into a non-precipitating and precipitating component. These components have identical properties and acentric factors, but different interaction coefficients with the light components. This approach is essential for the use of the solid model in predicting asphaltene precipitation. Laboratory asphaltene precipitation data for hydrocarbon gas injection, pressure depletion and for an asphaltene precipitation envelope are matched successfully with the proposed model.;Inside the reservoir, the precipitated asphaltene can deposit onto the rock surface or remain as a suspended solid in the oil phase. Adsorption and mechanical entrapment are the main deposition mechanisms. The deposited asphaltene may cause blocking of pore throats, which results in permeability reduction. Methods for modelling the above dynamics are proposed. To model the dynamic aspects, the thermodynamics model is implemented into an equation-of-state compositional simulator, which also incorporates the equations for multiphase multicomponent flow, adsorption, mechanical entrapment and formation plugging. Simulation results are in agreement with field observations in showing important phenomena associated with asphaltene precipitation in reservoirs.