Determination of Asphaltene Precipitation Amount under the Condition ofthe Solvent Assisted SAGD Process by the Application of PVT Apparatus

摘要

Solvent Assisted-Steam Assisted Gravity Drainage(SA-SAGD)has been studied as a more efficient processfor extracting bitumen from oil sands than the SAGD process.In the SA-SAGD process,solvent is injectedwith steam to decrease the viscosity of bitumen by dissolution of the condensed solvent.The dissolution of solvent causes a composition change of bitumen,which can lead to asphalteneprecipitation.The effects of the asphaltene precipitation have been studied as part of a solvent-basedrecovery process such as Vapor Extraction(VAPEX).One of the advantages of the asphaltene precipitationis in-situ upgrading of the bitumen,whereas the disadvantage is that it causes a formation damage.To evaluate the effect of the asphaltene precipitation in the SA-SAGD process,it is essential to investigatethe asphaltene precipitation under the conditions expected in the SA-SAGD process.However,it takes alot of time to obtain sufficient data with a conventional method to quantify asphaltene precipitation underhigh-pressure/high-temperature(HP/HT)conditions.Therefore,the aim of this study is to develop an experimental procedure to evaluate the asphalteneprecipitation with pressure/volume/temperature(PVT)apparatus in a reasonable time.The complexphenomenon at the edge of the chamber in the SA-SAGD process was simplified to a model of repetitionsof mixing and drainage processes,and the experiment was configured in this manner.Solvent was addedto a pre-diluted bitumen sample in a PVT cell.The supernatant liquid was sampled to analyze theasphaltene weight fraction remaining in the liquid phase and evaluate the asphaltene precipitation amountin the PVT cell.This process was repeated with increase in the solvent concentration.The asphalteneprecipitation amount(APA)is calculated from the sample analysis data with recurrence relations underseveral assumptions.This procedure enables a wide range of APAs to be obtained from a mixture of bitumen and solventin a single experiment,which enables sensitivity analysis under various conditions.In this research,theexperiment was conducted under two different temperature conditions of 120°C and 150°C and the pressurewas fixed at 3.5 MPa.The APA curves obtained from both experiments had almost the similar trend.Another important observation is that even the multi-component solvent(as used at the operation site)can still induce asphaltene precipitation under the HP/HT conditions expected in the SA-SAGD process.