Analysis of formation flow impairment in carbonate reservoir due to asphaltene precipitation and deposition during gas flooding

Hydrocarbon gas injection proved to be one of the most efficient enhanced oil recovery (EOR) methods, especially for tight reservoirs with light to medium API oil, where water flooding is expected to be inefficient due to low permeability. Asphaltene precipitation and deposition, however, might occur due to fluids compositional changes happening with the gas injection. This may lead towards not only near well bore formation damage but also it might cause some formation flow impairment deep in the reservoir if conditions for asphaltene precipitation and deposition are encountered.;Asphaltene precipitation and deposition in porous media is very complex and requires experimental and numerical investigation to understand the conditions at which formation damage may occur, as this will have detrimental effect on the flow capacity of wells and in turn on the ultimate oil recovery from the reservoir.;The phenomenon of asphaltene precipitation and deposition has to be studied in relation with the reservoir rock types and pore throat size distribution for its proper characterization. Depending on the particles sizes, asphaltene may or may not precipitate and deposit in the rock causing temporary or permanent formation damage and fluid flow impairment. This all have to be studied in conjunction with the reservoir fluids and the composition of the injected gas under reservoir conditions.;In this experimental study, low permeability carbonate rock core samples of two different rock types, saturated with live oil, were flooded with hydrocarbon gas under reservoir conditions. As a prelude to these experiments, asphaltene onset pressure and concentration of the oil under study with the injected gas has been achieved through numbers of flow assurance tests, such as Solid Detection System tests, SARA and Titration analysis.;Core flooding experimental setup was designed to mimic the actual reservoir conditions in terms of pressures, temperature, and flooding rates. The entire study reveals important findings to analyze the flow problems in reservoir and near well bore due to asphaltene precipitation and deposition as a result of reservoir fluid composition and pressure changes. The influences of different core lengths, operating pressures and the rock types were analyzed through a number of core flooding experiments. Formation impairment was analyzed through permeability measurements and visualization using the Scanning Electron Microscopic (SEM) images of core plugs before and after the gas flooding process.;Generally, the presence of asphaltene contents in the reservoir fluid is not a problem but their precipitation and deposition causes an irreversible damage causing serious flow impairment problems. The experimental data of the specific reservoir rock and fluid under study indicated that asphaltene precipitation and deposition is a serious problem both near the producers' wellbores and deep in the reservoir rock. It was also concluded that the rock type, core length, and operating pressures directly influence the formation of asphaltene precipitates and their deposition in the reservoir rock pore throats.;It was found that the higher the pressure, the less will be the problem of asphaltene precipitation and deposition while this effect became more pronounced with increased length of core sample. Also it was observed in comparatively tighter rock samples with smaller pore throats were subjected to more serious formation flow impairment.