Abstract
The purpose of this work is to study the effect of carbon dioxide oil solubility on the aggregation of asphaltene associates and decrease of oil permeability of sandstones. Consideration is given to the interaction variants of oil and carbon dioxide in a free volume before being injected into a porous medium and immediately in the porous medium. The influence of oil composition on the aggregation of asphaltene associates is studied. The effect of the dissolved carbon dioxide on associate dispersion in oil is examined through oil filtering in sandstones. If asphaltene aggregation occurs in a porous medium it causes pore plugging leading to reduced permeability, complicates the development of carbon dioxide injection wells and, as a result, prevents from achieving the planned indicators of oil production and oil recovery. It is found that in the case when oil interacts with carbon dioxide in the free volume before being injected into a porous medium, the increase in the volume of filtered oil and the concentration of carbon dioxide dissolved in oil, and decrease in sandstone permeability reduce the relative mobility of oil with the dissolved carbon dioxide. The significant influence of sandstone permeability on the experimental results indicates that the sizes of asphaltene aggregates are comparable to the sizes of small pores. We have not observed complete attenuation of filtration after passing of oil with dissolved carbon dioxide through sandstones. Based on the analysis of changes in oil composition and properties carried out in the laboratory experiments on oil displacement by carbon dioxide rims, it has been determined that aggregation of asphaltene associates takes place under immediate contact of oil and carbon dioxide in a porous medium. The higher the asphaltene content in oil, the lower the formation permeability, whereas tight formations feature a more significant decrease in permeability.
Highlights
Науки о Земле и недропользование / ISSN 2686-9993, 2686-7931 Earth sciences and subsoil use / ISSN 2686-9993, 2686-7931 permeability reduce the relative mobility of oil with the dissolved carbon dioxide
The significant influence of sandstone permeability on the experimental results indicates that the sizes of asphaltene aggregates are comparable to the sizes of small pores
Based on the analysis of changes in oil composition and properties carried out in the laboratory experiments on oil displacement by carbon dioxide rims, it has been determined that aggregation of asphaltene associates takes place under immediate contact of oil and carbon dioxide in a porous medium
Summary
На практике вблизи нагнетательных скважин, а также в зонах, обойденных фронтом вытеснения, нефть контактирует с оторочкой углекислого газа. Далее после каждой ступени растворения углекислого газа определялась подвижность нефти при фильтрации через образцы больших ее объемов. Обобщение результатов проведенных опытов показало, что относительная подвижность нефти существенно зависит от объема нефти, прокачанного через песчаник, содержания в ней асфальтенов и проницаемости пористой среды. С увеличением объема профильтрованной нефти и концентрации растворенного в нефти диоксида углерода, а также с уменьшением проницаемости песчаника относительная подвижность нефти с растворенным диоксидом углерода снижается. Результаты анализа состава нефти при фильтрации ее с диоксидом углерода в пористой среде приведены в табл. В дальнейшем при контакте нефти с оторочкой углекислого газа наблюдается повышение содержания асфальтенов в составе профильтрованной через модель пласта нефти. Изменение состава малосмолистой нефти (проба No 3) при вытеснении оторочки диоксида углерода из модели пласта с проницаемостью 1,14 мкм
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