Productivity Decline in Oil Wells Related to Asphaltene Precipitation and Emulsion Blocks

Abstract

Abstract A few oil wells in a Saudi Arabian field have shown significant oil productivity decline in recent years. A few of them have ‘died’ prematurely while others have become intermittent producers. It has been noticed that the oil productivity decline is aggravated with water encroachment. The oil productivity decline has come about with relatively low water rates and without any significant drop in reservoir pressure. These wells have low productivity index (PI) resulting in relatively low flowing bottom hole pressures (FBHP). This paper presents the results of an investigative case study to determine the causes of productivity decline in these wells. A multi-disciplinary team was set up with engineers and scientists from reservoir management, production engineering and the R&D Center for the investigative study. The team focused on multiple aspects including reservoir and production engineering, as well as a comprehensive laboratory and field investigation. The results of this study indicate that one of the main causes of productivity decline in these wells is related to asphaltene precipitation and the subsequent formation of tight emulsions downhole. The emulsions block the pore throats and cause formation damage leading to productivity decline. Another factor that further aggravates the productivity of these wells is poor rock quality in the area. Possible causes of formation damage due to inorganic scaling, and leakage and mixing of gas from a deeper reservoir have been eliminated. Well test analyses on some of the affected wells shows the formation damage mechanism in the affected area is further aggravated by poor reservoir rock quality. The time-lapse pressure transient analysis also indicates a deterioration of skin and productivity with time. Based on these findings a special solvent treatment was recommended and designed as a pilot trial for one of the dead wells. The treatment included squeezing xylene and demulsifier to dissolve the asphaltenes and break the tight emulsions around the wellbore area. The treatment resulted in only a slight improvement in the productivity index and the well died after a few days. Currently a stimulation treatment with acid and demulsifier is being implemented in selected wells. The results of the field trials will be described in the paper.