Assessing the impact of groundwater mixing and sea water intrusion on oil production in coastal oil fields using resistivity sounding methods

Issaran oil field is a major heavy oil field in the Western shoreline of the Gulf of Suez, Egypt, which is facing challenges in field development and operations. Therefore, it is under development for many years to identify the required parameters to improve the quality of the produced oil. Identifying the source of groundwater mixing with heavy oil during the production process is a prerequisite. Geoelectric resistivity survey is suggested to identify aquifer characteristics, as well as the distribution of structural elements affecting the groundwater aquifer in Issaran oil field. A total of 94 Vertical Electrical Resistivity Soundings (VESs) were conducted to evaluate the groundwater aquifer. The recorded VESs were corrected and modeled to create two-dimensional profiles (2D) and areal contour maps throughout the studied site. Geoelectric modeling revealed five distinct resistivity subsurface layers. The top three layers are corresponding to dry friable gravelly sand and alluvial sediments of a total thickness of about 15–70 m and resistivity values ranging from 15 to 200 Ω m. The fourth layer represents the groundwater bearing horizon and is characterized by high degree of saline water saturation, where resistivity ranged from 0.5 to 15 Ω m. Finally, the lower stratigraphic layer is characterized by its relatively high resistivity (greater than 70 Ω m), and it is not observed through all the conducted VESs. The findings shows that the groundwater bearing horizon is structurally controlled and is mainly affected by the Red Sea structural regime, which could act as seawater passages to the oil field area.