Core Flood Study of Injectivity Decline by Mixing Produced Oily Water with Seawater in Arab-D Reservoir

Abstract

Abstract A study was initiated to investigate impact of co-mingling produced water with seawater. The objective of the study was to assess injectivity decline in power water injectors caused by introducing produced water into the seawater injection system using core samples from Arab-D. A series of core flood experiments was conducted to study formation damage aspects. The core flood study was done using water samples collected from shipping lines from Qurrayah to represent seawater and produced water from HRDH GOSP-2, due to lack of actual produced water from X field. The core flood experiments were performed to assess the effect of produced oily water on core permeability. Experimental results showed that introducing different ratios of produced water (5, 10, 15 and 100 vol.%) to the seawater resulted in permeability loss of core samples. The damage was found to be proportional to the concentration of produced water. More reduction in permeability was found in low permeability core samples. However, lost permeability was restored by reversing flow in high permeability core (83 md). Based on the obtained results, it is recommended to inject produced water into a dedicated disposal wells to avoid any injectivity decline in power water injectors and to maintain the injection rate target of 30 MBWPD. It is also recommended to maintain a good quality of the injected seawater. Low level of oil and solids in produced water should also be maintained. Introduction X field is a north-south trending anticline with a 3 oil-bearing reservoirs: Arab-D, Hanifa, and Lower Fadhili all of which are carbonate formations with reservoir quality ranging from coarse calcarenite to fine-grained limestone. Arabian Light crude has been produced from both the Arab-D and from Hanifa. The Lower Fadhili, which also contains Arabian Light crude, has not been produced yet. The reservoir quality, especially in the Arab-D, deteriorates towards the peripheries of the field. As such, the aquifer is generally weak and primary drive mechanism is solution gas. Therefore, any significant volume of production will require power water injection. Injection of water for pressure maintenance, water flooding or disposal of produced oily water is a common practice in oil industry(1). For successful water injection, water quality issues should be considered.