What is the relationship between groundwater pollution and oilfield water injection wells

When the oil field oil extraction to a certain stage, the oil production will have a substantial decline, in order to improve the oil production and recovery rate, through the injection of water can achieve certain results. Oilfield water injection is to inject water into the reservoir containing the original oil, gas, water filled pores, in order to drive the remaining oil and gas out of the pores to achieve recovery, but the oil reservoir is often located in the underground hundreds to thousands of meters, so the oilfield water injection generally has no effect on the surface water and shallow groundwater, but the injection of wells is often some abandoned or very little oil out of the old wells, the injection of water may occur after the occurrence of a well leakage situation and pollution of the groundwater, as well as The leakage of wells during drilling or the failure of cementing after drilling through different water-bearing strata may also cause groundwater contamination by connecting groundwater of different compositions.