Abstract
Most of the high permeability reservoirs in Daqing oil field have been conducted by water flooding and polymer flooding.
The average oil recoverable recovery has reached to 53% after polymer flooding. Currently, the further development of such reservoirs has become a big challenge due to both serious heterogeneity reservoirs and highly dispersed residual oil. Foam flooding, as a candidate EOR technique integrating both properties of gas injection technique and chemical flooding, has been proposed. In this study, systematic laboratory experiments on foam flooding EOR technique for Daqing reservoirs after polymer flooding have been performed.
Several operating parameters have important influences on the recovery efficiency. ➀ Both the foamability and stability are the key factors to ensure high performance of recovery. The foam formulas were optimized with good performance of foamability and stability. ➁Injecting mode is another important factor. Three main injection modes, including co-injection of gas and solution, alternative injection of gas and solution, and direct injection of foam were compared. The direct injection of foam is the most effective mode and the alternative injection of gas and solution is the poorest. ➂The gas liquid ratio can also affect the flooding efficiencies greatly. The optimized gas liquid ratio was proposed as 3:1–4:1 for direct injection mode at the reservoirs condition. EOR effect evaluation of foam flooding after polymer flooding has been conducted upon three-layer positive rhythm sandpack cores flooding tests. Results indicate that foam flooding can contribute 12–22% OOIP recovery even if the recovery after polymer flooding is nearly 55%. The obviously increasing of injection pressure during the foam flooding indicates that nitrogen foam flooding has excellent profile control ability.
Foam flooding can block thief zones for highly heterogeneous reservoirs. It may become a promise EOR method for Daqing reservoirs after polymer flooding.
