Abstract:

Over many years of oilfield development by waterflooding, problems such as rapid rise of water cut, low waterflooding efficiency and low recovery percent of reserves have been encountered in deep heavy Triassic oil reservoirs in Lukeqin oilfield. In order to improve waterflooding development effect and increase well production, a hypoxic air huff and puff program was put forward. Then based on laboratory physical simulation experiments and numerical simulation, the mechanism of hypoxic air huff and puff was analyzed, and waterflooding parameters were optimized. Finally taking the deep Triassic heavy oil reservoirs in Lukeqin oilfield as a case, a field test of hypoxic air huff and puff was carried out. The results show that the mechanism of increasing oil production through hypoxic air huff and puff is that a pseudo bubble point would appear after injecting hypoxic air into heavy oil reservoirs, and the heavy oil changes to foam oil which can reduce the viscosity of crude oil and block dominant water channels, as a result expanding the sweeping volume. Air injection rate and volume and soaking time have great influences on the effect of hypoxic air stimulation. It is suggested that the injected gas volume should be about 400, 000 m³, injection rate should be 40, 000 m³/d, and soaking time should be 8-10 days in a single well. Hypoxic air huff and puff has been implemented in the deep Triassic heavy oil reservoirs in more than 400 wells in Lukeqin oilfield, among which 82% of the wells are effective, namely, the oil production increases by 4.5 t/d per well and water cut decreases by 42% at the initial stage; the valid period is 168 days and the cumulative oil production has been increased by 480.0 t per well. These results have proved that hypoxic air huff and puff is an effective technology for increasing oil production while decreasing water cut for deep heavy oil development. These findings are important references to improving oil recovery of similar reservoirs after experiencing waterflooding development.

Key words: Lukeqin, Triassic, deep heavy oil reservoir, hypoxic air huff and puff, foam oil, production increase and water cut decrease