Horizontal well, nitrogen and viscosity reducer assisted steam huff and puff technology: Taking super heavy oil in shallow and thin beds, Chunfeng Oilfield, Junggar Basin, NW China, as an example

Chunfeng Oilfield in the Junggar Basin has shallow burial depth (400–570 m), low formation temperature (22–28 °C), thin reservoirs (2–6 m, averaging 3.5 m), high underground crude oil viscosity (50 000–90 000 mPa·s), but high sensitivity to heat, it is suitable for thermal recovery. In view of these features, a development method for this oilfield combining horizontal well, viscosity reducer, nitrogen and steam flooding (HDNS) was put forward, and pilot test was carried out in Northern Pai 601 sand body. The results show: injecting nitrogen through annulus can insulate thermal, high expansibility of nitrogen works to compensate formation energy, and nitrogen overlapping in reservoir has insulation effect. The combination effect of all parts of HDNS significantly increased steam sweep volume, oil displacement efficiency and crude oil flow ability, and reduced oil viscosity. Thanks to this technique, Chunfeng Oilfield has built up a production capacity of 40×104 t, with an oil recovery rate of 3%, marking the successful high-speed and high-efficiency development of low-grade shallow thin super heavy oil. Key words: shallow and thin bed, super heavy oil, enhanced thermal recovery, horizontal well, steam huff and puff, nitrogen, oil-soluble viscosity reducer