Liquid Nitrogen Gasification Fracturing Technology Applicable To Shale Gas Development

Shale gas isvery important nonconventional energy, it’ssuccessful commercial exploitdepends primarily on the development of horizontal drilling and fracturing technologybreakthrough. Although hydraulic fracturing can realize large-scale fracturing, it can’tavoid problem of clay hydration swelling. The influence of fracture orientation by theground stress is also larger. Besides, it consumes a lot of water. The French governmenthas brought forward legislation to ban shale gas development using hydraulic fracturingfor resource and environment reasons.Based on reasons above, Professor Li zifeng puts forward a new technology-liquidnitrogen gasification fracturing technology. Liquid nitrogen gasification fracturing processinvolves liquid nitrogen pressure fracturing, rock contraction fracturing, rockembrittlement fracturing and nitrogen expansion fracturing, and this technology canrealize large-scale fracturing，have no problem of hydration swelling of clay minerals,have no water resource limit and no environmental pollution. In short, it can guide shalegas development practice better.This paper introduces the properties, preparation on site and applications of nitrogenin the oil and gas industry, and analyses economic benefit of liquid nitrogen fracturingfluid; based on the energy balance principle, anumerical model of the distribution of wellbore and fracture temperature fieldwas established,according to the calculating result ofthe well bore temperature field during process of liquid nitrogen fracturing, it is knownthat choosing insulated tubing and injecting liquid nitrogen with high velocity can ensurethat liquid nitrogen remain liquid until it is rejected to the target zone. On the basis ofelastic mechanics theory, combined with the azimuthal angle of horizontal well, afterconsidering the combination of natural stress,wellbore pressure,heat stress, establishedaround the wellbore stress field modelof open hole and perforating horizontal well,according totension fracturing criterion，deduces the calculating formulae of initiationfracture pressure and crack initial angleand discusses two special cases. At last, this paperanalyses that the heat stress makes effect on fracturing results of liquid nitrogen, and thelow temperature characteristic of liquid nitrogen makes effect on the rocks nature.