冲击式取心子弹会伤害低强度地层且无法获得令人满意的岩心,特别是在疏松地层进行取心,大多数井壁取心会导致岩心部分或完全损伤,甚至无法获取岩心。地层冷冻会增加局部地层强度从而提升地层抗击强度,取心前冷冻地层不仅能增加疏松地层的强度,受冷冻后的地层流体会减少气体膨胀或驱动从而降低因此造成的岩心损害,同时,也有助干克服在低压差下的取心困难。采用原地岩心冷冻技术可极大改善地层取心质量、岩心寿命以及岩心收获率,因而能得到更好的储层各项参数的描述。目前该项技术正处于实验完善阶段。原地岩心冷冻技术是采用新型的井壁取心工具在实施取心作业前通过释放液氮冷冻地层后再进行井壁取心的一种技术。地层流体或可能侵入地层的钻井液暴露在超低温液氮(-321℉,非法定计量单位,1℉=9/5℃+32)介质时会立即被冷冻。冷冻过程受液氮速度、储层温度、孔隙度和被冷冻的流体等因素的影响,其冷冻深度可 Impact coring bullets can damage low-strength formations and fail to obtain satisfactory cores, especially in loose formations. Most borehole coring can result in partial or complete core damage, or even inability to obtain core. Stratum freezing increases the local formation strength and thus enhances the formation resistance. Pre-cautiously freezing the formation can not only increase the strength of the unconsolidated formation, but also reduce the core damage caused by frozen gas in the formation fluid after being frozen. Dry overcomes difficulty in coring at low pressure drop. Using in-situ core-freezing techniques can greatly improve formation coring quality, core life, and core collection rates, resulting in better reservoir characterization of the parameters. At present the technology is in the experimental stage of improvement. In-situ core freezing is a technique that uses a new borehole coring tool to coring the borehole by releasing liquid nitrogen to cool the formation before coring. Stratigraphic fluids or drilling fluids that may intrude into the formation are immediately frozen when exposed to cryogenic liquid nitrogen (-321 ° F, non-legal units of measurement, 1 ° F = 9/5 ° C + 32 ° C). The freezing process is affected by factors such as liquid nitrogen velocity, reservoir temperature, porosity and the fluid being frozen. The freezing depth can be