超低渗透油层温度-应力-渗流的流固耦合效应

目的在于研究由于注入流体的温度过低而引起超低渗透油层渗透率和孔隙结构变化的温度-应力-渗流的流固耦合效应.实验选用了长庆超低渗油藏的岩心,在恒压和各种不同温度下测定了岩心的渗透率.实验结果表明:①随着温度的降低,岩心的渗透率不断降低,大约2/3的超低渗岩心在25℃左右时会出现裂缝直至断裂.在25~15℃温度段内,流体通过超低渗透多孔介质的渗透率对温度最敏感,其变化程度最大(要么降低的幅度最大,要么出现裂缝),且这种变化是部分不可逆的.②随着温度的升高,岩心的渗透率稍有增加,当温度再开始下降时,渗透率下降,温度下降到原始地层温度时渗透率的值比初始值要大,但增加的幅度不大.因此,注水开发低渗透和超低渗油田时应尽量避免冬季投产和施工作业.在正常的开发状态下应在合理的生产压差下,合理选择或保持适当的注水温度,尽量降低冷伤害对开发效果的影响,保持油藏的稳产和高产.

Temperature stress seepage coupling effect in super- low permeability reservoirs

The changes in the permeability and core structure of super-low permeability reservoirs caused by the lower temperature of injected fluid will result in the temperature stress seepage coupling effect in the super-low permeability reservoirs.The cores for the experiments are selected from the super-low permeability reservoir of Changqing Oilfield.And their permeability is measured under constant pressure and different temperature.The experimental results show that,(1) when temperature decreases,the permeability of the cores decreases,and about two-third of experimented cores will fracture even break at about 25 ℃.In the range of 25～15 ℃ the permeability of the cores is the most sensitive to temperature,the change of the permeability is also the greatest,and the change is partially irreversible.(2) When temperature increases,the permeability will increase slightly;when temperature decreases again it will decrease,and when temperature decreases to original formation temperature the permeability of the cores is greater than the primary value,but the increment is not great.Therefore,the water-injection operation of the super-low permeability reservoirs should not be carried out in winter.The normal development of the reservoirs should be carried out under reasonable production pressure difference and suitable water injection temperature should be maintained.