富有机质页岩高温热激增渗效果实验评价方法

Experimental evaluation method for permeability changes of organic-rich shales by high-temperature thermal stimulation

高温热激可有效缓解致密型油气层钻完井及水力压裂过程中造成的水相圈闭损害,并因诱发岩石破裂而一定程度地增加储层渗透率。然而目前关于高温热激岩样的预处理、实验程序及评价指标等方面尚未取得共识。以四川盆地志留系龙马溪组页岩储层为研究对象,建立了高温热激增渗效果评价实验流程,分别考虑干燥岩样和含水岩样的情况,开展了5℃/min递增温度的高温热激实验,并采用阈值温度、4 MPa围压下及原地应力条件下渗透率的增渗倍数等指标,评定了页岩储层的高温热激增渗潜力。实验结果显示:干燥页岩的阈值温度为650~700℃,含水页岩呈现2个阈值温度,低值为100~150℃,高值为450~500℃;高温热激后原地有效应力下,干燥页岩样增渗倍数为1.5~10.0,含水页岩样增渗倍数可达20~50。研究表明:在页岩气藏水平井+分段水力压裂开发背景下,适合应用高温热激增渗法解除水相圈闭损害并可大幅度改善气井生产行为,所推荐的实验方法和评价指标有助于客观评定页岩储层的热激增渗潜力。

High-temperature thermal stimulation(HTS)can effectively release the damage of water phase trapping,which was caused during the drilling and completion of tight oil and hydraulic fracturing of gas reservoirs.The permeability of a reservoir will increase to a certain extent because HTS induces new rock fracture. However,there are no uniformed methods on the pretreatment,experimental procedures,and evaluation indicators of HTS rock samples. Taking the Longmaxi Formation shale in the Sichuan Basin as the research object,an experimental process for evaluating the impact of HTS on permeability was performed. The conditions of dry and water-bearing rock samples were taken into consideration,and the temperature increasing rate was 5 ℃/min. The evaluation index for HTS of shale reservoirs includes three aspects:threshold temperature,the increase multiples of permeability in 4 MPa confining pressure and in-situ conditions. The results show that the threshold temperature of dry shale is 650-700 ℃ and the water-bearing shale presents two threshold temperatures. What is more,the low value is 100-150 ℃ and the high value is 450-500 ℃. After HTS,under the in-situ effective stress,the increasing ratio of permeability of drying shale samples is 1.5-10.0,and that of water-bearing shale samples reaches 20-50. Our work has shown that it is suitable to apply the HTS method to release water phase trapping damage and it greatly improves the production of wells,under the background of horizontal wells +staged hydraulic fracturing in a shale gas reservoir. Our recommended experimental methods and evaluation indicators are helpful to assess the HTS potential of a shale reservoir.