Abstract
It is an important task for reservoir engineers to determine whether and how to optimize the shut-in-time of shale gas wells after volume fracturing. In this study, a new considering the shale hydration capacity and the clay minerals content shut-in-time optimization method was proposed. First, a new water spontaneous imbibition apparatus under the conditions of formation temperature and confining pressure was designed. Then, we conduct a set of experiments on shale samples from the Longmaxi Formation (LF) located in the south of the Sichuan Basin. The water imbibition index was measured to quantitatively evaluate the water imbibition ability and classify reservoir types. Finally, the quadrant analysis method was used to evaluate the shut-in potential of different types of shale reservoirs considering both clay mineral content and shale hydration capacity. The experimental results shown that with the increase of clay mineral content, the water imbibition capacity of shale increased at first and then decreased, and the critical clay mineral content was 39.5%. The shale reservoirs can be divided into two types: the type I reservoir with a clay content of less than 39.5% and the type II reservoir with a clay content of more than 39.5%. The shut-in-time of shale gas wells in different quadrants were Q2, Q1, Q3 and Q4 from small to large. the optimal shut-in-time of type I shale reservoir and type II shale reservoir were about 20 days and 15 days respectively. The average daily gas production was 20.1×104 m3/day after the appropriate shut-in treatment. The study results provide a scientific basis for the optimization of shut-in-time for the development of similar shale gas reservoirs.
