Thus, a hydrated place would develop all around the wellbore. Once the distance from the hole axis excesses 20cm, the water content of shale nearly no longer alterations with all the time increases, and the water content approaches the original water content; scientific study in hydrated region, the longer the time, the a lot more the shale water content material once the distance is frequent. Figure 7Water content distribution all-around the wellbore.The distribution character of UCS of shale around the wellbore is presented in Figure eight. Whenever a wellbore is opened, the UCS would lessen because the time increases. Once the time is consistent, the UCS would maximize since the distance from the wellbore axis increases. The expanding price close to the wellbore wall would be the highest. Figure 8UCS distribution about the wellbore.
The variation of collapse strain with drilling time underneath various water diffusion coefficients is proven in Figure 9. The outcomes show that the collapse strain increases rapidly within a brief time after the wellbore opening because of shale hydration. Then the escalating rate of onlycollapse stress would decrease. At last, the collapse strain would improve linearly that has a very very low growing fee. After the wellbore is opened 10 days, the collapse pressure almost no longer modifications. In accordance to Figure 9, following the wellbore opening, increasing the drilling fluid density to 1.45g/cm3 steadily is far more effective for long-time wellbore stability once the water diffusion coefficient Deff = 0.0238cm2/h. The greater the water diffusionEfaproxiral Sodium coefficient is, the bigger the increasing variety of collapse is.
Alternatively, the likelihood of wellbore instability is going to be increasing with more smectite in shale. Figure 9Time-dependent collapse pressure.5. ConclusionsWater content at distinctive distance through the end face of shale sample is measured applying the built equipment in the condition of downhole temperature and strain. The water material of shale with the wellbore wall reaches to saturated state speedily once the wellbore is opened; the water content material of shale would lessen using the increment of distance from wellbore axis, and the reducing price may be the highest near the wellbore wall. Due to the affect of shale hydration, the power in the circumferential formation all around the properly is steadily lowered using the raise of drilling time and increases with the boost of the distance away from the wellbore.
Collapse strain of shale increases sharply inside a short time immediately after drilling and after that slows down. The collapse stress is in essence regular just after a number of days from the open-hole time. The first steady wellbore may well collapse using the maximize in the open-hole time.Shale containing additional smectite is a lot more vulnerable to react with drilling fluid. The probability of wellbore instability of shale is higher with extra smectite because the escalating variety of collapse stress is bigger.