So, a hydrated spot would develop close to the wellbore. When the distance from the hole axis excesses 20cm, the water information of shale just about no longer changes with all the time increases, plus the water content approaches the original water articles; mtor in hydrated place, the longer the time, the a lot more the shale water material once the distance is constant. Figure 7Water content material distribution all-around the wellbore.The distribution character of UCS of shale about the wellbore is presented in Figure eight. When a wellbore is opened, the UCS would lower as the time increases. Once the time is frequent, the UCS would raise as the distance through the wellbore axis increases. The growing fee near the wellbore wall will be the highest. Figure 8UCS distribution around the wellbore.
The variation of collapse stress with drilling time beneath distinctive water diffusion coefficients is shown in Figure 9. The results display the collapse strain increases rapidly inside a quick time after the wellbore opening as a result of shale hydration. Then the rising price of Efaproxiral Sodiumcollapse strain would lessen. At final, the collapse strain would maximize linearly that has a incredibly very low growing fee. Following the wellbore is opened 10 days, the collapse strain just about no longer alterations. According to Figure 9, following the wellbore opening, escalating the drilling fluid density to 1.45g/cm3 gradually is additional advantageous for long-time wellbore stability when the water diffusion coefficient Deff = 0.0238cm2/h. The increased the water diffusionphase 3 coefficient is, the larger the growing array of collapse is.
On the flip side, the likelihood of wellbore instability might be growing with a lot more smectite in shale. Figure 9Time-dependent collapse stress.5. ConclusionsWater articles at different distance from your finish face of shale sample is measured applying the built products in the condition of downhole temperature and stress. The water content material of shale in the wellbore wall reaches to saturated state speedily when the wellbore is opened; the water information of shale would decrease with the increment of distance from wellbore axis, as well as the decreasing charge is the highest close to the wellbore wall. Due to the effect of shale hydration, the strength in the circumferential formation all over the very well is progressively decreased with the improve of drilling time and increases with the improve of your distance far from the wellbore.
Collapse strain of shale increases sharply within a short time immediately after drilling and then slows down. The collapse pressure is essentially steady soon after several days with the open-hole time. The preliminary stable wellbore may collapse with all the improve of the open-hole time.Shale containing a lot more smectite is far more prone to react with drilling fluid. The chance of wellbore instability of shale is higher with additional smectite as the raising array of collapse pressure is more substantial.