Challenges and Countermeasures of Directional Drilling Through Abnormal High Pressure Salt/Anhydrite/Calystone Layer in HFY Oilfield of Iraq, A Case Study

摘要

The Lower Fars formation located at the depths of 1350-1950meters, it mainly consists of alterations of claystone, anhydrite and salt layer with a 2.22 g/cm~3 high pressure aquifer in 1400~1600m, the safe drilling window is limited to 0.15g/cm~3 ,the 10~15m interval under this formation is the main Jeribe-Kirkuk reservoir in this oilfield. More than 100 clusters of directional and horizontal Jeribe-Kirkuk wells will be drilled. The high risk of wellbore instability in Lower Fars has resulted in wellhole collapse, overpull, pipe sticking, and sticking during running casing and the high-density salt-saturated drilling fluid is easily deteriorated and loss of liquidity while directional drilling through the Lower Fars interval. In the 1~(st) directional well JKD007, stuck pipe was encountered 3 times and drilling sidetrack holes were required 2 times. In the 1~(st) horizontal well JK060H,a stuck casing resulted in setting the casing shoe in shallower depth. This study has been carried out in order to decrease the risk of sticking and ensure drilling a smooth, directional hole in the Lower Fars formation. So the lithologic creepage rules and the hole deformation rules in the Lower Fars, major causes for pipe sticking, a safe window of drilling fluid, critical the density of drilling fluid under the different inclinations and technology countermeasures were determined through build the wellbore stability analysis models based on the results of rock mechanics tests of the salt, anhydrite and claystone, the pore pressure, in-situ stress and rock deformation and failure law. The critical density of drilling fluid increase to 2.35 g/cm~3 is proposed while the inclination about 35°in Lower Fars formation in order to reduce the risk of pipe sticking; the more stable well trajectory is recommended baesd on the lower Fars deformation rules through adjusting the location of KOP to reduce the inclination and directional length in Lower Fars and considering the distribution of the salt/anhydrite/claystone, and a new kind of the high-density saturated salt- water mud was developed through introducing a kind of new polyamine type inhibitors, synthetic polymer thinner and optimizing the composition and dosage of weighting materials. Since then,11 directional wells and 2 horizontal wells have been drilled and completed with great success for the Jeribe-Kirkuk wells. Average directional drilling time in Lower Fars is reduced from 74days to 59days and the average ROP has improved by 9.64% using a 2.35g/cm~3 drilling fluid with a controlled viscosity of less than 120s. This paper will systematically describe the details of the sticking mechanism, the Lower Fars wellbore stability analysis method, and the effectiveness of the countermeasures used in directional drilling through the high- pressure salt/anhydrite/claystone layer.