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Description:
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A successful cement job results in complete zonal isolation while saving time and money . To achieve these goals , various factors such as well security , casing centralization , effective mud removal , and gas migration must be considered in the design . In the event that high -pressure and high -temperature (HPHT ) conditions are encountered , we must attempt to achieve permeability in the set cement to prevent gas migration and to prevent any other fluid passing through to collapse the entire structure . Therefore , the design of the cement must be such that it prevents : Micro -annuli formation Stress cracking Corrosive fluid invasion Fluid migration Annular gas pressure In HPHT cases , we need more flexible cement than in conventional wells . This cement expands more at least 2 to 3 times more in some special cases . The stress in the cement is strongly connected with temperature and pressure , as well as lithology and in -situ stress . If we can define a method which connects the higher temperature to the lower stress field , we would have the solution for one side of the equation , and then we could model the pressure (stress principles ) at the designated depth and lithology . Since the stress is so dependent on temperature , the temperature variation must be accurately predicted to properly design the fluid and eliminate excessive time spent waiting on cement . In addition , a post -job analysis is necessary to ascertain zonal isolation and avoid unnecessary remedial work . By increasing the flexibility of the set cement (lowering the Young's modulus ) , we can reduce the tensile stress in the cement sheath during thermal expansion . This could be a solution to the problem of cement stability in high temperature cases . Here we report the use of the finite -element method (FEM ) to investigate the stress fields around and inside the cement , and to forecast the time of failure and its affect on cement integrity . This method is more powerful than conventional stability methods since complex boundary conditions are involved as initial conditions and are investigated simultaneously to more accurately predict cement failure . The results of this study show the relevant dependency of stress principles with temperature and pressure . These results clarify the deformation caused by any disturbance in the system and the behavior of under -stress locations based on their relative solid properties . |