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Drilling fluid with the high density has been successfully used in many kinds of special formations such as gypsum salt bed, salt aquifer, or compound salt formation. Some problems with this kind of the fluid, however, still have to be considered, for example the high temperature resistance in some complicated deep wells, rheological properties control, and the influence of solid content to rheological properties. The authors introduce, based on the research about some important elements such as rheological properties and the quality of sedimentation stability, a drilling fluid with the high density of 2.45 g/cm 3 that has good rheological properties, excellent qualities of sedimentation stability, low water loss, well antisloughing, and small lubrication coefficient, and which can be perfectly used in the deep slim-hole well with the high pressure salt aquifer. In addition, this drilling fluid system with the density of 2.45 g/cm 3 , no matter in the laboratory test or in the field case (No. 3 well of Jeddah), both performs excellently and controls well the salt crystallization, reducing the rate of the crystallization and preventing sticking, jets blocking, or torque increasing. Finally, with the successful application, this drilling fluid can be regarded as a good example for other deep wells or ultradeep wells with the complicated formation in Fergana Valley, Uzbekistan.

To alleviate the problems of casing collapse induced by the coupling effect of rock salt creep and casing wear, the effects of salt creep, attrition rate and casing abrasive position on the equivalent stress on casings in non-uniform in-situ stress field is analyzed by finite-difference model with worn casing, cement and salt formation. It indicates that, creep reduces the yield strength of worn casing to a certain extent; Equivalent stress on casings is bigger and more non-uniform when the abrasion is more serious; Wear position obviously changes the distribution of equivalent stress on casing, and when the wear located along the direction of the minimum in-situ stress, equivalent stress on casing could be the largest that leads to the casing being failed more easily. Equivalent stress on casings increases gradually with creep time increasing and will get to balance in one year or so; In addition, new conclusions are obtained which are different from before: the maximum equivalent stress on casings is in the direction of the minimum horizontal stress, only when the attrition rate of the casing is little; otherwise, it is not. This method could help to improve the wear prediction and design of casings.