| abstract |
Well drilling and servicing fluids for use in producing formations comprise water,na water-soluble salt and a particulate solid bridging agent selected from magnesiumnoxychloride cement, magnesium oxysulfate cement, magnesium potassium phosphatenhexahydrate, magnesium hydrogen phosphate trihydrate and magnesium ammoniumnphosphate hexahydrate. The filter cake so deposited is removed by contact with annaqueous clean-up solution containing an organic acid, a hydrolyzable ester, an ammoniumnsalt, a chelating agent or a mixture of an ammonium salt and a chelating agent. |