| Popis: |
Physical and chemical interactions do occur between clay minerals and drilling fluids. The interactions will result in permeability and porosity decrease in reservoir formations. We especially want to know what happened in the formation after drilling. In the process of studying formation damage, well log information is practicable and important. Well logging is done after drilling, so well log information contain a lot of knowledge related with the interaction between drilling fluids and clay minerals. In order to study the effect of drilling fluids/clay minerals interaction on formation permeability and use well log information to evaluate formation damage quantitatively after drilling, an apparatus which can measure resistivity, acoustic velocity, core deformation and pressure change along the length of the sample simultaneously under conditions of elevated temperature and pressure is developed. Experiment were done on artificial shale samples, natural shale samples and shaly sand samples utilizing different aqueous solutions at temperatures ranging from 25°C to 60°C and pressures ranging from 2.5Mpa to 12Mpa. In the shale formation, the changes in resistivity and acoustic velocity are always corresponding to the shale deformation. In the permeable shaly sand formation, the incompatibility between formation water and drilling fluid is the one of reason that result in drilling fluid filtrate invasion. Using these data, the model that describe the relationship between resistivity and contacting fluid properties, interaction time between formation and drilling fluid, permeability and acoustic velocity derived porosity is obtained. The model predictions agreed with the experiment. Well log information is abundant and low cost relative to sampling, so this study is useful for improving understanding of formation damage. |
