On the causes and mechanism of deterioration of the properties of drilling mud when drilling wells in the intervals of water-saturated layers of jurassic sediments at the Uzen and Karamandybas fields

Background: This work is devoted to the problem typical for the Uzen and Karamandybas deposits of the formation of downhole packs of drilling mud in the trunk of drilling wells with degraded viscosity, rheological and filtration characteristics in the intervals of occurrence of water-saturated layers of Jurassic sediments after the working drilling mud has been in these intervals in a static state for several hours to 1 day or more. Moreover, this happens even without fixed signs of water ingress. It is explained that the reason for this is the effect on the drilling mud of formation waters with higher mineralization and hardness than the aqueous phase of the mud. However, in the absence of water manifestations in a static state, this effect does not occur as a result of direct physical mixing of these liquids, but as a result of diffusion and osmotic mass transfer between formation waters and the dispersion medium of the drilling mud. Aim: The article reveals the mechanism of deterioration of the technological properties of the drilling mud caused by a significant increase in mineralization and the overall hardness of the aqueous phase of the solution as a result of the above-mentioned mass transfer processes. Materials and methods: The test drilling mud samples used were actual samples taken from the circulation systems of drilling wells at the Uzen field, as well as a model of Jurassic formation water prepared in the laboratory using sodium, calcium, and magnesium chloride salts. The main research methods were expert analysis and laboratory-experimental modeling of the interaction of field samples of drilling mud with a model of formation water without direct contact in a static state, with visual and instrumental determination of the properties of the mud before and after the specified interaction within 24 hours. Results: The study showed that the deterioration of drilling mud properties when it interacts with highly mineralized formation water of Jurassic deposits without direct mutual contact is due to diffusion-osmotic mass transfer between these two fluids, interacting in the “wellbore – drilling mud filter cake – formation” system. The results of laboratory and experimental studies conducted with modeling of all the specified elements of interaction between these fluids confirmed this explanation. Conclusion: As a result of a series of expert analytical and laboratory experimental studies, an answer was obtained regarding the causes of the deterioration of the technological properties of drilling muds located in the wellbore in a static state in intervals of formations saturated with highly mineralized formation waters with high hardness. The mechanism of this phenomenon, which occurs in the wellbore even without direct physical contact between these two fluids, has been explained. The practical application of the results obtained can and should find its place in the development, research, and practical application of drilling muds that are resistant to the polyminerals aggression of formation waters similar or close in their ion-salt composition to those described in this article.