No abstract

No abstract

No abstract

The paper presents the relevance of enhancing wellbore stability by developing and applying efficient drilling fluid compositions for well constructions in fractured argillite. In the process of well constructions, there comes a range of complications associated with instability of rocks forming borehole walls, which sometimes results in lower penetration rates, higher construction costs and well abandonment. Often, drilling problems occur at drilling through mudrocks that account for up to 70 % of field sections. When using water-base drilling fluids, the mudrock swelling due to the contact with the fluid dispersion medium adversely affects the drilling process and can significantly increase well construction costs. The accumulation of wellbore cavings inhibits well circulation, causes landing of drilling tools and may result in tool sticking. An analysis of drilling problems in fractured argillite is presented; the mechanisms affecting open hole stability in the fractured argillite deposits are shown. The use of potassium chloride is recommended to enhance the stability of argillite-formed borehole walls. The results are supported by experimental studies using the Chenevert method, as well as fracture propping tests. When the argillite sample was placed in potassium chloride (KCl) solution, there was a minor fracture expansion and propagation over the entire sample length, which is a positive result. To enhance wellbore stability, further study approaches are proposed: upgrading mud by adding inhibiting compounds, such as salt solutions in combination with high-molecular polymer compositions.

Studies of wood in the Arctic were carried out on Vaygach Island, Hooker Island (Franz Joseph Land) and Novaya Zemlya. During the expedition “Arctic Floating University – 2013”, wood samples (cores) were taken from the buildings in key areas of the Arctic islands. Conforming to the wood samples we constructed tree-ring series and obtained floating chronologies, which were linked to dendroscales of standing trees with known year of each annual ring formation. Crossdating of floating chronologies was performed as follows. Dendroscale and floating chronology were overlapped and the synchronicity coefficient was calculated, then the dendroscale was shifted for a year and the coefficient was calculated again; the procedure was repeated until all possible options were checked. Visual similarity was assessed and the annual rings of floating chronology were dated based on the results with the maximum synchronicity coefficient, and the object was dated by the outermost ring. The year of formation of each annual ring of the buildings logs was determined by the dendrochronological method, resulting in assumption of the time of their construction, taking into account that it occurred a year or two after the tree felling. All the studied objects were located in areas with preserved history of their creation, which is highly important for confirming the objectivity of the obtained results. The dates of the buildings were determined as follows: Vaigach Island, 1945; Hooker Island (Franz Josef Land), 1936; the former bathhouse on Cape Zhelaniya (Novaya Zemlya), 1935; timber from the pillbox, 1938; the lighthouse, 1952; the frame on the coast of Ledyanaya Gavan’ Bay (Novaya Zemlya), 1938; a relatively modern building on the coast of the bay, 1991. Interesting to note that according to the obtained historical records the Lighthouse was built in year 1954, while dating by annual rings shows that the logs were in 1952 and they were probably imported in advance. The years for the construction research based on the use of the dendrochronological method opens up great opportunities at determining the age of unnamed wooden in the Arctic.