ANALYSIS OF THE CAUSES OF CIRCULATION LOSS IN THE LOWER CRETACEOUS DEPOSITS DURING THE HORIZONTAL DRILLING UNDERCROSSING THE DANUBE RIVER (GIURGIU-RUSE SECTION)

Abstract

The geotechnical, electrometric and magnetometric investigation data, correlated with the technological data from the horizontal directional drillings made for the undercrossing of the Danube River with gas pipelines, showed that in the Giurgiu-Ruse section, under a clastic sequence of 14-19 m thickness, consisting of layers of sandy clays, sands and white-grey, alluvial gravels, are developed Cretaceous grey altered limestones, yellowish-brown lumachelle limestones and grey-pink, compact limestones. The altered, eroded, and karstified limestones seems to be the explanation of drastic circulation loss of mud in the technological process of digging through horizontal directional drillings. In the studied studied, on the Giurgiu-Ruse alignment in the southern area of the Moesian Platform (Wallachian sector), there are several relevant papers occasioned by the construction of the Saint Gheorghe harbour channel related to the Giurgiu harbour, at the time of the 19th century (1888-1890), as well as the papers related to the investigations occasioned by the construction of the Giurgiu-Ruse Bridge in 1959. Older or newer papers are added, relating to the carbonate deposits of different ages of the Cretaceous in the outcrops of the Bulgarian bank of the Danube, as well as descriptions from drillings adjacent to the studied section.