The article provides the results of studies on the causes of total mud losses in Neogene and Permian deposits in Samara region oil fields. The problem of total loss of mud during exploration and production wells drilling in the upper intervals is insufficient knowledge of the nature of these complications, the lack of information on the territorial distribution of theif zones, as well as the lack of detailed description of the section with possible complication zones. Based on the analysis of exploration, production and structural wells drilling reports from 1960s to the present, the causes of total mud losses in the Neogene and Permian deposits (on the example of the Zhigulevsko-Pugachevskiy fold) are determined. These causes are associated with destruction of rock masses left after complete erosion of overlying bedrock, incisions of channels of paleo rivers. There is an established regional trend of territorial distribution of total loss of mud circulation zones and their intensity from Buzuluk depression to Zhigulevsko-Pugachevskiy and South-Tatar uplifts, Sokskaya upfold. For a more accurate prediction of complication zones, the article recommends to use detailed geological and technological information that is included into structural wells drilling reports. It is noted that, based on the analysis of structural wells drilling, it has been able to identify four main zones of total loss of mud circulation at the fields of the Zhigulevsko-Pugachevskiy fold depending on the depth and age: in the Neogene deposits; in the Kalinovskaya suite of the Kazanian strata; in the Sakmarian and Asselian strata. The article provides justification of typical well design with overlapping of the Neogene, Kalinovskaya, Sakmarian and Asselian deposits based on thickness and depth of these bedrocks and strata. A method for prediction of lost circulation zones in the Neogene and Permian deposits is proposed. This method is based on detailed description of geological profile of designed well according to the results of drilling of exploration, production and structural wells.
References1. Tyurin V.I., Krasilnikova Z.A., Verevkina N.S., Svodnyy litologo-stratigraficheskiy razrez paleozoyskikh otlozheniy Samarskoy oblasti (Consolidated lithologic-stratigraphic section of the Paleozoic sediments of the Samara region), Leningrad: Publ. of VSEGEI, 1988.