Conditions of forming of upper devonian and lower carboniferous lost-circulations formations within Romashkinskoye field Kuakbashskaya area

Abstract

© 2020, Neftyanoe Khozyaistvo. All rights reserved. Actual field data from the Kuakbashskaya area of the Romashkinskoye oil field are used in this paper for analysis of lost circulation problems during well drilling typical of high permeability carbonate reservoirs confined to Upper Frasnian-Lower Famennian and Okskian-Serpukhovian sediments. Lost circulation control treatments are associated with considerable material loss as well as with significant unaccountable losses in oil production due to formation damage, poor quality of casing cementing in difficult wells, and delayed well bringing into operation. In light of the above, improvements in lost circulation control technologies and implementation of innovative cost-beneficial technologies and materials become of utmost importance. Understanding of the conditions that cause circulation losses enables optimization of these processes. The paper presents different conditions resulting in drilling mud losses. In the north-north-eastern part of the Kuakbashskaya area presence of lost circulation zones in Upper Frasnian-Lower Famennian and Okskian-Serpukhovian sediments is attributable to irregular tectonic compartmentalization of the rocks following the plane of fault system in the crystalline basement and associated troughs in the sedimentary cover. An indirect evidence of the above is the presence of calcium-chloride brines in Okskian-Serpukhovian aquifers, which is peculiar to underlying aquifers. Good transmissibility of the structures in this region is also confirmed by prevalence of nitrogen in the composition of water-dissolved gas. Other conditions favorable for development of fracture system are typical of central and southern parts of the Kuakbashskaya area. Here, domination of neotectonic fracturing associated with lithogenesis processes and neotectonic activity is observed.