Forecasting of Hazardous Layers at the Exploration Wells Drilling Stage

Abstract

Abstract In the process of well construction in difficult drilling conditions and in the Arctic, the technologies that let us forecast formation heterogeneity and possible zones of complications and drilling hazards at early stages of field development become especially relevant. It has been found that a considerable number of drilling hazards and complications with drill bit failures and mud losses is associated with abnormal reservoir leyers. Anomaly show as alternation of hard and soft rocks; as a result in productive area we can observe both super-reservoir layers with up to 40–50% porosity and up to 1 m thickness, and abnormal consolidated and abrasive zones. Rock density in super-reservoir layer may decrease by 35–40% and increase to the same extent in the precipitation zone, which inevitably affects the strength and filtration properties of rocks. Based on the results of core and thin section analysis of 6 major fields of Volga-Urals oil and gas province, innovative catagenetic model of oil and gas deposit was built which can be used for any field. There is a clear relationship between catagenetic heterogeneity and zones of ancient oil-water and gas-fluid contacts, which allow us to develop a method for forecasting of drilling hazardous layers based on core data on one drilled well. Generation of catagenetic reservoir model for a new field will enable us at the exploration and planning stage to identify zones of possible complications and use appropriate technical and technological decisions for trouble-free drilling of new wells. Testing of the method made it possible to increase the life cycle of the drill bits due to reduction of their abrasive wear, select proper measures to minimize mud losses, save time and money for elimination of accidents related to drill bits. Regularities emerged in location of abnormal layers, their relationship with catagenetic processes was established, and a method was developed for forecasting possible complication zones based on core data on one well. To eliminate hazards in well drilling, we suggest using a model forecasting real depth of occurrence of hazardous layers. This can help implement deep and ultra-deep well drilling program, incorporating technical solutions aimed at prevention of complications.