Energy independence is an important component of sustainable development and security of the state. Ukraine has a great hydrocarbon potential of the subsoil, which is why the priority objective is a search and exploration of new deposits of hydrocarbon raw materials. One of the important directions for increase of potential resources and reserves of oil and gas is the development of large deep (over 4500–5000 m) deposits, as hydrocarbon reserves at small and medium depths are quite depleted in many regions.
For a long time, hydrocarbon reservoirs in basement rocks were underestimated during geological exploration works. Obtained results indicate that new concepts of the formation of hydrocarbon deposits can dramatically change the system of oil production, methods of prospecting and development of deposits. It is important to assess possible oil-and-gas-bearing capacity of sediments and rocks of the basement by identifying prospective areas of hydrocarbon deposits, including in the rocks of the crystalline basement.
In Ukraine, main prospects of discovery of oil and gas deposits at great depths are associated nowadays with the Dnieper-Donets Rift (DDR). Deposits with accumulations of hydrocarbons at depths of more than 5000 m are concentrated in the main oil-and-gas-bearing areas of the Rift that coincide with the central paraxial and marginal zones of the graben. It was in the central segment of the DDR that the main regularities of oil-and-gas-bearing capacity of deep-lying geological formations were first discovered: secondary nature of reservoirs, discovery of the phenomenon of supercollectors and associated huge debits. It is relevant and promising to study the process of recovery/replenishment of gas reserves by the example of deposits that are at the final stage of development.
The zone of infiltration of the drilling fluid filtrate into the reservoir rock creates significant difficulties for the study by logging methods and during further testing of the formation. Due to the penetration of filtrate, significant contamination of the near-wellbore zone occurs. The porosity and filtration characteristics of reservoir rocks are changing. There is a possibility of blockage by filtrate in the invaded zone of oil or gas flow from the formation to the well. As a result of the studies carried out using well logging data, it was found that the presence and distribution of a mud cake on the borehole wall opposite the reservoir is an important factor influencing the process of filtration of the drilling fluid into the layers. On the examples of the Yablunivske oil and gas and Kolomatske gas fields of the Dnieper-Donets basin, it is shown that the absence of a mud cake on the borehole walls leads to the formation of maximum, anomalous zones of filtrate invasion. The determining of the diameter of the invaded zone was carried out according to the data of electrical logging methods. In addition, the diameter of the invaded zone was calculated as a solution direct task equation for the case of direct filtration without blocking by the mud cake. Comparison of the results of determining the diameter of the invaded zone by two methods made it possible to draw certain conclusions. An important conclusion is that even partial absence of mud cake on the reservoir wall in the well leads to horizontal and vertical filtration of the drilling fluid from the well into the formation. As a result, the invaded zone may be so deep, that the gas flow rate is absent even at high values of porosity, permeability and gas saturation
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