Impact of geomechanical processes on formation pressure during the long-term operation of gas deposits

Abstract

Practical experience in the exploitation of hydrocarbon deposits confirms the presence of geomechanical processes and their significant impact on the state of gas-saturated rock massif. The purpose of the paper is to clarify the geological conditions for the formation of technogenic reservoirs and involving additional volumes of gas under the impact of geomechanical factors while operating the gas deposits. A detailed analysis of the known gas and gas condensate fields at the Eastern oil-and-gas-bearing region of Ukraine has been carried out. In particular, changes in formation pressure of in-operation hydrocarbon deposits have been determined, the values of geostatic and effective rock pressures have been calculated, the thickness of the gas column and the volume of gas reserves growth have been compared. All of the abovementioned have granted the possibility to determine the role of geomechanical processes in assisting to produce additional volumes of gas. A formation pressure increase in a number of gas condensate fields at a late stage of development confirms the action of the formation of additional sources of hydrocarbons due to the geomechanical factor. It is shown that at the first stage of the exploitation of hydrocarbon deposits, geological criteria play a decisive role in the formation of the gas-saturated massif condition. Over time, during field exploitation, geomechanical criteria are added to the geological ones, which help to involve additional volumes of gas. At the same time, the resulting increase in reserves at some deposits is up to 50% or more. It has been established that additional volumes of gas are directly proportional to the capacity of the gas-bearingness stage and the total volume of the gas-bearing structure. Multilayer deposits of sandy-aleuritic composition with a large number of productive horizons and without thick persistent reservoir-seal rocks within a single gas-bearingness stage with a hydrodynamic link between productive layers are the most promising from the viewpoint of the researched mechanism (favorable due to the formation of additional reservoirs of technogenic genesis).