Assessment of ground surface subsidence during Chayanda field development with regard to changes in petrophysical parameters of oil and gas reservoirs

Abstract

The geodynamic consequences of long-term mineral mining can involve both extensive ground surface subsidence in the mining area and local activations of fault zones. Estimates of the ground surface subsidence in Chayanda field of hydrocarbons in Eastern Siberia are considered. The nature of changes in the pore space of the Vendian-age Botuoba, Talakh and Khamakin reservoirs was studied by modeling the development of the field up to depletion at the increasing effective pressure from 37.0 to 50.0 MPa. It is revealed that the average value of the porosity coefficient will decrease from 8.976% to 8.916%, the compressibility of the pore space will decrease from 2.844 to 2.616 1/GPa by 0.228 1/GPa or by 8.0% relative to the beginning of development. Estimates of the possible subsidence values in the modeling of the field development process were made using Kuzmin’s genetic model of a deformable reservoir. The parameters of the geomechanical model of productive gas-bearing layers were adopted in accordance with the geological and structural characteristics of the field. The maximum values of possible surface subsidence in the field development modeling are estimated as 33.0 cm and 33.5 cm at the decrease in the reservoir pressure by 5 MPa with and without regard to the dynamics of petrophysical parameters, respectively. When the reservoir pressure decreases by 13 MPa, the maximum subsidence is estimated as 78.0 cm and 83.0 cm with and without regard to the dynamics of petrophysical parameters. The studies have shown that taking into account the dynamics of petrophysical characteristics of reservoirs during long-term development of hydrocarbon deposits significantly diminishes the values of ground surface subsidence above the field and reduces the level of geodynamic risk of oil and gas facilities. The study was carried out in the framework of the state contract with the Sсhmidt Institute of Physics of the Earth, Russian Academy of Sciences.