Deformation Consequences of the Development оf Oil and Gas Field
Yu. O. Kuzmin
Abstract
The results of long-term repeated levelling observations with increased spatial and temporal resolution (distance between benchmarks of 0.3–0.5 km or less and intervals between measurements of 0.5–1.0 years) at oil and gas fields and underground gas storage in Russia and Turkmenistan are considered. Various forms of deformations were found: a weak general uplift or absence of subsidence of the within oil fields, the absence of subsidence during long-term development of a gas field, cyclic deformations (uplift and subsidence) during injection and withdrawal at underground gas storage, and local subsidence in fault zones at all facilities (including underground gas storage during the period of gas injection). Three-dimensional analytical models of deformations of the surface of a weightless elastic half-space with prismatic poroelastic inclusions and inhomogeneous mechanical properties (bulk elastic moduli) are constructed. To assess the total subsidence in oil and gas fields caused by a decrease in reservoir pressure, the solution for a weightless medium was modified to take into account the weight of the overlying rocks, the dynamics of changes in poroelastic parameters, and the genesis of the field formation. It is shown that superposition of solutions for displacements of the half-space containing inclusion and inhomogeneity may explain paradoxical phenomena such as the absence of subsidence during the long-term development of a gas field and the presence of local subsidence under conditions of gas injection into an underground storage. The calculations are compared with the data of repeated geodetic observations to obtain consistent parameters of the development and operation of the underground gas storage.