A Method of Calculating the Gradients of Earth Surface Displacements for Assessing Geodynamic Hazard of Oil and Gas Complex Facilities

A unified methodology for analyzing the results of geodynamic monitoring is proposed, based on the conversion of observed and model displacements into their gradients, and a comparison of their values with the regulatory parameters governing safe subsoil use. A selection of existing numerical and analytical models of the formation of subsidence, uplifts of the Earthʼs surface due to the development of productive strata, as well as local anomalies confined to fault zones, was made. The choice of the analytical model used for the current study in the article is substantiated. A three-dimensional problem was solved and an analytical formula for the distribution of horizontal displacements of the surface of an elastic half-space containing a rectangular (sheet-like) poroelastic inclusion was obtained, as well as formulas for calculating the gradients of vertical and horizontal displacements in a three-dimensional setting. Such formulas made it possible to estimate the threshold values of relative deformations for their comparison with regulatory criteria. The implementation of the method for calculating the gradient of earth’s surface displacements is demonstrated using large fields in Russia and the CIS as an example. The modeled extensive subsidence at an oil and gas field in the Republic of Kazakhstan showed complete mutual agreement with the observed displacements, and the analytically calculated gradients of displacements specified the zones of increased geodynamic hazard. A similar result was obtained when modeling an anomalous uplift of the Earthʼs surface at a super-viscous oil field in the southeast of Tatarstan. The advantages of this method are most clearly demonstrated by the example of the Yu. Korchagin shelf oil field, where geodetic measurements are absent. Here, an assessment of seabed deformations was given based on calculations of horizontal gradients of vertical displacements, as well as their effect on the stability of the production platform. Using the example of the Romashkinskoye oil field, the results of leveling observations were compared with model vertical anomalies characterizing fault zones. The calculated slope gradients indicated abnormally high values in the wellbore curvature zones. It was established that the obtained analytical distributions of displacement gradients allow identifying geodynamic hazard zones both in local areas and over the entire area of the deposits.