Mathematical modeling of thermal impact on a closed hydrate-saturated reservoir

Abstract

In 2014, a crater was discovered in Yamal near the Bovanenkovo oil and gas condensate field. A number of researchers indicate among the possible causes of its occurrence an avalanche-like release of gas formed during the dissociation of gas hydrates. To carry out numerical experiments for analyzing such phenomena, a mathematical model of gas-liquid flow in a saturated porous medium was constructed taking into account the phase transition “gas + water  gas hydrate”. A two-dimensional axisymmetric formulation of the problem of heating from above through impermeable rocks of a closed hydrate-saturated reservoir, initially containing gas hydrate and gas, was carried out; to take into account external heat exchange, it is assumed that the reservoir is surrounded by rocks impermeable to matter. An algorithm for numerically solving the equations of the mathematical model is presented. A series of calculations was carried out, on the basis of which an analysis was made of the processes occurring in a closed hydrate-saturated reservoir, namely, changes in temperature, phase saturations and pressure. Calculations have shown that during the dissociation of gas hydrate in a closed reservoir, for a certain set of parameters, a significant increase in pressure can occur from 2.7 to 17.4 MPa. It has been revealed that the shallower the depth of a hydrate-saturated reservoir, the smaller its size and the greater the initial hydrate saturation, the greater increase in pressure can be observed, and, accordingly, the greater risk of violating the integrity of a closed impermeable porous medium and the subsequent avalanche-like release of gas from such object.