Modeling of heat mass transfer in the well while drilling in frozen and gas hydrate layers to prevent emergency of gas blowouts

The analysis of hydrocarbon formation features in cryolithozone indicates availability of gas hydrated formations in the cryolithozone and below it. To study the conditions of occurrence of sudden gas blowouts during boring of wells in frozen gas hydrate rocks and to substantiate the heat pressure parameters of safe drilling, the mathematical model of heat mass transfer in a boring well is constructed taking into account the gas hydrate decomposition in drilled cuttings and heat exchange between borehole and environmental rocks. Three drill ing techniques have been determined at penetration in gas hydrate horizons, depending on hydrate phase condition at the bottom hole. The condition is considered to be critical when the surface of phase transition is on bottom hole and is considered to be safe when the decomposition of hydrate in drilled cuttings occurs above the gas hydrate interval. The analytical dependence between the parameters allowing one to determine the area of safe operation condition of well boring in space of these parameters has been received. The influence of various parameters of drilling and of cryolithozone characteristics on the intensity of gas blowouts is analyzed. © V.F. Buslayev, Z.A. Vasilyeva, I.I. Sharovar, 2004.