Numerical simulation of an oil–gas fire: A case study of a technological accident at Tengiz oilfield, Kazakhstan (June 1985–July 1986)

Abstract

A gusher from accident well 37 at the Tengiz oilfield (Kazakhstan) led to a catastrophic fire and produced melt combustion metamorphic rocks in its thermal halo (aureole). According to the obtained data on the mineralogy and petrology of the combustion metamorphic rocks and inferred thermal conditions of metamorphism, the protolith sand and clay can become fully molten at a temperature no lower than 1200℃. Four models have been tested for the thermal effect of the Tengiz fire on the country rocks: (a) a single straight-flow vertical gas flare, (b) a single vertical gas flare with oil droplets, (c) a single oil–gas flare with lateral wind load, and (d) a composite oil–gas flare consisting of one vertical and two horizontal spouts. Modeling with SigmaFlow software takes into account the spatial turbulent airflow mechanics of the flare, convective, and radiative heat transfer, burning of gas and oil droplets, as well as conductive heat flux in soil. Model 4 simulates the best the Tengiz fire in the period from 26 June 1985 to 05 September 1986. As the model predicts, a flare with the parameters as in the Tengiz case can cause partial melting of sedimentary material (1100℃) in a local zone but cannot maintain its bulk melting which requires higher temperatures (1200–1400℃). Additional heat may have come from ignition of oil spilled over the surface. The heat from a single oil–gas flare from a wellhead with a 0.5-m stickup turns out to be insufficient for combustion metamorphism ( T = 1000–1400℃).