Modeling on Gas Hydrate Formation Conditions in the Qinghai‐Tibet Plateau Permafrost

Abstract

Based on the field‐investigated gas geochemistry, the modeling of gas hydrate formation conditions is conducted in the Qinghai‐Tibet plateau permafrost (QTPP) in combination with predecessors' data such as the permafrost ground temperature (T0), the thermal gradient within the frozen layer (G1) and the thermal gradient below the frozen layer (G2). The modeled results show that the permafrost characteristics generally meet the requirements for gas hydrate formation conditions in the study area. Gas composition, temperaturerelated permafrost parameters (e.g. T0,G1,G2) are the most important factors affecting gas hydrate formation conditions in the study area, whose spatial variations may cause the heterogeneity of gas hydrate occurrences. The most probable gas composition to form gas hydrate is the hybrid of methane and weight hydrocarbon gases (ethane and propane). In the predicted gas hydrate locations, the minimal upper depth of gas hydrate occurrence is less than one hundred meters and the maximum lower depth can reach one thousand meters with the thickness up to several hundred meters. Compared with Canadian Mallik gas hydrate field, the QTPP is favorable for gas hydrate formation in aspects of G1, G2 and gas composition, except for relatively thin permafrost, still suggesting great gas hydrate potentials.

Assessment of Gas Production Potential from Hydrate Reservoir in Qilian Mountain Permafrost Using Five-Spot Horizontal Well System

“…The basic parameters of T0, G1 and G2 shown in Table 1 are determined based on field measurements [7,8]. Then the initial temperature and pressure at the bottom of the HBL (TB and PB) are initialized to be 277.84 K and 4.19 MPa, respectively (Table 1).…”

“…Previous studies indicated that the annual average of the permafrost ground temperature (T0) was around −1 to −3 °C. Based on in situ measurements in this area, the geothermal gradients within and below the frozen layers (G1 and G2) of the QTPP were approximately in the range of 0.011-0.033 °C/m and 0.028-0.051 °C/m, respectively [7,8]. These thermodynamic conditions are favorable for the formation of natural gas hydrate in the Qilian Mountain.…”

Evaluation of gas production from Qilian Mountain permafrost hydrate deposits in two-spot horizontal well system

“…The physical parameters (T 0 , G 1 and G 2 ) come from the field measurements (Lu et al, 2009;Wu et al, 2010), as shown in Table 1. Then the temperature at the bottom of the HBL (T B ) is initialized to be 277.84 K ( Table 1).…”

“…where ρ r is the rock density of the permafrost layer (2000 kg/m 3 ) (Lu et al, 2009), ρ w is the fluid density under the permafrost layer (l000 kg/m 3 ), g is the gravitational acceleration (9.81 m/s 2 ), and P 0 is the atmospheric pressure (1.01 × 10 5 Pa). Eq.…”

“…The annual average temperature of the permafrost ground (T 0 ) was around −1 to −3°C. In recent years, the geothermal gradients within the frozen layer (G 1 ) and below the frozen layer (G 2 ) of the QTPP were measured to be 0.011-0.033°C/m and 0.028-0.051°C/m, respectively (Lu et al, 2009;Wu et al, 2010). So the pressure and temperature were both favorable for the stability of natural gas hydrate in the Qilian Mountain.…”