A new approach to the assessment of hydrate content in the sediments by the geothermal method is proposed. The transition of pore water to gas hydrate significantly reduces the heat capacity of the sediment. The amount of hydrate contained in the pores can determine by measuring the volumetric heat capacity of sediments in two different states: with and without hydrate in the pores (after its complete decomposition, only water remains in the pores). The volumetric heat capacity can calculate as the ratio of thermal conductivity to thermal diffusivity. The thermal conductivity and diffusivity of the sediment in different states can be determined using a two-needle probe according to the method proposed in this work. The proposed approach in laboratory experiments was tested. The volumetric heat capacity of the sample in its various states is measured. The sample is the sand with synthetic carbon dioxide hydrate formed in a thermostatic high-pressure chamber (the volume of the obtained hydrate-containing sample is about 1000 cm3). We used not the standard method of pulsed heating, but the method based on the constant heating of the medium by a linear source. The accuracy of determining the heat capacity of the medium can increase by describing the entire useful interval of the experimental thermogram by using the proposed method. The paper presents an estimate of the content of CO2 hydrate in the art sample. This based on measurements of the thermal properties of the sample in two states: before and after the formation of CO2 hydrate in sample pores. Additionally, an estimate of the amount of CO2 hydrate produced in the sample is given. The estimate obtained from the record of the pressure and temperature of the sample state during hydrate formation. The results confirm the possibility of determining the hydrate content based on measurements of the heat capacity of the medium in two states. The minimum fraction of hydrate that can be fixed in the bottom sediment pores with the accuracy indicated in this work should be approximately 10 %.
State classification of scientific and technological information
- 37 GEOPHYSICS