Detection of gas hydrates by the measurement of instantaneous temperature

Abstract

Natural gas hydrates are icelike crystalline substances formed by gas molecules trapped in a water lattice. Suitable thermodynamic conditions and the presence of gas are required for the formation of natural gas hydrates in ocean sediments. Several major problems are associated with hydratebearing sediments. Detailed study of hydrate properties is difficult due to the complications faced in recovering insitu samples for laboratory testing. The presence of hydrates near the foundation zone of deepwater structures may pose problems to the stability of the foundations of these structures. Since the presence of gas hydrates could limit the development of oil exploration in the oceans, the first logical step would be to develop a method to detect hydrates in ocean sediment. Detection of gas hydrates is possible due to the significant differences in the physical properties of hydrates and the surrounding sediments. In this research, the physical properties of hydrates and ocean sediment and the past methods used to measure sediment temperature were studied. A new method to detect hydrates was developed based on sediment temperature and its effectiveness was tested. This method involves the measurement of instantaneous temperature as a probe is pushed continuously into the sediment at a rate of 2 cm/sec. Validation tests were performed in the laboratory using glass marbles as a substitute for gas hydrates. The effectiveness of this method to "hydrate nodule" layers was tested. effectiveness of this method to detect "hydrate" and "hydrate nodule" layers was tested. The temperature versus depth profile indicated the presence of hydrates. The temperature measuring device could be mounted on a Standard Cone Penetrometer. Thus in addition to temperature measurements, simultaneous measurements of electrical resistivity, cone penetration resistance and pore pressure could be made to aid in the detection of hydrates.