In situ characterisation of gas hydrate-bearing clayey sediments in the Gulf of Guinea
Increasing needs for energy resources have moved deep offshore developments and research efforts towards regions where high pressure and low temperature conditions allow gas and water to form Gas Hydrates (GH). However, owing to difficulties in sampling and preserving GH under in-situ stability conditions, GH-bearing sediments remain particularly challenging to characterise using conventional laboratory methods. This paper presents the experience gained in the use acoustic and piezocone soundings in characterising gas-hydrate bearing clayey sediments offshore Nigeria. Acoustic measurements of compressional wave velocity are shown to be an expedient means of both detecting and quantifying GH in sediments. Piezocone data and their location in normalised soil classification charts highlight trends in response suggesting that GH-bearing clayey sediments are predominately contractive at large strains. The observed trend of increasing cone resistance combined with increasing pore pressure suggests that the sensitivity of GH-bearing sediments tend to increase with their stiffness and strength.