High-pressure and temperature-controlled CPT calibration chamber based on deep-sea hydrate reservoirs

Ensuring safe extraction is a prerequisite for the development of deep-sea resources. As an in-situ exploration technique, cone penetration test (CPT) can accurately analyze the physical, strength, and deformation characteristics of deep-sea sediments and hydrate reservoirs after data interpretation, thereby ensuring the safe extraction of deep-sea resources. CPT calibration chamber (CCC) testing is considered one of the most effective means to determine the correlation between lab measurement values of soil and its undisturbed mechanical properties. Currently, the stress conditions of the CCCs that have been established are limited in scope and insufficient to simulate the high-stress field conditions of deep-sea sediments as well as the high-pressure and low-temperature conditions where deep-sea hydrates occur. Therefore, based on the traditional CCC, this article independently developed a high-pressure and temperature-controlled CCC with a type of boundary condition one (BC1), which can be used to simulate the process of CPT penetrating marine sediments (including the in-situ environment of hydrate reservoirs). This CCC features a maximum loading force of 200 KN at the top and 150 KN at the bottom. With a maximum confining and pore pressure of 25 MPa, and a temperature range from −15 °C to room temperature, it can effectively replicate in-situ effective stress, pore pressure, and temperature conditions necessary for hydrate formation. The maximum sample size is 300 mm in diameter and 600 mm in height, and two sizes of CPT probes (2 cm 2 and 5 cm 2 ) can be replaced to test the boundary effect. To verify the feasibility of the CCC, a series of CPT penetration experiments were conducted on silty sediments under high-pressure and temperature-controlled conditions in the established CCC. It was found that cone tip and friction resistance increase with the increase of effective stress. This CCC contributes to establish the relationship between CPT data and various mechanical properties of marine sediments, and providing theoretical support for evaluating the stability of marine hydrate reservoirs during exploitation.