Large Scale and High Simulation Experimental Study on Physical Property Response of Combustible Ice Formation in Offshore Deepwater Drilling

When deep water drilling meets combustible ice formation, the invasion of drilling fluid accompanied by mass and heat transfer will have an important impact on the mechanical stability of the formation near the wellbore, changing the physical properties of the formation, and affecting the quality and accuracy of subsequent well logging. To address the problem, this paper takes the Gulf of Mexico Gas Hydrate Joint Industry Project (JIP) as the research object. Firstly, the artificial formation skeleton with physical parameters close to the actual is prepared by pressing cementation method. Then, the physical property response law of the formation near the wellbore during the invasion of drilling fluid under the conditions of in-situ reservoir geology and drilling technology is experimentally studied, and the effects of mass transfer and heat transfer behavior on formation temperature, pressure and resistivity are analyzed. The influence mechanism of temperature difference and pressure difference is obtained, and the functional relationship between invasion depth and time is established. The results show that the porosity and resistivity of the artificial reservoir skeleton optimized by orthogonal test are very close to those of the in-situ formation, with the difference of 1.29% and 4.0% respectively. The influence range of pressure is much faster than that of temperature and resistivity, and their influence range has a strong mathematical relationship with time. The decomposition of hydrate occurs successively with the increase of invasion depth, which is manifested in the change of resistivity. The free gas and water produced by decomposition migrate to the deeper, which is easy to reform hydrate in the area between the temperature and pressure variation range, showing a highly saturated hydrate zone. In the range of formation fracture pressure, the positive differential pressure plays a positive role in maintaining the stability of hydrate phase, which is conducive to the stability of near wellbore formation, while the effect of temperature difference is just the opposite. In the process of field drilling, the impact on the formation can be reduced by increasing the density and salinity of drilling fluid, reducing the filtration loss and adding inhibitors. The 12 hours resistivity variation depth is about 0.65 m. Therefore, in order to obtain the resistivity data of undisturbed hydrate reservoir during resistivity logging, the time interval between drilling and logging should be reduced. Logging while drilling or logging methods with appropriate detection depth, such as non-shallow lateral logging, can be used.