Numerical Simulation Of Saturation Parameters In Gas Hydrate-bearing Reservoirs

Natural gas hydrates are kinds of unconventional energy with huge resourcepotential, which are widespread in permafrost regions of continents and marinesediment, and are expected to be the ideal alternative energy of oil and gas in thefuture.Well logging, as an important geophysical methods, plays an irreplaceable role inthe exploration for natural gas hydrates. Firstly, we can identify gas hydrate-bearingreservoirs by logging; Secondly, it can provide necessary parameters for gas hydratereserve estimation, such as porosity, saturation and reservoir thickness, using variouslogging interpretation technology; more importantly, logging is carried out under thein-situ high pressure and low temperature conditions, so its reliability and precisionare far higher than other exploration methods.Archie’s formula is most commonly used in calculating reservoir saturation usinglogging data, and it plays an important role in logging evaluation for traditional oiland gas reservoirs. Gas hydrates resemble oil and gas in high resistivity properties,and the resistivity anomalies are evident in the gas hydrate-bearing intervals. Thus, forthe cases that gas hydrates are uniformly distributed in dispersed state in pore space,Archie’s formula can be used to calculate gas hydrate saturation. Good applicationeffect has been achieved by some foreign scholars when Archie’s formula was appliedto evaluate gas hydrate-bearing reservoirs.Archie’s formula is objective law obtained by means of experiments and theseparameters in the formula are usually determined by core electricity experiment andvary with different areas. However, it exists some difficulties to conduct coreelectricity experiment on gas hydrate-bearing cores currently. Firstly, marine gashydrates are usually distributed in unconsolidated shallow sediments and easy todecompose at normal temperature and pressure so that it’s difficult to ensure theintegrity of gas hydrate-bearing core samples; in addition, natural gas hydrates aresolid minerals, which are different to oil and gas in physical state so that coreelectricity experiment equipment for oil and gas reservoirs can’t be directly used toconduct measurements on gas hydrate-bearing cores. Up to now, although there are individual laboratories having tried it, these works are only preliminary exploration.In order to accurately evaluate gas hydrate-bearing reservoirs, it tries to study thevariation regularity and influence factors of Archie’s parameters by means ofnumerical simulation in this thesis. It includes two steps in detail:(1) learn from thebasic idea of digital core technology and construct various porous media models ofdifferent gas hydrates distribution forms (such as dispersed, layered, vein and block);(2) calculate the resistivity of dispersed and layered models respectively using finitedifference method, compare and analyse the differences of the two, study therelationship between resistivity and porosity, saturation respectively, then study thevariation regularity and influence factors of Archie’s parameters.The results show that the results of numerical simulation are in good agreementwith the general variation regularity of Archie’s parameters.