Effect of Rock Wettability on the Electric Resistivity of Hydrate Formations: An Experimental Investigation

Gas hydrates are large energy resources with estimated global reserves of approximately 500–10 000 Gt of carbon, which can be extracted from underground reservoirs. In addition, such reservoirs can potentially catastrophically release greenhouse gases (such as methane or carbon dioxide). Classically, rock wettability is one of the key factors in predicting fluid flow behavior, fluid distribution, reserves, and productivities. However, the effect of wettability on the electric resistivity of hydrate formations is poorly understood. Thus, to evaluate the influence of rock wettability on the electrical resistivity (note that resistivity logging is a key well logging tool) of hydrate-bearing sandstone, nuclear magnetic resonance experiments were conducted. Clearly, the effective porosity and liquid saturation increased with increasing temperature, due to hydrate dissociation. Furthermore, the resistivity index and rock resistivity (R_t) increased with increasing hydrate saturation, and the formation factor demonstrated a positive correlation with hydrate saturation, though the formation factor for oil-wet (OW) sandstone was higher than that for water-wet (WW) sandstone. This work will thus significantly improve the fundamental understanding of the petrophysical properties of gas hydrate reservoirs so that energy production can be optimized, geohazards can be avoided, and the hydrate gun hypothesis can be better assessed.