Permeability is the most important factor affecting water and gas production in hydrate-bearing sediments (HBS). In this study, we combined in-situ microfocus X-ray computed tomography (CT) and pore network model simulation to obtain insights into the dynamic permeability of the hydrate dissociation process. Microfocus X-ray CT is used to visualize the three-dimensional pore structures of the specimen. Then an equivalent pore network can be extracted, which is used as input to pore network flow simulator to simulate the water and gas flow process. Results show that secondary hydrate formation causes effective permeability k(eff) decreases and effective connate water saturation increases as hydrate saturation S-h increases from 0.40 to 0.48. The water relative permeability k(rw) decreases and gas relative permeability k(rg) increases due to larger patchy hydrates (S-h = 0.33). The k(rw) and k(rg) are largely affected by the pore and throat sizes and pore space connectivity. Hydrate dissociation in HBS also influences its permeability anisotropy. Secondary hydrate formation causes k(eff) decreases in the x, y, and z directions when S-h increase from 0.40 to 0.48. Large patchy hydrates influence preferential flow direction for water flow. Predicting the dynamic permeability of the hydrate dissociation process would improve pore-scale water and gas flow analyses in HBS.
Internal microbiologically influenced corrosion (IMIC) is recognized as one of the primary reasons causing failures of natural gas pipelines. In this work, a critical review was performed to analyze the uniqueness of pipeline IMIC, including the corrosive environment, biofilm formation, mechanism, novel research methods, and scientific gaps to be filled in the further research activities. The IMIC of gas pipelines occurs in corrosive environments where a thin layer of water condensate presents on the internal surface of pipe wall. Corrosion occurs upon dissolution of gases such as CO2 and H2S. A biofilm generates to isolate the environment underneath the film from fluid flow to support microorganism population. Due to a limited volume of aqueous solution, the biofilm is mixed with corrosion products to affect the further IMIC. Challenges exist to measure and characterize the bacterial activity under the biofilm, and the localized nature of IMIC. The electron transfer process during IMIC has remained unclear, lacking convincing evidence to support proposed mechanisms. Novel research techniques are suggested investigating IMIC to develop mechanistic understanding for effective management of the problem.
