Experimental Investigation of Spontaneous Imbibition of Water into Hydrate Sediments Using Nuclear Magnetic Resonance Method

Abstract

Field observations show that less than one percent of dissociation water can be produced during gas hydrate production, resulting from spontaneous water imbibition into matrix pores. What’s more, the hydrate sediments are easily dispersed in water, and it is difficult to carry out spontaneous imbibition experiments. At present, there is little research work on the imbibition capacity of hydrate sediments. In this paper, a new method of water imbibition is proposed for hydrate sediments, and nuclear magnetic resonance (NMR) technique is used to monitor water migration. The results show that as the imbibition time increases, the water is gradually imbibed into matrix pores. Water imbibition can cause dramatic changes in pore structure, such as microfracture initiation, fracture network generation and skeleton dispersion. When the imbibition time exceeds a critical value, many secondary pores (new large pores and micro-fractures) start to appear. When imbibition time exceeds the dispersion time, fracture networks are generated, eventually leading to dispersion of the sediment skeleton. The imbibition curves of hydrate sediments can be divided into two linear stages, which corresponds, respectively, to water imbibition of primary pores and secondary pores. The imbibition rate of secondary pores is significantly larger than that of primary pores, indicating that the generation of new fractures can greatly accelerate the imbibition rate. Research on the characteristics of water imbibition in hydrate sediments is important for optimizing hydrate production regime and increasing natural gas production.

Experimental Investigation on the Imbibition Capacity and Its Influencing Factors in Hydrate Sediments

“…The imbibition capacity of the hydrate can be evaluated by observing the surface changes of the sample, such as fractures initiation and dispersion. The entire imbibition process can be divided into four stages: sediment wetting stage, microfracture initiation stage, fracture network stage, and dispersion stage . In the sediment wetting stage, the sample is invaded by water and wetted gradually.…”

“…According to the Handy model, the relationship between the imbibed volume per unit area and time can be given by where V imb is the imbibed volume, A c is the contact area of the sample and water, A is the imbibition rate, and t is the imbibition time …”

“…Hydrate sediments are also called “flammable ice”, and their main component is methane. Hydrates in the deep sea are stable under the pressure of thick water layers, so their environment is low temperature and high pressure . The methane gas generated after the dissociation is a clean energy source, and no harmful gas is generated after combustion.…”

Advances in Characterizing Gas Hydrate Formation in Sediments with NMR Transverse Relaxation Time

“…Although there have been a lot of excellent studies on the gas hydrate formation in sediments using NMR T 2 method, a few of them combined NMR T 2 with other methods to characterize the formation process of gas hydrate and the pore structure in sediments in a more effective way [30,45,[50][51][52][53]56,[66][67][68][69][70]74,[147][148][149]. The combined use of these techniques can provide more information about the gas hydrate formation in sediments than any single technique.…”

Experimental Study on the Propagation Characteristics of Hydraulic Fracture in Clayey-Silt Sediments

“…Up to now, majorities of research focus on the fracability of hydrate-bearing sandy sediments, but the studies rarely involved fracture propagation characteristics of clayey-silt sediments in the hydrate dissociation area. The formation energy depletes at the later stage of hydrate gas production, causing the decline in thermal and pressure conductivity of the reservoir, which is difficult to spread to the far end of the wellbore [33][34][35]. Meanwhile, lack of gas channel to flow 3 Geofluids from the dissociation front to the wellbore, the gas production is seriously affected [36][37][38][39].…”