Fundamental Investigation of the Effects of Modified Starch, Carboxymethylcellulose Sodium, and Xanthan Gum on Hydrate Formation under Different Driving Forces

Abstract

The development of a new drilling fluid system with hydrate inhibition is of great significance for drilling safety in gas hydrate-bearing sediments. Considering the importance of the selection of a suitable thickener for drilling fluid systems under weak and strong driving forces, the hydrate inhibition of 0.1–0.5 wt% modified starch (MS), carboxymethylcellulose sodium (CMC), and xanthan gum (XG) aqueous solutions was studied. The applicability of these three thickeners were investigated through hydrate formation experiments, mesostructure observations, water activity tests, bubble retention observations, and rheological property tests. The results show that (1) under weak driving force, 0.3 wt% or higher concentration CMC and 0.3 wt% XG can almost completely inhibit hydrate formation due to the interactions between relatively small amounts of free water and CH4 molecules. Furthermore, the hydrate inhibition of higher XG concentrations was decreased due to their strong foam stability, leading to good contact between free water and CH4 molecules. Meanwhile, the hydrate inhibition of MS was weaker when compared with that of CMC and XG at the same concentrations. (2) Under strong driving force, the existence of the three 0.1–0.5 wt% thickeners could only slow down the hydrate formation rate, and hydrate inhibition due to XG was slightly better than that of the other two. This result implies that the effects of the different mesostructures on hydrate formation were severely weakened. Finally, (3) the tackifying effect of CMC was found to be stronger than that of XG and MS, and the rheological properties of the CMC solution were shown to be relatively weak compared to those of the XG and MS solutions; the CMC solution showed a more significant increase in viscosity with decreasing temperature, which is related to the differences in the mesostructures. Therefore, when the driving force of hydrate formation is relatively low, CMC is a good choice for the drilling fluid system when there is no requirement for cooling, while XG is more applicable for a system that needs cooling. In the case of a stronger driving force, XG is the optimal choice irrespective of whether the drilling fluid system needs cooling or not.

Kinetic Inhibition of CO2 Hydrate by Carboxymethylcellulose Sodium through Retarded Mass Transfer

“…The products of CMC are promising KHIs due to their excellent properties. However, there are relatively few reports in the open literature about the inhibition performance of CMC on gas hydrates or the related inhibition mechanism. − …”

Comprehensive Review on Exploration and Drilling Techniques for Natural Gas Hydrate Reservoirs

“…Considering the environment and the associated cost, the most common drilling fluid system preferred is water-based mud (WBM) . Bentonite is a common gas hydrate drilling fluid additive used for viscosity and filtration control, but the increase of bentonite in mud can enhance the risk of hydrate formation as a result of higher nucleation sites, owing to its increased surface area. , Modified starch (MS), carboxymethylcellulose (CMC), and xanthan gum (XG) are the common biodegradable polymer thickeners used with bentonite for drilling fluid formulation for hydrate drilling and work similarly to a kinetic hydrate inhibitor (KHI) . CMC is more applicable to a system that does not require cooling.…”

“…CMC is more applicable to a system that does not require cooling. XG is more suitable when chilled mud is used for hydrate drilling . However, XG requires a defoaming agent to be used with the drilling fluid because its enhanced foaming characteristics can weaken the hydrate inhibition properties of the drilling fluid .…”

“…hydrate drilling and work similarly to a kinetic hydrate inhibitor (KHI). 199 CMC is more applicable to a system that does not require cooling. XG is more suitable when chilled mud is used for hydrate drilling.…”

“…XG is more suitable when chilled mud is used for hydrate drilling. 199 However, XG requires a defoaming agent to be used with the drilling fluid because its enhanced foaming characteristics can weaken the hydrate inhibition properties of the drilling fluid. 199 Likewise, the molecular weight of these polymers also plays a vital role in hydrate inhibition.…”