Measurements of Hydrate Formation Behavior in Shut-In and Restart Conditions

Abstract

Transient operations in oil and gas production can result in conditions with a high potential for the formation of hydrate plugs. In restart operations, the shear flow and the increased pressure can induce rapid hydrate formation possibly leading to a plug or severe flow reduction. In order to study favorable and unfavorable restart conditions, experiments were performed in a high pressure cell coupled to a rheometer. Hydrate slurry behavior was investigated under transient conditions. Experiments were carried out in three-phase systems containing mineral oil or crude oil, water, and a model natural gas mixture of 92/8 mol % methane/propane. Two commercial antiagglomerants were added in the tests. Experiments were conducted at varying water volumetric fractions (10, 30, 50 vol %), subcooling (6 °C, 10 °C, 15 °C, 16 and 18 °C), pressure (42, 56, and 70 bar), and mixing rates (100, 200, and 300 rpm). The viscoelastic behavior was observed in most shut-in and restart tests. The experiments showed subcooling as an important parameter that affects hydrate morphology. Also, experiments varying the rotation speed showed that the apparent viscosity was unaffected by decreasing the rotation speed, suggesting that hydrate particle/aggregate size was unchanged. However, increasing the rotational speed resulted in a decrease of the apparent viscosity, in the case without an additive, or an increase in the apparent viscosity in the case with an antiagglomerant. Results using crude oil, antiagglomerant, and high water cut did not show viscoelastic behavior at shut-in and restart conditions. Both antiagglomerants formed hydrate dispersions, indicating that a flowable hydrate slurry had formed due to the antiagglomerant effect.

Rheological Properties of Hydrate Slurry in the Water-Based Drilling Fluid

“…Different from Silva et al's 16 work in which hydrates were formed at different shear rates, hydrates in the current study were formed at a constant shear rate and then the shear rate was changed. Kakitani et al, 19 in a recent work, have outlined that some kinds of antiagglomerants can completely change the maximum shear rate rule. In other words, the material viscosity decreases with the maximum shear rate but increases after adding the antiagglomerant.…”

“…The rheometric tests were performed using a Haake Mars III (Haake Co., Germany) stresscontrolled rotational rheometer that can control the shear rate indirectly by a feedback PID controller and can measure a minimum and a maximum torque of, respectively, 1 × 10 −8 and 2 × 10 −1 Nm. As apparent wall slip is a concern in rheological tests of hydrate slurries, 16,19,30,32,37 two different sensors were employed in the experiments: a Couette geometry with a serrated surface cup (internal cylinder diameter of 25 mm, length of 40 mm, cup diameter of 26 mm, and 0.5 mm groove depth) and a four-blade Vane geometry (cup diameter of 27.2 mm, vane diameter of 22 mm, and length of 16 mm) with a piece of waterproof sandpaper glued on the cup wall to prevent wall slip, as proposed by Ahuja et al 30 The sandpaper reduces the effective cup diameter to 25.7 mm which was considered in the data analysis. The system temperature was controlled by a Peltierthermostatic bath system.…”

“…The particle size, the crystal morphology, and the cohesive force between particles may affect directly the rheological properties of hydrate slurries . Despite being naturally stochastics, the nucleation, crystal growth, and agglomeration processeswhich dictate the mean size and the morphology of the solid structuresare mainly affected by the fluid composition, the shear imposed to the sample, and the subcooling degree. − Additionally, the water in the drilling fluid consumed to form hydrates crystals also affects the rheological properties of the suspension …”

“…Despite considerable efforts to determine the thermodynamic conditions that avoid hydrate formation and to develop inhibitors, there is a lack of information about the rheological properties of hydrates formed in drilling fluids. Different authors have studied the rheological properties of hydrate slurries in water, ,,,, mineral oil emulsions, ,,− and crude oil emulsions. ,,− The main characteristics observed in most of the studies are the shear-thinning behavior of the hydrate slurry and the increase in both viscosity and elastic modulus at the time the hydrate is formed. Some authors noticed the time dependency of hydrate slurry rheological properties ,,, and others observed the influence of the shear applied during the hydrate formation on the suspension final viscosity .…”

New Anti-agglomerants : Effect of Coconut Oil Amide Propyl Betaine on Hydrate Agglomeration

“…Therefore, it is urgent to explore hydrate formation and flow characteristics under shutdown and restart conditions. Some studies have been devoted to the flow characteristics of transient hydrate slurry and the influence of rheological properties and Anti-agglomerants on the plugging characteristics of hydrate during restart Kakitani et al 2019;Kakitani et al 2022;Shuard et al 2017;Sohn et al 2017). ) carried out a series of experiments on the shutdown and restart of carbon dioxide hydrate in water-dominated system.…”