Energy Policy Act of 2005 (Ultra-deepwater and Unconventional Resources Program)
Hydrate Plug Characterization & Dissociation Strategies
University of Tulsa, Tulsa, OK 74104-3189
BP America, Inc., Houston, TX 77079
While there are a number of cases for formation and recovery of hydrate plugs, very few have been quantified for model baselines to enable future plug prevention. When plugs form, invariably it is an emergency situation, so that plug data are not gathered in an accurate and deliberate manner suitable for documentation. As experience-based hydrate kinetic models are developed it will be important to combine them with transient flow simulation tools to predict plug location and timing. Efforts are ongoing to incorporate hydrate kinetic models into industrial transient simulators. It is vital to benchmark such predictions, against thoroughly-documented flow loop and field studies of hydrate plugs.
In deepwater oil wells, thermodynamic conditions are favorable for the formation of hydrates which tend to agglomerate and eventually plug pipelines. One of the offshore industry’s major concerns is how to eliminate hydrate plugs from pipelines after they form due to the difficulty and costly nature of the hydrate remediation techniques. Different remediation strategies, such as melting, depressurization and inhibitors, may be implemented but little is known about the properties of the plug, mainly, the effective porosity and permeability to gas or liquids, and therefore, little is known about the most efficient dissociation methods under certain conditions. The main objective of this proposal is to bridge the knowledge gap between plug characterization and dissociation, leading to the selection of the most effective plug dissociation method for different plug scenarios.
The University of Tulsa will utilize its Flow Assurance Loop (FAL) to conduct the work proposed in this study with some minor modifications. The facility consists of a 3” pipe flow loop mounted on an 80-ft long tilt table. The flow path is 160-ft long and fluids can be set in motion by a Leistritz twin-screw multiphase pump or by the rocking motion of the flow loop deck. The process building contains all the equipment necessary to charge oil, water, and gas into the flow loop. The control trailer contains all the data acquisition modules and the operator computer interface.
Solid hydrate plugs will be formed in the high pressure flow loop by installing a witch’s hat. The length and density of the plug will be obtained by using a scanning gamma densitometer to obtain porosity values for the plug. A new fluid handling system, composed of a heat exchanger, a three phase separator, and a volumetric tank, will be utilized for displacing the liquids out of the system by injecting gas. Pressure drop data will be acquired after all the mobile liquids are displaced leaving only trapped liquid in the plug. Permeability values will be calculated from the pressure drop data and plug length measurements. Finally, different dissociation strategies will be applied to the plug, mainly, depressurization, wall heating and inhibitor injections (MEG and Methanol). A comparison of the dissociation times will be provided.
Knowledge of typical plug characterization, permeability and porosity, will be the key to evaluate the feasibility of some dissociation techniques. This research will introduce a new technology to characterize hydrate plugs and criteria for selecting the most effective dissociation technique. A graduate engineer will enter the industry with knowledge of how hydrate plugs form, what are plug properties and state of the art knowledge of the best approach to remediate the plug.
Principal Investigator Dr. Michael Volk