Hydrates are ice-like solids that form when a sufficient amount of water is present, a hydrate former is present, and the right combination of temperature or pressure is encountered (hydrate formation is favored by low temperature and high pressure). Hydrates are also notorious for forming at conditions where a solid would not otherwise be expected. Under the right conditions hydrates can form anytime and anywhere hydrocarbons and water are present. In wells, downhole separators, flowlines and meter discharges, accumulation and agglomeration of hydrates can form plugs that act as a hindrance to hydrocarbon flow. Shut-in and startup are primary times when hydrates form. On shut-in, the line temperature cools very rapidly to that of the ocean floor (40 deg F for depths greater than 2000 ft) so that the system is almost always in the hydrate region if the line is not depressurized. At that condition, multiple hydrate plugs can form. An understanding of how hydrates form deposits and how this leads to hydrate plug formation in well risers and flowlines is important to avoid plugging in deepwater production operations.
The overall project objective is to conduct experimental flow studies using 5 live crude oils and 3 model oils to quantify the amount of hydrates that could form in a pipeline and determine whether the hydrates formed would block a pipeline. Dissociation times for any blockages would be studied as will the use of inhibitors to prevent the blockage. In conjunction with Colorado School of Mines, Hydrate formation, transport and dissociation models will be developed and validated.
Large quantities of data will be gathered to better understand hydrate formation kinetics in live oil-water-gas systems. Two oils will have low water cut plugging tendencies (forms hydrate blockages at water cuts < 10 – 20%) and two will have high water cut plugging tendencies (form hydrate blockages when water cut is in excess of 50 to 70%). The JIP will focus on different hydrate production issues with the intent of providing valuable information to oil producers for a more economical approach of deep-water developments. These issues can be grouped into three categories: producing in the hydrate domain, shut-down and restart of production systems, and preventing hydrate formation.
Current project members include Anadarko, Baker Hughes, BG, BP, BHP, Calsep, Chevron, ENI, Hydro, Ondeo Nalco, Marathon, Maersk Oil, Petrobras, Statoil, Total, DOE, MMS and collaborations with CSM. Efforts to solicit additional members are ongoing.
Industry Members $40,000/year
Government $140,000/year (DOE & MMS)
Industry Members $45,000/year
Government $285,000/year (DOE & MMS)
Starting in 2008
Industry Members $50,000/year
Government $285,000/year (DOE & MMS)
Industry Leveraging: 20 to 1
Scope of WorkPhase 1
This work will focus on different hydrate production issues with the intent of providing valuable information to oil producers for a more economical approach of deep-water developments. These issues can be grouped into three categories:
Producing in the Hydrate Domain - Most oil producers today take precautionary measures to avoid producing in the hydrate formation region (inhibitors, insulation), resulting in higher capital or operating costs. Considerable savings can be achieved through better understanding and confidence in the hydrate formation process under deep-water flowing conditions. The impact of different parameters, such as oil chemistry, salinity, water cut, cooling rates, multiphase flow patterns and subcooling, on the hydrate formation process will be studied. Qualitative information, such as the structure of hydrates formed, and quantitative information on hydrate formation kinetics and transportation data will be generated from the flow loop tests. This data will be used to validate and/or enhance the model developed by CSM.
Shutdown and Restart of Production Systems - While designed to avoid the formation of hydrates under flowing conditions, deep-water systems become vulnerable if shut down occurs. Hydrates may form during the shut-in time as the temperature drops and plugging may occur on restart. The Tulsa University (Marathon) flow loop is very well suited to study the formation of hydrates under static conditions and study the restart process. Effects of shut-in time, cooling rates, water cut, salinity, and oil chemistry on hydrate formation and accumulation while restarting will be studied. In an attempt to provide information on the best strategies to restart plugged pipelines, dissociation data will be gathered, if and when, hydrate plugs occur. This data will be used to validate and/or enhance the dissociation model developed by CSM.
Preventing Hydrate Formation - Finally, many different additives or inhibitors can be used to prevent or delay the hydrate formation process, or to prevent accumulation of hydrate particles, eventually leading to the formation of a hydrate plug. More qualitative and quantitative information is needed on the performance of these chemicals under various conditions. The study of additives will be included in this effort to identify the key parameters involved in the selection process and in their performance, and help oil operators and chemical companies improve their selection process. Scale up comparisons of lab data to flow loop data will be made.
The goal of this project in phase 2 is to obtain experimental data to be used in defining successful operating conditions of a bare steel flowline operating in the hydrate formation region. This section describes the proposed set of experiments to be conducted and deliverables.Test apparatus
A 3” - 160-ft long flow loop will be used to conduct the experiments. This flow loop has been designed, constructed and operated by Marathon Oil Company and donated to the University of Tulsa. The proposed experiments will be tied into a Joint Industry Project on Hydrates Flow Performance to reduce project costs.
Pressure, temperatures and pressure drops are measured along the flow loop. Three densitometers and 4 sapphire windows will provide additional and visual observations. Hydrate particles morphology can be observed through the sapphire windows.Test procedure
The flow loop will be charged with oil, water and gas at an initial temperature to be specified. A period of cooling and steady-state flow conditions will begin the test, followed by a 48-hour shut-in. The flow will then be restarted progressively at increasing rates. A step-up restart is recommended to determine the critical shear rate, since a restart at high rates may lead to shearing of hydrates particles during the process and affect test results at the lower rates. The step-up process prevents the shearing of the hydrates particles until flow is resumed. After each test, the flow loop will be cleaned up and prepared for the next experiment.
Each test conducted with the above procedure will take 5 to 7 working days to complete, including test preparation and cleanup.Low Spot Test Rig
Due to terrain configuration, many pipelines have low spots where significant amounts of water may accumulate. Low spots in jumper lines and manifolds may also be critical to restart because of the amount of water that can be found. Restart of wells usually starts with large amounts of gas produced; when the gas hits the low spots, several scenarios may occur. If the gas rate is fast enough, hydrates will form rapidly but water in the low spots may be evacuated and re-dispersed downstream of the low spot; however, if the gas rate is too slow, the water will remain in the low spot, hydrate formation will be slower but the large retention time of the water will favor plug formation.
To conduct low spot experiments, the flow loop will be inclined in order to create a low spot where natural gas will be circulated at various restart rates using a CNG compressor and/or CNG trailer.
This project is divided in three phases.
Focused on deriving some key relationships between fluid properties, operating conditions and plugging tendencies of crude oil systems, and complete the findings unveiled by the prior phase of studies. From these relationships and correlations, tools will be further developed to better address the risk of hydrate plugging for a given system, resulting in better planning and implementation of hydrate management strategies. The second objective is to further studies oilwater dispersion characteristics and their relationship to plugging behavior while the third objective is to improve the slurry flow model developed in-house.
Focused in greater detail on some of the parameters which could potentially affect the findings from Phase I, such as liquid loading, salinity and water cut. The expected outcome of this research is a set of conclusions and guidelines helping the operators to better manage the hydrate risk upon restart of uninhibited flow lines. Since the focus of this study is the feasibility of restarting flow lines without deploying the hydrate prevention equipment, combined with selection of the appropriate restart rate, these guidelines for restart could be deployed in the field almost immediately without additional investments from operators.
Focuses on the development and implimentation of a riser test facility to closely mimic the geometry of a deepwater production system, and provide a better understanding of hydrate plugging during restart operations. The program will improve the understanding of blockage occurrence in wells-jumper-manifold systems allowing less conservative designs to be implemented. The risk of hydrate plugging in risers, jumpers, flowlines and chokes will be compared. The impact of inhibitor injection point on hydrate prevention will also be studied. The impact of production variables such as fluid properties, water cuts, GORs, rates, salinity and inhibitors may also be studied.
Major DeliverablesCurrent phase deliverables
Upcoming phase 3 deliverables
The hydrate facility was donated by Marathon to the University of Tulsa in June 2001. Relocation of the flow loop, process building and control trailer occurred in the summer of 2002 and commissioning occurred in the summer of 2003.
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, gas and additives into the flow loop. The control trailer contains all the data acquisition modules and the operator computer interface. A 40’x 30’ contained storage slab is used to store the test fluids. A boiler system has been added to the original facility as well as a boiler room.
Overall View of Hydrate Facility
Why Join the JIP?
By joining the JIP, your company would have access to a large database of tests and results that have been conducted using state of the art procedures that are backed by many of the industry leaders.Cost
Current cost for industry members is $45,000 per year on our current phase which will complete at the end of 2007. In 2008 we will be starting phase 3 which will cost $50,000 per year for industry members.Proposals
Interested in Joining Us?
If you would like to join the project or would like to request more information. Click on the link below to access the request form. Once we process your request, we will contact you and get more material to your organization.