Hydrate Prevention and Methanol Distribution on Canyon Express
- C. Cooley (Total E&P USA Inc.) | B.K. Wallace (Marathon Oil Company) | R. Gudimetla (INTEC Engineering)
- Document ID
- Society of Petroleum Engineers
- SPE Annual Technical Conference and Exhibition, 5-8 October, Denver, Colorado
- Publication Date
- Document Type
- Conference Paper
- 2003. Society of Petroleum Engineers
- 5.2 Reservoir Fluid Dynamics, 5.5 Reservoir Simulation, 7.2.1 Risk, Uncertainty and Risk Assessment, 4.5.10 Remotely Operated Vehicles, 2.7.1 Completion Fluids, 4.5.7 Controls and Umbilicals, 5.2.1 Phase Behavior and PVT Measurements, 4.3.4 Scale, 4.2.3 Materials and Corrosion, 4.6 Natural Gas, 4.5 Offshore Facilities and Subsea Systems, 4.3.1 Hydrates, 4.2 Pipelines, Flowlines and Risers, 4.1.5 Processing Equipment, 3.4.1 Inhibition and Remediation of Hydrates, Scale, Paraffin / Wax and Asphaltene
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The Canyon Express field in deepwater Gulf of Mexico is a development consisting of multiple subsea gas-condensate wells owned by different companies. Each deepwater well (ranging from 6400 to 7250 foot water depth) flows into one of two 57 mile, 12" flowlines which tie the subsea wells to a shallow water host platform on the Continental Shelf. The production from each well is predominantly methane gas but also consists of produced water and condensate. Due to the nature of the production and the combination of high pressures / low temperatures expected, the potential for hydrate formation is a serious concern to system operability. To adequately protect the system against hydrate formation and deposition, injection of hydrate inhibitor (methanol) at each subsea well from a common umbilical system is being employed. Although wet gas metering is being used at each well to measure gas and liquid rate, water content per well cannot be accurately predicted. Thus, a robust methanol injection strategy was required to effectively inhibit hydrate formation. This paper presents the design of the methanol injection system and development of the overall injection strategy. Examples from the early field life of the Canyon Express development will be presented which demonstrate the application of this injection strategy to the system operation.
The Canyon Express transportation system (Figure 1) consists of two 12" uninsulated flowlines running parallel from Camden Hills (Marathon Oil operated) through Aconcagua (Total E&P USA Inc. operated) and Kings Peak (B.P. operated) to a host platform (Williams operated Canyon Station) located in block MP261JP approximately forty miles north of the northernmost King Peak well. As the produced fluid within the flowlines consists predominantly of water-saturated methane and free water at high pressure (~4000 psig to ~2000 psig) / low temperature (~36°F), the potential for hydrate formation is significant as the normal operating point lies within the hydrate formation region of the Hydrate Dissociation Curve. Even if the system can be operated outside the hydrate formation envelope under steady-state and steady flow conditions, the potential for problems during shutdown and startup must be addressed. As a result it was necessary to provide a means of hydrate inhibition to the wellstream fluid.
To measure production from each well, a wet gas flowmeter (WGFM) is installed in each well production jumper. The WGFM has been designed to measure the mass flow rate of the gas and liquid phases. The optimum WGFM operation is when the measured fluid is 95% to 98% gas void fraction (GVF). Beyond 98% GVF, test results revealed that the measurement of liquids by the WGFM is not reliable. The range of operation of Canyon Express, especially during early field life, is greater than 99% GVF for some of the wells. Typical flowrates in each flowline range from 200-250 MMSCFD of gas, from 75-150 bpd of water, and from 100-400 bpd of condensate.
First gas for Canyon Express occurred in October 2002. Various problems with the methanol system were encountered and subsequently addressed by Canyon Express operations and engineering personnel.
Hydrate Prevention Philosophy
Prevention of hydrates is vital to the Canyon Express system as hydrates within the flowlines create the potential for disruption to gas production operations resulting in significant economic impact. During the design phase of the Canyon Express system various studies were performed to assess the risk of hydrates forming within the flowlines. The primary objectives of the hydrate risk assessments were:
Determine hydrate formation conditions for Canyon Express well fluid
Determine which hydrate inhibition option is best for Canyon Express.
Estimate the produced water volume (over time) for each individual well and total for Canyon Express operation.
Determine proportion of hydrate inhibitor required per produced water volume (including meter uncertainty) to calculate hydrate inhibitor injection rates, umbilical size, and injection pressure.
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