07121-DW1301

Goal
This project seeks to address gaps in industry’s ability to deploy and operate multiphase and wet gas meter technology in deepwater production systems. Continuous measurement information collected on individual subsea wells using this technology will allow for a better assessment of well performance and thus can improve recovery from deepwater reservoirs beyond that possible with current capabilities.

Performers
The Letton-Hall Group, LLC, Houston, TX 77057
Oceaneering, International, Inc., Houston, TX 77041
Multiphase Systems Integration, LLC, Tulsa, OK 74135
axept, Inc., Palo Alto, CA 94301

Background
The advent of deepwater production systems, and especially the need to commingle production from marginal developments, dictates measurement capabilities beyond the current state of the available technology. Since commingled streams often represent different ownership and/or royalty interests, any measurement irregularities may result in fiscal inequities – perhaps on the order of tens of millions of dollars. Unless the risk of such occurrence is minimized, many easily produced fields may never be considered for development.

There is a strong imperative to improve recovery from deepwater reservoirs beyond current capabilities. To accomplish this means that continuous measurement information on individual wells will be required. This can only be achieved through better information on well performance. Improving the reservoir recovery by even a few percent may translate into tens of millions of barrels of additional reserves. These additional reserves will be gained through better information on well performance. For example, an improvement of 5% in recovery of Thunderhorse reserves would be worth nearly $5 billion to the owners and over $600 million to the US Treasury at current prices. Better well rate and composition data are clearly key to attaining these improvements.

The need for measurement is especially great on HP/HT projects, where the environmental demands on the equipment pose problems. The issue is exacerbated by the fact that the current small number of HP/HT prospects will provide little incentive for manufacturers to develop special metering equipment that only has use in a few applications. Unless special programs such as this are carried out, it is possible that these deepwater, high-risk applications may never be developed.

A final key aspect of the work is its importance in the development of subsea processing capabilities, where the fluids produced from each well will be separated, compressed, pumped, dehydrated, re-injected, disposed of…essentially subjected to any process that is routinely done on a production platform today. By doing this, not only will hydrocarbon recovery be improved, but there will be less risk of an adverse environmental event. However, measurement improvements will be necessary since the human beings who normally insure that sampling and metering are carried out properly will not be available.

The objective of the Project DW1301 is to address gaps in the deployment and use of multiphase and wet gas meter technology in deepwater production systems. Specifically, the immediate tasks and goals of this project are:

• (1) to develop and standardize deepwater well fluid sampling,
• (2) to develop the means to convey clamp-on measurement systems to deepwater wells via ROV,
• (3) to understand the ways in which production alteration of meters affects their response,
• (4) to develop and qualify sensors for HP/HT environments,
• (5) to evaluate the effectiveness of wellbore flow models, such as virtual flow meters, and
• (6) to develop uncertainty models of the complete multi-well production system from subsea meter to topside.

Potential Impacts
The successful completion of the work prescribed in DW1301 will improve the accuracy with which is known the flow rate from each well, thereby improving the reservoir management and ultimate recovery from deepwater fields. Additionally, enhanced measurement accuracy will make the assignment of revenues and royalty payments more equitable. New fields with high pressures and high temperatures will be produced and measured where such was not possible before. And the ability to process well production on the sea floor will achieve greater recovery with reduced environmental impact than is possible today.

Accomplishments
The work on all six DW1301 tasks has now been underway for over 16 months, just past the halfway point for the project. While some tasks are behind their original schedules, it is anticipated that all work will be completed within the 30 months allotted, and within budget.

On Task 1, eleven different deepwater sampling concepts – existing and proposed – were reviewed and evaluated. Essential building blocks were selected, and key attributes to support subsea metering requirements were identified. Design and fabrication of one candidate concept into a prototype deepwater sampling mechanism conveyed via Remotely Operated Vehicle (ROV) is underway. Standardized sampling connections to subsea piping and ROV are being developed.

On Task 2, a “pathway” was defined for the progressive development of measurement conveyed by ROV in deep water. Selection of a meter to demonstrate the concept was made, and a contract was executed for provision of meter components expertise. Design and fabrication of a prototype ROV-conveyed metering system is complete. Functional testing of metering system components through the ROV umbilical and acquisition system is complete. Planning discussions and site inspection have been held with SwRI for reference testing and OII for ROV tank testing.

On Task 3, a study of commercially available sensors for ultra deepwater HPHT applications was completed and used to redefine the task objectives. A vendor was selected and contracted to design and fabricate the HPHT DP sensor cells. Manufacturers of DP sensors for subsea use were contacted to participate in this HPHT development; one (possibly two) has agreed.. The task working group agreed on the new objectives, making it easier to achieve the goals at a lower cost. The design and fabrication of prototype sensor chips has produced what should be fully functional prototypes. Integration into cells and later full units has begun.

On Task 4, an evaluation plan was agreed upon, in which the assessment of VFMs using both actual field data and simulated field data in single wellbores is performed, although real-world data in a form that can be used has been almost impossible to obtain. Invitations, interviews and selection of seven VFMs were carried out to establish the pool of systems to be evaluated. Simulations of multiphase flow in wellbores have begun to be conducted to evaluate the candidate VFMs. OLGA multiphase flow simulation software was selected for generating the test data, and its owner, the SPT Group, was kind enough to provide a free license for DW1301 use for the term of the project.

On Task 5, at its very beginning the effort received a boost when ConocoPhillips provided a data set that had been identified as one that must be acquired, viz. experimental liquid-sand erosion of a Venturi meter. Beyond that the working group identified scale as the primary form of deposits that would be investigated. The task is gradually working through obtaining both experimental and Computational Fluid Dynamics (CFD) results for both scale and erosion on three different meters in common use in upstream measurement, namely Venturi, cone, and wedge. Results of CFD erosion work in Venturi and Cone meters have been completed. Experimental scale deposition work in Venturi, cone, and wedge meters has been completed. CFD work on scale deposition and some final erosion tests are underway.

On Task 6, the intent is to develop a tool that will give users the ability to calculate the uncertainty in measurement at the subsea meter, at the separator topside, and at other points in between. The tool consists of separate models for gas-dominant and liquid-dominant systems, and provides Forward Models for calculation of overall uncertainty figures such as mass balance, and a Backward Model for attempting to identify the source of anomalies in uncertainty, such as an errant subsea meter. The Forward Model has reached a point of stability and is being beta tested. The Backward is almost ready to release a test version and begin beta testing.

Current Status
The work of this project will be in seven distinct task areas, six of a technical nature plus one overarching management/technology aspect. For each task, a description follows that includes the name of the task and its objectives.

Deepwater Subsea Sampling. The goal of this task is to develop hardware and procedures that allow an ROV-based mechanism to collect a sample at the subsea wellhead, and to document the work so that standards for the component hardware elements can be adopted. Prototypes will be built and then tested at the surface and in simulation (underwater) tanks. Success will accelerate the development of a subsea sampling capability that can be applied across a variety of equipment platforms. This will in turn accelerate the application of subsea sampling, with a resulting improvement in the accuracy of produced fluid volume measurements and allocation, greatly aiding reservoir management and resulting in better recovery of oil and gas. Major participants will be the Letton-Hall Group (LHG) and Oceaneering International (OII).

ROV-Assisted Subsea Measurement. The goal of this task is to develop and prove methods for conveying a clamp-on meter to the sea floor by ROV. The hardware components will be documented as drafts of future standards. Meters/sensors will be marinized for prototype demonstration in surface flow loops and in simulation tanks. The same benefits outlined above will accrue. Major participants will be LHG and OII.

HP/HT Qualification. The goal here is to make the necessary sensors available for extreme high-pressure, high temperature (HP/HT) subsea production, which, due to the small numbers required, might not be developed through conventional commercial market forces. The key component needed is a combination pressure-differential pressure (P-DP) sensor that can be used at pressures and temperatures that are far higher than current standard conditions. The benefit from this work will be the ability to measure flow in these hugely important HP/HT fields, thus permitting accurate revenue/royalty allocation and improved recovery. LHG and axept are the participants in the qualification task.

Evaluation of Flow Modeling. Virtual Flow Meters (VFM) employ pressure and temperature sensor data to quantify flow, in lieu of a physical multiphase flow meter. A thorough test of current commercial VFMs is the goal of this task, with a resulting report that rigorously evaluates and compares them. The desired outcome is the greater use of VFM in those situations where they are appropriate (e.g. backup of primary physical meters on wells). The main participants are the LHG and Multiphase Systems Integration (MSI).

Meter Fouling Effects. The goal of this task is the development of a greater understanding of the effects on meters of principal kinds of fouling – scale, wax, and erosion. Two kinds of meters will be tested at various stages of fouling in various simulated production (multiphase) conditions. The benefits from this knowledge will be the development of improved models for predicting the effects on meter readings of common fouling mechanisms, and thus an improvement in meter accuracy. The primary participant in the work will be the LHG.

Metering System Uncertainty. The intent of this task is to develop a “tool” that will give users the ability to calculate the uncertainty in measurements made at the subsea meter, at the separator topside, and at other points in between. Merging carefully developed models of multiphase flow with separator and meter models in a unified system will result in a useful tool for the production engineer. The primary participants in the work will be MSI and the LHG.

Project Management, Reporting and Tech Transfer. Overall project management includes the management of day-to-day operations, coordination of 2nd tier subcontractors and consolidation of 2nd tier subcontractor reports, incorporation of recommendations and findings into a deliverable, and technology transfer.

Project Start: October 27, 2008
Project End: April 26, 2011

DOE Contribution: $ 3,600,126
Performer Contribution: $ 900,032

Contact Information:
RPSEA – Jim Chitwood (jchitwood@rpsea.org or 713-372-2820)
NETL - Jay Jikich (Sinisha.Jikich@netl.doe.gov or 304-285-4320)
Performer Company – Winsor Letton, Ph.D. (letton@ix.netcom.com or 713-974-7328)

Additional Information

Final Project Report [PDF-16.6MB]

26th International North Sea Flow Measurement Workshop Paper - Deepwater Measurement Verification – a DeepStar-RPSEA Mandate [PDF-390KB]