Increasing Liquid Hydrocarbon Injection and Withdrawal Rates
Decreasing Cavern Dewatering Time – Improving Cavern Safety
The PRCI Field Test to Develop a Solution
The Problem
Fluid injection rates in hanging tubulars (or the annulus between the hanging tubular and the
production casing) in solution mined storage caverns are restricted, without a strong scientific basis, to
avoid flow induced vibration leading to buckling or structural failure. Such failures can have significant
financial impacts, with a gas cavern de-watering string failure replacement costing upwards of $1
million, not counting lost service. Of even greater concern, a string failure can cascade into a product
release with accompanying consequences.
Cavern operators wish to avoid hanging tubular failures, but also want to maximize flow rates. A
design tool that would allow the operator to determine the maximum allowable flow rate is highly
desired. Similarly, new well completion technologies that allow higher maximum flow rates would be
welcomed by the cavern storage industry.
Solution mined storage caverns with hanging tubulars – Flow in the tubing and in the annulus
Liquid Storage Cavern
Natural Gas Storage Cavern
Understanding Case History Data
In 2008, Pipeline Research Council International (PRCI) cofunded a case history study of storage cavern
operator experience with hanging string failures (and “non-failures”) with the objective of trying to
determine if a maximum injection/withdrawal rate design tool could be developed. PRCI’s cofunded
project resulted in a number of significant conclusions:
1. A significant number of brine string failures have been experienced.
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2. Contemporary mathematical models of flow-induced vibration (assuming “zero displacement” at
the casing shoe) do not reproduce displacements that could explain the observed flow-induced
vibration failure of brine strings.
3. “Annular and leakage flow” at the casing shoe may be responsible for the observed flow-induced
vibration damage.
4. Mathematical models of leakage flow at the casing shoe of a storage cavern do not exist in the
literature. Development of such models would benefit the industry and should be undertaken in a
future project. In the meantime, measures such as “stiff centralizers” on the brine string near the
casing shoe may hold promise in reducing flow-induced vibration and may allow for increased
flow velocities without risk of brine string failure.
The Idea for Increased Flow Rates and Minimization of Tubing Failures
The potential for “annular flow” to induce flow-induced vibration in hanging tubulars at high flow rates
has been further studied by the Solution Mining Research Institute (SMRI) with some confirmation. The
“stiff centralizer” idea that resulted from the PRCI Case History project is aimed at mitigating the impact
of annular flow on flow-induced vibration, and has been proposed as a practical method for attaining
high flow rates in hanging tubulars. PRCI has developed a field test in a cavern to determine the
effectiveness of a stiff centralizer in mitigating the impact of flow-induced vibration at high injection and
withdrawal rates.
The Field Test – Instrumentation
The heart of any field test of flow-induced vibration of hanging tubulars is the
deformation measurement instrumentation. The hanging tubular in solution mined
storage caverns typically extends from the wellhead to depths of more than 4000 feet.
The bottom hole location is in a brine environment of high pressure and high
temperature. The deformation character of these very long hanging tubulars is of such a
low frequency that an accelerometer based deformation measurement instrument must
have a unique design.
PRCI funded a year-long project that included comprehensive delineation of
instrumentation performance requirements, prototype instrumentation development, insitu testing, and instrumentation manufacture. SOCON, a German-based cavern
instrumentation and monitoring specialist company, developed and manufactured two
instruments for PRCI and several in-house tools to be used in the proposed PRCI field test.
The PRCI field test instrumentation will consist of four SOCON tools (Illustrated to the
right) deployed in a cavern hanging string. The SOCON tool has been successfully used in
a cavern field test in Europe and PRCI has every confidence that the instrumentation will
be just as successful in the PRCI field test.
The Field Test – Execution
The PRCI field test configuration will use a hanging string with approximately three “stiff centralizers”
positioned near the casing shoe. The SOCON instrument string will be deployed into the hanging string.
An accelerometer array will be attached to the wellhead. It is expected that any downhole pipe
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vibration will be detected and be correlatable to the wellhead instrumentation such that the string
movement can be determined.
Phase 1 Testing
The testing will be initiated with brine injection into the hanging string accompanied by brine
withdrawal from the annulus. The flow rate will be increased in a stepwise manner – potentially up to a
fluid velocity of nearly 25 feet/second. Following this phase of the testing, the brine injection will be
stopped and re-started with injection into the annulus and associated brine withdrawal from the tubing.
The string movement will be monitored and characterized during each operating mode.
Phase 2 Testing
The hanging string will be removed from the well following the Phase 1 testing. The stiff centralizer will
be removed and the hanging string will be re-installed in the well. The brine injection executed in Phase
1 will be repeated in Phase 2. The flow rate will be increased up to the level where significant tubing
movement (and possible deformation) is experienced. This is a unique opportunity to observe the
dynamic behavior of a bring string as it is operated beyond typical flow limitations. The information
from this test should provide significant insight into brine string stability as a function of fluid velocity
and string fixturing methods. Data will be collected from the downhole instrument and the wellhead
accelerometer on a real-time basis for subsequent detailed analysis.
The Path Forward
Test planning at a site in Mont Belvieu, TX has led to an estimated project cost of $1.0 to $1.5 MM.
While PRCI has ~$500,000 available to support the project, additional resources are required – either as
cash and/or access and support at a cavern that could host the test at a potentially lower cost. The test
location is not required to be in North America. Given the substantial investments previously made by
its members, and the large amount it has pledged for the future test, PRCI is seeking non-member
corporate partners who are able to provide a minimum of $100,000 (as cash or in-kind equivalent). The
results of the test will be maintained within the sponsoring organizations and PRCI. With sufficient
funding commitments, the field test could commence 4Q/2013 at the Mont Belvieu location. The
schedule at an alternative site will not be known until those site details emerge.
For more information, please contact:
Mike Whelan
Pipeline Research Council International, Inc.
630-983-2697
[email protected], or,
Joe Ratigan
Ratigan Engineering & Consulting
605-394-6445
[email protected]
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