CO2 Well Testing via the SPIDR System
By Anil Joy and Chad Cluver |
Thu, 7 Aug 2008
When reviewing recent SPIDR work for pressure transient
testing of CO2 wells, DRC has encountered a wide range of
conditions; from high temperatures (300+ oF), high pressures (10K+
psia), and high rates (60 MMSCF/D) to low temperatures (90 oF), low pressures
(600 psia), and low rates (2 MMSCF/D). CO2
production, for enhanced oil recovery (EOR), is becoming an important
part of the Oil & Gas industry. DRC
is currently performing pressure transient testing at two of the largest CO2
producing fields in the U.S. An example from each will be presented that
illustrates the broad range of well conditions that are suitable for SPIDR
surface well testing of CO2 producers. The common factor that allows accurate
conversion of the wellhead data to bottom-hole conditions for pressure
transient analysis is that the wellbore is in single phase from the reservoir to
surface.
The first example is a large CO2 field in Arizona
that is a low pressure, low rate and low temperature reservoir. Because of the
very low flow rate and large tubing diameter, frictional losses are negligible
and can be ignored for the flowing data. DRC uses its proprietary software to
model the thermal profile of the well, and incorporates this with the calculations
of the hydrostatic head to convert the wellhead pressure data to bottom-hole
conditions. Through the use of our PVT simulation software, the conditions in
the well stream are then determined which allows for an accurate calculation of
the hydrostatic head via an iterative process.
Accurate thermal modeling is critical in ensuring accurate conversion of
build-up data, especially in this case as CO2 is very sensitive to
small changes in temperature. Without
accurate thermal modeling, the shape of the build-up is distorted, and would
result in an incorrect analysis. Due to
the great success of the initial testing, the operator has relied completely on
the SPIDR system and the DRC engineering staff for all of their pressure
transient testing needs.
The second example is a large CO2 field in Mississippi
that is a high pressure, high rate, and high temperature reservoir. Because of the high rate, frictional losses
are not negligible and must be taken into account. Using DRCís proprietary model for high rate
wells, the frictional losses can be accurately determined, and then the thermal
profile of the well can be modeled using DRCís proprietary software for
modeling thermal effects. This is then incorporated
into the iterative process used to determine the hydrostatic head using our PVT
simulation software. It is important to
be able to accurately determine the frictional loss as they will have a
significant affect on the conditions in the well stream when determining the
hydrostatic head. After combining these
calculations it is possible to accurately convert the wellhead pressure data to
bottom-hole conditions. Without DRCís
proprietary models to determine frictional loss, the flowing BHP data would be
in error resulting in erroneous skin and flow efficiency calculations. Once again, without accurate thermal modeling
any analysis of build-up data would result in erroneous permeability and P*
calculations.
With the wide-range of CO2 producers, DRC is now
giving operators a low cost, no risk alternative to running pressure gauges into
the wellbore. Along with CO2 producing
wells, the SPIDR well testing system is a perfect application for CO2 injection wells. This gives operators a way to monitor their
injection wells without the risk or the extra cost of running gauges in the
hole. In addition to capturing injection
pressure, the SPIDR can also record injection rate and density, if
required. SPIDR gauges are always
available for rental with same day shipping and DRC engineers are available
24/7 to answer any questions the engineer or field personnel may have.
