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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 DRC’s 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 DRC’s 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 DRC’s 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.