PINNACLE
Reservoir Evaluation
Identifying proper target reservoirs
Developing your asset will always carry some economic risks.
ese risks come in part from gaps of knowledge and uncertainty in the geologic conditions of the reservoir. Pinnacle's PermPT testing helps reduce uncertainty in coalbed methane (CBM) wells by carefully examining the following:
• Coal Permeability
• Skin Factor
• Determine Completion Strategy
• Frac or P&A?
project, a threshold gas content and threshold permeability must be determined to eliminate areas of low potential for economic development. Each year, many coal seams which do not meet the above criteria for commercial success are hydraulically fractured
(at large expense). PermPT testing ensures that available completion dollars are spent on the candidate seams that offer the best opportunity for maximizing NPV.
On location with one of Pinnacle's PermPT testing units.
Not All CBM Reservoirs are Equal
Aer sealing the land deals and conducting a geologic assessment to define target resources and potential development areas, the next step in most successful CBM projects is a pilot well program. A pilot program will determine reservoir quality and gas-in-place for the potential development areas.
Coalbed methane reservoirs are typically marginal reservoirs compared to conventional oil and gas reservoirs. e gas in place is usually sufficient but commercial production results from a) exceptional reservoir properties and b) exceptional economic parameters (gas prices). Reservoir characteristics must be understood for an economic play to emerge or expand beyond a pilot project.
e reservoir properties which have the greatest impact on methane gas productivity from coal seams are 1) gas content, 2) permeability, 3) the desorption isotherm, 4) initial water saturation, and 5) net coal thickness. In order to have a successful
PermPT testing uses a simplified gauge setup at the wellhead.
Using Injection-Falloff Tests for Reliable and
Accurate Reservoir Characteristics
PermPT testing determines the in-situ reservoir permeability of target coal seams utilizing injection-falloff tests, which are very effective and efficient for testing water-saturated coal seams. In the past, injection-falloff tests were performed on water disposal or waterflood injection wells to estimate permeability to water, skin damage, and in some cases reservoir geometry. We use injection/falloff tests to estimate permeability and skin factor on wells that will not flow naturally such as coalbed methane wells. It is imperative that the test be performed without exceeding the fracture gradient of the formation in order to obtain accurate analysis results. In lower permeability reservoirs, very low injection rates of 0.2 to 2.5 gallons/minute are oen required to prevent fracturing. is is nearly impossible to perform with larger stimulation-type pumping units, thus the PermPT testing concept was born—to build a fit-for-purpose high pressure, low injection rate unit capable of precisely metering small volumes of water into a formation without exceeding fracturing pressure.

PINNACLE
An injection-falloff test is very similar to a conventional pressure drawdown or buildup test except the fact that the pressure transient is generated from the mechanical equipment on the surface rather than the natural reservoir energy. us, injection rate and pressure are critical to the successful application of the injection-falloff test.
Many times, tests are performed without regard or careful planning of these two parameters and the resulting pressure responses appear to be analyzable, but give misleading or erroneous results.
e PermPT testing method of conducting injection-falloff tests considers these pitfalls and provides to the operator reliable and accurate reservoir characteristics needed for CBM development.
A Better Understanding of Reservoir Permeability
Permeability controls the rate at which the reservoir can be dewatered and the producing time required to achieve maximum gas production from the reservoir. Consequently it is extremely important for operators to have reliable estimates of permeability to optimally develop and manage a reservoir. Permeability measurements from PermPT testing are used to determine whether individual coal seams are a good candidate for fracturing or if they should be bypassed, leading to substantial cost savings through better interval targeting.
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Elapsed Time (min.)
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e above data set is from a typical PermPT testing coal seam injection/falloff test. Pressure was measured on the surface and is seen to slowly increase until injection was halted. e injection rate remained constant during this test except for one rate change in the middle of the test (to evaluate the effects of the transient behavior in the data). e analysis of the falloff portion is shown in the plot below.
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Perm = 17md
Skin = -1.2
Radius of Inv. = 450’
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Dimensionless Time
e analysis of the injection falloff data is illustrated in the traditional pressure transient type-curve analysis plot shown above.
is coal seam was about 6' thick and at a depth of approximately
1450'. e test just barely reached radial flow when a boundary was encountered. is interval was subsequently fracture stimulated and is producing economically.
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