Guidelines for Step Rate Testing

1. If possible, have a reasonable conception of what the in-situ stresses are so that the step rate test can be appropriately designed. Be certain that there will be adequate data points before breakdown or reopening of the fracture.
2. Under any circumstances, have an approximation of the conversion between surface and bottomhole treating pressure. In addition to determining in-situ stress levels, this can be useful for evaluating the completion efficiency.
3. Under certain, restricted circumstances onshore, dead string calibration may be possible if the backside has enough integrity.
4. If reasonable, obtain bottomhole pressure measurements. If bottomhole data are being acquired, tandem gauges are a reasonable option. Have continuous surface readout under any circumstances. This is a particular issue if some of the injection is on vacuum. Some operators will not opt for tandem gauges if the supplier is reliable, if past history shows few failures and if the cost of failure is minimal.
5. Check and calibrate all rate meters prior to testing.
6. Be certain there is enough water on location.
7. Use uniform rates and time steps! This will be demonstrated in the section on multi-rate analysis. Record pressure and time and provide the analyst with this information.
8. Ensure that there is appropriate equipment available to fracture the well initially. If breakdown is required, mud or cement pumps are often used. Be reasonably certain of what will happen during the fracturing operation or use the test to make an inference of this. Can the injection interval accept the required rates? If not, out-of-zone fracture growth can occur.
9. It has been recommended that each time step is one hour long to ensure that the radius of investigation is large enough. Obviously, this may not always be practical. Either shorter times are called for because of economic or operational limitations or substantially longer times are required to allow for thermal stabilization. At a minimum, consider these issues before the test. Earlougher states that "in relatively low permeability formations (k < 5 md), each injection should last for one hour; 30-minute injection times are adequate for formations with permeability exceeding 10 md."
10. Attempt to obtain at least three readings above and three readings below the "parting" pressure.
11. Ensure that the pressure and rate gauges are calibrated and will accommodate the largest anticipated pressures.
12. Fracture gradient can be dependent on the average reservoir pressure. Is there an independent measurement of the reservoir pressure (temporal) or can a measurement be made in conjunction with the test?
13. After the rate increasing segment, two approaches are possible. The first is to back down on the rates to assess if the cement has been damaged. Alternatively, some specialists prefer a long falloff after the last rate because it can be analyzed to get fracture properties (dimensions). Deterioration of the cement bond can be a cause of altered step rate signatures or a risk to the injection process if there are multiple zones and/or aquifers.
14. Compile all data to determine if there is a consistent relationship between apparent in-situ stress and reservoir pressure.
15. Where possible, combine falloff testing with the measurements, as described in item 13, above.

Where Possible, Falloff Should Be An
Integral Part Of Step Rate Testing.

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