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Basic Concepts of Surface Pressure Transient Testing (SPTT)


 

Basic Concepts of Surface Pressure Transient Testing (SPTT) Related Terms

Basic Concepts of Surface Pressure Transient Testing (SPTT), DFIT, Frac Monitoring, Surface Pressure Transient Testing

Since Cullender and Smith developed their WHP to BHP conversion program in the early 1950ís, surface pressures have been used to calculate bottomhole pressures on shallow, dry gas wells. If the original Cullender and Smith equations are modified to account for produced liquids, and the higher pressures and temperatures encountered in deep wells, the correlation may be extended to gas/condensate wells that are single phase in the well bore. This then means that single-phase liquid wells (water injectors and oil wells above the bubble point) can also yield accurate well test results from the surface.

Testing from the surface reduces the cost and eliminates the risk of running tools into well bores. Surface testing also allows the testing of high-pressure/high-temperature wells that cannot be tested with a downhole gauge because of harsh conditions. Thus, to reduce the cost and risk (or when no other option is available), many operators have chosen to run their pressure transient tests from the surface on single phase wells. In addition to the traditional pressure transient testing methods of build-up and drawdown, surface testing is an invaluable tool for other pressure transient tests. These include DFIT or pre-fracture injection fall-off tests, waterflood optimization, CO2 injection and production testing, injectivity and withdrawal testing on storage reservoirs.

It is possible to test most naturally-unloading gas/condensate and oil wells from the surface. This is due to advances in multi-phase wellbore modeling which take into account the fluidís behavior in the well bore. Thousands of wells in the USA Gulf Coast / Gulf of Mexico and in many locations around the world routinely take advantage of this proven technology when used under the appropriate well conditions.


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