Inflow tests are generally carried out to verify if there is communication with the formation through the casing, a liner lap or past a cement plug (bridge plug).
Most of the applications are in connection with testing or squeezed off perforations and casing leaks, testing liner-laps, float shoes and float collars, cement plugs and bridge plugs.
An inflow test is performed by reducing the hydrostatic head above the item to be tested by circulating to a lighter fluid.
Procedure for Circulating to Lighter Fluids (Diesel etc.)
- RUN retrievable packer with circulating valve, safety joint and short tail on drillpipe, to depth to be advised by Operations Engineer.
- SET retrievable packer at advised depth and test annulus with 1000 psi in order to check that packer is properly sealing and that the tool assembly is functioning properly before RIH any further.
- Generally, the retrievable packer should be set at some 50 ft above the interval to be tested (or 50 ft above TOL) in order to minimise any possible influx. OBTAIN prior approval from the Head of Onshore/Offshore Operations for inflow testing during the hours of darkness.
- CIRCULATE the drillpipe to a lighter fluid until the required drawdown is accomplished. (An air cushion may be used)
- After having circulated the well to achieve the required drawdown, PERFORM the inflow test on the well for 15minutes as detailed in the Drilling Programme.
- REVERSE well to completion fluid.
- UNSEAT retrievable packer. CIRCULATE and OBSERVE well dead.
- POOH and L/D retrievable packer.
Interpreting Inflow Test Results
The “Horner Plot” method should be used for interpreting inflow tests to confirm the integrity of liner laps for over pressured gas wells. Traditional methods are often ambiguous and require unnecessary long rig time.
Traditional Interpretation method
The mechanical integrity of e.g. liner laps can be tested by creating a underbalanced situation over the zone of interest. This is usually done by displacing the well to water. Once the well has been displaced to water, the fluid returns are monitored for a duration of say 4 hrs. This back flow from the well is caused either by thermal expansion, or an influx into the well bore (leak) and thermal expansion
The observed flow rates are plotted against a time scale allow to determine if the situation is one with both an influx and thermal expansion or with temperature effects only. In order to positively determine whether and when zero flow will materialise, the inflow test has to be conducted for much longer than 4 hours.