| Title | PREDICTING SUCCESS OF WELL DISCHARGE AND AIR COMPRESSION OF TIWI WELLS USING THE RATIO OF AREAS OF FLASHING TO CONDENSATION (Af/Ac) METHOD |
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| Authors | A.M. Bravo, J.A. Tolentino, A.J. Menzies |
| Year | 2019 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Air Compression, Well Discharge, Af/Ac Ratio Method |
| Abstract | The Tiwi Geothermal Field has a number of production wells that have difficulty in being re-discharged when they cease flow, resulting in loss of production. The wells are usually allowed to build up pressure and are then discharged to the sump to stimulate production but this may take quite a long time and is not always successful. An air compressor has therefore been mobilized to Tiwi to stimulate wells that are no longer able to self-discharge. The downhole temperature and pressure data from the wells have been used along with the Af/Ac (Area of flashing to Area of condensation) ratio method (Sta. Ana, 1985) to help predict the likely success of self-discharge and air compression. In one of the test wells, the correlation predicted success for self-discharge, as Af/Ac was >0.85 based on the pressure and temperature survey and shut in wellhead pressure, but when the well was opened, it was unable to flow. The compressor was then used to stimulate the well to a higher wellhead pressure, which then resulted in a successful flow. The flow test results provided additional data and suggesting modifications to the Af/Ac ratio method to be able to account for: (1) surface discharge pressure effects as the well was flowed to a surface piping system which had higher back pressure than either flowing the well vertically or horizontally to an atmospheric test rig, (2) how the “Area of flashing” is defined below a wellbore obstruction or the total depth to consider for wells with shallow obstruction, and (3) the correct wellbore temperature survey to use for well leaking to the surface. After applying these corrections to the candidate well, the results then agreed with the threshold ratio of 0.85 described in the correlation. In other test cases, recently reworked wells were successfully flowed to the system sooner than planned. The Af/Ac ratio method was used in evaluating if air compression was likely to be successful in stimulating the wells, which led to calculating a target pressure to achieve the 0.85 threshold ratio. |