| Title | Performance Analysis and Stimulation of Dry Steam Wells in Mak-Ban Geothermal Field, Philippines |
|---|---|
| Authors | Frederick LIBERT and Ryan ALVAREZ |
| Year | 2015 |
| Conference | World Geothermal Congress |
| Keywords | MakBan, wellbore model, scale, clean out, injection stimulation, dry steam, deliverability |
| Abstract | Currently, there are ten (10) wells in MakBan that have been producing dry steam. It had been noticed that steam decline in some of these wells was higher than in others but it had been assumed that this was due to pressure decline associated with an increase in shallow production. The wells were recently analyzed using Wellhist, a Chevron in-house application for wellbore simulation that is used for calibrating well hydraulic models to match production history. The Wellhist application can also be used in production forecast to produce a series of well deliverability calculations at future sub-surface conditions or well capability which represents reasonable production potential of a well assuming 100% reliability and no mechanical well constraints. By comparing the expected well capability calculated with WellHist with actual production, it is possible to recognize change in well performance due to mechanical well constraints or other flow assurance issues that could lead to trouble shooting or in depth performance analysis and possibly remedial wellwork. The WellHist analysis strongly suggested that production performance of three (3) wells namely Bul-20, Bul-23, and Bul-60 have been lowered either due to a change in wellbore geometry and/or reduction in effective permeability. The data from these three wells were also further analyzed using the method developed by Acuna (2008) where data from well deliverability tests or from records of wellhead pressure and production rate can be used to solve two unknown parameters in the equation (CWB and PI). Those parameters should not change with time unless there is a variation in wellbore geometry or effective permeability. For the case of Bul-20, 23, and 60 the CWB and PI do change with time which indicates that those wells experience changes/reduction in wellbore geometry, probably associated with scaling in the wellbore of some type. It is also possible that those wells may have experienced permeability reduction due to scaling in the formation. Based on the analysis, successful work overs on these wells could recover 205 kilo pound per hour (kph) of steam production. The result from this evaluation is to provide a recommendation to conduct necessary recovery works to return the wells to their expected performance. A series of diagnostic works were performed and it was decided to initially try and improve well performance by injecting cold condensate. This was applied to Bul 23 with the intention of exposing the casing to a cold environment thus inducing a thermal shock to the casing that is expected to contract the casing and spall-off the deposited scale. This technique was successful in recovering the well to its expected performance. |