| Abstract |
The PGB-01 was the first deep well drilled in the Borinquen area to begin the feasibility studies. The temperatures measured in the well were very high (275°C). Nevertheless, the permeability was very low. The tests carried out during drilling measured the injectivity index to be 1.4 l/s/bar (Castro, S., 2006). It was considered that these conditions could be partly responsible for the low productive characteristics obtained during the first production tests carried out in the well. (Castro, S. and Torres, Y., 2006) With the objective to improve the well permeability, a water injection test was planned. The two factors considered to increase the permeability of the well are the temperature difference between the water injected and the reservoir, and/or the increase of pressure generated in the deeper permeable levels. The theoretical reasons to expect that it would be able to improve the well permeability are the secondary fracturing of the rock (Castro, S., 2007) and the mechanically cleaning of the permeable well zones. The injection test started on July 17, 2007 at 8:30 am, injecting a flow of 35 l/s. The flow rate was constant until July 31, 2007 at 8:28 am, when the flow rate were increased to 60 l/s for 7 hours, and finally, an injectivity test of three different flow rates was carried out to calculate the injectivity index of the well. Data analysis indicated that the injectivity index of the well was doubled with regard to the last test carried out during drilling, increasing from 1.4 l/s/bar to 2.8 l/s/bar, and the product kh increased from 0.6 D-m to 1.6 D-m. The absence of seismic activity associate with the injection process seems to indicate hydraulic fracturing did not occur, so it was interpreted that the increase in permeability was related to the cleaning of the permeable zones that were partly blocked with cuts and materials utilized during the well drilling. After four months of thermal recovery an output curve was carried out during short time to evaluate the new productive conditions of the well. The output showed a positive variation of the productive parameters. Nevertheless, that is not enough to convert the well to be commercially exploitable. From the results obtained, it was decided to carry out a new injection test in the PGB-01. Similar tests are planned in others wells of Las Pailas geothermal project and in the future wells that will be perforated in the Miravalles geothermal field in order to increasing the permeability of the wells. |