| Title | Inferring Production Performance from Early Injectivity Tests |
|---|---|
| Authors | Marc PERREAUX, Patrick EGERMANN, Martial SAQUER |
| Year | 2020 |
| Conference | World Geothermal Congress |
| Keywords | injectivity test, productivity index, production performance, well modelling |
| Abstract | While exploring for high-enthalpy geothermal resources, getting early information on the performance of new exploration wells can accelerate the decision process. Indeed, once a new exploration well is drilled, the wellbore and its vicinity have been cooled down during the drilling because of mud circulation and mud losses. Waiting for the wellbore warm-up is necessary to be able to start the well production. Considering the significant cost of rig time, accelerating the decision process leads to an optimization of the rig usage and thus, can lead to significant savings in drilling costs, which is a large part of the exploration and development costs in geothermal developments. The methodology proposed aims at assessing quantitatively the production performance from the results of injectivity test. A specific workflow was defined to match the results (temperature and pressure gradient) measured during the injectivity test to identify the feed zones and their respective injectivity index. The methodology also includes an extrapolation of the first heating up temperature profiles to estimate a static temperature gradient relevant of the future conditions before production test. Then, the productivity index of the different feed zones are deduced from their injectivity index. The correction factor for each feed zone depends on the temperature difference between the conditions prevailing during the injectivity test and the one supposed during the production test and allows to account for the thermo-mechanical mechanisms which rules the feed zone permeability evolution as a function of the fluid circulating temperature. Thanks to an iterative process using a well flow model, the performance (rate and power) of the well once in production can be estimated. A specific program was developed to perform this workflow, including an assisted matching of the temperature gradient measured during the injectivity test. The methodology is illustrated on a well-documented case study where production data were considered as blind test. Following the proposed workflow, the production performance estimation and the resulting geothermal power were found very close to the values effectively found during the production test. It demonstrated that the methodology and its associated tools consist in an useful and convenient way to fast track estimate the well production performance from early injectivity test data. |