| Popis: |
A new method for estimating formation temperature from wireline formation tester temperature measurements has been developed1. This method is based on the reconstruction of thermal history, which involves drilling, no-mud-circulation and pumping-out phases, using the model of heat transport in the formation. The model calibration is achieved by fitting the predicted temperature at some intermediate distance from the borehole for the temperature data measured in flowline during pumping-out. The temperature found in intermediate zone is then extrapolated to the boundary of cooled zone surrounding borehole for estimating initial formation temperature. The forward model used for thermal history simulation is simple and robust. It does not involve the borehole temperature modeling during drilling and can be calibrated with a single parameter - either the average mud temperature opposite the tested interval or the average heat flux from the formation during drilling. Although this model cannot predict accurately the initial phase of thermal history (drilling and no- mud-circulation), it becomes adequate for the pumping-out phase when the details of borehole temperature variation with time during drilling become insignificant. The only parameter that affects solution during this phase is the total amount of heat extracted from the formation during drilling. This approach in order to be successful imposes some constraints on the timing of thermal history phases. In particular, the no-mud-circulation phase should not be too long and the pumping-out phase should not be too short, otherwise the deterioration of resolution may occur. The examples are given that illustrate the capabilities of new technique. |
