Predicting and Applying Wellhead Temperatures for Steamflood Field Operation and Production Performance Monitoring

Producer flow line temperatures (FLT) can be measured automatically with a thermistor on an emergency shut-down system (ESD), or manually on a specified spot on flow line with a hand-held unit. Measured FLTs can usually be mapped to represent the formation temperature distribution for steamflood reservoir management purposes (Hong, 1994). In the meantime, predicting the long-term flow-line temperature trend in steamflood operation is necessary for designing surface facilities for both oil dehydration/separation and produced water recycling. This predicted temperature will also be applicable for production performance monitoring. In addition to FLT, wellhead temperature (WHT) is another surface temperature. FLT and WHT are comparable for their close typical distance of 5-10 ft. To predict the wellhead temperature, Hasan, Kabir and Wang (2009) derived a steady state analytical solution for calculating WHT from bottom hole temperature (BHT) under flowing conditions of a multiple section slant wellbore for the isothermal primary depletion process with both WHT and BHT being time independent for a given gross rate. This steady-state analytical solution has been extended to calculate steamflood producer WHT from BHT (both are time-dependent) by approximating WHT and monthly average of FLT measurements to a steady state solution consecutively. The monthly averaged FLTs are seasonally variable and higher in the summer months of July to September and lower in the winter months of December to February. Both WHTs (if measured) and monthly averaged FLT measurements depend on an annual ambient temperature cycle within the depth needed for reaching undisturbed ground temperature (typically 30-50 ft, Gwadera, Larwa and Kupiec, 2017). WHT prediction, however, are only process dependent and not seasonally variable due to the inability in describing seasonally undisturbed depth in the geothermal gradient. Therefore, WHT prediction can be validated with the monthly average of measured summer month FLTs. BHTs in this analytical approach is predicted by Lauwerier's analytical model (1955) and improved by calibrating with the available reservoir simulation model or several years’ FLT measurements for steamflood response timing. A field case study for the South Belridge diatomite steamflood was investigated. WHT prediction is compared with FLT measurement for diagnosing and understanding the production performances such as water or steam premature breakthrough, interference by the waterflood on the steamflood boundary producers, as well as the FLT variation related to steam injection target rates. This diagnostic analysis approach combined with the Buckley-Leverett theory based displacement efficiency analysis, and injection pressure and rate signal, will help to develop an improved understanding of the displacement detail and form a decision base to optimize the production performance.