Thermal Transient Analysis Applied to Horizontal Wells

Abstract

Abstract The effectiveness of heat injection into a target formation has a great impact on the efficiency of bitumen and heavy oil recovery and energy savings under many steam heating processes such as the startup phase of SAGD (Steam Assisted Gravity Drainage) (Butler 1991). However, this parameter is hard to calculate due to many unknown variables such as variations in operational conditions and steam saturation along the horizontal wellbores, heat return rates, and losses to the vertical section above the target formation. This paper proposes a new technique to estimate cooling time and formation thermal diffusivity by using thermal transient analysis (TTA) along the horizontal wellbore under a steam heating process. A novel concept of a heating ring is also introduced to measure the heat storage in the heated bitumen at the time of testing. Heating ring can be considered analogous to a drainage area in a conventional pressure transient analysis. The proposed cooling time and formation thermal diffusivity calculated along the horizontal wellbore can be used to assess the effectiveness of the conduction heating. Cooling time in this paper is defined as the theoretical time required to cool the heated formation to the initial formation temperature. A longer cooling time indicates a higher net heat gain in the formation while the calculated thermal diffusivity is used to predict wellbore conditions and the type of fluid saturation along the horizontal wellbore. Thus, a combination of cooling time and formation thermal diffusivity can be employed to assess the effectiveness of heat injection during various steam heating processes. By knowing the effectiveness of each heating scenario, the process can be selected and optimized not only to save heat energy and steam consumption but also to enhance bitumen recovery. This paper is limited to the new heating operation processes. Introduction Knowing the heat influx distribution along a horizontal wellbore is crucial for determing the effectiveness of a heating process such as SAGD startup. However, direct estimates of the net heat influx in the target formation during startup are difficult to measure mainly due to the uncertainties in:–heat loss in the vertical section,–steam quality along the horizontal segment,–distribution of steam along the wellbore,–operational conditions, and–additional effects of convection heating.