Using transient temperature analysis to evaluate steam circulation in SAGD start-up processes

摘要

Steam circulation in SAGD start-up processes has significant impacts on the whole SAGD process. The start-up aims to heat the fluid sufficiently to improve oil mobility to establish communication between the injector and the producer. An efficient and economic approach is needed by the industry to identify the communication between the well-pair and to minimize the steam-circulation period. Knowing the hot-zone size and shape distribution formed by steam circulation along the horizontal wellbore can also help better understand the start-up process and obtain a long-term SAGD performance. This paper proposes a new technique called Transient Temperature Analysis (TTA) to estimate the hot-zone size and shape by interpreting the temperature falloff data in the injector and the producer obtained from fiber optics after the wells are shut in. Both forward and inverse mathematical models are presented to facilitate the application of this technique. Three forward mathematic models, two-system model with a hot-zone and a cold-zone, three-system model with an additional transition zone, and superposition of multiple two-systems model for irregular hot-zone shape were developed to model the temperature falloff. An inverse model is proposed to automatically interpret the hot-zone size through matching the temperature falloff. Sensitivity analysis shows that the hot-zone size and shape and observing location strongly affect the temperature falloff behaviors. Synthetic case studies suggest that the proposed models can be used to identify the hot-zone size and shape around the producer and the injector, and then to identify whether those hot-zones have established communication. Because of the ready-to-use temperature data and the semi-analytic solutions presented in this paper, the TTA technology can provide fast and economical estimation of the hot-zone size.