Development of Effective Numerical Model for Heavy Oil Production Using Steam-Assisted Gravity Drainage

摘要

One of the modern technologies for heavy oil and bitumen recovery is SAGD (Steam Assisted Gravity Drainage), which use two horizontal wells, one above the other with spacing 5-10m. Upper well is used for steam injection and creating the high- temperature steam chamber (SC). On the SC boundary the steam is condensing and water together with the heated oil flow downward into production well. Pressure and temperature (P/T) measurements in injection and production well are used to control production process. This data contains only indirect information about the steam chamber parameters and oil inflow profile along the well length, therefore various mathematical models should be used to interpret measurement results. P/T measurements interpretation, optimization of steam injection regime and analysis of reservoir heterogeneity influence on SAGD parameters are commonly performed on 3D models, which need tremendous computational resources and provide results within an inapplicable time (several days and even weeks) for field usage. Present work is devoted to development of the effective SAGD numerical model. It is based on the well admitted in literature assumption, that horizontal steam flow along the injection well prevail over the horizontal steam flow along the reservoir. Thus 3D simulation can be substituted for by the 1D simulations for the injector/producer connected with N 2D cross section reservoir models which are connected only through injection and production boreholes (an example is in paper4). Injection well model provides steam pressure/temperature profiles for 2D cross section models. In turn these models calculate profile of steam injection rate which is an input data for injection well model. Developed 1D + N*2D SAGD model can be used for fast SAGD simulation and for injectivity profile inversion from P/T data recorded in injection well. 1D model of injection well with tubing inside the well for steam injection at the heel and/or at the toe was developed. It assumes two phase (water/vapor) flow with 'drift flux' and heat exchange between tubing and annulus flow. Nevertheless, analysis of field data recorded by DTS in injector shows that assumption of joint flow of the water and vapor along the injector, and hence simultaneous injection of the vapor and the water in reservoir can be violated in some cases. Modification of the 1D injection well model with separated distributed vapor/water injection in the reservoir was developed. Simulation results obtained obtained with modified model are able to reproduce qualitatively field data behavior.