The Characterization Method Of Liquid Level During Steam Assisted Gravity Drainage Process With Dual Horizontal Wells In Oil Sands

As conventional oil development has come to its later period and could no longer meet the increasing demand for energy,unconventional oil resources such as heavy oil/oil sands has been paid more and more attention.The technology of steam assisted gravity drainage(SAGD)with two horizontal wells has gained its popularity for the development of heavy oil reservoirs and oil sands.Although it has achieved initial success both in the domestic and overseas,neither the movement of the liquid level between two horizontal wells nor the theoretical research for the prediction of SAGD development have been fully explored.Consequently,the popularization and application of SAGD technology are restricted.In order to solve these problems,combining with physical simulation,reservoir engineering method,thermo-mechanical analysis and numerical calculation,the movement mechanism of liquid level during SAGD process is investigated.Besides,a multi-stage theoretical model to characterize the liquid level is built for SAGD development with dual horizontal wells.And based on this model,strategies for liquid level adjustment are offered considering different conditions.Firstly according to the results from a 2D experiment for SAGD with dual horizontal wells,features of the production and steam chamber expansion during SAGD process are investigated.On the basis of these features,three development stages(namely rising stage,lateral expansion stage and downward stage)are divided.In addition,the movement characteristics of the liquid level between injector and producer indicate its dimensionless performance.In order to build a model to characterize the moving mechanisms of liquid level between injector and producer during SAGD process,the relationship among the height of liquid level,subcool and the pressure difference between two wells is built by theoretical calculation and statistical method with numerical simulation,respectively.Combining with the heat loss model and geometry features of steam chamber,mass conservation,energy conservation and gravity drainage theory are applied to build a multi-stage theoretical model for liquid level characterization during SAGD process in this paper.The new model is verified against both field data and CMG simulations,results show a high accuracy.Based on this model,optimal production-injection ratio at different time could be calculated to remain a stable liquid level above producer,which is able to prevent steam channeling.Besides,optimal steam injection rate is predicted for constant-pressure injection.Other SAGD performance data,such as steam chamber expansion speed,could also be derived from this model.In addition,suggestions for PIR adjustment are offered considering field conditions and this model is also able to conduct various works such as parametric sensitivity analysis.