Geomechanics Issues of Steam Assisted Gravity Drainage

Abstract

Abstract After successful testing and full scale implementation of the steam assisted gravity drainage (SAGD) process at AOSTRA's (now Department of Energy, Oil Sands and Research Division) Underground Test Facility (UTF), many operating companies are applying this recovery process (or variations thereof) in bitumen and heavy oil projects. The thermal SAGD process with adjacent sets of wellpairs provides a process geometry where the geomechanical response of an unconsolidated sand reservoir may have an impact on the efficiency of the recovery process. This paper describes a series of numerical analyses which illustrate how fluid pressure increases and thermal loading combine to create an optimum stress environment for shear failure of unconsolidated sand formations. Shear failure in dense unconsolidated sands results in a volumetric increase in sand pore volume due to dilation of the sand grains. To date, bitumen production rates for the SAGD process have been history matched for the UTF Phase A and Phase B tests by increasing the absolute permeability within the formation to a very high value; typically to the maximum value within a range of possible values. It will be shown that for the UTF geometry, absolute permeability increases resulting from dilation in advance of the growing steam chamber is likely a factor in the SAGD process. Due to the nature of SAGD, however, reservoir modelling for UTF scenarios are not be significantly effected since dilation in advance of the steam chamber would create the same "absolute permeability" effect as selecting an initially high absolute permeability value. For different reservoir conditions, such as stress conditions, or wellpair spacings then at the UTF, not including geomechanical phenomena in process simulations may adversely affect the results.