Three-dimensional studies of in situ combustion - Horizontal wells processwith reservoir heterogeneities

The effect of reservoir heterogeneity on the stability, sweep, and fluids p roduction during in situ combustion of medium heavy West of Shetlands Clair oil has been investigated in a three-dimensional combustion cell. The expe rimental conditions simulated a post-waterflood state, and the process of a ir injection involved a producer well arrangement, such that the combustion front propagation and hence displacement of oil occurred in a toe-to-heel manner. This is called the "Toe-to-Heel"-Horizontal Wells Process (THHW). F ive experiments were conducted, using two base homogeneous sandpacks. The : heterogeneous sandpacks involved two dual permeability layers, one with the higher permeability in the top layer and the other with the higher permeab ility layer in the bottom layer. The third heterogeneity type was a central high permeability streak layer, :sandwiched between two homogenous sand la yers. The results show that the steam and combustion gases downstream of the comb ustion front tend to channel through the high permeability layer causing so me measure of gas overide This effect is less exaggerated when the high per meability layer is at the bottom of the sandpack. The presence of a high pe rmeability streak layer promotes the channelling and bypassing of the injec ted air around the combustion front. In all cases, stability was enhanced b y the gravity assist mechanism created by the drawdown of steam and combust ion gases into the exposed section of the horizontal producer well, ahead o f the combustion front. The increased stability and control achieved by the THHW process enabled the propagation of the combustion front to be sustain ed. Very high oil recoveries were achieved, except for the case involving t he high permeability streak layer.