Experimental and numerical studies of discontinuous shale effects on first-contact miscible water alternating gas injection

Most clastic reservoirs contain discontinuous shales that act as barriers or baffles to fluid flow and cannot be correlated between wells. To our knowledge, there are no published studies on the effect of discontinuous shales on first contact miscible water alternating gas processes and how they might alter the sweep efficiency. This work aims to remedy this deficiency. A series of well-characterized laboratory experiments in two-dimensional heterogeneous beadpacks were carried out. Simultaneous first contact miscible water alternating gas displacement experiments were performed in the porous media containing discontinuous shale. Simultaneous injection was conducted at water alternating gas ratios of 1:1, 4:1, and 1:4. All experiments were then modeled using an IMPES finite difference simulator without using history matching (all simulations used directly measured porous media properties as inputs) to quantify the accuracy of the simulation when modeling the first contact miscible water alternating gas displacements in a porous media with a discontinuous shale. Experiments and simulations have demonstrated that there is an optimal water alternating gas ratio, at which oil recovery is maximized. Additionally, the simulator predicted fairly the location of the bypassed oil, which was mainly downstream of the shale unit. However, a poor match was found between measured and predicted water and solvent cuts because in the simulation it is assumed that the injected water and gas flow simultaneously, whereas the experiments show that solvent and water prefer to flow in segregated paths rather than flowing simultaneously across the whole porous media, and that due to the segregate flow, water laterally blocks solvent from contacting the bypassed oil, which reduces first contact miscible water alternating gas efficiency.