Enhanced oil recovery from a vertically-stacked layered reservoir with lateral wells completed in the layers is often challenging due to inadequate understanding of the complex dynamics of the displacement process. A mobility ratio, which considers reservoir layers, well design and fluid properties, is derived to search for stability condition in the displacement process. Fluid displacement in real time is considered.
Displacement stability is monitored using mobility ratio derived from pressure distribution for each lateral well completed in each layer of the reservoir, and the enlarged single reservoir. Any well can be used for injection, depending on displacement and injection fluid type. Crossflow interface is assumed as responsible for communication between the layers. A computer program is written to compute mobility ratios in real injection time. Fluid injection time at which mobility ratio is greater than unity and as high as 10 is identified for any well design, layers, and injection fluid properties.
Complete individual layers dimensionless pressure characterization, using layers interface conditions, gives an expression for mobility ratio of interlayer displacement process involving lateral wells. Depending on the nature of injected fluid and overall recovery objectives, any of the layers can be selected for injection or production. Basal waterflooding and gas cycling and crestal gas injection can be studied directly using the expression derived for mobility ratio. The ratio derived gives indication of the duration of optimum clean oil production for any combination of fluid injected. The mobility ratio is affected by individual layer well design, layers fluids and injected fluid breakthrough time. Ratios of well lengths affect length of time of oil production. Longer oil production is possible if the wells have unequal lengths. If the top layer permeability is larger than the bottom layer permeability, waterflooding yields prolonged oil production. Viscosity ratios only slightly affect stability. However, if the bottom layer is used for injection, gas injection for gas cycling, gives appreciable results. Water-free oil production increases as the spacing between the layer wells increases. But well spacing beyond a certain limit does not contribute to further increment in oil production.