Locating faults from well testing analysis ○Ĭonsequently, the areal sweep efficiency is traditionally regarded as the unknown in reservoir-development studies. In terms of the areal heterogeneity, however, uncertainties exist in defining this heterogeneity since methods used are indirect, e.g.: ○ Therefore, if the data are interpreted correctly, it should be possible to quantify the vertical sweep “ E V” quite accurately. Logging and coring appraisal wells will all permit direct observation of vertical heterogeneity. h, k, φ, S wc ○īoundary conditions due to the presence of an aquifer or gas cap. ○Īreal heterogeneity includes areal variation in formation properties and geometrical factors such as: ○ Although a flood will generally continue beyond breakthrough, the economic limit is often reached at an earlier time. Consequently, at the time of the injected water breakthrough in higher-permeability zones, a significant portion of the less-permeable zones will remain unflooded. When water injected into a stratified system, the injected water will preferentially enter layers with the highest permeabilities and will move at a higher velocity. This stratification can result from many factors such as change in depositional environment or change in depositional source. A reservoir may exhibit many different layers in the vertical section that have highly different rock properties. Vertical heterogeneity is considered by far the most significant parameter influencing the vertical sweep and in particular its degree of heterogeneity variation in the vertical direction. The most important two types of heterogeneity affecting sweep efficiencies are the reservoir vertical heterogeneity and areal heterogeneity. (Permission to publish by the Society of Petroleum Engineers) Values of W i/W ibt at which E A = 100 percent Values of W i/W iBT at which E A = 100 percent A comparison of the areal sweep efficiency and the ratio d/a is shown in Figure 4.7 for direct and staggered line drives, and a review of the early work was provided by Crawford. From a mathematical study the breakthrough sweep efficiency of the staggered line drive was presented by Prats. The effect of sweep-out beyond the pattern area was studied as well.
, Caudle and Witte, and Haberman (5-spot) and Kimbler, Caudle, and Cooper (9-spot). Experimental studies on the effect of mobility ratio for different patterns were presented by Dyes, Caudle, and Erickson (5-spot and line drives) Craig, Geffen, and Morse, Prats et al. In the early work on sweep efficiency and injectivity, Muskat and coworkers presented analytical solutions for direct line drive, staggered line drive, 5-spot, 7-spot, and 9-spot patterns. Areal sweep efficiency of an oil recovery process depends primarily on two factors: the flooding pattern and the mobilities of the fluids in the reservoir.