Infill drilling is a common approach to improve oil recovery in the Permian Basin. The economical success of such projects depends on the guessed reservoir characterization. In this paper, the impact of infill drilling locations on oil recovery is discussed. The major characteristic of this study compared to previous work is the reservoir description used to select the infill locations. The reservoir was totally characterized by using an automatic history matching algorithm that solves an inverse problem using the simulated annealing method (SAM). The major advantages of this approach are:

  1. it can estimate a large number of reservoir parameters and

  2. it is able to integrate various disciplines, such as geology, petrophysics, and reservoir engineering.

The parameters estimated from a recent study for the pilot area of the East Vacuum Grayburg San Andres Unit (EVGSAU) were discussed for designing infill and waterflood projects.

The oil saturation map obtained at the end of waterflood period helped in locating interwell areas with a high saturation of mobile, unswept oil as potential infill drilling locations. By combining the oil saturation map with other parameters estimated by the inverse model, isolated infill locations were suggested in the pilot area. The incremental oil recovery of various schemes of infill and waterflood are compared. It appears that infill drilling locations selected with scientific criteria do improve the oil recovery of a very heterogeneous reservoir.


For carbonate reservoirs such as the ones located in the Permian Basin (West Texas and New Mexico), obtaining a reservoir description for simulation is challenging because of the heterogeneous nature of the reservoirs and the scarcity of available field and laboratory data. On the other hand, the more a reservoir deviates from ideal behavior, which is normally the result of heterogeneity, the greater the opportunity for incremental recovery by infill drilling. However, implementing an infill drilling project without a careful reservoir description may lead to an economic failure. Permian carbonate reservoirs are stratified and have areal discontinuities. Thus, heterogeneity causes the primary and secondary production to reach the economic limit at unexpectedly early times. To accelerate production or to produce incremental oil, a reliable reservoir description is required. The importance of reservoir description in infill drilling projects has been discussed and stressed by previous authors. Today, it is commonly accepted that the success of any infill and/or waterflood projects depends entirely on the reservoir description.

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