Peripheral and Line-Drive Water-Injection Projects

Introduction The question of the pattern to be employed is one of the most important considerations necessary to the proper planning of a water-injection project. Before the decision can be made as to what type pattern should be employed, a thorough study of the reservoir parameters must be made. In some reservoirs, it is impractical to employ the five-spot pattern; in others, peripheral or line-drive patterns cannot be used. Table 1 lists the reservoir data on four waterflooding projects employed in peripheral and the line-drive waterflooding patterns. The results obtained from these projects to date indicate that high sweep efficiencies in water-injection projects can be obtained with a minimum of hazard. The Sojourner Peripheral Flood The Sojourner sand unit in Haskell County, Tex., is a waterflooding project which employs the complete peripheral waterflooding pattern (Fig. 1). This waterflooding unit has 57 wells drilled on irregular 40-acre spacing and is completed in the Strawn sand penetrated at approximately 5,100 ft. The average porosity and permeability for this sand are 14 per cent and 12 md, respectively, as determined from 35 complete core analyses. The peripheral pattern was recommended for this project primarily because of the irregular drilling pattern employed. Because of the depth and the waterflood reserves anticipated, it was impractical to employ in-fill drilling to design a workable five-spot or conventional water-injection pattern. Because of the low natural permeability, however, it was questionable if sufficient water could be injected into the sand to obtain the desired injection rate for an economical floodout time of the reservoir. From calculations using air permeability as a criterion, it originally was estimated that the maximum injection rate per well would be approximately 300 B/D at 1,800-lb surface injection pressure. A pilot water-injection program was initiated in Feb., 1956, into three water-input wells. Results of this pilot indicated that 600 to 900 B/D injection rates were permissable with 600-lb surface injection pressure.