Infill Drilling as Related to kh Contrast Between Injectors Producers

Infill drilling in conjunction with waterflooding is being used to accelerate production and improve recovery efficiency. Many authors have discussed the reasons for infill drilling and the factors which affect the success of an infill drilling project.I,2,3,4,5,6 Reservoirs are heterogeneous rather than homogeneous. Van Everdingen1 related this to spacing and infill drilling. He noted that the East Texas field has been developed on a five-acre spacing. Recovery in this field with close spacing will be about 87% whereas other fields usually average 30%. He studied a number of fields, both carbonates and sandstones, and noted that recovery efficiencies improved as acre-spacings decreased. Barber et al2 discussed the carbonates in West Texas. They reported that the reservoirs were found to be more discontinuous than originally thought as more wells were drilled. In the Fullerton Clearfork Unit infill wells were drilled and some producers were converted to injectors. The infill wells produced higher rates with lower water cuts than the offset wells. This was interpreted as additional pay being opened up with some of the pay not having been flooded. Thus, infill drilling increased reservoir continuity which they defined as the percentage of pay that is continuous from one well to the next. Driscoll3 reported on the factors affecting increased recovery after an infill drilling project. The one which ties in with our study is minimizing lateral discontinuities. Often a producing section will contain many pay zones which are vertically separated. In addition, these zones are often not continuous in a lateral direction. Closer spacing increases the percent of continuous pay.The discontinuities are particularly evident in carbonates. This is also evidenced by the waterflood pattern used with a reservoir. Ghauri et al note that in the West Texas Denver Unit initially a peripheral injection was used. However, because of the discontinuous zones, much of the reservoir was not being flooded. According to Stiles5 there are three requirements for a pay zone to be successfully waterflooded: a) Continuous and homogeneous between injector and producer b) Injection supported c) Effectively completed in offset producer. Obviously, discontinuous zones will have some difficulty meeting the first and third requirements. George and Stiles reported on the Robertson, Fullerton and Means fields They noted that these fields have many porosity stringers over several hundred feet of thickness. Some of these stringers are continuous over several thousand feet while others extend only a few feet. Rarely does one stringer cover the entire field. In addition, thicker formations such as these are more apt to have several permeable layers.