A numerical simulation study was undertaken to determine the best completion scheme for the sidewell in an inverted nine-spot pattern Simulation results showed that completing the sidewell across the bottom 20% (1/5) of the target interval produces the largest cumulative oil at the lowest cumulative steam-oil ratio, This completion scheme was found to be best regardless of the pattern size (2.5 or 5.0 acres) and the initial reservoir temperature (90 or 200F).
If an intermediate shale lense is present in the sand, the oil addition-ally recovered by partially completing the sidewell over that fully completing it decreases with a decrease in vertical permeability of the shale lense, This results because the effects of steam override and gravity drainage diminish with decreasing vertical permeability.
Five-spot and inverted nine-spot patterns are commonly used in steamflooding. In the inverted nine-spot, the injector is closer to the side producer than the corner producer. If both producers are fully completed and the reservoir is a really homogeneous, steam breaks through to the sidewell first, delaying steam propagation toward the corner well. The result is that when a project reaches an economic limit, much oil remains unrecovered, especially in the lower part of the formation near the corner producer.
Intuitively, it is desirable to complete the sidewell only partly at the, bottom to delay steam breakthrough to the sidewell. This would promote steam propagation toward the cornerwell and improve steamflood promote steam propagation toward the cornerwell and improve steamflood conformance.
The effect of sidewell completion on steamflood Performance in inverted nine-spot patterns has received little systematic evaluation.
A previous simulation study indicated that converting a five-spot pattern to an inverted nine-spot by drilling infill Producers at the pattern to an inverted nine-spot by drilling infill Producers at the midpoints of the pattern boundaries increases and accelerates oil recovery. Partially completing the infill wells in the lower half of the drive zone was found to give higher oil recovery than that obtained by fully completing the sidewells. This study, however, did not consider the effect of sidewell completion on the performance of a steamflood pattern initially completed as an inverted nine-spot.
Because of the extensive use of inverted nine-spot patterns in steamflooding, this numerical simulation study was undertaken to determine the best sidewell completion scheme. This paper presents the results of the simulation study and discusses the advantages of completing the sidewell partially in an inverted nine-spot pattern when vertical permeability is not excessively low.
The reservoir model was an areal 7 × 4 grid system representing one-eighth of an inverted nine-spot pattern, as shown in Figure 1. Pattern areas of 2.5 and 5.0 acres were selected. For a 5-acre Pattern, Pattern areas of 2.5 and 5.0 acres were selected. For a 5-acre Pattern, the distance between the injector and producer is 330 ft. The area was divided into seven blocks in the x-direction, parallel to the line between the injector and producer, and four blocks in the y-direction. Apex cells at the three corners of the triangle were combined with blocks adjoining them, resulting in a total of 22 active blocks in each layer.
The reservoir with a gross thickness of 75 ft was divided equally into 5 communicating layers, each 15-ft thick. Steam was injected into the two bottom layers in all cases except the last two (to be noted later), in which the injector was fully completed. The corner producer was fully completed in all cases, while the sidewell producer was fully completed in all cases, while the sidewell completion was varied from bottom 1/5 to full 5/5.