In 1984, Texaco initiated a field test of multizone thermal recovery with dually completed injection wells. With a single tubing string and packer, a concentric injection arrangement was implemented. Hot water was injected down the tubing into a previously-steamflooded sand, While high quality steam was injected down the tubing casing annulus into an overlying active steamflood zone. While both floods have demonstrated favorable production behavior, the heat transfer between the tubing and annulus has had a major impact on the planned injection strategy, with indications that the "hot waterflood" has actually been a low to mid-quality steamflood for most of its project life. Furthermore, regional gravity drainage has unexpectedly been a dominant recovery mechanism in the lower zone, creating regions of distinct production characteristics within the project area.
This paper analyzes the field results from the first 2–1/2 years of the dual injection project and discusses the identified recovery mechanisms in addition to the heat transfer consequences of dual steam/hot water injection.
The Kern River Field is a 10,000 acre (4,000 ha), shallow, heavy-oil deposit located near Bakersfield, California. The reservoir is comprised of up to seven sand members that are separated by silt and clay interbeds.1 The structure of the field is a simple homocline dipping at 3–6 ° to the southwest. Oil sands are present at depths of 400–1400 feet (122–427 m). The unconsolidated sands have high permeabilities of 1 to 5 darcies and porosities of 28% to 33%. The produced oil gravities range from 9 ° to 16 ° API, and the corresponding viscosities also vary from 10,000 to 600 cp (10.0 to 0.6 Pa-S) at 100 °F (38 °C).2
Since heat effectively reduces the viscosity of the crude, thermal recovery operations have long played a major role in the development of the Kern River oil sands, with steamflooding the preferred process among the various operators. There have been numerous publications on steamflooding in Kern River 1–7, attesting to the success of the steamflood process.
More recently, there has been interest in following high-quality steam injection with low-quality steam or hot water.8–10 The major benefits of this practice include: 10 better vertical placement of heat, since the hot water will presumably underride into the cooler lower section of the sand not contacted by steam; and 20 scavenging of residual heat remaining in the formation rock. Given the success reported by Chevron of post-steamflood hot water injection in Kern River, Texaco in 1984 also began field testing this process.
The first project area for testing hot waterflooding as a post-steamflood recovery process was in District Project (DP) 1457, located on the Omar and Cordes properties near the center of the Kern River Field (Figure 1). This project began as an R1-sand steamflood in 1977 (Figure 2). In 1983, steam injection was terminated into the R1-sand and the injection wells were recompleted into the overlying R1-sand.