Cyclic water injection: improved oil recovery at zero cost

Abstract

Cyclic injection is a process that improves waterflooding efficiency in heterogeneous reservoirs. The concept of cyclic injection is based on (1) pulsed injection and (2) alternating waterflood patterns. Cyclic injection has been successfully applied in a number of sandstone and carbonate oil fields in Russia. In the rest of the world, pulsed injection has had limited application, and only in naturally fractured reservoirs. Although changing the waterflood patterns is a common approach to deal with increasing water cuts, a more systematic approach with both pulsed injection and alternating flow directions is not.Cyclic injection has the greatest potential for improved recovery in heterogeneous, high-permeability-contrast sandstones and in naturally fractured carbonates and dolomites. The efficiency of the process is high in preferentially water-wet rocks saturated with compressible fluids. Capillary pressures and relative permeability effects are responsible for the improved cyclic oil displacement at the micro level. Improved sweep of the less permeable layers in communication with more permeable thief zones, better horizontal sweep achieved by changing waterflood patterns, and alternating the dominance between gravity and viscous forces are the key effects of cyclic injection on the macro level.The potential of cyclic injection at the Lower Tilje/Åre formations of the Heidrun Field in the Norwegian Sea has been evaluated. Some of the reservoir levels are highly heterogeneous, with large permeability contrasts vertically and horizontally. The current drainage strategy for these formations is water injection, with gas lift in producers when needed. Cyclic injection will improve waterflooding efficiency at virtually zero additional cost. Improved sweep, accelerated oil production, and reduced water cut are the main positive effects expected from cyclic waterflooding. The reserves are predicted to increase by 5 to 6% from the targeted reservoirs at Heidrun after 10 years of cyclic waterflooding.

Control of viscous fingering and mixing in miscible displacements with time‐dependent rates

“…Such injection rate with pulsed injection and alternating flow directions would result in noticeable differences in sweep efficiency and oil recovery in field scale and lab experiments, as well as in flow dynamics and mass transfer in miscible displacements, depending on the actual situations. There are many different types of time‐dependent displacement rates u ( t ), either in a sinusoidal or step‐size manner, or with hammer pulsing or bang–bang types . However, to easily identify the effect of different displacing stages, we adopt the step‐size injection/extraction rates as that in previous studies .…”

“…Moreover, a series of lab experiments with temporal variation of injection rate in vapor extraction (VAPEX) process showed that the oil recovery was improved by 19–60%, depending on the permeability of model . Other successful applications of the time‐dependent fluid injection rate were also reported . However, in other studies, the oil recovery with time‐dependent displacement rate is not apparently improved or even lower than that of constant injection rate .…”

Flow instabilities of time‐dependent injection schemes in immiscible displacements

“…Additionally, the injection rates are formulated in dimensionless form as expressed by Equations (16)(17)(18)(19)(20):…”

“…[19] From the experiments, high oil recovery rates were reported for injections characterized by shorter periods and large amplitudes. In particular, Surguchev et al used cyclic injection with water to enhance oil production.…”

Maximization of wave motion within a hydrocarbon reservoir for wave-based enhanced oil recovery

“…Similarly, in a fractured reservoir ( Fig. 1(b)), direct application of hydraulic wave sources to a fracture can induce a periodic pressure gradient between a fracture and the surrounding rock matrix, such that transport of the bypassed oil from the rock matrix into the fracture space can be enhanced (Groenenboom et al (2003); Jeong et al (2011); Owens and Archer (1966); Stirpe et al (2004); Surguchev et al (2002)). On the other hand, it has been suggested that the seismic waves increase permeability within hydrocarbon formations.…”