The Myths of Waterfloods, EOR Floods and How to Optimize Real Injection Schemes

Abstract

Waterflood implementation accounts for more than half of the oil production worldwide. Despite the observations and extensive research from a large number of floods and thousands of simulation studies, managing waterfloods and Enhanced Oil Recovery (EOR) floods is still a technical challenge. A major contributor to this challenge are waterflood induced fractures (WIF). Managing waterfloods is a multivariable problem although WIF are one aspect, it is by no means the only controlling factor.The best evidence that WIF are one of the main factors controlling flow in reservoirs is the insensitivity of injection pressure to injection rates. With our experience, in hundreds of waterfloods, we have frequently observed this phenomenon in the field data. If fluid flow depended on diffusive Darcy flow alone, we would expect higher injection rates with higher injection pressures. However, it is common to observed relatively constant injection pressures over a wide range of water injection rates. Rapid well communication and changes in water cuts that vary with injection rates also support an interpretation of high permeability induced fractures between injector and producer. In some reservoirs, interwell tracer data can be used to determine the influence of induced fracture features. The interwell tracers usually show very fast water movement.Induced fractures in waterfloods and EOR projects can be caused by a number of mechanisms such as but not limited to, pressure depletion, changing pressure regimes, thermal effects, or plugging effects. These fractures can either be beneficial to the reservoir performance or effect performance negatively. Benefits include improved injectivity and increased throughput of the displacing fluid. Negative effects can come in the form of reduced volumetric sweep efficiency, impaired ultimate recovery or injected fluid losses out of zone.Case studies, theory, and available literature from Western Canada will be reviewed in order to suggest and improve reservoir management strategies for waterfloods. We have completed hundreds of waterflood feasibility, waterflood management and EOR flood studies worldwide and continue to be amazed and humbled by the complexity that many waterfloods and EOR floods exhibit due to induced fracturing. WIF and EOR induced fractures (EIF) are common and should be analysed to optimize production. Growth of the WIF, response to waterflood with the presence of WIF, implication of WIF and reservoir management are the main areas which will be addressed.

Investigation on the pressure behavior of injectors influenced by waterflood-induced fractures: field cases in Huaqing reservoir, Changqing Oilfield, China

“…This long fracture continues to grow as the process of water injection, which can even reach several times of well spacing. The waterfloods in Western Canada [12] and Ordos basin in China validate this phenomena. This dynamic process is sketched in Figures 3c I and 3d I .…”

“…As the continuity of water injection, if the water injection rate into the fracture exceeds the rate flow from fracture to the matrix, the pressure in the fracture increases and then the fracture would continue to grow until the injection and leak-off rate balance again [12]. According to monitoring and analysis results in oilfields, two scenarios are given:…”

Influence of Heterogeneity and Fracture Conductivity on Supercritical CO2 Miscible Flooding Enhancing Oil Recovery and Gas Channeling in Tight Oil Reservoirs

“…Channeling and Oil Displacement. 3 permeability cores are shown in Figures 3 and 4. Figure 3 shows that, after 3.3 PV CO 2 displacement, the recovery degree of the low-permeability core (0.253 mD) and the highpermeability core (0.594 mD) can reach 50 and 59%, respectively, and the displacement efficiency of the highpermeability core is about 9% higher than that of the lowpermeability core.…”

“…According to the results of laboratory and field tests, gas injection is the most applicable enhanced oil recovery (EOR) method . Many scholars have evaluated the gas displacement method in tight reservoirs, and CO 2 injection seems the most feasible technique. − The Ordos Basin and Songliao Basin are the main producing areas of tight oil in China. − The results of core displacement experiments indicate that CO 2 flooding can improve the oil displacement efficiency by 24.3% compared to water flooding and is an important technology for efficient development of Chang 7 tight oil resources. At the same time, field tests show that CO 2 flooding is feasible and economical .…”

“…The results show that the oil recovery factor of CO 2 continuous injection is about 16–25%. ,,, In the past few years, there have been a number of pilot tests for gas injection in North America, including North Dakota and Montana in the United States and Saskatchewan in Canada; however, the pilot tests, in general, show early breakthrough times and relatively low productivity, and the exploitation was not expanded much. Thus, there is the gap between lab work conclusions and field test performance. ,, One reason for the fast breakthrough is that the injection process created induced fractures; thus, the fractured tight reservoir with natural or artificial fractures affects the field test results. In addition, reservoir heterogeneity also affects the sweep of injected gas.…”