Early in the life of a well, the natural pressure in the reservoir is great enough to overcome gravity and to push fluids to the well and up the well to the surface. Artificial LiftĪrtificial lift was discussed briefly and is defined as an IOR technology used to ”lift” reservoir fluids once they enter the well. Matrix acidizing is typically used in sandstone and carbonate reservoirs while acid-fracturing is used in carbonate reservoirs which are susceptible to breakdown by acid. Several variations of the acidizing process are used to stimulate a well including: matrix acidizing where the acid solution is pumped into the reservoir below the fracture pressure (or parting pressure) to clean pores near the well and acid-fracturing where an acidic fracturing fluid is injected above the fracture pressure in order to simultaneously fracture the reservoir and dissolve the formation (creating flow channels linking the rock to the fracture). These residual drilling fluids may impair fluid flow to the well. AcidizingĪcidizing is a well technology that uses the injection of an acid solution into a porous reservoir to dissolve any residual drilling fluids or natural sediments in the well perforations and the near-well vicinity. Hydraulic fracturing can be applied to most rock lithologies, including sandstones, carbonates (limestones and dolomites), coals, and shales. Injection of the fracturing fluid is normally followed by the injection of a proppant slurry, composed of natural sand or man-made ceramic beads, used to prop-open the induced fractures once pressure is relieved after the well stimulation treatment. Hydraulic fracturing, or frac’ing, refers to the high-pressure injection of a fracturing fluid, typically water (slickwater), gas, or gel, into a reservoir causing the rock to mechanically fail or fracture. The two most common well stimulation methods are hydraulic fracturing and acidizing. Well stimulation is an IOR technology that is used to clean well perforations and improve the flow capacity of the reservoir rock in the near-well vicinity. Source: Based on Sadegh Elyasi: " Assessment and evaluation of degree of multilateral well’s performance for determination of their role in oil recovery at a fractured reservoir in Iran,” Egyptian Journal of Petroleum, January 2016 Well Stimulation As discussed earlier, the design and execution of these complex wells is the task of the drilling engineer. Figure 1.08 shows some of the more advanced well designs used in the current Reservoir Management. This definition of IOR allows for the use of additional vertical wells for greater well coverage (infill drilling) than considered in the initial development plan or the use of more complex well designs to improve well performance from a single surface location. This definition of IOR encompasses a wide variety of production technologies including additional vertical wells (infill drilling) or complex well designs (deviated, or slanted, wells horizontal, or single-lateral, wells multi-lateral wells), well stimulation (hydraulic fracturing and acidizing), artificial lift (beam pumps, ESPs, and gas lift), secondary recovery methods (waterflooding and gas flooding), and EOR (thermal recovery, miscible displacement, and chemical flooding). This baseline represents the simplest production technology available to the petroleum and natural gas engineer and was a common development option up to the 1960s – 1970s and often resulted in recovery efficiencies of less than ten percent. IOR is defined as any recovery method used to improve oil recovery above the use of non-stimulated, naturally-flowing vertical production wells (Please note that with this definition, each reservoir will have a different baseline because each reservoir will respond differently to the application of these wells). Improved Oil Recovery (IOR) and Enhanced Oil Recovery (EOR) Methods are methods used to target the resources not capable of being produced with conventional production methods.
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