Reinjection zones

Waste gas from produced hydrocarbons can be safely disposed by reinjecting into a formation. The waste gas is mixed with a surfactant to form a foam that, in turn, is placed within a disposal zone of a subterranean formation. The waste gas is trapped within the foam, thereby reducing the mobility of the gas in the formation, which, in turn, restricts the ability of the waste gas to readily flow out of the disposal zone and into the producing zone of the formation. The waste gas foam can be placed into the formation by coinjecting the surfactant and the waste gas, or it can be formed in situ by first injecting the surfactant and then injecting the waste gas [1356]. 

The following design example of an injection and extraction system (Figure 18.7) illustrates the bioremediation process. Both the soil and groundwater are contaminated. Groundwater is extracted downgradient and reinjected upgradient of the zone of contamination. Water is also injected to flush... 

Backflushing of injected wastes can also be a good way to observe waste/reservoir geochemical interactions. Injected wastes are allowed to backflow (if formation pressure is above the elevation of the wellhead) or are pumped to the surface. Backflowed wastes are sampled periodically (and reinjected when the test is completed) the last sample taken will have had the longest residence time in the injection zone. Keely165 and Keely and Wolf166 describe this technique for characterizing... 

A recirculation system extracts contaminated groundwater from the site, adds to or amends the extracted water ex situ, and reinjects the activated water to the subsurface, generally upgradient of the contaminated zone. As an alternative, extraction and injection are performed at different elevations in a single well, creating vertical circulation. A groundwater recirculation configuration may be used to provide containment of a plume or to allow the addition of amendments in a more controlled environment. 

The use of extraction cartridges in the separation of azines, discussed in the last Section, is an example of on-column concentration using off-line column switching. A chromatogram can be cut off-line by collecting the zones of interest at the detector outlet followed by reinjection of the collected fraction onto a secondary column. The mobile phases used with the two columns should be compatible, eg they should be miscible and the mobile phase used with the first column should not have too high an eluting power in the second column. If the mobile phases are incompatible it may be possible to evaporate the primary mobile phase and redissolve the sample in a suitable solvent. 

FIGURE 5.1 Heart-cut 2DLC where a zone from the first-dimension separation is reinjected onto a second-dimension column for improved resolution of three analytes coeluting on the... 

In the heart-cutting mode of operation, one or several discrete zones are collected from the first-dimension column and reinjected into the second-dimension separation system. The resulting data are one or more individual one-dimensional datasets and are useful for resolving fused peaks from specific region(s) of the fust-dimension separation system. An example of zone reinjection is shown in Fig. 5.1 clearly, the second column provides the selectivity for the three peaks that the first column did not have. 

Coproduced groundwater can be reinjected within, above, or below the LNAPL zone depending on subsurface conditions, LNAPL occurrence and removal strategies, and site-specific constraints. These options and their respective advantages and limitations are discussed below. 

In summary, when undertaking a project such as the recovery of LNAPL, treatment of the coproduced water, prior to reinjection, may not be beneficial or technically necessary. A large percentage of the spilled or leaked petroleum hydrocarbon (40 to 60%) will be retained in the unsaturated zone as residual saturation. This residual hydrocarbon cannot be recovered by conventional withdrawal techniques. Without removing this continual source of contamination to the groundwater system, dissolved contamination will continue. Therefore, in most cases, it may be pointless and extremely costly to treat the coproduced groundwater prior to reinjection while the free- and residual-phase hydrocarbon contamination exists. 

Aerobic treatment of aquifer oxygen is usually supphed by one of three methods direct air sparging of air or oxygen into wells screened below the contaminated zone, saturation of water with air or oxygen prior to reinjection, or addition of an oxidant (typically a peroxide compound) directly into an injection well or injection water. Regardless of the mechanism of introduction, the important factor is that the oxidant is distributed throughout the contaminated zone at a concentration and rate such that it can be utilized by the microorganisms. 

For over a decade, LNAPL occurrence has been investigated beneath an active refinery site in southern California. Numerous monitoring wells along with LNAPL samples have been used to evaluate the extent and character of LNAPL occurrence. LNAPL was found to occur as five pools. The main pools each consist of individual accumulations of distinct product types occurring under both perched and water table conditions. Two different recovery and mitigation strategies have been utilized. In relatively high permeability zones, a system of two-pump recovery wells was used to recover fluids recovered water is reinjected without treatment. In relatively low permeability zones, a system of one-pump recovery wells was used. In the latter case, recovered water is treated prior to disposal. 

Two of the larger LNAPL hydrocarbon occurrences, site No. 1 and 4 (see Ligure 12.23), formerly reinjected coproduced groundwater into generally the same hydros-tratigraphic zone from which it is withdrawn site No. 1 reinjected without treatment into the Gage aquifer, whereas site No. 4 reinjected into the Old Dune Sand aquifer. Because of the presence of dissolved hydrocarbons, notably benzene, in the coproduced water that is typically returned to the aquifer during LNAPL recovery operations, immediate application of the EPA toxicity characteristic rule may result in classification of the reinjected water as disposal of a hazardous waste. This, in turn, would terminate use of UIC Class V wells (which many of these operations currently... 

Most of Bahrain s oil wells produce from different zones, and production from each zone is not segregated. Compatibility of reinjection water with the disposal strata cannot be guaranteed. 

Recycling A chromatographic process in which a fraction of the mixed zone is reinjected on-line, without intermediate collection and pooling. See Chapter 18, Section 18.5. Recently, recycling has been generalized to include various procedures of rechromatography of collected fractions. 

The results obtained by the most simple recycling procedure shown in Fig. 4.6.4 are undermined by the contamination and reinjection of the sample, and by the excessive zone broadening within the pump. The above effects can be suppressed by the recycling procedure based upon the alternate elution of the eluate through two columns by means of an extra valve. The effluent does not flow through the pump (24). 

Figure 2.18. Gradient dilution is based on selecting readouts at the tail of the dispersed sample zone (right-hand side of left curve), where elements of fluid can be located within which the sample material has been diluted by the disperson process. The selection may be mechanical, that is, the zone is selected via the delay time, captured by means of a second valve, and then reinjected into a second FIA system. Electronic dilution is achieved by means of a microprocessor, by selecting via the delay time a detector readout from which a calibration curve is constructed (middle curves). The peaks, recorded with four different concentrations of analyte (labeled 25%, 50%, 75%, and 100%) were sliced at different delay limes yielding readouts from which calibration curves of different slopes were recorded (right curves).

Clotworthy, A. 2000. Reinjection into low temperature loss zone. In Proc. World Geoth. Cong. 2000, Kyushu-Tohoku, 28 May-10 June 2000 pp. 2063 - 2067. 

Recirculating bed media are fed hot into the primary bed zone at a ratio of 50 to 100 times the coal feed rate. Various types of reinjection, nonmechanical valves and seals are used, such as seal pots, L-valves, J-valves, and others. These are simple refractory lined ducts having solids holding volumes that provide a loop seal, and appropriate aeration nozzles that induce and control solids flow. Cyclones are normally used to separate recirculating solids from the over-... 

The Dos Cuadras field has two limits which confine the operation of the wells. First, the wells have maximum pressure limitations of 200 and 400 psi (1380 and 2760 kPa), for the EP and FP zones, respectively. Second, produced water must be reinjected. Since polymer injection will lower the injectivity, injection rates will drop after the pressure limit is reached. Most of the injectors were successfully acidized to boost injectivity prior to polymer injection. After initiation of polymer, total Injection rates were similar to the pre-acid rates, maintaining injectivity. For those wells showing a drastic loss in injectivity, additional stimulation is warranted since water disposal is a requirement for operation. When Platform "A" was first started up with polymer, drastic declines in the injectivity occurred. To continue polymer Injection subject to the operating constraints, a sheared polymer fluid with improved injectivity was tested. 

From the beginning of the project, the average injection rate of polymer solution was kept dose to 420 m3/day. The cumulative volume of solution injected has been nearly equal to the cumulative volume of oil and water produced from wells located in the enhanced oil recovery zone (fig. 4 and 5). The polymer was diluted in treated field water. Produced formation water was separated from the oil and the sediments (shale particles) under anaerobic conditions and formaldehyde was added at an active concentration of 300 ppm to kill the bacteria. The water was then distributed to the polymer-mixing stations (fig. 6). The polymer was supplied in a water-oil emulsion form containing 30% active polymer dissolved in water. Because the continuous phase is oil, an inverter was added to the water before mixing. The polymer solution was then filtered through 10 micron screens before reinjection into the formation. 

---