Recovery mechanisms

As reservoir pressure is reduced by oil production, additional recovery mechanisms may operate. One such mechanism is natural water drive. Water from an adjacent more highly pressured formation is forced into the oil-bearing formation by the pressure differential between the formations. Another mechanism is gas drive. Expansion of a gas cap above the oil as oil pressure declines can also drive additional oil to the wellbore. Produced gas may be reinjected to maintain gas cap pressure as is done on the Alaskan North Slope. Additional oil may also be produced by compaction of the reservoir rock as oil production reduces reservoir pressure. 

The project began with an extensive evaluation of 900 reported incidents involving failures of fixed pipework on chemical and major hazard plant. As part of the analysis a failure classification scheme was developed which considered the chief causes of failures, the possible prevention or recovery mechanism that could have prevented the failure and the underlying cause. The classification scheme is summarized in Figure 2.13. A typical event classification would be... 

As suggested above, the main recovery mechanism of surfactants retained in the rock can be interpreted as a micellization phenomenon inside the pores. Upon contact with micelles from the desorbent agent, the adsorbed surfactants are solubilized in the form of mixed micelles. This also explains the effectiveness of the desorbent still observed at low concentration (0.27% in Test 3 in Table in, concentration much higher than the CMC of NP 30 EO equal to 0.016%). 

RECOVERY MECHANISMS. Being surface active, TFSAs lower oil-water inter facial tension, but not by the three orders of magnitude needed to increase the capillary number sufficiently to recover a substantial amount of incremental oil. Instead, TFSAs enhance the recovery of oil by changing the wettability of reservoir rock surfaces from oil-wet and intermediate wettability to strongly water-wet, and by coalescing emulsions in the near-wellbore region of the production wells. 

An alternative gas for ECBM is N2, which has a different enhanced recovery mechanism from C02. N2 is less sorptive than methane, with a sorptive capacity roughly 40% that of methane for high volatile bituminous B coal (Fig. 1). The N2 process works by reducing the partial pressure of methane in the secondary system, increasing the rate of desorption from the primary system, and the rate of methane diffusion through the primary system. Some N2 sorbs into the primary system but the majority remains in the secondary system. N2 also increases the... 

Hydrophobicity loss and recovery in silicone rubbers has been extensively studied and reviewed in a few recent publications with numerous references.581,582 The ability to recover hydrophobicity after oxidation or contamination is considered as one of the important features determining the applicability of silicones in electrical and other outdoor insulation. The methods of studying of what is known as aging and recovery mechanisms are discussed. 

Nutritional status can also influence the toxic potency of carbon tetrachloride. Animal studies have clearly demonstrated that brief fasting or consumption of diets low in antioxidants (vitamin E, selenium, methionine) can lead to increased carbon tetrachloride hepatotoxicity. The same may be true for humans, although this is not known for certain. Another aspect of nutritional status affecting carbon tetrachloride toxicity is hepatic energy status. Hepatic ATP levels might influence the ultimate outcome of toxicity (low levels may inhibit recovery mechanisms). 

The guideword process can be supplemented by additional topics/questions based on an analysis of previously experienced design deficiencies and operational incidents. For instance, ICI has collated a database of over 350 operational incidents that it uses to refine its CHAZOP Study process. Some example questions for the CHAZOP Study are given in Appendix 8E at the end of this chapter. Of particular interest to the study is the effect of partial or catastrophic failures, recovery mechanisms (e.g., rollback and roll-forward), and the general usability of the system (e.g., the need for multiple screens to access data, screen refresh times, meaningful information displays). The list of questions can be expanded with operational and regulatory experience. 

It is apparent that the addition of the mobility control agent did not affect the miscibility process, as evidenced by the comparable oil recovery to that of the no mobility control case. At the same time the mobility of carbon dioxide was decreased more than twenty-fold. This important flnding demonstrates that the mobility control method produces effective mobility control without adversely affecting the miscible recovery mechanism. 

In the reservoir imder consideration the energy available for expulsion of oil and gas comes entirely from the evolution of solution gas on pressure reduction. Consequently, this type of reservoir is designated as a solution gas drive reservoir to distinguish it from those whose recovery mechanisms involve energy from the expansion of a gas cap (gas expansion reservoirs) or from the encroachment of water (water drive reservoirs). The behavior of a solution gas drive reservoir may be predicted if the following data are available (1) the original reservoir pressure and temperature (2) values of r, and v as a fimction of pressure (3) values of the reservoir fluid viscosities r as a function of pressure at reservoir temperature (4) the constant water saturation 8w) (5) values of Kg/Ko as a fimction of saturation and (6) the number of barrels of stock tank oil originally in reservoir (iV). The computations are carried out stepwise as shown below. 

O Brien TJ, Ceryak S, Patierno SR. Complexities of chromium carcmogenesis Role of cellular response, repair and recovery mechanisms. Mutat Res 2003 533 3-36. 

Gas injection can also recover oil by reducing oil viscosity and residual oil saturation, even when miscibility is not achieved. Reduction in viscosity is more significant if the oil viscosity is large, and this process is attractive in viscous or semiviscous reservoirs, especially when accompanied by some other improved recovery mechanism. Residual oil saturation in three-phase flow in water-wet rock is very low (essentially zero), even at very low capillary numbers. Two main problems in such a process are the low relative permeabilities and sweep efficiencies. This process can be implemented in a highly dipping reservoir to take... 

The procurement agency should be able to effect national and international financial transactions as required. Funds must be available to ensure continued operations, whether or not cost recovery mechanisms for key activities,... 

Injected alkaline concentration and volume appear to vary depending on the recovery mechanism involved. Concentrations are generally lowest for emulsification mechanisms, from about 0.001 to 0.500 wt.%. Higher concentrations ranging from about 0.5 to 3.0 wt.% or even as high as 15.0 wt.% usually have been required for wettability reversal. Generally, a slug of alkaline solution can... 

The recovery mechanisms associated with alkahne-surfactant flooding may be summarized as follows ... 

Bourdarot, G., Sardin, M., Putz, A., 1984. Chateaurenard fleld test recovery mechanisms and interpretation. Paper SPE 12685 presented at the SPE Enhanced Oil Recovery Symposium, Tulsa, 15-18 April. 

Castor, T.P., Somerton, W.H., Kelly, J.E, 1981b. Recovery mechanisms of alkaline flooding. In Shah, D.O. (Ed.), Surface Phenomena in Enhanced Oil Recovery. Plenum, pp. 249—291. 

Pusch, G., Lotsch, T, Muller, T, 1987. Investigation of the oil displacing efficiency of suitable polymer products in porous media, aspects of recovery mechanisms during polymer flooding. DGMK—Report, German Society Petrol. Sci. Coal Chem., 295-296, Hamburg. 

Yang, P.-H., et al., 1992. Oil recovery mechanisms of alkaline/polymer flooding. Paper presented at the Second and Tertiary Recovery Symposium, Chengdu. 

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