Viewpoint Of Balance Research Articles

Mechanism of Water Flooding in the Presence of Free Gas

Published in Petroleum Transactions, AIME, Volume 207, 1956, pages 215–221. Abstract Experimental studies covering a wide range of core materials and fluid properties have been conducted to determine the mechanism of oil displacement by water in a partially gas-saturated porous medium. In all instances, the presence of a gas phase was found to have a beneficial effect in reducing residual oil saturations. The practical significance of this benefit is discussed, and a simplified procedure is outlined for evaluating the effects of free gas on water flooding by means of short core tests. Introduction In addition to oil and water, reservoirs subjected to water flooding frequently contain, also, a gas phase. Common engineering procedures account for the presence of this "free gas" only from the viewpoint of volumetric balance, implying that the only role of the gas consists of providing "fill up" space. It is usually visualized that during the initial stages of the water invasion, the oil, moving ahead of the water, displaces part of the gas and that subsequently the remaining portion of the gas phase is totally compressed and dissolved in the advancing oil bank. Thus, consideration of a two-phase, water-oil flooding mechanism supplies an adequate basis for predictions of oil recovery if the pressure build-up caused by the flood is sufficiently great, so as to reduce the free gas saturation to a negligible value in any portion of the reservoir by the time that portion is reached by the advancing flood water. In many in stances, however, waterflooding operations are carried out when the reservoir pressure is still relatively high so that the pressure build-up associated with the water flood may not result in complete dissipation of the gas phase. Under such circumstances it is necessary to ascertain whether or not the presence of free gas has an effect on waterflood behavior and, if so, to account for any such effect in the evaluation of field operations.

ON THE MAINTENANCE OF ZONAL CIRCULATION IN THE ATMOSPHERE

The maintenance of a jet-type zonal circulation is discussed from the viewpoint of vorticity balance. Through skin friction, the atmosphere gains vorticity from the earth in the region of anticyclonic vorticity at the surface, and returns it to the earth in the region of cyclonic vorticity at the surface. There are two processes to carry out the vorticity transfer from low to high latitudes: meridional circulation and large, horizontal vortical systems. The efficiency of the two in compensating the frictional effect is about the same in low latitudes. In middle latitudes, the large, horizontal vortical systems are far more efficient. In high latitudes, the role of the mean circulation in maintaining the zonal circulation is negligible.

Gravity Drainage in Oil Fields

Abstract Gravity drainage is the self-propulsion of oil downward in the reservoir rock.Under favorable natural and operational conditions, it has been found to effectrecoveries comparable to water displacement. With modern technical knowledge, the operator can often make a choice between dissolved gas drive, water driveand gravity drainage as the principal recovery agent in a reservoir. It isdesirable that the operator be able to determine which of the three agents willbe most effective under each set of conditions. So far, gravity drainage hasreceived less consideration than the other two. In this paper an endeavor ismade to set forth some of the principles of gravity drainage, to point out thetypes of reservoirs favorable for it, and to show how it may be applied inthem. Field examples are described and discussed. Introduction Since early in the history of the oil industry, it has been recognized thatgravity is one of the three important natural forces for expelling oil from thereservoir rock. As knowledge of the technology of oil recovery progressed, ideas changed with respect to the relative importance of the three forces andwith respect to the manners in which they functioned. For a time, disproportionate emphasis was placed on the importance and function of gas andthe need for conserving gas pressures. More recently, disproportionate emphasishas been placed on encroaching edge water. Only lately has there been evidencethat the function and importance of gravity was to receive dueconsideration. Study of this 'neglected phase of oil recovery is needed to round out ourknowledge of reservoir behaviors and to gain a balanced viewpoint of theinterplay of forces that may operate in varying importance in reservoirs. Thepurpose of this paper is to discuss mainly in a qualitative way, the functionsof gravity, to present some concrete instances where it has been important andto raise some questions that should be investigated further. Oil-Recovery Agents The important natural agents for effecting oil recovery that may be originallyavailable in a reservoir are gas, both dissolved in the oil and free in gascaps, encroaching edge water and gravity. Each of these agents can act in adual capacity-physically to overcome the surface energies that hold the oilwithin the pores and mechanically to overcome viscous resistance and to propelthe oil through the porous reservoir 'rock to the wells. Advancing edge water displaces the oil from the pores and lifts it up dip tostructurally lower wells. Gravity drains the oil from the pores and flows itdown dip to the wells. Gas displaces oil from the pores, entrains it in the gasstream and flows it to the wells, but gas in solution also affects the physicalproperties of the oil and thus can influence oil recovery by the other agents, whether or not the mechanical energy in the gas is utilized. T.P. 1664

Thin Oxide Films on Iron

The degradation behavior of four prepassivated stainless steels (SSs) in the alkaline solutions with different Cl- concentrations and pH values were investigated by cyclic potentiodynamic polarization (CPP), electrochemical impedance spectroscopy (EIS) and Mott-Schottky analysis and the X-ray photoelectron spectroscopy (XPS). The results indicated that the pH value and Cl- concentration, together with the phase ratio difference in the microstructure of SS, played a critical role in the degradation process of passive film. At low pH and high Cl- concentration, the passive film gradually enriched in Fe3+ and Cr3+ species and depleted in Fe2+ oxides and its self-regeneration process became more difficult. As the pH decreased, the passive film exhibited clear n-type and p-type semiconductor characteristics more clearly, and the decrease in dopant density well reflected the changes in Fe2+/Fe3+ ratio and electrochemical behavior. Based on the viewpoint of adsorption balance between OH- with inhibitory effect and Cl- with promotion effect on the degradation process, a mechanism for the degradation process of prepassivation film was proposed.