Cold-water Zone Research Articles

Formation and Breakdown of an Offshore Summer Cold-Water Zone and Its Effect on Phytoplankton

Estuarine plume frontal zones typically form a vertical two-layer structure with low-salinity and a high-temperature plume during the summertime. However, two field surveys in the Changjiang River Estuary and its adjacent shelf waters identified a significant surface cold-water zone (CWZ) formation in the summers of 2014 and 2015. The sea surface temperature of the CWZ was 4°C lower than the multi-year summer average. Satellite images showed that the CWZ mainly appeared in the Yangtze Shoal during the periods of July 1–17, 2014, and July 3–19, 2015. A three-dimensional physical-biogeochemical coupled model was used to explore the formation mechanism of the CWZ. Our investigation revealed that an uncharacteristic northerly wind during the southerly monsoon resulted in a significant onshore retreat of the plume front. Vertical tidal mixing is stronger than the decreased stratification in the former plume-covered region, which resulted in the formation of the CWZ. This process was accompanied by relatively lower net heat flux, which also promoted CWZ formation. The formation of CWZ had a strong ecological impact; enhanced vertical mixing transported nutrients from the lower layer to the surface column, relaxing the CWZ’s phosphate limitation. CWZ formation also increased the depth of the mixed layer and turbidity level in the water column, forming a temporary light limitation in the center. At the margin of the CWZ, it formed a patch with a high concentration of chlorophyll a. The underwater light was sufficient once the plume was restored and the CWZ was stratified again, and the phytoplankton grew rapidly in the center of the CWZ.

Oil Vaporization During Steamflooding

Here is a procedure, intended for use with other techniques, for predicting the amount of oil vaporized, or distilled, in a steam zone predicting the amount of oil vaporized, or distilled, in a steam zone during steamflooding. Calculations indicate that oil vaporization during steamflooding increases with increasing volatility of the oil and temperature of the steam, but decreases with increasing steam injection rates. Introduction When steam is continuously injected into an oil-bearing formation, four zones of fluid advancing radially from the injection well are visualized:the steam zone,the hot-water zone,the cold-water zone, andthe oil zone (Fig. 1). The theory of multiphase fluid flow in these zones, including the effects of oil expansion and viscosity reduction from temperature increases, has been described in the literature. However, one mechanism of oil recovery from the steam zone that has received little attention is oil vaporization, or distillation. Marx and Langenheim and Willman et al. have suggested methods for calculating the areal advancement of steam during continuous steam injection into a petroleum reservoir. Willman's experimental work showed that distillation functions as a recovery mechanism within the steam zone. These two methods, however, require that the amount of distillation products and the amount of residual oil left in the products and the amount of residual oil left in the steam zone be determined by laboratory experiments before the oil recovery can be calculated. Several mathematical models have been presented that include a steam-condensing front. The models by Gottfried and Chu include the steam-condensing zone subsequent to the combustion zone in forward in-situ combustion. Although Gottfried considered three-phase flow, he excluded a hydrocarbon phase change in the steam zone. Chu included a phase change; however, he assumed a single equilibrium ratio for the combined components in the oil. Steamflood models have been presented by Shutler and Satter and Parrish. Shutler considers interphase mass transfer between water and steam, but the oil was assumed to be nonvolatile and the hydrocarbon gas insoluble in the liquid phases. The Satter and Parrish model describes two-dimensional heat loss Parrish model describes two-dimensional heat loss in the steam zone and phase change of the steam, but it does not consider oil phase changes. Our purpose here is to develop an approximate engineering relationship for estimating only oil vaporization during steamflooding; the method is not intended to be an accurate analytical representation of the steamflood process. The calculative method developed can be used with the Willman et al. technique for calculating total oil recovery from a reservoir during steam injection. The results of one such calculation are shown. Part of the calculative method requires the determination of the percent of oil vaporized as a function of the amount of live steam contacting the oil. Because of the time required to perform each experiment, only two laboratory experiments were made to determine this relationship. Emphasis was placed on the development of a calculative method to approximate this function. We have included here a description of the laboratory equipment and procedure so that experimental values for this function may be obtained if desired. Several vaporization calculations, using an idealized reservoir, show the effect of injection temperature, type of oil, and injection rate on recovery from the steam zone. JPT P. 731