The suitable protein‐to‐lipid ratio for juvenile large yellow croaker, Pseudosciaena crocea Richardson (initial body weight, 0.57 ± 0.11 g) was determined using practical diets in a 4 × 3 factorial experiment. Four dietary protein levels (34%, 37%, 42% and 47%) and three dietary lipid levels (7.5%, 10.5% and 14.0%) were tested. Each of the 12 diets was fed to triplicate groups of croaker juveniles for 60 days in floating netcages (1.0 × 1.0 × 2.0 m3) in the sea. The effects of dietary treatments on survival, weight gain, feed conversion ratio, protein efficiency ratio, hepatosomatic index and carcass composition of the fish were evaluated. At all three lipid levels, the best growth was always obtained in the fish fed diets of 47% protein. At 34% protein, better growth was observed for the fish fed the diet with 10.5% lipid, whereas at the protein levels above 37% the diets containing 10.5% and/or 14.0% lipid proved better. Based on the results of current experiment, the dietary protein:lipid ratio of 47:10.5 appeared to be suitable for this fish. Feed conversion ratio ranged from 1.40 to 1.98, declining with the increases of both dietary protein and lipid. The carcass lipid was correlated positively to dietary lipid, unlike the carcass protein that was independent of dietary protein. There was no interaction between dietary protein and lipid except for carcass lipid. Further investigations should be conducted to determine the optimal protein‐to‐lipid ratio for large yellow croaker juveniles using diets containing higher levels of protein and lipid than 47% and 14%, respectively.

Summary Chemical combination flooding techniques, particularly alkali/surfactant/polymer (ASP) flooding, have proved to be effective in enhanced oil recovery (EOR). The development of this flooding technique in the Daqing Oil Field (China) shows that it can prevent production declines and help oil companies increase profits. However, ASP chemical loss and the resulting chromatographic separation in sandstone formations remain as limitations in the practice of ASP flooding. Laboratory investigations have analyzed the behavior and characteristics of chemical loss in sandstone reservoirs recently subjected to strong-base [sodium hydroxide (NaOH)] and weak-base [sodium carbonate (Na2CO3)] ASP flooding. A set of experiments were reasonably designed to study how formulation compositions, slug combination patterns, and heterogeneity affected the chromatographic separation and consumption loss characteristics of chemicals in sandstone reservoirs subjected to ASP flooding. Our investigations determined chemical-loss ratios through various experiments, described the underlying mechanism behind the discovered consumption loss characteristics, and discussed the effects of comparative ASP flooding processes. Furthermore, the incremental oil recovery factor and degree of permeability damage in heterogeneous sandstone reservoirs subjected to strong-base and weak-base ASP flooding processes were assessed and compared. Then, the role of alkali type in chemical loss, EOR efficiency, and reservoir flow assurance in sandstone formations were ascertained for the first time. The results indicated that chemical-loss behaviors and chemical chromatographic separation could be alleviated in a weak-base ASP flooding. In particular, in heterogeneous sandstone reservoirs, the average loss ratios of alkalis and surfactants could be reduced by 9.61% and 15.67%, respectively, compared to the strong-base ASP flooding. A profitable EOR of 20% or more could also be obtained with a weak-base ASP flooding. Moreover, a reduction of approximately 15% in the permeability-damage ratio could be realized in weak-base ASP flooding compared with the strong-base system, and the reservoir flow-assurance issues related to chemical loss could be addressed. The optimal designs for ASP formulations and slug combination patterns could technically and sustainably achieve high oil recovery in sandstone reservoirs with a weak-base ASP flooding. The results help illustrate the chemical combination flooding mechanism and can contribute to the existing knowledge regarding the additive effects of chemicals during the EOR process. Moreover, they are significant for further improving oil displacement efficiency and reducing the injection cost in heterogeneous sandstone reservoirs subjected to the weak-base ASP-flooding process.

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TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe Upper-Convected Maxwell (UCM) model has been normally used to describe the rheological properties of polymer solutions. However, this model considers only viscosity and elasticity of a fluid without including the non-Newtonian power law behavior, a very important property to polymer solutions in reservoirs. Therefore, we present a Modified Upper-Convected Maxwell (MUCM) in this paper to take into account this property.The steady flow mathematical model of MUCM fluids is established. The flow characteristics of viscoelastic fluids in the dead ends of porous pores in reservoirs are simulated numerically. The contours of velocity and stream function are drawn and micro-scale sweep efficiency is calculated quantitatively. The various regularities, corresponding to the change in visco-elastic properties of the fluid, are studied.Numerical results show the visco-elasticity of polymer solutions is the main factor influencing sweep efficiency. With increasing elasticity, the flowing area in the dead end of pores is enlarged significantly, thus the area with immobile zones becomes smaller. Flow velocity is much larger than that for a Newtonian fluid, the sweep area and displacement efficiency increase as the elasticity increases. The visco-elastic nature of the displacing polymer fluids can in general improve the displacement efficiency in pores compared to using Newtonian fluids. This conclusion should be useful in selecting polymer fluids and designing polymer flooding operations.