No abstract

The determination of microscopic residual oil distribution is beneficial for exploiting reservoirs to their maximum potential. In order to investigate microscopic residual oil during the carbon dioxide (CO2) huff-and-puff process in tight oil reservoirs, several CO2 huff-and-puff tests with tight sandstone cores were conducted at various conditions. Then, nuclear magnetic resonance (NMR) was used to determine the microscopic residual oil distribution of the cores. The experiments showed that the oil recovery factor increased from 27.22% to 52.56% when injection pressure increased from 5 MPa to 13 MPa. The oil recovery was unable to be substantially enhanced as the injection pressure further increased beyond the minimum miscible pressure. The lower limit of pore distribution where the oil was recoverable corresponded to relaxation times of 2.68 ms, 1.29 ms, and 0.74 ms at an injection pressure of 5 MPa, 11 MPa, and 16 MPa, respectively. Longer soaking time also increased the lower limit of the oil-recoverable pore distribution. However, more cycles had no obvious effect on expanding the interval of oil-recoverable pore distribution. Therefore, higher injection pressure and longer soaking time convert the residual oil in smaller and blind pores into recoverable oil. This investigation provides some technical ideas for oilfields in design development programs for optimizing the production parameters during the CO2 huff-and-puff process.

In order to quantitatively evaluate the pore-scale formation damage of tight sandstones caused by asphaltene precipitation during CO2 flooding, the coreflood tests and Nuclear Magnetic Resonance (NMR) relaxometry measurements have been designed and applied. Five CO2 coreflood tests at immiscible, near-miscible and miscible conditions were conducted and the characteristics of the produced oil and gas were analyzed. For each coreflood test, the T2 spectrum of the core sample was measured and compared before and after CO2 flooding to determine the asphaltene precipitation distribution in pores. It is found that, the solubility and extraction effect of the CO2 plays a more dominant role in the CO2-EOR (Enhanced Oil Recovery) process with higher injection pressure. And, more light components are extracted and recovered by the CO2 and more heavy components including asphaltene are left in the core sample. Thus, the severity of formation damage influenced by asphaltene precipitation increases as the injection pressure increases. In comparison to micro and small pores (0.1–10 ms), the asphaltene precipitation has a greater influence on the medium and large pores (10–1000 ms) due to the sufficient interaction between the CO2 and crude oil in the medium and large pores. Furthermore, the asphaltene precipitation not only causes pore clogging, but also induces rock wettability to alter towards oil-wet direction.

No abstract

In recent years, new concepts in textile dyeing technology have been investigated which aim to decrease the use of chemicals and the emission of water. In this work, dyeing of cotton textiles with reactive dyes has been investigated in a silicone non-aqueous dyeing system. Compared with conventional aqueous dyeing, almost 100% of reactive dyes can be adsorbed on cotton textiles without using any salts in non-aqueous dyeing systems, and the fixation of dye is also higher (80%~90% for non-aqueous dyeing vs. 40%~50% for traditional dyeing). The pseudo-second-order kinetic model can best describe the adsorption and equilibrium of reactive dyes in the non-aqueous dyeing systems as well as in the traditional water dyeing system. In the non-aqueous dyeing systems, the adsorption equilibrium of reactive dyes can be reached quickly. Particularly in the siloxane non-aqueous dyeing system, the adsorption equilibrium time of reactive dye is only 5–10 min at 25 °C, whereas more time is needed at 60 °C in the water dyeing system. The surface tension of non-aqueous media influences the adsorption rate of dye. The lower the surface tension, the faster the adsorption rate of reactive dye, and the higher the final uptake of dye. As a result, non-aqueous dyeing technology provides an innovative approach to increase dye uptake under a low dyeing temperature, in addition to making large water savings.

No abstract

No abstract

No abstract