Renjing Ji,Xiaorong Yu,Huan Yang,Xiying Wang,Gaoshen Su
As an effective drilling pressure control technology, the gel valve offers a potential alternative to casing valves by utilizing its own strength to isolate downhole pressure. This paper presents a self-breaking gel valve synthesized using acrylamide and degradable crosslinker, which addresses drawbacks of existing gel-breaking techniques, such as time consumption and incomplete breaking. Firstly, the effects of monomer concentration, initiator concentration, and degradable crosslinker concentration on the performance of the gel valves were investigated. The results indicate that the gelation time can be controlled within 1–3 h, while maintaining degradation time control within 5–20 days at 90 °C. Then the pressure-bearing capacity and the effect of temperature on the degradation properties of the self-breaking gel valve were evaluated. The average pressure-bearing gradient of the gel valve at 90 °C can reach to 0.66 MPa/m. More importantly, the mechanism of gel breaking was studied. The results show that the ester groups hydrolyze gradually during the degradation process, leading to fracture of the crosslinking point inside the gel valve, a reduction in binding degree of intermediate water within the gel valve, and a decrease in crosslinking density. Additionally, there is a change in microstructure from a regular dense three-dimensional network structure to a linear random structure. The self-breaking gel valve eliminates the need for subsequent gel-breaking operations, reducing costs and preventing pollution from chemical gel-breaking agents. The self-breaking gel valve is expected to be used in pressure control for whole process underbalanced drilling.
Chunge Li,Yufeng Qian,Shuang Zhao,Yuji Yin,Junjie Li
Porous microcarriers are increasingly used to expand and harvest stem cells. Generally, the cells are harvested via proteolytic enzyme treatment, which always leads to damages to stem cells. To address this disadvantage, a series of alginate/PEG (AL/PEG) semi-interpenetrating network microcarriers are prepared in this study. In this AL/PEG system, the chemically cross-linked alginate networks are formed via the reaction between carboxylic acid group of alginate and di-terminated amine groups of cystamine. PEG is introduced to modulate the degradation of microcarriers, which does not participate in this cross-linked reaction, while it interpenetrates in alginate network via physical interactions. In addition, chitosan are coated on the surface of AL/PEG to improve the mechanical strength via the electrostatic interactions. Biocompatible fibronectin are also coated on these microcarriers to modulate the biological behaviors of cells seeded in microcarriers. Results suggest that the size of AL/PEG microcarriers can be modulated via adjusting the contents and molecular weight of PEG. Moreover, the microcarriers are designed to be degraded with cleavage of disulfide crosslinkage. By changing the type and concentration of reductant, the ratio of AL to PEG, and the magnitude of chitosan coating, the degradation ability of AL/PEG microcarriers can be well controlled. In addition, AL/PEG microcarriers can support the attachment and proliferation of human umbilical cord blood mesenchymal stem cells (hUCB-MSCs). More importantly, the expanded hUCB-MSCs can be detached from microcarriers after addition of reductant, which indeed reduce the cell damage caused by proteolytic enzyme treatment. Therefore, it is convinced that AL/PEG based microcarriers will be a promising candidate for large-scale expansion of hUCB-MSCs.
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