摘要：Fast dissolving polyester oil-soluble polymers seriously compromised the rheological properties as well as the plugging efficiency of oil-based drilling fluids(OBM). In this study, an oil-soluble expansive copolymer (EPDM-LCM) constituted of ethylene propylene diene monomer (EPDM)grafted with 4-tert-butyl styrene (t-BS)in the presence of cross-linking divinylbenzene(DVB)was prepared by free-radical copolymerization in order to reinforce the hy-drophobic property which is beneficial to reduce the dissolution rate of copolymer and the molecular structure was characterized by Fourier trans form in-frared spectroscopy(FT-IR). Test the thermal stabil-ity of EPDM-LCM by differential scanning calorim-eter (DSC). The oil-expansive rate of EPDM-LCM examined with respect to time and temperature was compared with other conventional plugging agents. EPDM-LCM showed lower solubility in oil at room temperature(25oC)but the expansive rate reached 210% after 150 min at high temperature(180°C)as to indicate not only its relatively little impact on the rheological properties of drilling fluid before inva-sion into high-temperature formation zones, but also to boost the expansivity of plugging materials in the formation. In combination with EPDM-LCM, bridg-ing material (calcium carbonate), filling material (graphite), and tensile materials(fiber) were ex-ploited to develop a composite plugging agent suita-ble for different cracks. The formulation of compo-site plugging agent for micro-cracks obtained as fol-lows:1% EPDM-LCM+1% CaCO3(600 mesh)+0.5%GP (30-50 um) could achieved a maximum pressure bearing capacity of 7.75 MPa while that of macro-cracks prepared as follows:1%EPDM-LCM +1%CaCO3(600 mesh)+0.5%GP(35-65 um)+1.5%f-ber(3-5 cm)was 7.0 MPa.Both composites demon-strated good plugging performance. In addition, the formulated composite plugging agents had relatively little impact on the rheological properties of OBM. This strongly translates the developed oil-absorbing expansive rubber-based composite could be espe-ciallyinteresting for application in OBM as plugging agent.
