| With the promotion of oil and gas development around the world,the exploration scope has been gradually extended to complicated geological reservoirs,such as deep,deep-water and unconventional reservoirs.Lost circulation has been becoming the most serious problems,which puts forward higher requirements on preventive and curing drilling fluid lost circulation technology.The synergistic effect of fibrous plugging materials in common bridging plugging systems has attracted more and more attention at home and abroad.Therefore,it has important significance to study the synergistic plugging mechanism,basic rules of fibrous plugging materials and novel efficient plugging fiber.The influence of plugging fiber's properties on the plugging effect was investigated experimentally by means of the novel plugging simulation experimental device with long fractures.The results showed that,with the increase of plugging fiber's concentrations and lengths,the 3D network structure was formed,which formed aggregates of fiber and particles.The pressure resistance of sealing layer increased gradually and the lost circulation volume decreased.With the increase of plugging fiber's breaking strength,the net structure could bear more loads.The pressure resistance of sealing layer increased,but lost circulation volume and the sealing zone kept invariant.The diameter of plugging fiber had no obvious effect on plugging effect.Based on the analysis of failure mechanism of fracture sealing layer,the compressive and shear strength of composite samples with plugging fiber and bridging plugging particle were tested.Combining with the micro-structure analysis of fracture sealing layer,the plugging mechanism of plugging fiber was discussed.The experimental results showed that the plugging fiber could obviously improve compressive and shear strength of the sealing layer,enhanced the stability of the plugging layer and improved its pressure resistance.At the same time,plugging fiber could significantly improve the internal structure of the sealing layer and improve its pressure resistance through 3D meshing and bending extrusion.The commonly used fibrous plugging materials cannot meet the technical difficulties of high temperature preventive and curing lost circulation technology in deep formations.Therefore,the high temperature resistance plugging fiber SDHTF had been developed.The properties of SDHTF was evaluated through thermal stability analysis,dispersity test,alkali resistance property test and so on.Experiments showed that SDHTF was tolerant to the degree of 220,the dispersity of SDHTF in water-based drilling fluid was excellent and the alkali resistance was good.High temperature resistance fiber-based preventive and curing lost circulation formulas were obtained by incorporating with SDHTF and other high temperature resistant lost circulation materials(LCMs)after optimizing experiments,which could effectively plug microcracks and wedge long fractures with opening widths from 1 mm to 4mm.The high temperature resistance preventive and curing lost circulation technology provides technological support for solving the lost circulation problems in high temperature formations.In order to meet the technical requirements of efficient temporary plugging and acid soluble plugging removal during reservoir plugging,the highly acid soluble plugging fiber SDHAF was optimized,based on the acid soluble property,dispersity,heat resistance property,and alkali resistance property test.Highly acid soluble fiber-based preventive and curing lost circulation formulas were obtained by incorporating with SDHAF after optimization experiments,which could effectively plug microcracks and wedge long fractures with opening widths from 1 mm to 4 mm.The sealing layer had high pressure bearing capacity.Highly acid soluble fiber-based preventive and curing lost circulation formulas' acid solubility were higher than 80%.SDHAF can effectively solve the outstanding contradiction between efficient plugging and reservoir protection performance. |
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