Research On Oil-based Gel Microspheres And Water-based High-temperature Cross-linked Gel For Plugging And Crack Width Prediction Technology

With the increasing of the exploration and development of oil and gas resources,complex formation wells such as deep wells,ultra-deep wells,and complex structure wells have gradually increased,and lost circulation is often encountered during drilling.Lost circulation and the complicated problems caused by stuck holes and well collapse have caused huge economic losses.Developed drilling fluid anti-leakage and plugging treatment agent with excellent performance has become the key technology of"neck"for plugging and preventing leakage during drilling.This paper analyzed the action mechanism of the inverse emulsion polymerization gel microsphere for oil-based drilling fluid and designed molecular structure.Gel microspheres was synthesized by inverse emulsion polymerization method,which is suitable for oil-based drilling fluids to prevent leakage and plugging.Based on the product sand plate leakage amount as the evaluation standard,the HLB value,oil-water ratio,monomer ratio,crosslinker addition amount,and total monomer concentration were optimized,and the optimal synthesis conditions of the gel microspheres were determined.ABS-coated initiator microcapsules were prepared from the core and wall materials of the capsules using a physical-chemical synthesis method;rosin-coated initiator capsule particles were prepared from the microcapsule core and wall materials by a physical synthesis method.With the two delayed initiators as the key additives,a high-temperature delayed-crosslinked polyacrylamide gel plugging agent was constructed.By using infrared spectrum analysis,nuclear magnetic resonance analysis,scanning electron microscopy analysis,thermogravimetric analysis,particle size analysis and other methods,the structure characterization of gel microspheres and delayed initiator was studied.The results showed that the prepared gel microspheres and delayed initiator.Through the plugging test,the plugging effect of gel microsphere emulsion in oil-based drilling fluid was studied.The results show that after adding 2%effective content of gel microspheres to the oil-based drilling fluid base slurry,it has obvious performance of filtration control.The leakage loss per unit pressure drop from 7.5 m L/MPa to 1.45 m L/MPa.The results of temperature resistance experiments show that the gel microspheres have a good plugging effect below the aging temperature of 200°C.The compatibility experiment results show that gel microspheres will not have a negative impact on the demulsification voltage,but will be beneficial to improve the stability of the emulsion in oil-based drilling fluid.Based on the gelation test,the gelation time,viscoelasticity,stretch ability and plugging properties of the delayed-crosslinking polyacrylamide gel plugging agent constructed with the delayed initiator as the core were studied.Gelation time experiments show that the gelation experiments of polyacrylamide gels with a delayed initiator can be controlled within 2-6h at 150°C,and are compatible with similar gel plugging agents HPAM-PEI gel system,HPAM-Cr~3+system Compared with the delayed cross-linked polyacrylamide gel plugging system,the plugging effect is better.Based on the previous research results,the mathematical models of permeability leakage and fracture type leakage were summarized and integrated for solving the problem of leak diagnosis.The key parameters for judging the type of leakage were given,and a leakage diagnosis system based on field leakage data was compiled.Field tests show that the prepared leak diagnosis system is close to the particle size of the plugging material successfully plugged on site.