| As an effective measure of reservoir stimulation,hydraulic fracturing has made great contribution in exploiting oil and gas from the formation.Self-generating proppants fracturing is one of the most advanced hydraulic fracturing technologies,expected to solve the problems of sand plug,low effective support area and proppants pumping equipment for conventional sand fracturing.So far the new technology is still in the early stage.The phase change fracturing-fluid system cannot meet the requirements of the new technology,which have high phase transition temperature,and the phase transition behavior is uncontrollable.This paper developed a thermo-responsive and controllable self-generating proppants fracturing-fluid system,based on the self-generating proppants fracturing technology and phase change fracturing-fluid system,combined with organic synthesis,infrared spectroscopy and other experimental methods.The self-generating proppant fracturing-fluid system is consists of a phase change solution that spontaneously forms a proppant in response to temperature stimulation,and a non-phase change liquid that does not respond to temperature stimulation,and studies the autogenous solidification behavior of the autogenous proppant.Through the establishment of evaluation criteria and methods,the performance of the self-generating proppants and the self-generating proppants fracturing fluid system was evaluated systematically.(1)Based on the theory and practice of polymer chemistry,the molecular structure of phase change liquid is designed.And using the method of multi-assembly and cross-linking for the self-generating proppants,the phase change liquid is constructed,which is consist of building unit cross-linking unit and functional unit.The optimum formula was determined as follows:the mass ratio of the building unit BU to the crosslinking unit was 8:5,and the functional unit SA-T03 was 2%(accounting for the sum of the mass of the building unit and the crosslinking unit).The non-phase-change liquid was constructed,which matched with the phase change liquid,and the best formula is 1.5%SA-T04+0.01%SA-T05+4.5%SA-Y-2.The thermo-responsive self-generating proppants fracturing-fluid system was developed,which provided a liquid basics for the self-generating proppants fracturing technology.Finally,the structure was verified by infrared spectroscopy and scanning electron microscopy.(2)The self-generating proppant was prepared by free radical suspension copolymerization,using self-generating proppant fracturing-fluid system,and the thermo-responsive behavior was studied in depth.It is analyzed that the formation of self-generating proppant has the characteristics of free radical suspension copolymerization mechanism.The synergistic effect of auxiliary unit SA-T06 was used to control the behavior of self-curing.The self-generating proppant mass yield was 97%,and the solidification volume retention rate was 91%.(3)Through the study of compressive strength,stability,resistance to external fluid dissolution and conductivity,it is found that when the mass ratio of SA-T01 to SA-T02 is 1:1,the self-generating proppant has the best physicochemical properties.When the mass ratio of crosslinker unit SA-T01 to SA-T02 is 1:1,the crushing rate is no more than 3.62%,and the deformation rate no more than 0.2,the conductivity is equal to that of ceramsite proppant,much higher than that of quartz sand;the mass loss under formation conditions is not more than 1.72%,and the stability is good;and the maximum acid solubility is 1.25%.(4)For the purpose of evaluating the performance of the new self-generating proppants fracturing-fluid system,compatibility,drag reduction,dispersion and reservoir damage were tested by several experiments.The results showed that the new self-generating proppants fracturing-fluid system has an excellent performance for field application.This paper provides a key materials and controlling methods for the new self-generating proppants fracturing technology,which laid the foundation of field application. |
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