Method for improving complexity index of deep shale gas crack

Method for improving complexity index of deep shale gas crack

  • CN 106,567,702 B
  • Filed: 10/10/2015
  • Issued: 08/06/2021
  • Est. Priority Date: 10/10/2015
  • Status: Active Grant
First Claim
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1. A method for improving a complexity index of deep shale gas fractures is provided, and aims at a deep shale gas reservoir with a burial depth of more than 3500m, natural fractures filled with carbonate minerals are distributed in an artificial main fracture modification range, and a certain included angle exists between a fracturing main fracture and the natural fractures;

  • it includes N section construction operations, and every section construction operation includes;

    step I, bridge plug setting and perforation;

    putting a bridge plug and a perforating gun at a preset position, releasing after a bridge plug seat is sealed, and then perforating;

    step II, acid pretreatment;

    adding acid liquor II into the shaft for treatment so as to clean the pollution of the area close to the shaft and reduce the crack bending friction of the area close to the shaft;

    when the included angle between the crack direction and the horizontal shaft direction is less than 30 degrees, the acid liquid II is earth acid;

    step III, artificial main cracks are made;

    injecting slick water III into the shaft to open the artificial main crack;

    in step III, the slickwater III is injected in a mode of upgrading the discharge capacity in a stepped mode, and the injection discharge capacity of the slickwater III ranges from 2m to 14m3Min;

    when brittleness index>

    Designing 3-4 stages of discharge capacity when the discharge capacity is 60 percent;

    when brittleness index<

    Designing 2-3 stages of discharge capacity when the discharge capacity is 40 percent;

    step IV, communicating natural cracks;

    injecting acid liquor IV into the shaft to form a natural fracture channel communicated with the artificial main fracture;

    the viscosity of the acid solution IV is equivalent to that of the slickwater III;

    injecting acid liquor IV in a stepped displacement increasing mode;

    the injection amount of the acid liquid IV is 20-30m3

    And V, expanding the natural fracture;

    injecting slick water V into the well bore to extend the natural fracture and to extend the length and width of the branch joints of the natural fracture;

    in the process of injecting the slickwater V, injecting a mixed proppant V, wherein the construction sand ratio is more than or equal to 3 percent;

    the mixed proppant V is a mixture of two kinds of proppants with different particle sizes, wherein one particle size ranges from 70 meshes to 140 meshes, and the other particle size ranges from 40 meshes to 70 meshes;

    in the mixed proppant V, the mass content of the proppant with the particle size ranging from 70 meshes to 140 meshes is 5 percent to 10 percent;

    step VI, expanding the artificial main crack;

    injecting glue solution VI into the shaft to expand the artificial main crack;

    the viscosity of the glue solution VI is 2-3 times of that of the slickwater III;

    step VII, repeating the operation of the steps IV-VI;

    repeating the steps IV-VI for at least 1 time in the same construction operation, and sequentially increasing the viscosity of the acid liquor VII and the viscosity of the glue liquor VII;

    when the step IV is repeated, stopping the pump for 5-10 minutes after the acid liquor VII enters the preset crack position;

    step VIII, expanding the artificial main crack;

    injecting glue solution VIII into the shaft to expand the length of the artificial main fracture;

    wherein N is a positive integer.

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