Influence of horizontal control holes on fracture height containment in low permeability layered coal measure gas reservoirs

Abstract

In view of the difficulty of fracture height containment during fracturing in low permeability layered or thin-layered coal measure gas reservoirs, this paper proposes a method of excavating horizontal control holes in the barriers to contain the fracture height. Considering the influence of excavating control hole on the ground stress at hydraulic fracture tips, a calculation model of hydraulic fracture height in layered strata is established. Taking the coal measures tight sandstone reservoir of Shihezi Formation in Linxing block as an example, the effect of horizontal control holes on fracture height was simulated, and the influence of various factors on the containment effect was studied. The results showed that: the excavation of horizontal control holes can effectively prevent the hydraulic fracture propagation in its height within a certain range (about 0-10r from the center of the hole, r is radius of the control hole) and reduce the penetration depth of the barrier. The greater the ground stress difference between reservoirs and barriers, the stronger the containment effect of the control holes on the fracture height. When the ground stress difference is greater than 2 MPa, the fracture height can be effectively controlled. The fracture toughness difference between reservoirs and barriers has little effect on the control holes' containment. The greater the control hole radius is, the stronger the containment effect on the fracture height is, and the greater the effective containment range will be. The optimal height of the control hole is within the stratum which the ground stress is larger, and near the interlayer interface. The research results can provide new ideas and theoretical support for fracture height containment in low permeability layered or thin layered coal measures stratum.