Study on the acid fracturing method for fracture height control based on micellar soft barrier suitable for the Tahe Oilfield

In the Ordovician carbonate oil reservoir of the Tahe Oilfield, bottom water is developed in some blocks, the vertical stress difference of reservoir is small and high-angle fractures are developed, so in the process of acid fracturing, the fracture height tends to be out of control and connect the water layers. And as the water avoidance height of acid fracturing decreases year after year, the fracture height control acid fracturing gets more and more difficult. Therefore, it is necessary to study the fracture height control acid fracturing method so as to control the propagation of fracture height and improve the stimulation effect of bottom-water reservoirs. In this paper, the essence of artificial barrier controlling the propagation of fracture height was revealed, the mechanism of micellar soft barrier was analyzed, and the method to control the fracture height using micellar soft barrier was proposed. It is experimentally indicated that when the mass fraction of viscoelastic micellar barrier material is 5%, keeping the shear viscosity of micellar solution above 430 mPa · s at 120 ℃ is favorable for the increase of the vertical stress difference of fracture. When the barrier strength of viscoelastic micellar barrier material reaches 12.2 MPa, stronger flexible barrier can be formed in the carbonate reservoirs with small vertical stress difference (≤2 MPa) in the Tahe Oilfield to control the vertical propagation of fractures. Combined with the technological characteristics of acid fracturing in the Tahe Oilfield, the micellar solution acts as the barrier to the fractures near the wellbore in the process of acid injection. As acid fingering continues, with the erosion of acid and the propagation of fracture, the mass concentration of barrier material declines and the erosion effect of acid on the fracture increases in the deep part of the fracture. In this way, the excessive propagation of fracture height near the wellbore is hindered, and strong-erosion and high-conductivity fracture channels are formed in the deep part.