关键词: 鄂尔多斯盆地, 太原组, 致密灰岩, 酸压, 高杨氏模量, 水平井, 缝网加砂压裂

Abstract: Ordos Basin has abundant natural gas resources in Taiyuan Formation limestone reservoir, which is a major replacement field for gas exploration and development in Changqing Oilfield Company. However, no gas production breakthrough has been made before by using various acid fracturing technologies due to the factors such as tight limestone, thin reservoir thickness, and fast acid-rock reaction rate. As a result, after changing idea of well stimulation technology, study on fracture propagation mechanism, research and development of support technologies of fracturing fluids and key materials, and fine characterization of volume fracturing mode have been strengthened, developing an integrated horizontal well composite fracture network sand fracturing technology with “multiple stages, less clusters, dense fractures, and composite acid-sand fracturing”. Based on the physical simulation experiments on large outcrop, and combined with geological characteristics and rock mechanic properties, the reservoir characteristics of high brittleness, low difference between the two horizontal principal stresses and well-developed natural fractures are determined, and the volume fracturing technology enables to obtain complex fracture network. By applying the double technological advantages of “deep acid fracturing + large-scale sand fracturing”, a high-conductivity fracture flow pathway with “hydraulic fracture network + acid corrosion fracture” has been constructed, which supports to significantly increase fracture volume together with densely cutting fracturing in horizontal well. In view of the limestone characteristics of high Young’s modulus, high fracture pressure, high fracture propagation pressure and low fracture width, the anti-pressure level of casing pipe has been improved and differential design of sand placement for fractures has been conducted, forming a continuous sand adding mode with multi-scale small size proppants, which solves the problem of difficult sand fracturing of reservoir with high Young’s modulus. Based on the three-level damage evaluation of matrix, wall surface and fracture, a low damage variable viscosity slick water system has been developed to propagate fractures, form fracture network and achieve sand carrying in high modulus reservoirs. This fracturing technology has been applied in four wells, obtaining an average gas rate of 59.7×10⁴ m³/d in single well, which is 5-20 times higher than that by acid fracturing in vertical well, indicating a significant increase in production. At present, the horizontal well composite fracture network sand fracturing technology has been used as the main reservoir stimulation technology for Taiyuan Formation limestone in Changqing Oilfield, which provides strong technical support for the exploration breakthrough and effective development of this type of gas reservoirs.