Fracturing technology of searching for vugs along fractures in fractured-vuggy carbonate reservoirs

Deep and ultradeep fractured-vuggy carbonate vugs are the main oil and gas reservoir spaces. Under the control of in-situ stress, hydraulic fractures propagate mainly along the direction of the maximum horizontal stress to connect the vugs in this direction, while the vugs in the other directions cannot be connected with the boreholes, so the circumferential reserve producing degree is low. The reservoir stimulation idea of searching for vugs along fractures was put forward according to the development characteristics of the associated fractures and vugs of carbonate reservoirs. That is to inject the fluid by controlling the pumping pressure in the process of fracturing, so that the fluid can flow along the distribution forms of primary natural fractures to form interconnected hydraulic fracture pathways to connect multiple vugs in different directions and reduce the influences of in-situ stress on the morphology of hydraulic fractures. Then, the influential laws of the quantity and strike of natural fractures on the connection of vugs by hydraulic fractures were studied by using the TOUGH2-AiFrac coupling algorithm and constructing the model containing natural fracture network and vug. It is indicated that the strike of natural fractures has greater influence on the propagation tracks of hydraulic fractures, and when the strike of natural fractures is deviated towards vugs, it is favorable for the hydraulic fractures to connect vugs. In addition, natural fracture networks of different quantities and strikes can effectively connect multiple vugs in different directions, indicating that efficient production of circumferential reserves can be realized by searching for vugs along fractures. The technical scheme formulated according to the idea of searching for vugs along fractures has been applied on site 85 well times and the incremental oil in 2020 is 16.12×10⁴ t. The research results provide the direction for the stimulation of deep and ultradeep fractured-vuggy carbonate oil and gas reservoirs.