Application and Optimization for Network-Fracture Deep Acidizing Technique of Fractured Carbonate Reservoirs

Abstract

The fractured carbonate rock reservoir is widespread in Sichuan Basin, and the characteristics of different areas are different. The development of natural fractures is varying degrees, lost circulations occur frequently, and the formation heterogeneity is strong, which causes the formation not sufficiently stimulated by acidizing. It may affect the effectiveness of reservoir stimulation. To advance the whole stimulation effect of the heterogeneous fractured carbonate reservoir, a new solution for determining the invasion radius during drilling in a fracture network reservoir is presented, which is based on solute transport and convection-diffusion equations. It can predict the invasion radius caused by mud loss and determines the range of mud loss invasion, which clarify the scope and degree of reservoir damage. The formation of skin factors polluted by mud loss was calculated. The experiments verified that the acidizing technology can remove reservoir damage and reduce the polluted formation of skin factors. The opening pressure of the nature fracture closed is calculated which can control the acidizing area. It is confirmed how many fractures in the carbonate reservoir can be opened under the wellhead pressure limit, which meets the construction conditions of acidizing fractured reservoirs. The framework of network-fracture deep acidizing technology was established, which can efficiently break through the detrimental zone caused by lost circulation, break down the natural fracture network, and decrease the formation of the skin. The restart pressure of natural fractures was calculated, and the design parameters such as pump pressure and displacement were optimized to quantify the scope of reservoir stimulation and the scale of acid fluid. The technique of network-fracture deep acidizing was applied for well A, the formation of skin after acidizing can be reduced to -4, and the testing production of well A was 58.87×104 m3/d. The technique of network-fracture deep acidizing can quantify the acid scale and sweep area in acid fracturing design, which develops the fracturing efficiency and improves the fracturing engineering.