Experimental Study on Interaction Behavior Between Caves and Fractures in Fractured-Vuggy Carbonate Rock

Deep fractured-vuggy carbonate rock oil reservoir storage spaces are complex, and natural reservoir structures develop randomly. The natural fractures and caves are the primary oil-containing zones within carbonate rock reservoirs. Conventional acid fracturing methods often encounter challenges in effectively communicating with these natural caves. Therefore, in order to reveal the interaction dynamics between acid fracturing and these caves, clarify the dominant factors affecting communication between natural caves and acid fractures, and improve the effect of acid fracturing, this study involves the preparation of 70mm×70mm×5mm thin rock plate samples from carbonate rock outcrops. Subsequently, indoor true triaxial acid fracturing experiments are conducted. For a model specimen of fractured-vuggy carbonate rock, the results show that: (1) Under the condition of the same in-situ stress field and fracturing construction conditions, the acid fluid will erode the nearby holes and disturb the large-scale holes at close range after the acid fracturing fractures connect the small-scale holes; (2) Under the conditions of the same hole structure and fracturing construction conditions, the expansion process of acid fracture is mainly influenced by the stress difference factor; (3) In high stress difference conditions, the expansion path of acid fractures in fractured-vuggy carbonate reservoirs becomes more complex, and it is highly likely to activate nearby natural fractures in the vicinity of the hole group, leading to the formation of a short and dense fractured-vuggy network structure. 1. INTRODUCTION Acid fracturing is one of the most commonly used methods for reservoir modification in carbonate reservoirs[1,2], and the complex distribution of hole clusters and highly developed natural fractures are the most representative geological qualities of carbonate reservoirs[3-5], which not only affect the expansion path of acid fracture, but also lead to changes in the geostress near the body of the holes[6-9], so that the connectivity effect of the hole clusters often determines the oil and gas recovery rate[10-13]. In this paper, we adopt a visualized experimental method for real-time observation of acid fracture initiation and extension[14-15].