# Hydraulic Expansion Techniques for Fracture-Cavity Carbonate Rock with Field Applications
###### Abstract  
Fracture-cavity carbonate reservoirs provide a large area, fracture development, high productivity, long stable production time, and other characteristics. However, after long-term exploitation, the lack of energy in the formation leads to a rapid decrease in production, and the water content in crude oil steadily increases, thereby disrupting normal production. To recover normal production, it is necessary to connect the cracks and pores that have not been affected during the original production, so as to allow the crude oil inside to enter the production cracks and replenish energy through methods such as hydraulic expansion of fracture-cavity carbonate rock. Accordingly, we propose hydraulic expansion techniques based on the following four processes for implementation: (1) applying high pressure to prevent a nearby fracture network from opening the seam, (2) connecting a distant fracture-cavity body, (3) breaking through the clay filling section of a natural fracture network, and (4) constructing an injection production well pattern for accelerating injection and producing diversion. Hydraulic fracturing involves closing or partially closing the original high-permeability channels, which usually produce a large amount of water, while opening previously unaffected areas through high pressure to increase crude oil production. We also introduce two composite techniques: (1) temporary plugging of the main deep fractures, followed by hydraulic expansion; and (2) capacity expansion and acidification/pressure processes. Hydraulic expansion allowed us to recover and supplement the formation energy and efficiently increase production. We tested various wells, achieving an effective hydraulic expansion rate of up to 85%. In addition, the productivity of conventional water injection and hydraulic expansion after on-site construction was compared for one well, clearly indicating the effectiveness of water injection and the remarkable crude oil increase after hydraulic expansion.  
hydraulic expansion; fracture-cavity carbonate reservoir; temporary plugging; capacity expansion; acidification/pressure process +
Footnote †: journal: Applied Mechanics  
0000-0001-5851-0 drilled. Instead, various processes are used to connect these reservoirs with existing drilled reservoirs for exploitation. For instance, acid fracturing is used to transform or exploit this type of reservoir. However, due to the strong heterogeneity of fracture-cavity carbonate reservoirs, acid preferentially results in high-permeability or fracture-developed areas during injection, while low-permeability and seriously polluted reservoirs remain unaffected. Moreover, acid fracturing is not applicable to distant fracture-cavity reservoirs [10]. Alternatively, the main fractures in a reservoir can be exploited to recover the remaining oil around or between wells through high-pressure water injection and supersaturation expansion. These methods are collectively known as hydraulic expansion.  
In this paper, we present and propose various problems, along with measures to address them by implementing volume fracturing. These problems include (1) multiple sets of fracture and pore bodies developed around the well but failing to deliver proper oil and gas production, (2) fractures blocked by mud filling, (3) constant volume characteristics and multiple rounds of water injection with adverse effects, and (4) wells with ineffective fluid supply after pre-injection fracturing. These problems are common and should be properly handled to increase production.