Study on Hybrid Volume Fracturing and Its Application of High Clay Carbonate Shale Oil Reservoirs

The-high-bury depth, complex lithology, high clay content and well-developed natural fracture development of Shulu sunken muddy limestone tight oil reservoirs results in the extreme tough oil reservoirs stimulation and thereby crying for a set of suitable stimulation model. This paper discusses the formation model of etched network fractures, the condition of network fractures, and the ability of fracture conductivity maintenance by means of macro to micro experiment testing method whereby analyzing the feasibility of volume acid fracturing in muddy limestone reservoirs in China. The results show: First, the routine practice seems dis-functional to achieve non-connected fracture system communication by virtue of acid dissolution, therefore the combination of hydraulic fracturing with acid dissolution is needed to maximize fracture network. Second, the inability of provision enough fracture conductivity of acid-rock reaction resulting to fracturing treatment design should be based on volume stimulation with the assist of acid fracturing for muddy limestone reservoir. Third, the reservoir is more prone to damage by ultra-low permeability and developed a clean acid which was compatible with reservoir and low damage to reservoir, as well as a new-type fracturing fluid system. Field application of designation in ST 1H well, ST2x well and ST3 well justifies better effect of stimulation results: the most distinguished one is in ST2x well with the test production of 232 t/d and stabilizing at approximate 16 t/d after stimulation.