Experimental study on hydraulic fracture propagation behavior on dolomite rocks with open-hole completion

To determine to discuss fracture mechanisms and the possible encounter problems in open-hole fracturing in tight carbonation, tri-axial hydraulic fracturing experiments were performed on dolomites with acoustic emission monitoring. The results demonstrate that a complex fracture network is difficult to create in most cases even if the dolomite has high brittleness. In general, fractures likely have three types of fracture geometry, namely, bi-wing fractures, local multiple fractures and complex multiple fractures. However, even if multiple fractures can be initiated with open-hole completion, they still can finally merge into one dominant hydraulic fracture (HF). Branch fractures can be observed with low horizontal stress difference and low fluid viscosity. The breakdown pressure on dolomites has a positive relationship with the high fluid viscosity and fluid injection rate, but a negative relationship with the high horizontal principal stress difference. The existence of natural fractures and critical engineering parameter differences should simultaneously contribute to the ratio of branch fracture and diverge fracture. The microscopic observation results reveal that natural fractures that are infilled with mixed calcite minerals are more likely activated due to the lower strength of these minerals, and the main HF is arrested with a natural fracture that is infilled with high-strength calcite minerals. The separation of calcite clusters may exert competing effects on the fracture conductivity. On one hand, the debonded calcite clusters can seal and plug open HFs and reduce the fracture conductivity if the fracture width is not substantial. On the other hand, a calcite cluster can be a type of natural self-proppant to sustain long-term conductivity. The selection of open-hole completion in dolomite selection increases the risks of wellbore deformation but no serious wellbore collapse can be observed. Thus, hydraulic fracturing using open-hole completion can be recommended in dolomite reservoir development if the fracture height containment problem is not a critical issue.