An unified technique with perforation, well test before and after stimulation, ground cross linked acid fracturing, foreign fluid recovery in one down hole pipe string is put forward in a carbonate reservoir, and the pilot test well is well A, located in Erlian Oil Field, Inner Mongolia. The advantage of above mentioned pipe string is that it can complete above four works by sequence just in one pipe string so it can improve work efficiency and reduce reservoir damage in a great deal. What's more, the new developed ground cross linked acid with high viscosity (more than 100 mPa.s), more compatibility, easily controlling of cross linking and gel breaking, etc. is applied so as to get a longer and wider fracture by acid corrosion, which has been verified by field case. Consequently, the post-acid fracturing rate of Well A was as high as 226 m3/d with no water. It has a great significance both in improving well performance and reduces cost as well.
Perforation, well test before fracturing, acid fracturing treatment, fracturing fluid recovery, well test after fracturing are conducted by sequence just in one down hole pump string is a new technique developed recently. It can both reduces down hole job time and formation matrix damage as well. As for well A, located in a limestone reservoir in Erlian basin, there are many natural fractures, past ordinary acid fracturing technique cannot get an expected penetration depth, therefore, a new developed ground cross-linked acid was applied in well A for a longer acid penetration and higher conductivity with viscosity as high as 100 mPa.s around. And it can be cross-linked and gel broken down easily just as that of cross-linked hydraulic fracturing fluid. It has a great significance in improving fracturing effect and reduce down hole job time and damage as well.
The lithology of well Well A is limestone, which locates in Carboniferous System of Paleozoic Erathem. The target zone of stimulation is between 1275.00m to 1300.43m with effective porosity 1.8%, core permeability 0.004?10−3 µm2, temperature 56 °C, pressure coefficient 0.96 Mpa/100m.
Fig 1 is the Stress-Strain curve of the well, which demonstrates that the Young's modulus of rock reaches to 49660MPa, unfavorable for the extension of fracture width. Consequently, it is difficult to pump proppant while fracturing. As a result, we utilize surface cross-link acid as to get a high conductivity fracture through non-uniform sculpture. Figure 1 the Stress-Strain curve of Well A(Available in full paper)
The stress of target zone averages at 20MPa. However, upper layer has relatively lower stress, so the fracture is prone to extend upward. As a result, we should control the pumping rate as to decrease fracture height while increase fracture length, guaranteeing effective acidizing depth to enhance acidizing effect.