Optimization design for volume fracturing of horizontal wells in tight oil reservoir of Ordos Basin

Chang 7 tight oil reservoir of Ordos Basin features tight and low-pressure reservoir. It is shown from natural microfracture development degree and rock brittleness assessment of the reservoir that, properties of tight oil reservoir of the basin are highly adaptable to segmented volume fracturing of horizontal wells. The construction parameters which match with flood pattern are optimized for the purpose of improving compatibility between multi-segment fracturing pattern form and fracture distribution of horizontal wells, and results indicate that volume fracturing is realized by displacement between 4 m3/min to 8m3/min, single-segment sand amount between 40 m3 to 80 m3, and buried liquid amount between 300 m3 to 700 m3. The mixed fracturing design mode of fracture formation by low-viscosity liquid, sand carrying by high-viscosity liquid, propping agent with combined grain sizes, and injection with different displacements is formed. Influence on fracture spreading form by volume fracturing is compared with that on fracture spreading form by conventional fracturing in underground micro-seismic monitoring in mine field, and results show that transformation volume and complexity indicator for tight oil reservoir by volume fracturing are about 2 times of those for tight oil reservoir by conventional fracturing, and the data match with well pattern properly. It can be seen from pilot test for tight oil exploitation in mine field that initial output of a single horizontal well reaches 8 t/d to 10 t/d, accumulative oil production reaches about 2 000 t in the first year, and there is no breakthrough well with fracture It proves that for tight oil exploitation of Ordos Basin, the technology of five-point pattern with mixed water volume fracturing for horizontal wells can realize high single-well output and favorable exploitation benefits. Therefore, the technology is of certain significance for reference for exploitation of unconventional reservoirs of other oilfields.