鄂尔多斯盆地致密油水平井体积压裂优化设计

鄂尔多斯盆地长7致密油储层致密、油藏低压。储层天然微裂缝发育程度和岩石脆性评价表明,盆地致密油储层物性对水平井分段体积压裂具有良好的适应性。以提高水平井多段压裂井网形式和布缝的匹配性为目的,优化了与注采井网相适配的施工参数,结果表明,实现体积压裂的排量为4~8 m3/min,单段砂量40~80 m3,入地液量300~700 m3,并形成了"低黏液体造缝、高黏液体携砂、组合粒径支撑剂、不同排量注入"的混合压裂设计模式。矿场井下微地震监测对比了体积压裂与常规压裂对裂缝扩展形态的影响,结果显示致密储层采用体积压裂的改造体积和复杂指数是常规压裂的2倍左右,且与井网适配性良好。通过开展致密油开发矿场先导性试验,水平井单井初期产量达到8~10 t/d,第1年累计产油量达2 000 t左右,且无裂缝性见水井,证明对于鄂尔多斯盆地的致密油开发,采用水平井五点井网+混合水体积压裂可以获得较高的单井产量和良好的开发效益。该项技术对其他油田的非常规储层开发有一定的借鉴意义。

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.