超低渗透油藏菱形反九点井网合理排距

摘要

超低渗油藏往往方向性裂缝发育,菱形反九点井网放大了裂缝方向的井距,从而延缓主向井见水时间,但如果排距不合理仍会导致主侧向油井见效差异大,严重影响油井开发效果.因此,在流管法确定低渗透油藏菱形反九点井网油井见水时间的基础上,依据边井与角井见水时间相等时,注入水能够最大程度达到均衡驱替效果的原则,提出了确定超低渗油藏菱形反九点井网合理排距的新方法,考虑了启动压力梯度,同时能够适应超低渗油藏较强的各向异性,并选取了鄂尔多斯盆地长6某油藏进行实例应用.将该方法计算结果和油田调整井实际开发效果进行对比验证,结果表明,该计算方法可靠性高.试验区采用菱形反九点井网的合理排距应为90～93 m,在目前140 m排距下无法建立完善的驱替系统,从而导致了油井不见效.研究成果能够为试验区油藏以及同类型油田菱形反九点井网设计和调整提供理论依据.%Directional fractures are often well-developed for the ultra-low permeability oil reservoirs,the diamond inverted nine-spot well pattern enlarges the well spacing in the direction of the fracture propagation,thus the water breakthrough time can be delayed in the main direction of the oil well.However,if the row spacing is unreasonable,the developed effects will be seriously influenced due to the big contrast of the achieved effects in the directions of the main and lateral oil wells.Therefore with the help of stream-tube method,on the basis of the determined water breakthrough time of the oil well with the diamond inverted nine-spot well pattern in ultra-low permeability oil reservoirs,according to the principle of the obtained maximum balance water-flooded effect when the water breakthrough time of the edge well and corner well is equal,the new method to determine the reasonable row spacing of the diamond inverted nine-spot well pattern in the ultra-low permeability oil reservoir was proposed to take the threshold pressure gradient and the strong anisotropy in ultra-low permeability oil reservoirs into consideration.And furthermore the method was applied in one of Reservoir Chang 6 in Ordos Basin.The comparison and verification of the new method calculation results and the actual development effects of the oilfield show that the new method proposed in this paper is highly reliable.The reasonable row spacing of the diamond inverted nine-spot well pattern should be 90-93 m,but the actual row spacing is 140 m,which leads to no developed effects for the oil wells because there is no way to establish the perfect displacing system.The study achievements can provide theoretical evidences for the design and adjustment of the diamond inverted nine-spot well pattern in the oil reservoirs of this pilot area and moreover the same kind of the oilfield.