鄂尔多斯盆地致密储层井下控砂压裂技术

鄂尔多斯盆地储层致密且特征复杂，常规体积压裂难以形成复杂裂缝，单井产量低，为此引进了井下控砂压裂技术，并通过研发专用井下混砂工具、开展井下混砂工具全尺寸地面模拟试验、优化压裂工艺关键参数，形成了井下控砂压裂工艺，以实现实时控制井底砂浓度、形成缝内支撑剂架桥、提高裂缝复杂程度的目的。该技术在鄂尔多斯盆地30口井的压裂作业中进行了成功应用，最高砂浓度1 800 kg/m3（20/40目石英砂体积密度1.62 g/cm3、视密度2.64 g/cm3），与应用混合水压裂的油井相比，平均产油量显著提高，且可节省1/3左右水功率和用液量，大幅降低了压裂成本。应用结果表明，采用井下控砂压裂技术可以达到提高致密储层缝内净压力、增加裂缝复杂程度的目的，能够实现致密油储层的有效改造，提高单井产量。 

A Sand Control Downhole Fracturing Technique for Tight Reservoir Development in the Ordos Basin

Reservoir formations in Ordos Basin are tight and exhibit complicated features. Under such circumstances, conventional stimulated reservoir volume (SRV) fracturing could hardly produce desirable fracture networks, without which productivities of individual wells were low. To enhance productivity, innovative down-hole fracturing techniques with sand control were introduced. With the development of fit-for-purpose down-hole sand-mixing tools, full-scale simulation tests were performed on surface to determine optimal fracturing parameters. The innovative fracturing techniques may be deployed to control concentrations of sands at wellbore in real time to generate proppant networks in newly-formed fractures and to enhance complexity of fracture networks. These new techniques have been deployed successfully for fracturing operations in 30 wells in Ordos Basin with maximum sand concentration of 1 800 kg/m3 (20/40 mesh quartz sand with volume density of 1.62 g/cm3 and density of 2.64 g/cm3). Compared with oil producers fractured by using mixed water, producers fractured by using these innovative techniques have average productivity enhanced significant with reduction of hydraulic power and fluid volumes for approximately 1/3. In this way, operation costs were reduced dramatically. On-site application results showed the newly developed fracturing techniques with down-hole sand control could effectively enhance net pressures in fractures of tight reservoirs, promote complexity of fracture networks, improve the properties of tight oil-bearing formations and enhance the productivity of individual wells.