致密油水平井裂缝穿层及延伸规律

Fracture penetration and propagation laws in tight-oil horizontal wells

大庆致密油层砂体不连续,水平井钻井易出层,导致砂岩钻遇率低,采用常规压裂容易丢失上下目的层段,需要通过穿层压裂来提高动用程度。为此分别针对扶余和高台子油层钻遇特点,开展真三轴水力压裂物理模拟实验,研究了不同储层其水力压裂裂缝在纵向上穿层及延伸规律,确定了裂缝穿层及延伸规律的影响因素。实验结果表明:扶余油层自泥岩向砂岩穿层整体难度较大,高台子油层自砂岩向泥岩穿层整体难度较小;储层与隔层的应力差及层理对于水力裂缝穿层及延伸有明显影响,其中层间应力差越大,裂缝穿层难度越大,应力差5~8 MPa时水力裂缝易被限制于低应力层;穿层裂缝易沿层理面扩展从而使裂缝复杂化。研究结果可为致密油水平井穿层压裂选井选层及压裂方案优化提供借鉴和指导。

The sandbodies in Daqing tight oil reservoirs are discontinuous, so the horizontal wells are easily drilled out of the pay zones, which will result in the low drilled rate of the sandstones. It is easy to lose the upper and lower target layers if the conventional fracturing is applied in this type of horizontal wells, thus the developed degree of the hydrocarbon reservoirs should be enhanced by layer penetration fracturing. In the light of the drilled characteristics of Fuyu and Gaotaizi oil layers, the physical simulation experiment of real triaxial hydraulic fracturing was carried out respectively to study the longitudinal penetration and propagation rules of the hydraulic fractures respectively in different reservoirs and furthermore to determine the influencing factors on the fracture penetration and propagation. The experimental results show that they are rather difficult for the fractures in Fuyu oil reservoir to penetrate from the mudstone to sandstone;while those in Gaotaizi oil reservoir are just on the contrary;the reservoir-barrier stress difference and beddings have the obvious influences on the penetration and propagation of the hydraulic fractures. The greater the stress difference is, the more difficult the fracture penetration will be. When the stress difference is between 5-8 MPa, the hydraulic fractures are easily limited within the low-stress layer;the penetration fractures tends to propagate along the bedding plane, which will made the fractures complicated. The research results can provide the references and guidance for the well or layer selection and fracturing program optimization in the layer penetration fracturing of the tight-oil horizontal wells.