超前注水区油井水力压裂时机研究

Research on Hydraulic Fracturing Opportunity of Oilwells Advance Waterflooding

通过在超前注水区对压裂井进行井下微地震测试，首次认识到在低渗致密储层超前注水区水力压裂裂缝严重失控的问题。在水力压裂过程中，一旦裂缝穿透上下隔层，可能会引起压裂的失败。影响水力压裂裂缝高度的因素主要有地应力、弹性模量、断裂韧性和不同地层的胶结状况等，其中储层和隔层应力差的影响最为明显。本文采用物理模拟实验和数学模型分析的方法来研究水力压裂缝缝高和应力差之间的连续关系。用不同比例的砂和水泥做成的人工模拟试件．使人工试件的力学性质与实际地层基本一致，在MTS三轴应力仪上对人工试件施加变化的应力差，观察使人工裂缝从产层开始进入隔层的临界应力差。在物理模拟的基础上，建立数学模型，确定缝高进入隔层距离和应力差之间的连续关系．为超前注水区油井压裂提出合理的建议。

The main factors influencing the induced fracture heights of hydraulic fracturing are formation stress, elastic modulus, fracture toughness and the cementing situation of different strata, of which the impact of stress differences between the reservoir and insulation layer is most obvious. In this paper, the authors studied the successive relationship between the induced fractures heights and stress differences by using physical simulation experiments and mathematical model analysis methods. A different ratio of cement and sand is made up into an artificial simulating test specimen, so that the mechanical natures of the artificial test specimen and the actual formation are basically identical. Exert or impose various stress differences on the MTS three-axis strain gauge, to observe the critical stress differences at the time the artificial cracks entering the barrier layer from the pay zone. On the basis of the physical simulation, a mathematical model was established, to determine the successive relationship between the distance of induced fractures heights entering the barrier layer and stress differences. It can bring forward reasonable suggestion for the hydraulic fracturing of oil wells in the advance waterflooding districts.