Abstract: A new analytical model for pressure decline under the condition of forced fracture closure was developed on the basis of material balance theory and the former corresponding fracture models,such as PKN and KGD models.The effects of back flow of fracturing fluids just at the moment of shut-in and the continue propagation of fractures were considered in the new model. Furthermore,the problem about the leak off of the new propagated fractures was also considered.The condition of natural fracture closure was adaptable in the model.The calculation results indicate that the value of leak off coefficient obtained from the former models is higher than the real value when the forced fracture closure technique is conducted just at the moment of shut-in,while the new model can provide a true value of leak off coefficient and other parameters.The field cases verified that the calculation results with the new model is reliable and may be put into practical application.

Key words: hydraulic fracturing, fracture, forced fracture closure, pressure decline analysis, material balance theory, simulation model

摘要： 以物质平衡原理和相关分析模型为基础,对PKN和KGD两种裂缝模型建立了裂缝强制闭合条件下的压力降落解释模型.与以往模型相比,该模型既能考虑压裂后立即放喷对裂缝参数解释的影响,又能考虑停泵后裂缝继续延伸的情况,尚可考虑停泵后新延伸裂缝的滤失量及初滤失量.该模型也同样适用裂缝自然闭合的情况.模拟结果表明,当进行裂缝强制闭合时,以往模型解释的滤失系数比实际值偏大,而该模型可获得真实的滤失系数及其他油藏参数和裂缝参数.经矿场实例验证,本模型的计算结果稳定可靠,可用于实际分析.

关键词: 水力压裂, 裂缝, 强制闭合, 压降分析, 物质平衡原理, 模拟模型