煤层气直井压裂参数优化设计

The Parameter Optimization Design of CBM Vertical Fracturing Wells

考虑煤层气直井压裂近井地带裂缝中的非达西紊流效应及气、水两相流动特征,结合水力压裂裂缝中净压力约束、最小缝宽约束的限制条件,建立了完整的煤层气储层直井压裂裂缝水力参数优化设计方法。在常规气藏物质平衡法的基础上,建立了基于煤层气储层的物质平衡法的生产动态预测模型,并对压裂直井的生产动态进行预测。研究结果表明,直井压裂裂缝中非达西紊流效应对产能的影响明显,高渗透煤储层中紊流降低支撑剂有效渗透率来减小裂缝导流能力,对气井产能起到很大的负面影响。高渗透煤储层易形成短而宽的裂缝几何形态,低渗透煤储层易形成长而窄的裂缝几何形态。产能对比和经济评价指标表明,煤层气压裂直井数越多,越有利于动用储量和提高经济效益,净现值越高,投资回收期越短。设计结果为煤层气直井压裂产能评价和优化设计提供了理论指导。

According to non Darcy turbulent flow effect and the characteristics of two-phase flow（ gas and water） in the fractures near the wellbore have been considered in the fracturing of CBM vertical wells,combined with the restriction conditions of net pressure and minimum crack width in hydraulic fracturing,the optimization design method of hydraulic parameter for vertical well fracturing in CBM reservoir has been estabilished.On the basis of material balance method of conventional gas reservoir,the production performance prediction model for CBM was formed in terms of the balance method,so as to predict the production performance of vertical wells that treated by fracturing.Research results showed that the effect of non Darcy turbulent flow on the productivity in vertical well fracturing was obvious,and the turbulent flow in high permeability coal reservoir has reduced the effective permeability and conductivity that created by proppant,resulting in a great negative impact on gas well productivity.High permeability coal reservoir is easy to form short and wide fractures,but low permeability coal reservoir is easy to form long and narrow fractures.Production capacity comparison and economic evaluation index indicated that the more the CBM vertical wells by fracturing,the more beneficial to the use of reserves and improvement of economic efficiency,so the higher the net present value,the shorter the payback period of investment.The design results can provide the theoretical guide for evaluating production capacity and optimizing the design of CBM vertical well fracturing.