低压低渗气藏伤害因素分析及对策探讨

FACTORS AND COUNTERMEASURES OF DAMAGE FOR GAS RESERVOIRS WITH LOW PRESSURE AND PERMEABILITY

长庆气田为低压、低渗气藏,压力系数低、非均质性强,气藏类型复杂,压裂液对储层容易造成伤害。为了降低伤害,在地质特征分析的基础上,对压裂改造中引起储层伤害的因素进行了分析研究。通过岩心伤害流动实验、电镜对比分析、压裂液残渣粒径分析等室内实验研究认为,储层压力系数低、稠化剂的大分子集团对储层造成的伤害是引起伤害的主要因素,而储层的敏感性伤害、压裂液残渣的伤害虽对储层造成一定的影响,但并不是造成伤害的主要因素。在伤害因素分析的基础上,还阐述了目前在长庆低压、低渗气田应用的CO2 压裂和液氮全程伴注技术取得了较好的效果,特别是液氮全程伴注技术已得到了较大范围的应用,排液周期进一步缩短、返排率显著提高,压后不能及时喷通的井明显下降。同时结合压裂液伤害的主要因素,提出了压裂液发展的新技术思路。

Changqing gas field consists of the gas reservoirs with low pressure and permeability. Their pressure coefficients are low and heterogeneities are strong. The types of the reservoirs are complicated. It is easy to damage the reservoirs by fracturing fluid. To reduce the damage, based on the analysis of geological features, the factors causing the reservoir damage in fracturing stimulation are analyzed. With the in-house experimental study on the flow experiments of core damage, the comparison and analysis by electronic mirror, and the grain diameter analysis of fracturing fluid residue, etc. it is thought when the pressure coefficient of the reservoir is low, the damage caused by big molecular group of the thickener is the major one of the reservoir. The sensitivity damage of the reservoir and the damage of fracturing fluid residue are not the main factors to damage the reservoir though they have some influence on the reservoir damage. Based on the analysis of the damage factors, the techniques of CO2 fracturing and liquid nitrogen injection in the whole process are used and good results are achieved for Changqing gas field with low pressure and permeability. The technique of liquid nitrogen injection in the whole process is applied wider and wider, which makes the flow-back cycle further shortening, the flow-back efficiency obviously improving, and the amount of wells that can't open blow timely dramatically reducing. Aiming to the main factors of fracturing fluid damage, the new technical ideas are proposed to develop fracturing fluid.