江苏盐城地区气层损害及保护技术研究

RESEARCH ON THE DAMAGE AND PROTECTIVE TECHNIQUES OF GAS RESERVOIR IN YANGCHEN FIELD

盐城气田是江苏油田至今发现的储量最大的气田。该区上覆地层压力较高 (上覆地层压力系数高达1.2 0 ) ,又不下技术套管 ,钻井液密度不能平衡地层压力 ,发生严重垮坍 ,损失时间长 ,最后不得已把钻井液密度提高 ,造成了大量漏失 ,对气层造成严重的损害 (储层压力系数小于 1) ,而且该区岩心、气层特性等资料都缺乏 ,如何利用有限的资料 ,快速预测气层损害机理和损害程度 ,采取有效保护气层技术 ,是非常关键的、必要的。文章通过对盐城地区气层的储层特征分析及实验研究 ,表明该气藏属低渗气藏 ,粘土矿物以绿泥石和伊利石为主、具有各层组渗流能力变化大、气层压力低等特性 ;初步探讨了该地区气层损害机理 :含水饱和度较高、水敏性严重、水锁及液相聚集损害、入井液水锁严重、气藏应力敏感性较强 ;进行了气层保护技术的研究 ,提出了使用高抑制性的低界面张力型的水基钻井液、完井液及加速储层中入井流体的反排等预防措施 ;建议采用压裂和酸化对低渗气层改造 ,消除钻井及其它类型的损害。

Natural gas is a quality, high-efficient and clean energy and it will be utilized much wider in the twenty-first century. Yangchen gas field is the one which gas reserves are the largest of all the fields found in Jiangsu Oil Field up to now. At this region, because of high overlying formation pressure (pressure coefficient up to 1. 20), no technical Casing and low drilling fluid density, the drilling fluid column weight didn't balance with the formation pressure, thus causing serious wall sloughing and losing more drilling time. Finally, owing to the fact that the drilling fluid density had to be increased, a great deal of drilling fluid was lost, thus making the gas reservoir (pressure coefficient less than or equal 1) damaged seriously. Moreover, the region is deficient in the data on the core and reservoir properties, so that how to utilize the limited data to rapidly forecast the gas reservoir damage mechanisms and the degree of damage, and to adopt efficient reservoir protection technique are very important and necessary. Through the analysis and experimental research on the reservoir characteristics of Yangchen field, it is shown that the gas reservoir is of the characteristics, as low permeability, low formation pressure, various percolation capacities in different layers and mainly containing chlorites and illites in clay minerals, etc., and the gas reservoir damage mechanisms were primarily investigated, including high water saturation, serous water sensitivity, water locking and liquid phase accumulating damage, serious entering-into-well fluid locking and strong stress sensitivity, etc., On the basis of studying gas reservoir protection techniques, it is proposed that the high inhibitive, low interfacial tension, water-base drilling fluid and completion fluid should be adopted and the reverse drainage of the entering-into-well fluid at the reservoir interval should be speeded up; and it is suggested that the acidizing and fracturing are necessary for stimulating the low permeability gas reservoir so as to eliminate drilling and the other damages.