碳酸盐岩储层压井液漏失影响因素研究

Factors Affecting Loss of Kill Mud Used in Carbonate Rock Reservoirs

长庆碳酸盐岩气藏裂缝及孔洞较为发育,层间差异明显,非均质程度较严重,压裂改造后的储层裂缝更为复杂,此类气藏处于开发后期的气井在开展压井修井作业时,常规压井液漏失量大,漏失主要影响因素不清楚。围绕典型井的地质参数、生产数据,采用沃伦-茹特双渗模型,通过拟合产水量、产气量和地层平均压力修正模型,5种因素的数值模拟结果表明,井筒液柱正压差、压井液黏度和裂缝渗透率是影响压井液漏失最敏感的因素,但可控因素为液柱正压差和裂缝渗透率。适当增加压井液黏度和降低液柱正压差可较好控制漏失,但采取高黏度压井液会造成泵送困难,且易产生吸附滞留损害,增加黏度的另一个极端就是增加黏弹性(弹性),一方面可增加压井液往地层的渗流阻力,此外也可以有效承压。根据研究结果,提出了以弹性凝胶为方向的长庆碳酸盐岩暂堵压井液研究思路。

The carbonate gas reservoir in Changqing oilfield isfull of fractures and vugs,different zones have quite different characteristics,andsevere inhomogeneity exists in the formations.Fracturing stimulation only makes the fractures in the reservoir much more complex.In the late period of development,workover operation performed on a well killed with a kill mud has always been facing with high volume of mud losses and factors of the mud losses are not well defined.To find out the affecting factors of the mud losses,numerical simulation of 5 factors has been conducted using the Warren-Root dual-permeability model by analyzing the geological data and production data of the typical wells and by fitting the water production rate,the gas production rate and the average formation pressure.The results of the numerical simulation show that the most important factors affecting mud losses are the positive differential pressure of the fluid column inside the well,the viscosity of the kill mud and the permeability of the fractures,of which only the differential pressure and the permeability are controllable.By moderately increasing the viscosity of the kill mud and decreasing the positive differential pressure of the fluid column inside a well,mud losses can be well controlled.The problem is that the high viscosity will result in difficulties in pumping the kill mud and formation damage from adsorption and detention of the kill mud.Viscosity increase of a kill mud can be achieved by increasing its viscoelasticity;this not only increases the resistance to the flow of kill mud into formations,it also renders the kill mud pressure bearing capacity.An idea of using elastic gel as the kill mud with temporary plugging capacity in Changqing is presented in this paper based on the research achievements.