Research On The Mechanism Of Under-injection Of Water Injection Wells In Typical Blocks Of Jiyuan Oilfield

Water injection development is the main development method for ultra-low permeability reservoirs.Under-injection of water injection wells has a significant impact on reservoir development.Chang 8 Reservoir in Jiyuan area is a typical ultra-low permeability reservoir.In view of the problem of under-injection of its water injection wells,based on the analysis of the current situation of under-injection of water injection wells in the reservoir,combined with core analysis and water sample detection experimental results,From the perspective of geology,fluids and development factors,the effects of reservoir physical properties,sensitivity,wettability,injected water quality and water type compatibility on under-injection of injection wells were systematically analyzed,and on this basis,entropy weight method was established to identify the main under-injection controlling factors.This article mainly achieved the following understanding:(1)Jiyuan Oilfield is the area where the precipitation of barium sulfate and strontium is most likely to occur.The scale of barium sulfate scaling is more obvious in the oil field than calcium carbonate;however,the amount of barium sulfate scaling is much higher than that of calcium carbonate.The water quality of some blocks in the southern and northern parts of the oil field is poor,which is likely to cause under-injection.(2)The Chang 8 Reservoir in Jiyuan Oilfield has the characteristics of large number of under-injection wells,high degree of under-injection,wide distribution range,and long under-injection time.The number of under-injection wells gradually increased from north to south,and the degree of under-injection also increased rapidly.(3)Through statistical analysis of the influence of different factors on under-injection,it is known that there is a "critical value" for each quantitative characterization parameter.After breaking through the critical value,the degree of under-injection and the number of under-injection wells increased significantly and the upward trend was more obvious.Using the entropy weight method for analysis,the main controlling factor of under-injection in the Chang 8 reservoir in the study area is the reservoir physical properties.The cause of under-injection is characterized by "one main and three subordinates" : "one main" refers to poor physical properties of the reservoir and is widely distributed throughout the reservoir;"three subordinates" refers to incompatible water types,poor quality of injected water,and strong reservoir sensitivity,it has a greater impact on local areas.