Research On Reservoir Characteristics And Water Injection Reservoir Protection Technology Of Shahejie Formation In QK18-1 Oilfield

QK18-1 oil field is located in the west of the Bohai Bay,adopting the method of water injecting to exploit the oil since 2005.Now,it has exposed some problems,which include high injecting pressure,injecting water slowly and using acidification and anti-swell frequently,.scaling formation in reservoir and so on.All the problems caused low recovery degree and low injecting and production ratio,which are 17.3%and 0.61 respectively.The formation has large deficit.This thesis is based on systematically analyzing of the formation geological features,by the methods of analyzing dynamic curve of oil field,conducing experiment of compatibility between injecting water and formation water,monitoring the injecting water quality online and so on,figuring out the mechanism and type of reservoir damage,diagnosing the reason of difficulty of water injection,putting forward the reservoir protection technology correspondingly,helping the QK18-1 oil field inject water efficiently.By the comprehensive study,the main achievements are list as follow:(1)The main reservoir of QK18-1 oil field is Shahejie Formation,which belongs to delta sedimentation.It is mainly composed of medium-fine and fine-grained lithic feldspathic sandstone.The content of cement is 11.8%,which are mainly composed of clay,calcite and dolomite,in which the muddy cement is 6%.The clay mineral are mainly composed of illite,illite-smectite mixed layer,with 3%average content.Reservoir is high heterogenerous with medium porosity and permeability and with severe interlayer interference.(2)The injecting water have a high ability of scaling and are incompatible with formation water of reservoir and are liable to form calcium scale.By contrast of reservoir microscopic geological characteristic of exploration well and adjusting well,we can learn that the scale are rhomb,which are formed in the reservoir by injecting water.The rhomb has well euhedral.The particle size is 10-30μm.The scale are thin film shaped,mainly filled in the pore and secondly joined crystal.The type of scale in the reservoir are perfectly matched with evaluation of compatible experiment in laboratory with calcium scale content of 1-3%.So the critical factor that difficulty of injecting water is scaling now.(3)The scale of injecting water lead to the decrease of salinity of oil field produced sewage,which induced water sensitive damage through reinjection.What’s more the content of suspended substance and others are also key factors for difficulty of injection.(4)A11 in all,the effect of QK18-1 oil field inject difficulty is list in order according to strong-to-weak sequence:scale of injecting water>suspended substance blocking by substandard injecting water>water sensitive damage>blocking by corrosion under the water well.(5)We put forward the precaution to prevent calcium scale to decrease the secondary plugging damage by formation fine,secondary sedimentation and so on after plugging removal process of acidization.We advice to control the recovery and injecting velocity in the initial stage,which can prevent from particle migration,damage of velocity sensitivity,etc,which will increase effective period of acidification.