| Water injection is one of the common methods to improve oil recovery,it is essential in the process of oilfield production and development.With crude oil being produced,the energy of underground reservoir is consumed,the formation pressure begin to loss,oil well outputs diminish,at this time,water injection is urgently needed to supplement the formation energy,the water drive mode is established artificially in the reservoir to maintain normal production status.Penglai 19-9 oilfield was officially put into development in 2016 and injected water at the same time.Compared with the water injection wells in the adjacent area and their designed water injection volume,the difficulties in water injection and the shortage of water injection in the oil well are exposed.The oilfield has a short development time and few coring data.Meanwhile,the offshore oilfield is limited by the time and space of the platform,which requires strong injection and strong production.Therefore,it is urgent to study the reservoir damage mechanism in the process of water injection on the basis of deepening the study of reservoir geological characteristics,systematically evaluate the compatibility between injected water and formation water,reservoir rock,water quality condition of water injection,and identify the internal and external factors of difficulty in water injection in oil field,and provide an important basis for efficient development and stable production of oilfield.Based on the previous geological research results,through core analysis,logging interpretation and other data to deepen the reservoir pore structure and sensitivity of minerals,heterogeneous research,combined with sensitivity experiments,platform water quality online monitoring and compatibility experiments,the paper has made the following results and understanding.(1)Guantao formation developes braided river sedimentary system and sand bodies have good connectivity.The reservoir is mainly composed of medium-coarse feldspathic lithic sandstone and lithic arkose,and mainly cemented with clay,with an average clay mineral content of 16%.The main pores are primary intergranular pores,and the throat is dominated by lamellar throat.The reservoirs have middle-high porosity and middle-high permeability.Strong heterogeneity and high clay mineral content are the internal factors of low effect of water injection.(2)The evaluation results of sensitivity experiments show that the velocity sensitive damage degree of Guantao formation is strong,and the critical velocity is about 0.5ml/min.The degree of water sensitive damage is generally middle to strong,and the critical salinity is 20000mg/L.The stress sensitive damage degree is strong.The water absorption intensity of wells is uneven,a small part of the high water absorption section has a certain degree of velocity sensitivity.(3)For the reservoir pore structure of Penglai 19-9 oilfield,the main water quality indexes of platform J exceeded the standard seriously,among which the oil content was more than 10 times higher than the standard,and the suspended substance concentration was about 1 times higher than the standard,other water quality indexes are reasonable.The suspended matter in the injected water is mainly organic matter,the organic matter is mainly linear hydrocarbon,colloid asphaltene and trace componentsd in demulsifier;inorganic substances are mainly calcareous scale,iron-bearing corrosion products and minerals in formation.Standard-exceeding of water quality is the key external factor of low effect of water injection.(4)According to the industry standard and laboratory evaluation results,the injected water of platform J is not compatible with formation water and can form calcareous scale.The core permeability damage rate of the injected water injected with 40PV is less than 40%,and the degree of damage is middle to weak. |
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