E₃S Reservoir Characteristics Of JX1-1 Oilfield And Analysis Of The Reasons For Production Decline During Development

With the increasing difficulty of the exploration of petroleum industry,it is necessary to develop efficiently offshore oil reservoir for its abundant resources.Because of the extremely harsh conditions and great difficulty of offshore operation,reservoir damage will bring great losses in the production process,and it is of very important significance to do a good job of reservoir protection in the production process of offshore petroleum development.The eastern area of JX1-1 Oilfield is in the early stage of development at present.Because of the lack of coring well data and the complex geological characteristics of oil field,the reservoir geological characteristics were not clearly understood that caused the rapid decreasing of preliminary production,the high water cut of the oil well,the blocking frequently of oil well,and the low oil production in the production process.The paper is based on the in-depth study on the lithology,petrophysical property and pore structure characteristics of reservoir,combining with the field production performance data and laboratory experiment,reservoir damage mechanism and damage degree are determined,in addition,the proposals for the reservoir protection are put forward.The research results provide a theoretical basis for the scientific and efficient development for unconsolidated sandstone oil reservoirs,and also have very important significance for increasing reserve and production.The main research results are as follows:(1)The Shahejie formation of the eastern area of JX1-1 Oilfield is fan delta facies.Reservoir is mainly silty sand grained or fine-to-medium grained feldspathic litharenite with average content 10%of interstitial materials and high relative content of kaolinite and illite in clay mineral.The pore type is mainly primary intergranular pore with a good pore connectivity,and the reservoir can be called high to super-high porosity and medium to high permeability reservoir.(2)The signs of formation fines migration in the production performance curve is established,combining with velocity sensitivity test results,velocity sensitivity damage degree of Dongying formation is medium-to-weak to strong at the beginning of the production,which is the key reason of the sharp decline of oilfield production.In addition,according to the sensitive test results,the critical production is recommended to prevent velocity sensitive effect on the oil well production.(3)Excessive production pressure difference is the important factor that affects reservoir stress sensitivity,and reasonable bottom hole flowing pressure is the key to the efficient development of oil wells.Reservoir stress sensitivity is comprehensively evaluated combing with the methods such as the industry standard method,the stress sensitive coefficient method and the stress sensitivity index method,the stress sensitivity of Shahejie formation in the eastern area of JX1-1 Oilfield is weak,and then the method for determining reasonable bottom hole flowing pressure is put forword.(4)Based on the relationship curve between viscosity and water cut of crude oil and production performance curve of oil well,the crude oil emulsion signs in the production performance curve is determined,and the forecasting model for oil well reverse phase area forecasting is set up,and then the production performance inverse area is forecasted.The demulsifier is recommended to add in the stage that water cut is close to reverse phase area forecasted for reducing crude oil flow ability,reducing crude oil emulsion plugging and increasing oil well production.(5)The industry standard for evaluating fluid compatibility is improved and fluid compatibility degree evaluation method has been established,and then compatibility degree of the injection water and formation water is evaluated quantitatively.Results show injection water and formation water in the western area of JX1-1 Oilfield is extremely incompatibility and it is easy to generate the CaC03 scale for blocking pore throat.The blocking is one of the important factors causing the unbalance of injection and production,reducing of formation energy and sharply decreasing of oil field production.It is recommended to control scale-forming ions of injection water or add regularly scale inhibitors in the water injection system.(6)organic scale blockage is existed in the production process,especially when water or workover fluid in low temperature is pour into reservoir,that can lead to serious wax blockage in oil wells.Injection water temperature is recommended to heat to 50 to 55?,and workover fluid is recommended to add agent such as paraffin remover and viscosity reducer for removing organic scale blockage.