Study On Water Quality Decision Method Of High Water Cut Oilfield Based On Variable Permeability

After long-term water injection development in oilfield,the reservoir is blocked and the permeability is constantly changing.At present,the research on reservoir plugging of old oil fields caused by water quality in high water cut period mainly focuses on the damage mechanism of water quality on the reservoir.Therefore,there is a lack of qualitative and quantitative analysis of the impact of water quality on reservoir,and corresponding decisionmaking methods according to the water quality.In addition,due to the large differences of each oilfield in specific geological conditions and that of the permeability of each stratum,the current water injection quality industry standard(water quality standard and practice for analysis of oilfield injecting waters in clastic reservoirs)falls short.Therefore,it is necessary for oilfield to explore its own decision theory for injection-water quality to improve its yield.In order to describe the dynamic change of permeability more accurately and then to make a decision on water quality,we must simultaneously take into account the influence of two factors upon reservoir permeability: the quality and history of injection water.Therefore,taking Shengli Oilfield as an example,this paper explores the decision theory for injection-water quality,analyzes current problems existing in water injection,and studies the law of injected water damaging reservoir to establish variable permeability-based decision method for interjection water,which can help solve the problem of reservoir plugging caused by the incompatibility between water quality and permeability so that water injection can be more effective.Firstly,the water injection demands and existing problems in high water cut period of Shengli Oilfield are analyzed,and the damage mechanism of water quality to reservoir is studied.Secondly,the experiment is carried out to qualitatively study the relationship among different grades of water quality,permeability and cumulative injection water so that the law of injected water quality and injection history damaging formation permeability can be reached.Thirdly,the model of permeability attenuation is established to quantitatively and qualitatively characterize the law of permeability change.Finally,after studying water quality decision boundary,considering economic factors and determining the water quality criteria matching reservoir,the variable permeability-based decision method for water quality in Shengli Oilfield can be established.The decision method for interjection-water quality is used to simulate and prove the significant improvement in developing oilfields by the established theoretical model of Shengli Oilfield.It is proved that this decision-making method has a good application prospect and plays a theoretical guiding role on the development of high water cut oilfields.