Studied On Fluid Properties And Fluid Field Characteristics Of Chang 2 Reservoir In Southeast Jingbian Area Of Ordos Basin

After 28 years of development,the Chang2 oil reservoir in the southeastern part of Jingbian has entered the middle and late stages of oilfield development.In order to achieve the purpose of increasing and stabilizing production,increasing the degree of water driving and improving the injection and production technology,it is necessary to carry out the study of reservoir geological characteristics again,especially the study of fluid properties,so as to formulate reasonable and effective development countermeasures.Based on observations of field outcrop and core,analysis of geological logging data and experimental data,and referring to previous geological research results,the chang2 oil layer group is divided into three sub-oil layer groups:chang2¹,chang2² and chang2³,of which the chang21 sub-oil layer group is the main production layer in the study area.The sedimentary system of Chang2¹ sub-reservoir formation is meandering river distributary channel sedimentary facies.The lithology of the reservoir is gray medium-fine sandstone.Chang-2reservoir is classified as type?low permeability reservoir,type?extra-low permeability reservoir and type?ultra-low permeability reservoir,all these reservoirs are designated as effective reservoirs.The?class belongs to the dense layer,is designated as the inefficient reservoir.The total ratio of effective reservoir to inefficient reservoir is 97.4?2.6 The overall of Chang2¹ reservoirs the average permeability is 5.86×10^-3?m² and the average porosity is11.4%.Thus Chang2 reservoir is evaluated as low porosity and extra-low permeability reservoir.The reservoir traps are composed of structural-lithologic composite reservoirs,and hydrodynamic reservoirs reservoirs were found locally.In the study area it is found that the total mineralized value of oilfield water is in the range of 2.65g/L⁵4.3g/L,the average is 34.1g/L.The main water type of oilfield water was CaCl₂type and NaHCO₃ type.Crude oil exhibits two types of properties:conventional crude oil and heavy oil.The average density of heavy oil,freezing point,viscosity and sulfur content were0.9478g/cm³,24.8°C,175.7mPa·S and 0.66%,respectively.It has the characteristics of ordinary heavy oil.Heavy oil has been discovered for the first time in the middle erea of hydrocarbon structural unit in Ordos Basin.On the basis of Sulin oilfield water theory and guided by the basic principle of chemical reaction,this paper introduces the ksp*physical quantity of the empirical value of solubility product constant.By calculate the solubility product constant empirical value ksp* is 1 to 2index of the theoretical value ksp.Emphasising on that the ksp*value should be used to determine whether a chemical reaction will occur between water bodies.It is proposed that salinity and water type should be taken as two parameters respectively,and the water chemistry reaction of oilfield is taken as the core to classify the water property of oilfield,the water property is used to determine the distribution characteristics of the water chemistry field finallty.In addition,the mathematical model of the change of ion content in the process of water mixing and alternation is established,which can calculate the change of ion concentration and analyze the degree of water alternation.Thus,a set of systematic theories and methods for studying the characteristics of oilfield water quality and the movement law of hydrochemical field are established.This theory inherits the previous research theories represented by Sulin,and closely links the oilfield water properties which are concerned by exploration and development,enriches the research methods of oilfield water and develops the research content of oilfield water.Using the theory and method created,the oilfield water in the study area has been divided into four kinds of based oilfield water categories as medium mineralization CaCl₂ type?class I?,low mineralization CaCl₂ type?class II?,low mineralization degree NaHCO₃ type?class III?and extra low mineralization degree Na₂SO₄ type?class IV?.The results show that the first three types of water have distinct zonation and show different water chemical field characteristics.An abnormal low-value line of TDS has been found in the field of area A and area C,respectively.According to this line we can speculate that there should distribute a near NE-SW trending fault line,and which provides valuable information for geological research.By comparing the movement of the hydrochemical field in 2007 with that in 2017,it has been concluded that the intensity of the hydrochemical field transformed by water injection is much greater than that of the natural transformation.Therefore,it is emphasized that special attention should be paid to the property of oilfield water in the process of development,so as to coordinate and solve the contradiction between geological characteristics and development process.By using the knowledge of ksp*physical quantity,the prediction of water scaling in Chang2 oilfield has been successfully carried out.This paper makes up for the deficiency of <SY/T 0600-2009 Prediction of scaling tendency in oil-field water>,and solves the problem of unity of opposites between objective material world and subjective cognitive world of water quality compatibility.The operation steps of extracting suspended organic matter and microorganism from crude oil are designed,and the technical method to observe the microstructure of oil-in-water suspension is also presented.According to this method,the suspensions of organic matter and suspected palaeontology samples are successfully separated from the heavy oil in this area,and the formation mechanism of the indomitable oil-in-water is analyzed.At least 4 kinds of suspected palaeontology have been identified from heavy oil,indicating that there are abundant palaeontology communities in Chang2 reservoir in this area.The successful extraction of biological samples from crude oil and the discovery of palaeontology have not been reported in all kinds of literatures at home and abroad,so this discovery is of great innovative significance.A new topic has been put forward for the study of reservoir fluid properties,and a new direction has been found.Based on the study of reservoir characteristics and development status,three development countermeasures are put forward,such as optimizing injection-production well pattern,improving injection-production process and formulating thermal recovery technology of heavy oil.The paper not only pays attention to the depth of theoretical research,but also solves the practical difficulties in production.