Study On Visbreaking Parameters Optimization During Deep-water Heavy Oil Well Test

There is abundant heavy oil resource in the world and according to the statistics,15% of the petroleum reserves is the offshore heavy oil resource.Well testing is a key step at the initial stage of exploitation of the heavy oil in deep-water,because it helps us to evaluate and estimate exploitation value of the reservoir.By now,well testing technology for deep-water heavy oil reservoir is undeveloped and there are still some challenges that needed to be overcome: on one hand,the oil stored in the deep usually has poor physical property especially has high viscosity.Additionally,high heat loss as the heavy oil flow through the low temperature area near the seabed will cause the increase of viscosity,as a result,oil will solidify in the tube and cannot flow to the wellhead smoothly.Therefore,it is the premise to take some assistant visbreaking technology to ensure the flow in the wellbore.Based on the specificity of well testing for deep-water heavy oil reservoir,this thesis analyze the technology characteristics of existing visbreaking technology and evaluate the applicability for the well testing of deep-water heavy oil reservoir.Based on wellbore heat transfer theory,we study the wellbore heat transfer process of the following cases: no assistant visbreaking technology,hollow pumping rod electrical heating technology and blending light oil in heavy oil technology.Then we establish the wellbore temperature model of these cases and derive the overall heat transfer coefficients of the wellbore in both layer section and sea section.Also the computing method of the viscosity by using oil temperature is given in this study.For an instance of deep-water heavy oil reservoir,we study the optimal selection process of the visbreaking technology;analyze the oil mobility and evaluate the viscosity reducing efficiency under different technological parameters based on the wellbore temperature field we calculated.Finally,we get the visbreaking technology suitable for this well and optimize the correlating technological parameters.And we conclude that the flow cannot be assured by increasing production rate or by using insulating tube only;hollow pumping rod electrical heating technology can reduce viscosity effectively,with the increase of heating depth,the viscosity decrease,but the viscosity decrease slowly if the heating depth exceeds 1500m;the combination of hollow pumping rod electrical heating technology and insulating tube behaves excellent visbreaking effect.