Study On Technology Of Viscosity Reduction For Heavy Oil Well Shaft In Tahe Oilfield

The Tahe Oilfield belongs to the Ordovician carbonatite ultra deep heavy oil reservoir, which has better permeability. Because of the inherent characteristics of heavy oil in Tahe Oilfield, this oil can flow into wellbore freely, but due to the increase of heavy oil’s viscosity as the decrease of temperature during flowing from bottom hole to wellhead, resulting in weak liquidity, it cannot flow to wellhead smoothly, eventually oil well will stop production. Therefore, carrying out the research of wellbore viscosity reduction technology has important practical significance in the Tahe Oilfield.In order to solve this problem, based on analysis of physical properties of heavy oil and viscosity reduction temperature characteristics in Tahe Oilfield, current status of the study of wellbore viscosity reduction technologies at home and abroad is investigated. Combined with the practical situation of Tahe Oilfield, considering the influence of water cut in different development periods, assuming that the heat transfer is steady state inside the wellbore, between casing and formation is unsteady, and the wellbore temperature and pressure prediction models of several representative wellbore viscosity reduction technologies are studied applying basic theories of skin effect and heat transfer. The technological parameters design methods of closed thermal fluid circulation and hollow rod electric heating technologies is particularly studied, and accomplished research contents are as follows:(1) Analyzing effects of the key parameters of hollow rod electric heating technology on wellbore temperature and pressure distribution, it is known that electric heating power increases every10W/m, wellhead temperature will increase by about7%, which shows that heating effect is good; this technology exists an optimal heating depth;(2) Analyzing effects of the key parameters of closed thermal fluid circulation technology on wellbore temperature and pressure distribution, it is known that the larger closed thermal fluid circulation depth is, the lower wellhead temperature is; wellbore temperature ascends as circulation volume increases; the higher circulating fluid injection temperature is, the higher wellbore temperature is;(3) Insulated tubing influences on wellbore temperature distribution of these two viscosity reduction technologies above apparently; this will make hollow rod electric heating wellhead temperature increase from45℃to63℃(an increase up to40%), and make closed thermal fluid circulation wellhead temperature increase by about10℃;(4) Water cut, the ratio of heavy oil consumption to thin oil consumption, liquid production and will also affect wellbore temperature distribution in varying degrees; the higher water cut is, the bigger the ratio of heavy oil consumption to thin oil consumption and liquid production are, the higher wellhead temperature; among them, the effect of liquid production is the most pronounced;In addition, in order to make viscosity reduction technology optimization in the field with more reliability, aiming at achieving the same viscosity reduction effect by means of three viscosity reduction technologies of the hollow rod electric heating, closed thermal fluid circulation and mixing thin oil, a simple economic evaluation is made. It is obtained that closed thermal fluid circulation technology investment is higher at early time and daily operating cost is lower; mixing thin oil technology early investment is low, but daily operating cost is very high, total input cost of which will overtake that of hollow rod electric heating technology after15days, and will overtake that of closed thermal fluid circulation technology after24days; overall cost of hollow rod electric heating technology will overtake that of closed thermal fluid circulation technology after6months.