Application of Wellbore Viscosity Reduction Technology in Mining of Ultra-deep Heavy Oil Reservoirs

Application of Wellbore Viscosity Reduction Technology in Ultra-deep Heavy Oil Reservoir Mining Wang Shixing (Northwest Petroleum Bureau Tahe Second Operation Area) is an effective measure for wellbore viscosity reduction mining. By comparing heating methods, optimizing design parameters, effectively solving thickening The problem of oil flowing in the wellbore enables the ultra-deep heavy oil well to recover its self-spraying ability.

1 Characteristics of ultra-deep heavy oil in Tahe Oilfield and problems in mining 1.1 Characteristics of ultra-deep heavy oil The heavy oil reservoir in Tahe Oilfield has a buried depth of 5500~ 5700m, the middle temperature of the oil layer is 128*C (5600m), and the geothermal gradient is 2. For the low ground temperature system, the original reservoir pressure is 61.8 MPa (5600 m) and the pressure gradient coefficient is 1.1. It belongs to the normal pressure system, the average saturation pressure is 17.5 MPa, the viscosity of the formation crude oil is 34.5 MPa.s, and the crude oil is in the reservoir. Has a good fluidity Ordovician oil crude oil is a high freezing point (1 to 45C) high initial boiling point (60 ~ 85C) high salt content (23000 ~ 27000mg / L), containing wax, sulfur containing colloidal asphalt Heavy oil, crude oil density of 0. 9~3.3, the quality of colloidal asphalt is less than 50%. 2 The problem that needs to be solved in heavy oil mining. The temperature of heavy oil in Tahe Oilfield is (128 °C), and the viscosity of crude oil is 34. 5MPa.s, with good fluidity, but in the process of wellbore flow, due to overcoming the loss of various resistances and temperatures, the temperature drops, the viscosity of crude oil increases, and the energy of some heavy oil wells or super-heavy oil wells depends on the formation. Crude oil is lifted to the ground and cannot be self-sprayed or In order to achieve the production requirements of oil wells, in order to realize the mining of heavy oil, it is necessary to solve the problem of the flow of crude oil in the wellbore. At present, the heavy oil wells and super-heavy oil wells mainly adopt the temperature of the wellbore electric heating and the downhole mixed oil to reduce the viscosity of the crude oil. Sensitivity analysis The viscosity of heavy oil and super heavy oil in Tahe Oilfield is higher, but the temperature sensitivity of crude oil is stronger. According to the viscosity-temperature curve of crude oil, different types of heavy oil have different inflection points and are different types of heavy oil. The viscosity temperature curve shows that as the physical properties of crude oil become better, the inflection point temperature decreases. When the temperature is lower than the inflection point temperature, the viscosity of the crude oil decreases exponentially every 10*c of the crude oil temperature, higher than the inflection point temperature, and the crude oil temperature per When the temperature is increased by 10C, the viscosity of the crude oil is reduced by nearly one time. The inflection point temperature of T607 well is 40*c, the inflection point temperature of TK609 well and TK614 well is 60*c, the inflection point temperature of TK604 well, T606 well, S74 well and TK605 well is 7屮75C. 2 The principle of heavy oil heating and oil recovery process is currently thick. Power frequency heating and medium frequency heating method are commonly used in power heating and oil recovery. Power frequency alternating current adopts special transformer, which can convert three-phase electricity into required single-phase electricity. When the current passes through the heating body, it will produce a powerful set. The skin effect reduces the conductive area plus the impedance of the heating body, and generates a larger amount of heat with a smaller heating electric injection. At the same time, the electric heating tool is completely immersed in the wellbore, and the heat utilization rate is high.

The principle of intermediate frequency electric heating: the input 380V50Hz three-phase alternating current is rectified and filtered into 530V direct current, and then through the inverter circuit under the control of the main control board, the single-phase intermediate frequency voltage of 2601023Hz is transmitted to the heating cable through the transformer. The heating depth point is formed by the loop connection between the loop connector and the outer protective tube of the heating cable, so that the two intercepting conductors form opposite currents and equal magnitudes, and a skin effect is generated on the inner wall of the outer tube of the heater to concentrate the current on the outer sheath. The inner skin of the tube flows out in a very thin layer, and the AC impedance is greatly added. Under the combined effect of skin effect, iron loss, proximity effect and shielding effect, a large amount of heat is generated to realize electrothermal conversion. Table 1 power frequency electric heating and intermediate frequency Characteristics of electric heating Power frequency electric heating characteristics Medium frequency electric heating characteristics Heating power is large, heating power can reach 50-m mid-frequency current through the change frequency is more than 10 times of the power frequency, under the same current, the load obtains high energy heating efficiency High, more than 90% of the operation has a heat storage function, which can reduce the loss of electric energy. 10-The leakage voltage is low, and the corrosion of the wellbore is small. Fully reliable corrosion of the wellbore, small induced voltage and current at the wellhead, safe and reliable, can convert three-phase electricity into the required single-phase electricity, does not affect the grid balance program-controlled medium-frequency electrothermal oil recovery is the use of three-phase electricity, can ensure grid balance, Energy-saving for oil well heating to achieve automatic temperature control for oil well heating to achieve full intelligent control heating depth less than 2000m heating depth greater than 2000m 3 wellbore electric heating oil recovery process design wellbore electric heating oil production process design, the key is based on crude oil viscosity temperature curve and wellbore temperature Distribution, design electric heating depth, wellhead oil temperature and heating power, taking into account the oil production volume of the tubing depth, the annulus medium (medium viscosity, thermal conductivity) and other factors 1 Determination of heating depth Tahe The oil layer temperature of the pottery reservoir is higher, the heavy oil has better fluidity in the oil layer, and the heating depth can be controlled within the range allowed by the current technology. If the inflection point temperature of the heavy oil is determined as the lowest temperature of the wellbore crude oil flow, The influence of the heating power on the temperature The effect of the annulus medium on the electric heating effect According to the above research and analysis, the heavy oil well The temperature of the liquid is related to many factors, the heating depth is 2000m, the heating power is 140KW, the annulus is oil, the wellhead temperature can reach 70~75C, and the mining of oil wells with viscosity 5,000~ 20000MPa.s can ensure the normal production of oil wells. .

4 Application evaluation of wellbore electric heating oil production process According to the applicable conditions and technical parameters of electric heating rod, combined with the crude oil physical property of T606 well (25936MFs crude oil viscosity at 50*C, crude oil viscosity 3285MPa.s at 7C), crude oil temperature sensitivity and formation supply Liquid capacity, select the well for electric heating rod heating oil production technology experiment, electric heating rod under the depth of 1800m, effective heating power 0~120KW from April 17, 2001 to open well production, using 8mm nozzle production system, electric heating power 100MPa, the oil pressure is increased from MPa to 3. 5MPa and stabilized to 2. 7MPa, the sleeve pressure fluctuates between 5. 9~7.3MPa, and on October 31, 2001, the cumulative production of crude oil is 25166t, and the average daily crude oil is 128t/d. During the electric heating rod heating production process, the electric heating rod power is 100KW, the wellhead temperature rises by 20C on average after the electric heating rod is started, and the wellhead liquid temperature is 68~75C. The wellhead temperature change before and after the electric heating rod starts, the oil well production The dynamic situation is as follows. On April 17, the well electric heating rod starts to start production. After the electric heating rod is started, the crude oil temperature produced by the wellhead reaches 70~75C. After the crude oil exits the well, it is heated by the surface water jacket furnace.

2 The evaluation of the application effect of the heating rod production process According to the electric heating rod production technology in the T606 well and the production of the well: the self-controlled temperature electric heating rod can meet the production temperature of the well, and the wellhead discharge temperature reaches 70~ 75C; For oil wells with good temperature sensitivity, the process has good practicability. The viscosity of crude oil in T606 is 25936MPa.s at 50*C. When the temperature rises to 70*C, the viscosity of crude oil drops to 3285MPa.s. The heating rod heating meets the oil viscosity inflection point requires more heavy oil wells in Tahe Oilfield. The liquid supply capacity is relatively sufficient, the self-spraying ability is relatively strong, and the crude oil has low water content, and the crude oil has good temperature sensitivity. The viscosity of crude oil is 5000~ at 5C. The heavy oil well of 20000MPa.s is feasible with electric heating rod and thermal oil recovery, but the energy consumption is large and the oil production cost is high.

5 Conclusions and Recommendations 1 Wellbore heating and viscosity reduction oil recovery process For oils with a 50°C lower inflection point of crude oil, the super-deep heavy oil well with self-spraying capacity can be restored to self-spray production by lifting the well temperature.

5.2 Wellbore heating and viscosity reduction combined with rod pump to achieve effective mining of deep well heavy oil 5.3 As the water content of the oil well rises, the artificial lift volume decreases after the spray and pumping, and the wellhead temperature decreases, meeting the normal flow requirement temperature. Improvement, the existing heating power and depth are difficult to meet the requirements of fluids such as pumps. 5.4 When the water content of the oil well rises, the underground heating production process is prone to short circuit due to low insulation coefficient.

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