1 Introduction
The Northwest Branch of Sinopec Northwest belongs to the heavy oil block. Among them, the refractory reserves in the northwestern part of China are most typical. The viscosity of the crude oil in the well exceeds 10000mPa · s (50 ℃). Because of the large loss of wellbore flow resistance, Rely on the formation of energy crude oil can not flow to the wellhead. In the early stage, according to the characteristics of the crude oil temperature sensitive in the block, hot thermal cable, heating oil pipe and over-pump heating were successively tested. The maximum heating power of S711 well (viscosity of 34593mPa · s at 70 ℃) reached 310kW, TK6051 well (50 ℃ crude oil viscosity 24500mPa · s) maximum heating power reached 130kW, the oil well is still not able to form a production capacity.
Through the summary analysis of thermal recovery technology, the main reason for the failure of thermal recovery technology in the refractory reserves in the northwestern part of the country is that the reservoir depth in this block is large (the reservoir depth is more than 5500m) and the geothermal gradient is low ( 100 meters Wenti 2.2 ℃), loss of wellbore heat loss, at the same time low productivity wells, oil well production is difficult to form a stable temperature field.
The mining process of this block is finally located on the oil-dilution oil-reducing technology, which can reduce the fluid density and viscosity of the wellbore at the same time, so as to solve the problem that the wellbore flow friction loss is large. In April 2005, a pioneering experiment was conducted at TK6051 well for a hollow circulating pump compound spike-leaching process that resulted in stable production of 18t / d for a well that had been in operation for a year and for the next step, Oil recovery technology provides a basis for supporting the technology has a good prospect.
2, the basic characteristics of reservoirs and fluids
The trap type of Ordovician reservoir in Tahe No.6 Oilfield is trap unconformity carbonate karst cave. The heterogeneity of the reservoir is very strong. Generally speaking, the reservoirs in the vertical direction are connected directly by cracks or labyrinthine communication, and the closed reservoirs with hydrocarbon or water are partially controlled by the tight lithology and filling. Longitudinal oil and gas are mainly distributed in karst pores, holes and seams, and are continuously distributed, that is, there is no aquifer in the middle. In the reservoir, the formation pressure is 61.81MPa / 5664m and the pressure coefficient is 1.09, which belongs to the normal pressure system. The reservoir formation temperature is 129.4 ℃ / 5664m and the average geothermal gradient is 2.2 ℃ / 100m.
The difficult-to-use reserves in the northwestern part of Tahe No.6 oilfield are affected by the tectonic characteristics, and oil basically belongs to heavy oil and heavy heavy oil. For example, at 50 ° C,
The viscosity of crude oil in Well S711 was 320000mPa · s, 112776mPa · s, 34593mPa · s and 12357mPa · s at 60 ℃, 70 ℃ and 80 ℃, respectively. The viscosity of crude oil in well S741 was 8389mPa · s and 3699mPa · s respectively, 1380 mPa · s and 900 mPa · s respectively; the viscosity of crude oil in Well S661 is respectively 15997 mPa · s6799 mPa · s, 2759 mPa · s and 1620 mPa · s; the viscosity of TK4331 well oil is 16097 mPa · s, 6499 mPa · s, 2819 mPa · s and 1860 mPa · s respectively; TK6051 well crude oil viscosities were 24500 mPa · s, 6800 mPa · s, 3100 mPa · s and 1520 mPa · s, respectively.
3, Hollow circulating pump compound dilute lifting technology
The process is directly connected to the water-filled hose through the surface water mixing process, and the hot fluid or the chemical enters the hollow hole of the hollow rod through the well head hanger. The hollow rod is connected with the hollow circulating pump through the pump and the lower rod, Connecting the tailpipe, the hollow rod through the hollow circulation pump can be lengthened as required and positioned by the sucker rod centralizer, allowing the fluid to be pumped into the tubing below the pump and fully mixed with the heavy oil in the tailpipe to be pumped by the hollow- To the ground. Through this process can greatly improve the pump inlet conditions, reduce the viscosity of crude oil, while reducing the stress load sucker rod, to ensure the normal operation of the pump.
4, hollow circulating pump compound dilute lifting technology applications
In April 2005, a pilot test was conducted on the TK6051 well of a typical heavy oil well with a composite hollow spigot circulating pump.
4.1 indoor doping experiment
Addition of dilute oil viscosity of 25.53mPa · s, a density of 0.8836g / cm3, the experimental temperature of 30 ℃. A total of six experiments were conducted. Except for the first group of blank, the first group of the first group of thinning of the 26th group (diluted: thick) were 1: 2,1: 3,1: 4,4: 6,3: Viscosity of 52000mPa · s, the viscosity of Group 26 after doping were 3000mPa · s, 8310mPa · s, 12700mPa · s, 1240mPa · s and 4250mPa · s, respectively. The 26th group had the viscosity reduction rates of 94.2%, 84% and 75.6 %, 97.6% and 91.8%.
4.2 Field test situation
TK6051 pumping well mixed with rare technology pump hanging depth 1357m, the use of Ф57 hollow circulation pump, the theoretical displacement of 41m3 / d, the pump plus a tail pipe; sucker rod using D-class hollow rod, after strength check, Adopt Ф42mm plus Ф36mm two-stage combination, the pole is thinned to a depth of 1370m.
After the well is dipped into a dilute pump, the well is dipped in a ratio of 4: 6 with a daily dosage of 12t. The daily production of heavy oil is 18t / d, the injection pressure of the ground pump is 1.1-1.2MPa, the wellhead temperature is 33 ℃, Wellhead crude oil viscosity 700 ~ 800mPa · s, pump efficiency 73.2%. The test has achieved good results, enabling the long-term shut down of the special heavy oil wells to achieve normal mining, providing an effective new process for the overall development of heavy oil blocks, providing a new for the development of heavy oil fields at home and abroad Train of thought.
5 Conclusion
Through the successful application of the hollow circulating pump compound mixing dilute lifting technology in the Tahe No.6 oilfield, it is concluded that:
1. For heavy oil and extra heavy oil fields, hollow circulating pump compound dilute lifting technology can solve the problem of heavy oil into the pump, flow resistance, column strength is not enough and so on, so as to ensure the normal production of heavy oil wells;
2. For the heavy oil wells with insufficient liquid supply, through the combination of the column and the column, the pumping depth can be up to 2,100 m through the strength check calculation, thus solving the problem of low productivity of the oil well;
3. The technology can also be applied to the pump down the viscosity reducer emulsion viscosity reduction, pumping anti-wax admixture pump, pumping down the corrosion inhibitor and other technology, integrated solution to waxing, corrosion, scaling and other issues .