One of the most important tendencies featuring modern oil production industry of Russia is the transformation of the structure of oil reserves for the worse. A growing number of oilfields with high viscous oil, non-Newtonian oil, low formation pressure and low-permeable layers are placed under production. At the same time oil recovery rate and layer coverage (under natural drive) stay low. To increase the operation efficiency of wells with hard-to-recover oil reserves it is suggested to apply the injection of working agent along with a dual production by screw pumping units with surface drive (hereinafter - SPU with SD), which have proven themselves to be good at extracting heavy oil, particularly on oilfields of the Republic of Tatarstan. For example, on 4 oilfields of OAO “Sheshmaoil” 29 assemblies of SPU with SD are in use (as of 01/01/2010), and since 2001 SPUs with SD have been operated on 73 well sites. Nevertheless it is necessary to point out that in the course of heavy oil production SPU with SD have not found widespread application on OAO “Sheshmaoil” facilities, as well as in OAO “Tatneft” due to negative experience of operation. The followings are the basic reasons for this:
wrong selection of elastomers and a cover of a rotor; the oil production is being performed from various horizons, for example, in OAO “Sheshmaoil” these are: Tournaisian, Bashkirian, Vereian, etc.; in OAO “Tatneft” - Kizilovskiy and Zavolzhskiy horizons. Formation conditions and physical and chemical properties of a well fluid obviously differ, but this fact has not been considered, and the same configuration of pump with chromium-plated rotor and HNBR-type elastomer was used in all cases;
non-observance of the rules of equipment mounting, and mainly mishandling of the equipment. For example, wrong adjustment of a rotor led to 3 repairs (1.6%), and 41 repairs (21.8%) were carried out due to saturation of elastomers’ material with corrosive gases as a result of operating the unit under the pressure at the pump's suction point lower than the saturation pressure. Decrease of the dynamic level lower than 0.8 Hdyn leads to wear of an elastomer, and a pump starts dry running. Such cases were registered on 101 of the installed SPUs with SD (59% of the total number).