The article shows the results of combined analysis of statistical data and the laboratory studies of fluid seepage under the conditions when the gas is artificially pumped from the annular space of a well. As a part of statistical analysis, the performance profiles of producing wells of Sheshmaoil JSC, Ideloil JSC, Geology JSC and Geotech JSC operated by sucker rod pumping units and fitted with compressor units for extraction of annular gas have been examined. 438 wells were selected for analysis. In 25 % of wells the pump location depth is below the depth of the producing reservoir, and in 10 % of wells the bottomhole pressure is zero – these are the wells where the fluid dynamic level is located below the depth of the top of the formation. When the gas is pumped from the wellbore annulus, the bottomhole pressure of these formations corresponds to the gas pressure in the annulus and almost equals zero. For wells fitted with compressor units for extraction of annular gas, stable performance of reservoirs is observed even under the conditions of extremely low values of bottomhole pressure, particularly of oil-saturated reservoirs with low water cut (average value is 33 %). Firstly, this is due to the low gas-oil ratio of the crude oil (3,7 m3/t for the sample under consideration), and, secondly, due to the beneficial role of gas pumping and its effective removal from the reservoir. The gas released in the formation shall be recovered from the bottom-hole formation zone nearest to the well and shall retain fluid relative permeability. Besides, the gas evacuated using compressor units for extraction of annular gas will not enter the pump thereby having no adverse effect on its operation, which makes it possible to maintain a low value of pressure at the pump inlet. For reference, the average pressure at the pump inlet in wells with zero bottomhole pressure was about 0,65 MPa, while across the entire sample of examined wells the pressure was 1,4 MPa.
The method has been proposed to calculate the inlet pressure based on the data of field measurements (the gas pressure in the annular space and the dynamic level) using the linear dependence of the inlet pressure on these parameters. The results of statistical analysis indicate the applicability of the linear dependence for calculating the pump inlet pressure. The inlet pressure is generated as the aggregate of the annular gas pressure (equal to zero after pumping) and the pressure of the fluid column in the annular space between the depth of the dynamic level and the depth of downhole sucker rod pump location. The effect of gas pressure in the annulus on the generation of bottomhole pressure was examined, provided that the gas is pumped from a wellbore. It has been established that the nature of influence of annular gas pressure on bottomhole gas pressure is determined by the relative location of the dynamic level, the depth of pump setting, and the depth of the active reservoir. If the downhole sucker rod pump is placed below the depth of the producing formation, a situation may occur where the dynamic level will be below the depth of the formation. The analysis of well operation regimes revealed 10 % of wells operating under the mentioned mode. For the wells where the dynamic level is below the formation depth, the bottomhole pressure will be the same as the annular gas pressure. However, after pumping, the bottomhole pressure will be almost zero. For the 10 % sample of wells with the dynamic level below the formation depth, the average annular gas pressure (and, respectively, the bottomhole pressure) was equal to 0,03 MPa.
References
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