The results of laboratory investigations of liquids filtration under the conditions of forced gas extraction from the wellbore annulus have been analyzed. Based on the analysis of initial data, the method of fluid (oil) flow rate calculation with regard to porosity and permeability properties and operating conditions of reservoirs at the fields of Sheshmaoil Management Company LLC has been developed. The assumptions of the filtration model are that the reservoir is considered to be in the homogeneous cylindrical approximation, oil and water filtration is separated, the viscosity of live oil is constant and gas filtration occurs under any gas saturation values. It has been established that the filtration model yields underestimated results compared to the linear inflow model, while the actual fluid flow rate of 2,5 m3/day at the bottomhole pressure of 1,15 MPa is consistent with the linear inflow equation and exceeds the value predicted by the filtration model (1,9 m3/day). On the whole, the discrepancy between the estimated and field data may be due to inaccurate determination of the operating parameters of the reservoir (reservoir pressure, flow rate), as well as due to changes in the porosity and permeability properties of reservoirs in the course of operation (reservoir pressure, reservoir productivity, production water cut), for example, caused by the mutual influence of production and injection wells. It has been established that the radius of oil degassing (the distance where gas separation from oil begins) corresponds to the near-wellbore zone of the formation: when the downhole pressure decreases within 100–10 % of the saturation pressure, the degassing radius increases from 0,1 to 1 meter. It has been revealed that pumping gas from the annulus and/or evacuation has the greatest positive effect both in terms of reducing gas content at the pump inlet and in terms of removing gas from the wellbore zone of the formation thereby preventing the Jamin effect. The very fact that stable performance of oil saturated formations is observed for wells equipped with the set of equipment for gas extractions from wellbore annulus, even under conditions of extremely low downhole pressures, suggests that gas extraction from the formation is acceptable, since the whole process is limited to wellbore zone with a radius of up to 1 m, and the Jamin effect will be less important under small gas oil ratio.
References
1. Isaev A.A., Takhautdinov R.Sh., Malykhin V.I., Sharifullin A.A., Oil production stimulation by creating a vacuum in the annular space of the well, SPE-198401-MS, 2019, DOI: https://doi.org/10.2118/198401-MS
2. Isaev A.A., Takhautdinov R.Sh., Malykhin V.I., Sharifullin A.A., Percolation experiments to evaluate the effect of downhole pressure on oil relative permeability, and oil viscosity under partial degassing (In Russ.), Neftyanoe khozyaystvo = Oil Industry, 2023, no. 7, pp. 16–20, DOI: https://doi.org/10.24887/0028-2448-2023-7-16-20
