Capillary end effect of wells different types at undersaturated reservoirs
In this paper the author tried to analyze observable features of operation of wells of different type in low-permeable undersaturated oil reservoirs of West Siberia using flow simulations with account for capillary end effect. For this purpose, a special approach is presented to model "reservoir to wellbore / fracture" interaction.  Materials and methods Modeling in commercial flow simulator with special correction of the well inflow calculation method.  Results  Results of calculations show qualitative correspondence to the observable field data. The stabilized value of water cut of well production and its dynamics depend of the type of the well and operating regime. When depression changes, the capillary-stabilized zone is reformed with nonstationary change of water cut. Production intensification by means of bottomhole pressure decrease leads to release of a part of capillary-retained water forming a typical "peak" in the dynamics of water production. The water cut not only changes during the nonstationary processes, but also can stabilize on different level after the mode change. Duration and intensity of the nonstationary processes increase in the following order: "deviated/vertical well →deviated/vertical well with hydraulic fracturing→ horizontal well with multistage hydraulic fracturing". Time of transition to pseudo-steady state mode for inflow composition is measured by values of about a month or more, which, in case of typical operation pearameters’ instability, leads to undamped nonstationary effects with relevant essential fluctuations of well production water cut.  Сonclusions 1. Dependence of stabilized values of well production water cut and its dynamics on well type and operating regime is shown. 2. The author developed a special modification of the calculation methodfor well inflow to account for capillary end effects. 3. Undamped nonstationary effects with fluctuations of well production water cut are theoretically analyzed.