Early diagnosing of water coning on bottom water-drive high-viscosity fields by means of monitoring skin of horizontal wells

Background. Well coning is a top complication for reservoirs with high-viscosity oil and bottom water. The main reason is the higher mobility of bottom water relative to oil. Premature well watering leads to a decrease in oil recovery factors (ORF) and the economical efficiency of field development. Under these conditions, preventing or slowing well coning requires a method that allows monitoring the current position of the OWC.

Aim. The main objective of this study is to develop a new method for monitoring water coning in high-viscosity oil reservoirs. This is necessary for selecting the optimal operating mode for horizontal wells. The skin factor is proposed as a diagnostic indicator: it decreases as the water cone rises toward the horizontal well.

Materials and methods. The study was conducted using a three-phase dynamic model with. At the first stage, the position of the horizontal well relative to the oil-water contact (OWC) was varied: 1, 3, 5, 7, and 9 meters above the OWC. For each case, pressure buildup curves were obtained, and their interpretation in specialized sok ware enabled the determination of the skin factor. Next, the nature of the change in the skin factor depending on the well operating mode was analyzed. Additionally, a sensitivity analysis was performed, assessing the impact of changes in boundary conditions, petrophysical properties and geological structure (presence of shale breaks and a gas cap).

Results. All the calculations agree with the idea of «choking» the liquid inflow by the oil rim. Skin depends directly on the distance to the OWC, and inversely — on the current water-cut (water cone height). It was demonstrated that the methodology is applicable across a wide range of geological and physical conditions, except for cases involving shale breaks that screens water inflow to the well.

Conclusions. The proposed methodology, based on skin factor monitoring, is an effective methodology for diagnosing coning and can be used to optimize the development of heavy oil reservoirs. Specific parameters of the monitoring technique, such as the method and frequency of skin factor determination and limit values, must be established individually for each formation, taking into account its specific characteristics. 

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