Abstract

Horizontal wells with multiple zonal isolations have become a common completion technique in the oil and gas industry. Sand problems, damaged zones, and water or gas coning are the main reasons for using isolators to sustain or improve oil and gas recovery. However, they have certain effects on pressure behavior of horizontal wells.

This paper introduces new analytical models for studying the effect of this completion technique on pressure behavior of wells with multiple isolated zones. These models have been derived based on the assumption that reservoirs can be divided into multi-subsequent segments of producing and non-producing intervals. Based on the pressure and pressure derivative, the models can be used to estimate the impact of isolators on the pressure behavior. The effects of the number and length of isolators have been investigated for wells having different lengths.

A set of type-curves of dimensionless pressure and pressure derivative versus dimensionless time have been generated for two cases. The first case is for wells in an infinite reservoir having one, two or three isolated zones with three different lengths for the horizontal section and six different lengths for the isolators while the second one is for very long wells in an infinite reservoir. These plots can be used for the type curve matching technique to estimate the number, length, and damaged zones location, segments where sand is produced, and intervals of water or gas coning.

The main finding is that the pressure of these wells behaves similarly for all cases. The dominant effect of the isolators can only be noticed during the early time flow regimes, i.e. during the early radial or early linear. The behavior of the late time flow regimes, i.e. pseudo radial or late linear due to the boundary effects is not affected by the presence of isolators.

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