Understanding the possible tools and techniques available to control water production during the life of the well is the first step in planning the drilling program and completion. Wells that are mechanically structured incorrectly make water control difficult, expensive or in some cases not achievable, short of re-drilling the well.
Evaluating the drilling data can be an important aspect of the program as many potential
Figure 1. A jet pump combined with an inflatable packer allows selective isolation for operations. (All diagrams courtesy of Tam International Inc.) |
Exiting through a window, especially in old wells, should be fully evaluated for cement bond, either in the existing well or potential damage due to the window cutting process and drilling. If there are water producing sources near the exit point, completion plans should include isolation of the exit point and build section of the well. Even in wells where original cement bond was acceptable, the vibration and mechanical stress associated with the window cutting and drilling program may destroy bond.
In multilateral wells, the exit point of each leg should have departure point separation in the range of 100 ft (30 m) in order to provide a wider variety of water control solutions if required. One reason for such separation is that the actual departure track does not rapidly extend away from the prior drilled hole sufficiently to allow placement of a bridge plug or packer near the departure for testing, water control or stimulation without danger of breakthrough (mechanically or hydraulically) into the original well bore. A minimum of 20 ft (6.1 m) of lateral separation between boreholes is recommended to minimize the potential breakthrough.
Defining the problems
A variety of tools and techniques are available to selectively test the well in order to fully define the actual location of the water influx. Single or straddle, re-settable, inflatable
Figure 2. An inflatable packer allows cement squeeze to reduce water production in the Super K formation in the Middle East. |
One tool configuration used to achieve drawdown couples a hydraulic jet pump with an inflatable straddle packer tool. This tool string shown in Figure 1 allows selective isolation, steady state or variable production rates and downhole shut-in for build-up analysis with minimal after flow. A similar system can be configured using a shrouded electric submersible pump to provide the required drawdown.
The artificial lift test systems can be configured using either an inflatable straddle or single
Figure 3. A scab liner isolates the production section from water zones above the toe of a horizontal well. |
Wellbore conditions (borehole breakout, ovality, washouts, etc.) affect the reliability of the inflatable tools. In a Canadian well, the straddle tool was cycled 49 times without requiring a trip to re-dress tools with an average cycle rate of 10 tests per tool run.
Testing can be minimized following a full review of the drilling data but should always be considered versus “best guess” at the location of the water source.
Controlling water influx
Mechanical and chemical solutions are available once the source has been defined. In some areas, chemical control has been effective using high strength gels. Such chemicals can be selectively placed using inflatable packers.
During the drilling process, an inflatable packer system can be used to selectively squeeze-cement high permeability sections to reduce the possibility of water production and control losses while continuing to drill. This technique has been successfully applied in
Figure 4. A production profile of the well will determine placement of zone isolation packers to minimize water incursion. |
Mechanical isolation can vary from a simple bridge plug where the toe section of the lateral is the water source to scab liners where the water source is above the toe. A complete liner with zone isolation and production flow control devices can be designed more efficiently once the production profile is fully defined through the testing program. Some of these applications are shown in Figures 3 and 4.
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