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.)
water-producing problems are easier to repair before completing the well. Data such as mud logger information are valuable tools to predict the potential sources of water production. An example in a carbonate reservoir drilling program would be high calcite content in cuttings, stalling or high pressure/torque on the motor and lost circulation suggesting possible fractures or high-permeability sections. If cuttings from these areas do not have florescence, the potential for water production is generally great.

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.
packers can be used to isolate sections of the borehole(s). When coupled with various artificial lift systems and memory or real time pressure gauges, the produced fluid content and well test analysis can be achieved during the testing program. In some cases, the well test analysis can provide insight into segments that are potential stimulation candidates. An inflatable straddle tool, similar to the testing tool, may also be used to perform stimulation treatments of selected intervals, especially matrix acid treatments for removal of skin damage caused during the drilling program. Polycrystalline diamond compact bit and drill motors create a small cutting that can easily penetrate into natural fractures and cause some degree of plugging. Fortunately, these cutting are often carbonate and thus easily dissolved with matrix treatments using low concentration hydrochloric acid.

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.
packer depending on the well conditions and mechanical structure of the well. In many wells, swabbing has been used but is less conclusive than data from a steady state production rate and does not generally provide quality well test information other than fluid content. In many wells, loss of kill fluid to the reservoir alters the near wellbore relative permeability and thereafter requires high produced volumes to re-establish the specific relative permeability and/or achieve a valid test of true oil content.

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.
numerous wells in the Middle East where multiple “Super K” zones are encountered while drilling. Figure 2 provides a depiction of the procedure. One advantage of such a procedure is the ability to drill out the squeezed section and continue with the planned well trajectory. This technique does reduce the potential of high-rate oil production in the initial phases but does eliminate the need to perform water shut-off treatments later in the life of the well. In most cases, cumulative production from wells with and without shut off of the Super K zones merge within 12 to 15 months. The procedure of shut off of high permeability zone while drilling offers the additional advantages of 1) elimination of early life workovers and 2) longer drilled lateral length which would not be possible with severe loss circulation.

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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