In Situ Well Development Techniques for Efficient Production and Groundwater Restoration. John Cash Ur-Energy USA Inc.

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1 In Situ Well Development Techniques for Efficient Production and Groundwater Restoration By John Cash Ur-Energy USA Inc.

2 What is Well Development? Any action taken after the well is installed to improve specific capacity. For example: - Removal of drilling muds - Resorting/cleaning the gravel pack - Removal of scale through mechanical or chemical methods - Removal of drilling damage - Injection of chemicals like acid or clay dispersants

3 Why is Good Well Development so Important? Poorly developed wells have low flow rates and uneven vertical distribution of flow which may reduce uranium recovery and lengthen restoration The pumping costs with poorly developed wells can be substantially greater Because poorly developed injection wells must be operated at greater pressure, spills are more likely and larger

4 Well Development Techniques Typically Used in the In Situ Industry Under-Reaming Air Lift Surge Block Swabbing Over-pumping Chemical Treatment Jetting

5 Under-Reaming A retractable cutter is used to increase the diameter of the completion zone before installing the screen For each doubling of the completion interval diameter the flow rate will increase by 10% Cuts away any filtrate (drilling mud or cement) so water can flow into the well bore unimpeded Can be used to redevelop an operating well when other development techniques have failed

8 Air Lifting Uses a drill rig/air compressor to pump the well at around 600 m/min vertical velocity Simplest technique since rig is already there and is equipped Extremely expensive; $300/hour Generally not effective due to; low pumping rates, agitation in casing not screen, flow in one direction Because the air lift is often in the casing this technique has the same effect as over pumping

10 Surge Block Uses a weighted plunger to force water in and out of the screen Relatively cheap method that can be performed without a drill rig Does not remove fines once they are pulled into the well bore. This can actually cause the well to plug Slightly more effective than the pumping method since flow direction is reversed This method can be performed with an air compressor and valve at top of wellhead

11 Swabbing A swab cup is pulled rapidly from the well causing water to flow rapidly through the gravel pack Moderate cost; $90,000 rig and tools plus one person can swab seven 200 m wells per day Moderately aggressive with flow rates of around 1,100 lpm Flow is only in one direction Although unusual, it is possible to collapse a well

14 Over Pumping Very low cost since only $30,000 of equipment and one person can develop up to three wells per day Generally not effective due to; low pumping rates, minimal agitation, flow in one direction Backwashing is a variation of over pumping that occasionally allows the pumped water column to collapse back into the well so flow direction is reversed

15 Chemical Treatment Effectively removes carbonate scale but severely fouled screens must be physically cleaned first. Acid is also effective at removing bio-fouling and killing the responsible bacteria Clay dispersants may be useful in cases where significant infiltration into the rock occurs and physical development is ineffective

18 Jetting Jetting uses high pressure water or air to sort the gravel pack. Nozzle discharge pressures of 700 to 1,000 kpa at velocities of 30 to 50 m/s Start jetting at bottom of screen and move upward at 1 foot per 5 to 15 minutes Discrete intervals can be developed individually Jetting is generally not performed with plastic screens since it can erode the soft plastic away Cost effective method with little manpower required

19 Evidence of Poor Well Development Water flow is dominantly from narrow zones instead of from the entire completion Very common for the Geologist to say, That well should be making more water or more pounds Inconsistent discoloration or scaling on screens Down hole videos shows that sand/scale in the screen is not removed effectively

20 Which Method is Best? Dept of Energy study of development techniques resulted in the following specific capacity rates: Over pumping Surging Jetting 96.8 lpm/m lpm/m lpm/m Nebraska study has resulted in similar findings The bottom line is that each operator must asses their own rock type, well design, equipment availability, and cost

21 Design to Improve Development Minimize length of screen Maximize open area of screen Ensure screen material can withstand vigorous development Minimize mud use and focus on the use of polymers that can be easily broken down. Use of mud resulted in a 56% lower specific capacity compared to polymer (DOE 1980 study)

24 Design to Improve Development Cont d Thick filter packs hinder development. Keep packs under 20 cm. 8 to 10 cms is ideal Design screen so diameter doesn t limit desired development method

25 Recommendations Minimize the need for well development by using appropriate well installation techniques and controlling chemistry and bio-fouling Experiment with various development methods to see what is best for your project All wells should be in a maintenance program where specific capacity is routinely monitored and maximized Wells should be designed so that maintenance is possible

STANDARD OPERATING PROCEDURES

STANDARD OPERATING PROCEDURES PAGE: 1 of 7 CONTENTS 1.0 SCOPE AND APPLICATION* 2.0 METHOD SUMMARY* 3.0 SAMPLE PRESERVATION, CONTAINERS, HANDLING, AND STORAGE 4.0 INTERFERENCES AND POTENTIAL PROBLEMS* 5.0 EQUIPMENT/APPARATUS* 6.0 REAGENTS