In Situ Well Development Techniques for Efficient Production and Groundwater Restoration

By John Cash

Ur-Energy USA Inc.

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

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

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

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

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

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

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

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

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

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

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

Which Method is Best?� Dept of Energy study of development techniques

resulted in the following specific capacity rates:Over pumping 96.8 lpm/m Surging 147.6 lpm/mJetting 169.0 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

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)

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

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