Aquifer Airlift Testing

Transcription

1 Presentation for the CWWCA Annual Meeting 2008 by Hank Baski Colorado Springs January 12, 2008

2 Overview Ground Water: Fallacies & Forecasts Commonly believed fallacies hinder optimal development of water wells: The use of clear water as drilling fluid results in the best well Artificial gravel pack is needed for sand-free, high-efficiency wells Step pumping aquifer tests can determine well efficiency Air-lifting cannot be trusted for reliable aquifer pumping tests and can air-bind a well New technologies and innovations will impact the water well industry over the next decade: Horizontal wells will play a greater role in water recovery and injection Pricing for larger sedimentary wells will be based on well efficiency instead of footage Unique, new methods for well development will arrive Energy savings will drive widespread adoption of aquifer thermal energy storage Case Study: Development of the Denver Basin Aquifers Question & answer session 08jan2008 rev.1 1

3 Experience 08jan2008 rev.1 2 Hank s Guide to Wellness Builds on 40 Years Of: Drilling Started in water well business while in high school Helped to build a cable tool drilling rig for the family drilling business in Northern Minnesota Moved business to Pueblo, Colorado Consulting in Ground Water Hydrology Based in Denver, Colorado Projects nationwide Manufacturing Recognized need for ground water tools Decided to develop products: pitless units, inflatable packers, and downhole flow control valves (currently seven patents on these) My Motto (I m not an easy boss ): question everything & everyone - including yourself - and be willing to change

4 Experience My Experience with Air Lifting First used in 1959 with Ingersoll-Rand down-the-hole hammer rig in Northern Minnesota Aquifer testing 1968 to 1974 with Wright Water Engineers 1976 to 1987 as self-employed hydrologist 1978 to present in free consulting to various customers 08jan2008 rev.1 3

5 Basics How & Why Does Airlifting Pump Water - and Related Facts Column of water in a well is replaced with an air-water mixture that weighs less In most cases airlift aquifer testing is more reliable than other methods as casing and nearby fracture storage effects are minimized Pumping rates and pumping levels are easy to obtain 08jan2008 rev.1 4

6 Basics Example air 0 air-water mixture static water level pumping water level 1,000 1,200 1,600 non-aerated water end of air pipe Aquifer 08jan2008 rev.1 5

7 Basics Air-lifting: Principles, Definitions & Example Principles of Operation: 1. Aerated column is lighter than submergence (think of a lake and then progress to a well) 2. Aerated column during pumping + friction loss = submergence 3. Empirical relationships are state-of-the-art. Probably, it s impossible to derive and/or calculate accurate formulas describing requirements and performance of all air-lift operations. Key Definitions: Pumping Submergence PS % = (APD - PWL) / APD APD = Air Pipe Depth PWL = Pumping Water Level Static Submergence SS psi = APD - SWL APD = Air Pipe Depth SWL = Static Water Level 08jan2008 rev.1 6 Example Specifications: 8 inch borehole or well pipe I.D. 2 inch air pipe I.D. 40% pumping submergence 1900 cfm air compressor delivery 450 gpm air-lift pumping capacity Sources: Why Air-lift Pumping Tests by Hank Baski (Feb 79), Baski Inc. Catalog #6

8 Basics Approximate Air-lift Pumping Capacities Borehole or well Air Pipe Pumping Submergence % Pipe Tube Nominal Actual Air Compressor Delivery Size OD 10% 20% 40% 60% 80% (inch) (inch) (gpm) (gpm) (gpm) (gpm) (gpm) (cfm) 3/8 1/ /2 3/ /4 1/ / /2 1/ Pipe Pipe Nominal Nominal Size Size 2 1/ / / / / Air Compressor Requirements Pressure rating [psi] must be 20% greater than the Static Submergence [psi]. Volume rating [cfm or cubic feet per minute] must approximate values from this table for hydrology testing: If the water production surges, i.e. varies in gpm rate, then a GREATER cfm is needed. On the other hand, well development by air-lift pumping is enhanced by surging; therefore, a LOWER cfm is desired for part of the development period. Do not significantly exceed the listed air delivery rate [cfm] as this will dramatically increase the friction loss in the annular area, causing the water production to decrease to the point where if too much air is introduced, no water will be produced. NOTE: 1 foot of water = psi 1 psi = 2.31 feet of water 08jan2008 rev.1 7

9 How To Airlift Set-up For Aquifer Testing Maximize water production by using 1/3 of casing I.D for the air pipe O.D. Calculate air compressor volume requirement for 6,000 feet/min. velocity in annulus Pressure requirement for unloading is submergence (in PSI) plus 10 to 20% more 08jan2008 rev.1 8

10 How To Things To Consider For In Mountain Wells During drilling the drill cuttings load in the annulus reduces water production 4-1/2 drill pipe also reduces water production in a 6 hole: the optimum air pipe O.D. for testing would be 1-1/2 nominal 08jan2008 rev.1 9

11 How To Airlift Pumping Water Levels Can Be Determined Without Direct Measurement Pumping water level is a function of Hole size Drill pipe O.D. and type of joint Depth of drill pipe or hammer Water production 08jan2008 rev.1 10

12 How To Water Level Pressure Measurement air 0 air-water mixture static water level pumping water level 1,000 1,200 1,600 PVC piezometer pipe (actual water level inside) non-aerated water end of air pipe Aquifer 08jan2008 rev.1 11

13 How To Pumping Rate Measurement Flume in discharge ditch Orifice in side or bottom of discharge tank Bucket and stop watch Water meter in pipe from discharge tank 08jan2008 rev.1 12

14 How To Flow from Discharge Tank air-water mixture orifice orifice water meter 08jan2008 rev.1 13

15 How To Flow From Flume in Ditch 08jan2008 rev.1 14

16 Step Pumping & Well Efficiency The Bible Compares Two Kinds Of Pumping Tests Pumping Tests Principle Typical Analysis Constant Rate Install one or more observation wells at appropriate distance from the pumping well Pump at constant rate for 24 or 72 hours, depending on type of aquifer Take periodic drawdown measurements from the pumping and observation wells Time-drawdown graph in semilogarithmic plot Distance-drawdown graph in semi-logarithmic plot Step Drawdown Pumping rate is increased in steps at regular intervals Example: 100 gpm for 2 hours 200 gpm for next 2 hours 300 gpm for next 2 hours and so on Take data in both pumped and observation wells Time-drawdown graph in semilogarithmic plot Distance-drawdown graph in semi-logarithmic plot Source: Groundwater and Wells by Fletcher G. Driscoll / Johnson Screen (Weatherford), Second Edition 08jan2008 rev.1 15

17 Step Pumping & Well Efficiency Early Time Data is Almost Worthless in Most Cases The initial S-shaped component is due to casing storage In most cases, specific capacity is more reliable than slopes (semi-log) or matchpoints (log-log) of aquifer test data for calculating transmissivity 10% Rule: It is not necessary to have an uninterrupted aquifer test. I have found that a shut-down equal to about 10% or less of previous pumping time is OK. Drawdown 0 Casing Storage Effect Specific Capacity [gpm/ft] = Pumping Rate [gpm] Drawdown [feet] B ,000 A C log time [min] 08jan2008 rev.1 16

18 Step Pumping & Well Efficiency Comparing Theoretical and Actual Drawdown... Source: Groundwater and Wells by Fletcher G. Driscoll / Johnson Screen (Weatherford), Second Edition 08jan2008 rev.1 17

19 Step Pumping & Well Efficiency... Leads to the Concept of Well Efficiency Ground Level Distance - Drawdown Graph in Semi-log Plot Static Water Level Pumping Water Level Actual Drawdown Theoretical (Extrapolated) Drawdown assuming well efficiency remains the same over time Distance from center of well [casing radii] Well Efficiency [%] = Theoretical Drawdown [feet] Actual Drawdown [feet] 08jan2008 rev.1 18

20 Step Pumping & Well Efficiency Turbulent and Laminar Flow Components in Step Drawdown Tests Do Not Measure Well Efficiency Many investigators and practicing engineers have (erroneously) equated turbulent flow with well inefficiency They falsely assume that the laminar head loss is the ordinary aquifer loss and that the turbulent head loss component is strictly the inefficiency drawdown component due to aquifer damage and head loss through the well screen However, we have seen efficient wells which exhibit some turbulent flow - and also have seen inefficient wells where the excess head loss due to formation damage and flow through the screening device is essentially laminar! 08jan2008 rev.1 19

21 Step Pumping & Well Efficiency Not Mentioned Even in the Bible : There Are More Than Two Kinds of Pumping Aquifer Tests 1. Constant Rate, with step drawdown considered a variant 2. Constant Drawdown, where one records the pumping rate required to maintain a given drawdown 3. Variable Discharge & Drawdown (e.g. using air-lift pumping) Vertical Axis Variables: 1. s (drawdown) 2. 1/Q (gpm) 3. s/q Casing Storage Effect ,000 log time [min] Air-lift pumping proves the cheapest & most effective aquifer test 08jan2008 rev.1 20

22 Fallacy: Air-lifting Cannot Be Trusted Fallacy: Air-lifting Cannot Be Trusted for Reliable Aquifer Pumping Tests and Can Air-bind a Well Who here has experienced air-binding first-hand? Reasons why people have opposed use of air-lifting Unwarranted fear of air-binding Air-lift pumping tests force you to think of formation pressures rather than water levels. But this results in better data collection, analysis, and understanding of the aquifer regimes. Lack of easily-accessible, broad-based analysis methods Well development with air proves advantageous Surge block development can be improved by simultaneously using air. While surging, air can be used to pump out water and fines. For stubborn wells, high-pressure air-jetting loosens up and removes drilling mud and fines 08jan2008 rev.1 21

23 Fallacy: Air-lifting Cannot Be Trusted Air-lifting: Evolution, Design, and Advantages Air-lift pumping was used before centrifugals At least 80% of the aquifer tests that I have conducted used air-lift pumping Advantages include: Readily available equipment (difficult to obtain conventional pumps for well diameters < 4 inch or for productions > 2,000 gpm) Dependability (no moving parts so high sand pumping rates are no problem, no expensive components to lose) Lower cost, normally... There are some disadvantages: Limited by minimum submergence requirements Not well understood Air compressor availability may be limited 08jan2008 rev.1 22

24 Fallacy: Air-lifting Cannot Be Trusted Air-lifting Advantages (cont.) Versatile: anticipated well production does not need to be known - but it does need to be known for conventional pumping tests Suitable for both small diameter (1/2 or less) and large wells No practical depth limitation Very easy to obtain pumping and non-pumping water level measurements Can produce approximately twice as much water from a given well diameter Practically eliminates casing storage effects Well suited for conducting in-hole flow meter surveys during pumping. The results are a testing necessity for in-situ leaching or mining, and most valuable & powerful in describing aquifers. 08jan2008 rev.1 23

25 Fallacy: Air-lifting Cannot Be Trusted Why Fallacies Live On ( Psychology Behind Fallacies) Webster s defines: Fallacy: a false idea Myth: an ill-founded belief held uncritically, especially by an interested group Overcoming human resistance to change is very difficult as one must admit that he/she has been making mistakes in past It s not so much the not knowing that contributes to the sum of human ignorance as it is the knowing so much that ain t so. 08jan2008 rev.1 24

26 Resistance To Change Experience Shows Projects (Good, Bad & Ugly) Are Entangled in a Web Technical (1950 s & 60 s) Political (1990s) Legal (1970s) Dogmatic Beliefs (2000) Environmental (1980s) Economic (1970s) Timing (1970s) 08jan2008 rev.1 25