GROUND WATER EXPLORATION

EXPLORATION GOALS• UNDERSTAND THE HYDROGEOLOGIC SYSTEM

• MAXIMIZE QUANTIY OF WATER AVAILABLE

• MINIMIZE DISTANCE OF SUPPLY TO DEMAND

• MINIMIZE PUMPING HEAD AND COSTS FOR DESIRED QUANITY

Conceptual Model

A descriptive representation of a groundwater system that incorporates an interpretation of the geological & hydrological conditions.

DATA REQUIREMENTS• GENERAL

– TOPOGRAPHY– SPRINGS, STREAMS, AND OTHER WATER BODIES– SOILS– CROPS– EVAPORATION– PRECIPITATION– OTHER

• NATURE AND DISTRIBUTION OF GROUNDWATER– GEOLOGY– GEOMETRY OF AQUIFERS– HYDRAULICS OF THE AQUIFERS– PHYSICAL PROPERTIES OF THE AQUIFERS

• WATER CHEMISTRY– BASELINE DATA– WATER TYPES– SOURCES OF WATER

• WATER LEVELS• RECHARGE AND DISCHARGE CHARACTERISTICS

GROUNDWATER EXPLORATION• REQUIREMENTS

• PLACEMENT OF BOREHOLES

• EXPLORATION DRILLING

• PRODUCTION TEST WELL

Steps of exploration

• Desk study – the existing available information is assembled to provide an early opportunity to get a ‘feel’ for the groundwater system and start the conceptual modelling process.

• Initial reconnaissance – it is important to get to know the study area at first hand so that you can plan your fieldwork programme.

• Monitoring programme – defines the variation in groundwater levels, groundwater chemistry, rainfall, spring and stream flows etc both across the area and seasonally.

• Data management – a systematic way of noting data in the field and examining it as it is collected to determine its reliability and if it represents the groundwater in your study area.

• Exploration – may include drilling boreholes, pumping tests and geophysical investigations.

• Water balance – quantifies the volumes of water that are passing through the groundwater system. Computer simulations may be used in this process to help define recharge and flows through the aquifer.

• Completion of the conceptual model and providing a quantified description of the groundwater system.

PLAN• DEFINE DEMAND AND QUALITY OF WATER DESIRED

• LOCATE TYPES OF AQUIFERS IN THE AREA

• SCREEN AQUIFER TARGETS WITH RECONNAISSANCE

• CARRY OUT AN EXPLORATORY PROGRAM

• PERFORM DETAILED HYDROGEOLOGIC TESTING

BOREHOLE PLACEMENT

• GEOLOGIC MAPPING

• REMOTE SENSING

• SURFACE GEOPHYSICS

Remote sensing

Remote sensing

LIDAR

Remote sensing

Geophysics

Located the Aquifer----Now What???

Drilling ?????

Well Design

Well Design

• Thickness of aquifer• Length of screen• Slot size of screen• Blind pipe length• Pump• Annular Space• Bail plug• Seals

WELL DESIGN DEPENDS ON:

• THE DRILLING METHOD

• THE PHYSICAL PROPERTIES OF THE MATERIAL

• THE ESTIMATED YIELD OF THE WELL

• THE DEPTH OF THE TARGET AQUIFER

FACTORS IN WELL DESIGN

• Drilling method

• Drilling fluid - recommended that organic polymers be used

• Well diameter - mainly based on pump size

• Well depth - the well should fully penetrate the aquifer

• Screen - usually required for unconslidated sediment

• Gravel pack - used to filter out fines

• Construction - based on drilling equipment

• Development - the washing of fines and drilling fluids out of the well.

Sand Pack

Sand Pack

Well Screen

Well Construction when using a Cable Tool

Well Construction when using a rotary rig

Rotary Drilled Well in Limestone

Unconsolidated Aquifers

Consolidated Aquifers

DRILLING PROGRAM

• SELECTION OF PROPER DRILLING METHOD

• COLLECTION OF HYDROGEOLOGIC DATA DURING DRILLING

• PERFORMANCE OF HYDROLOGIC TESTS

• DEVELOPMENT OF A CONCEPTUAL GROUNDWATER MODEL

DATA COLLECTION DURING DRILLING

• STATIC GROUNDWATER LEVELS

• GEOLOGIC DATA (rock type, fracture density, etc.)

• PENETRATION RATE

• WATER QUALITY

• GROUNDWATER RECOVERY DATA

DRILLING METHODS

• CABLE TOOL• MUD ROTARY• AIR ROTARY• REVERSE CIRCULATION• DIAMOND CORE• GEOPROBE• AUGER

CABLE TOOL

MUD/AIR ROTARY

Rotary drilling relies on continuous circular motion of the bit to break rock at the bottom of the hole. Rotary drilling is a nearly continuous process, because cuttings are removed as drilling fluids circulate through the bit and up the wellbore to the surface.

Roller Bits• Roller bits have three or more cones ("rollers" or "cutters") made with hardened

steel teeth or tungsten carbide inserts of varied shape, length and spacing. • They are designed so that each tooth applies pressure at a different point on the

bottom of the hole as the cones rotate. • The teeth of adjacent cones intermesh so that self-cleaning occurs. • The cutting surfaces of all roller bits are flushed by jets of drilling fluid directed

from the inside (centre) of the bit.• Roller bits exert a crushing and chipping action, making it possible to cut hard

rock formations • If possible, use roller bits for reaming the 10 cm pilot hole open to 15 cm

because they produce minimal amounts of clay smearing etc on borehole walls.

Drag Bits• Drag bits have short blades, each forged to a cutting edge and faced with

tungsten carbide tips. • Short nozzles direct jets of drilling fluid down the faces of the blades to

clean and cool them • Drag bits have a shearing action and cut rapidly in sands, clays and some

soft rock formations. However, it does not work well in coarse gravel or hard-rock formations.

• Drag bits should be used to drill pilot holes because they produce cuttings which are easiest to log.

Drilling Fluid (mud) is used too• Lift soil/rock cuttings from the bottom of the borehole and carry them to a

settling pit; • Allow cuttings to drop out in the mud pit so that they are not re-circulated

(influenced by mud thickness, flow rate in the settling pits and shape/size of the pits);

• Prevent cuttings from rapidly settling while another length of drill pipe is being added (if cuttings drop too fast, they can build-up on top of the bit and seize it in the hole);

• Create a film of small particles on the borehole wall to prevent caving and to ensure that the upward-flowing stream of drilling fluid does not erode the adjacent formation;

• Seal the borehole wall to reduce fluid loss (minimizing volumes of drilling fluid is especially important in dry areas where water must be carried from far away);

• Cool and clean the drill bit; and • Lubricate the bit, bearings, mud pump and drill pipe .

REVERSE CIRCULATION

DIAMOND CORE

GEOPROBE

Hollow Stem Auger Drilling Equipment:

DRILL RIG TORQUE (foot-pounds)

BORING DEPTH

WELL DEPTH

2” 4” 6” 8”

CME 95 30,000 250’ + 250’ 250’ 140’ 120’

CME 850 15,100   140'    140'   100'     40'      -

MARL M10 21,000 210’ 200’ 200’ 100’ 100’

Marl M5T 5,000 150’ 100" 100’ - -MOBILE B-61 20,000 200’ 180’ 160’ 80’ 80’

  MOBILE B-53 6,000 140’ 120’ 100’ 40’ -

Hollow Stem Auger

WELL COMPLETION

WELL EFFICIENCY

REASONS FOR POOR WELL EFFICIENCY

• POOR CHOICE OF WELL SCREEN• POOR DISTRIBUTION OF SCREEN

OPENINGS• INSUFFICIENT LENGHTH OF WELL SCREEN• POORLY SIZE GRAVEL PACK

PUMPING TESTS

• How easily water flows through the ground into a well.

• Pumping in a controlled way• Predetermined rates• Measuring the resulting effects on water

levels in both the pumping well and observation well

Types of Pumping tests

• Proving tests• Step tests• Impact tests• Aquifer tests• Tests on single boreholes

PLANNING

• Length of test• Pumping rate• Discharge• Water levels• Observation wells• Other observations• Pre-test monitoring• Safety

Pumps

• Surface suction• Submersible• Airlift pumping

On site measurements

• Pumping rate• Water level measurements• Comments

PRODUCTION TEST WELL WITH OBSERVATION WELLS

STEP TESTS(VARIABLE RATE)

• USED TO EVALUATE– Degree of development– Well efficiency– Well changes over time

• MEHODOLOGY– Well pumped at variable rates (steps)– Specific capacity at various rates determined and plotted vs flow– Aquifer and well loss calculated

• B = aquifer loss (turbulent flow) (y axis intercept)• C = well loss (slope of the specific capacity vs flow line)

– Efficiency = BQ/(BQ + CQ2) x 100

WELL EFFICIENCY EVALUATED