Unconventional measurers sde11

transcript

Directorate of Groundwater Surveys and Development

Agency,Pune

Unconventional Measures for Source Strengthing

GEOLOGY OF MAHARASHTRA

Deccan Trap 82 %

Specific yield 2 to 4 %

GEOLOGY OF MAHARASHTRA

• 82 % Deccan trap formation.• Specific Yield not more than 2 to 4 %.• Groundwater is available due to Secondary porosity.• Drinking water sources particularly PWS Wells do not

have adequate yield during summer.• Drinking water sources are dependant mainly on Rainfall

in case of less Rainfall sources gives inadequate yield or get’s dried in summer .

• Hence these sources are need tobe strengthen by different measures which are conventional & Unconventional .

Conventional Measurers

Deepening of Wells . Augmentation of existing Schemes by Horizontal & Vertical bores In wells . Construction of new Bore well & Dug well . Check dams , Percolation tanks, Earthen nala bunds

, under ground bandharas etc. Augmentation of existing P.W.S

Following unconventional techniques have been developed for the strengthening of drinking water sources.

1. Bore-blast-technique.2. Jacket well -technique3. Stream blast- technique. 4. Fracture Seal Cementation5. Hydrofracturing to bore wells .6. Artificial recharge of bore well & dug well by flooding ,

Rainwater harvesting , Rechage shaft etc.

Implemented as per location and Characteristics of the aquifers.

GSDA’s SOLUTION SINCE 1983

Unconventional Measurers for Drinking Water Source

Strengthening.

Unconventional Measurers for Drinking Water Source Strengthening.

• Most suitable Techniques to improve the storativity and transmissivity of the aquifers in hard rock terrain.

• GSDA developed and implemented first such scheme during 1983 in the Saraste Village of Nashik District.

• Since then 2492 such projects have been implemented by GSDA.

METHODOLOGY & DESIGN OF UNCOVENTIONAL METHODS

1.Jacket Well Technique (JW)

• Jacketing of well with the blasted bore holes increases effective diameter of the well thereby improves the storativity and transmissivity of the aquifer. 9

Jacket well Technique

Boreholes are drilled around the targeted well to a depth little less than the depth of well.

• Subsequently blasting is carried out to create artificial fractures in the compact rocks.

• These bores are drilled either in circular, semi circular or any other desired pattern depending upon the prevalent topographical and hydro geological conditions.

• Explosives of required strength and quantity are used to create maximum fractures and to inter-connect them.

• Sand is generally staved in the boreholes for effective blasting operation and to keep cracks open even after blasting activity.

Jacket well

2.Bore Blast Technique (BBT) :-

• Bore blast technique is adopted to create more storage space for groundwater in massive and crystalline hard rocks by fracturing.

Boreholes for blasting

Source well

Underground bandhara

Highly weathered zone soil

Top view

Moderately weathered zone

Highly weathered zone

Source well

Ground level

• Hydrogelogical and Geophysical survey has to be carried out to know rock can be blasted to develop the cracks.

• Bores are drilled in staggered pattern.

• suitable explosives to be lowered in 2 to 3 sections for effective blasting.

Bore Blast Technique

OK: SIGNAL (Red Flag) Before Blasting

Bore hole Blasting

• This technique is applied in areas where landforms are mostly hilly.

• Being a high cost measure this technique should be adopted to provide drinking water, when no other measure is feasible/possible.

3.Stream Blast Technique ( SBT):- • Generally, drinking water wells are situated on nalla

banks.

• At some places, the groundwater flowing below the nala bed has no hydraulic connectivity with the well, and the well becomes dry or partially dry during summer months.

• Such well can be rejuvenated by this technique,

known as stream blasting.

• In this technique, the area of nalla bed within the vicinity of well is investigated geophysically and geohydrologically. 20

Stream Blasting

• Then bores are drilled in the nala bed to a depth of open dug well.

• These bores are in staggering pattern to get maximum blasting effect in minimum number of bores.

• Pattern and number of bores is decided considering the hardness of the strata to be fractured or shattered.

• These boreholes are further charged with

explosives and blasted to create fractures and joints artificially. 22

• These artificially created fractures get connected to the well and divert groundwater from nalla to the well.

Design Calculations.• Calculate the volume of rock of each bore-hole to

be fractured by blasting. • For example if,• Hard rock depth (h)= 7 meters,• Spacing between the bores = 4 meters • Radius = 2 mtrs. • Therefore volume of rock = ¶r2 x h• = 22/7 x22 x 7 = 88 m3 . • Quantity of explosives required is 150 gms.

per m3. ( 0.150 Kg) • Therefore for 88 m3 rock quantity of explosive

required = 88 x 0.150 • = 13.20 kgs.

Continued

• The diameter of the bore-hole is 100-115 mm. • Use 83 mm dia. slurry explosives (Class 2), the

weight of each bag being 2.78 kgs.

Continued

• Weathered Zone should not be charged.• 1.5 to 2.0 meters below the depth of

weathered zone, explosive charge of 2.78 kgs. = 1 bag should be provided.

• Distance between two explosive charged i.e. section interval may be taken as 2-3 meters.

• Bottom charge should be more.

Explosives charge2.78 Kgs

Explosives charge5.56 Kgs

Explosives charge 5.56 Kgs

Sand StemmingWeathered Zone

Design and Methodology of unconventional Blasting technology.

Bore-hole drilling pattern is decided as per site condition and, this pattern may vary from site to site depending upon the geological conditions.

Bore-holes of suitable diameter (100-150 mm) are drilled to the required depth or to a depth of shallow aquifer.

• Generally 10-15 meters deep drilling of holes would be adequate.

• Distance between the bore-holes i.e. spacing is decided as per site conditions and based on past experience.

• Generally spacing is kept 3-5 meters in basaltic hard massive rock.

Continued

• Staggering pattern of bore-holes is preferred.

• Suitable type of explosives and explosives charge should be lowered into bore-holes to be blasted.

• At any time, not more than 5-6 bore-holes should be charged and fired (blasted).

Continued

Charging and blasting operations should be started from the bore-hole which is lying at the centre of the site and then extended Radially in all directions till the operations are complete.

Controlled blasting of the bore-holes is preferred and if this is not possible or not practicable then, instantaneous blasting may be carried out.

Continued

• Blasting in hard rock only should be carried out i.e. weathered zone should not be charged and blasted.

Fracture Seal Cementation• Groundwater migration through a network of

shallow depth aquifer from the discharging location is arrested by this technique.

• Cementation may be defined as injection of cement slurry under pressure to fill voids, cracks seams, fissures or other cavities.

• The result is to ensure water tightness by establishment of very low permeability.

Fracture FSC-1 FSC-2

Hydrofracturing.Hydrofracturing is a Greek word.

Hydro means water. Hence Hydrofracturing means

Fracturing with the help of water.

Hydrofracturing is a process in which pressurized water is injected into the bore well to increase the permeability of the consolidated material or a relatively impermeable unconsolidated material.

Which improves the yield of the bore well.

Success ratio is about 65 %.

Successful borewell ?• Successful borewell should

provide hygienic, safe, potable drinking water to 250 souls through out the year , 40 liters per day

• maintaining swl less than 36 m.for easier operation of the pump.

< 36 mtrs

Poor yielding Bore wells

1.The b/w is isolated from the nearby water bearing zone by a massive rock intervening between the b/w and water bearing zone.

massive rock

water bearing zone

Poor yielding Bore wells

2.The aquifer contains closed fractures or the b/w is poorly connected to a nearby water bearing zone due to the low permeability of the intervening rock between them

water bearing zone

aquifer contains closed fractures

Poor yielding Bore wells3.The bore well yield low

because some of the open fractures are

choked with accumulates such as clay,resulting in large reduction of hydraulic conductivity of aquifer-fracture system.

Choked aquifer.

water bearing zone

• All these bore wells falling under above three categories can be considered for the treatment of hydrofracturing techniques to improve the yield.

Because

Hydrofracturing is a process in which pressurized

water is injected into the borewell to increase the

permeability of the consolidated material or a

relatively impermeable unconsolidated

material.Which improves the yield of the bore wells.

Methods of improving efficiency of the bore wells.

1.Augmentation of bore wells.

2.Improvement of storage capacity of the aquifer.

Methods of improving efficiency of the bore wells. ( Continued.)1.Augmentation of bore wells by improvement in the yield. a) Sectional blasting. b) Hydrofracturing.

2. Improvement of storage capacity of the aquifer by Accelerating Groundwater movement and recharge --use of HF

Methods of improving efficiency of the bore wells.( Continued.)

1. Augmentation of bore wells by improvement in the yield. a) Sectional blasting.Sectional blasting means blasting of a bore well at particular section to improve the permeability of that zone.

Explosive

Exploder

Bore well

• Results of sectional blasting are more or less futile,as blasting induced fractures could

penetrate to a distance of 2-3 meters only, which is not sufficient for connecting a Bw to

nearest water bearing zone. • It is not possible to control the propogation

of fractures because this is an instant action.

Methods of improving efficiency of the bore wells. ( Continued.)

• Most of the bore wells taken for the drinking water purpose are in the vicinity of villages hence sectional blasting is having restricted scope due to safety precautions.

Sectional Blasting . Continued.

Hydrofracturing.HF is carried out bysealing a section ofB/w & pumping waterat high discharge rateinto the sealed offsection.So thatenormous pressure iscreated into theconfined space whichcreates the fractures.

Hydrofracturing.

Due to creation of network of fractures

in the hard rock by Hydrofracturing:

• Yield of the BWs can be improved.

• Intake and storage capacity of aquifer improves, which in turn improves

recharge.

• Hence the Bw become a sustainable source

Hydrofracturing.

• To understand the principles of HF a good example is of pumping air into a balloon more than its capacity will result into the bursting of balloon.

Water tanker.HF Unit

Inflated Packer rubber seals

Hydraulic hand pump.

Pressure gauge

Hydraulic packer cylinder

Hydrofracturing Unit

Prime mover

High Pressure Water Injection Pump

Over head Crane

Generator Set

Line Diagram

Water Tanker

Booster PumpHigh Pressure water injection pump

(WOMA Pump)

Hydraulic Packer

HF Unit

High Pressure Hose.

Lowering of Dummy Tool

Lowering of Packer

Drain valve

Pressure Gauge.

Then release outlet valve of tee to drain water under pressure in the B/w.When pressure of drainage water falls down release packers and set it to next section and repeat the process.

HF ObservationsFluid pressure in

the sealed segment instantaneously increases till breakdown pressure(pc) is reached.

Pressure

Breakdown pressure

HF ObservationsThen the fluid

pressure suddenly drops

(pf)indicating that a

hydrofracture is initiated on the

b/w wall.

Pressure

Breakdown pressure

HF Observations

On further pumping of the frac fluid the fracture propogates.It may be observed that the pumping pressure

remains constant at pf during propogation hence it is called as the fracture extension pressure.

Pressure

Breakdown pressure

HF Observations

When the pumping is stopped and the B/w is

isolated from the pump by shutting in the valve in between them then the fluid

pressure i.e. pf instantaneously drops to psi called as shut in

pressure.

Pressure

Breakdown pressure

(pf) psi

Pressure

Fluid pressure suddenly rises till the breakdown pressure reached = pc

Then the fluid pressure suddenly drops= pf this is due to fracturingof rock.

When the the pumping is stopped then the pf drops to psi i.e. shut in pressure.

• During Hydrofracturing average dynamic aperture observed is 3 mm. However on releasing of pressure the fractures closes back.

Post HF Results

But the fractures do not come

back exactly to their original

positions.

which act as a channel to transport groundwater from the near by water

bearing zone into the B/w.64

This imperfect closure imparts

considerableImprovement in the permeability

Post HF Results

This results

in Rejuvenating

the B/w.

• The well yield after HF is mostly depends on the fracture created as well as on the permeability of the aquifer.

Post HF Results

HF Analytical Solutions.We can Predict required frac fluid pressure, to

initiate a vertical hydrofracture .Models provide theoretical basis to determine the

length and aperture of fracture as a function of :Frac fluid discharge rate.Pumping time.Frac fluid viscosity.Aquifer rock propertiesAquifer fluid properties.

• Also it predicts the distance to which the pre existing fracture reopen.

• Requirement of max pumping pressure,time of pumping,optimal discharge rate have been worked out for this.

HF Analytical Solutions .Contd

• Length and aperture of fracture created is idealized as below:

• fracture length is directly proportional to the discharge rate for a given time of pumping.

• Q is constant in HF as 335 LPM

For the Propagation up to

Pumping Time Required in minutes.

100 m 20

200 m 40

300 m 60

• It can be decided the Q and time required to get a particular frac length.

HF Analytical Solutions .Contd

Conclusion• For rejuvenating the low yielding borewells

HF is the most effective technique, provided HF is carried out by pumping frac fluid at fairly large discharge rate of 400-600 LPM.

• Success depends on the geohydrological conditions of the aquifer.

• Efforts will be futile if there is no water bearing zone near by.

Conclusion

• Every effort should be made to know the success and failure of the HF.

These are few methods GSDA is using for the

strengthening of Sources.

2.Accelerating Groundwater movement

and recharge by HF

Accelerating Groundwater movement and recharge by HF

• It is established that the HF can be used to improve the recharge conditions also.

• HF • creates new fractures,• cleans existing fractures,• widen and propogates the fractures.

• In other way the above physical changes in the properties lead to improve the intake capacity and storage capacity of the B/w.

• It is observed that the intake capacity of the B/w is improved by 3.5 times.

• It means the recharge can be improved up to 3.5 times more by HF .

Sr.No.

Particulars Basalt(bars)

Granite(bars)

1 Break down pressure -Pc 110 145

2 Reopening pressure -Pr 70 75

3 Propogating pressure- Pf 60 40

4 Shut in pressure- Psi 40 70

5 Max.H.P.stresses -SH 50 75

6 Min.H.P.stresses -sh 40 50

7 Tangential stresses -T 40 70777

Values determined for the basalt and granite.

Methodology.• Measure intake capacity of the B/w.• HF the B/w.• Measure the post intake capacity.• Select near by Surplus surface water source.• Install submersible pump on the B/w

(without foot valve.)• Connect delivery pipe to surplus water

source.

Methodology.

• Observe that the submersible pump is lowered below the level of intake pipe line.

• Check the system is leak proof.• Operate the sub.pump for few

minutes and stop the pump.

Methodology.

• Reversible flow will start from the surplus water source to B/w.based on siphon principle.

• Run the system round the clock till the surplus water is available.

• Detach the pipe line after completion of season.

Schematic diagram of Reverse flow for recharge

Open well/Village tank/Percolation tank Siphon/Piping

Borewell

Submersible pump

Borewell

Submersible pump

Borewell

Submersible pump

Siphon in action Dug well water is

recharged into the Bore well.

Siphon in action Dug well water is

recharged into the Bore well.

Interpretations.

• It is observed that the recharge is inversely proportional to the propogation pressure.

• Hence while carrying out Hf it can be predicted that if the propogation pressure is less, the B/w is likely to accept more recharge.

• Normally Dugwells can be taken as a surplus water source for recharge.

Success Stories.

DRINKING WATER SOURCE STRENGTHING AT VILLAGE HIVARE BAZAR DISTRICT AHMEDNAGAR.

Design of Bore Blast (BBT)

•The area selected in the village Hivare Bazar for blasting is about 5400 sq mt. •The purpose of the Project was to deviate the shallow aquifer water at the upper ridgethat was flowing outsidethe watershed .

DRINKING WATER SOURCE STRENGTHING AT VILLAGE HIVARE BAZAR DISTRICT AHMEDNAGAR.

Design of Bore Blast (BBT)

•The area selected in the village Hivare Bazar for blasting is about 5400 sq mt. •The purpose of the Project was to deviate the shallow aquifer water at the upper ridgethat was flowing outsidethe watershed .

• The bore blasting was designed in such a way that the water underground flowing outside the village boundary was deviated towards the village by creating artificial fractures in the compact massive basalt which was otherwise acting as a barrier for groundwater recharge.

• Total 103 bore holes were taken with a depth range of 5 to 18 Mts.

Vertical cross section

SR.NO LOCATIONS

13/7/07 14/7/07 20/7/07 31/8/07 15/10/07

(Before Project)(After project)

Static water level below ground level in meter

1 Bore Well at up stream side of project 3.9 3 4.4 4.4 1.2

2 Bore Well at down stream side of project 14 14 0 0 0

3 Dug well Of Shri.Thange Dry Dry 15 2.55 2.1

Monitoring of Static water level of wells around the project site

Date of implementation of BBT project 20th July 2007.

SAROLA PATHAR, TALUKA SANGAMNER,DISRTICT AHMEDNAGAR

• Village Sarola Pathar is among the ‘Hard Core Villages’ where due to adverse hydro geological condition, the inhabitants were deprived from the basic need of potable drinking water. The conventional measures like open dug wells and bore wells could not fulfill the need

• Due to the geomorphologic conditions that are not conducive to support the earlier measures and non-implementation of regional pipe water scheme, the tanker water supply was made since four years to fulfill the village demand during summer.

UCM MEASURES PROPOSED

• The measures proposed were examined in the field and suitable structures for arresting rain water flow, Augmentation of existing borewell by hydro fracturing, augmenting the ground water storage of existing open well, cutoff wall by bore well with fracture seal cementation, recharging the dyke at up stream by rain water harvesting through village tank, feeding the harvested water to dyke through recharge trench and plugging out flow from the dyke at down stream were proposed for implementation.

LOCATION OF UCM STRUCTURE

• In this village three measures have been completed successfully. The dyke which was running from SE-NW was found to be a carrier dykes in nature. This dyke was plugged with the help of an unconventional measure, fracture seal cementation. (F.S.C.) In this method number of borewells are drilled on the downstream of the source well and cement slurry is injected in the borewells with pressure. The plugging of dyke has restricted the movement of subsurface flow.

• After the F.S.C. this dyke was fed with existing village tank water by trenching, this made the availability of groundwater to the existing source, thus the groundwater source was rejuvenated.

• The last measure that was taken up was the hydro fracturing of the existing bore wells. A new bore well drilled in March 1993 yielded 19191 lph of water. A power pump of suitable horsepower was installed on this high yielding bore well and a mini pipe water supply scheme was established on this source. This indicates that there was an overall saturation of groundwater in the project area with a definite increase in the availability of groundwater after the project. As on today there is adequate drinking water in the village.

• The impact of hydro fracturing was seen with a sudden rise in the water level. The poor yielding bore well no. 3 has become a sustainable source for drinking water.

Graph showing differences in the yield of bore well after F.S.C. & Hydro fracturing

Borewell1

Borewell2

Borewell3

Yield in LPH Prior

Yield in LPH After

THANKS

Unconventional measurers sde11

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