TECHNICAL SPECIFICATIONS
TECHNICAL SPECIFICATIONS
1. Summary of the Works
The GAZI BORING will carry out the drilling of test/production boreholes at the drilling site, to be determined by …….? (the CLIENT). Each test/production borehole will require:
• Mobilization of personnel, drilling equipment, mechanical equipment, water supply, mud pump, site leveling, and generating site preparation as required to complete the works.
• Drilling, installation, and cementation-in-place of a permanent surface protective casing of approximately 20” diameter from 0.5 meters above ground level (mbgl) to 6 meters below ground level (magl). • Drilling at a minimum diameter of 18” (457mm) of a borehole to a maximum depth of 985 feet (300 m) (final depth to be determined by …….? drilling supervisor based on ground conditions encountered). The GAZI BORING will be permitted to drill by either direct or reverse circulation methods, although preference will be given to the use of reverse circulation.
• Downhole geophysical logging (resistivity, gamma, caliper).
• Fitting, fixing and installation of the good fixtures, as per the technical specifications including:
• Pump house casing: nominal 12” diameter
• From 0.4 m above ground surface to approximately 150 mbgl, installation of a continuous column of carbon steel casing.
• Installation of steel reducer section between the 12” and 8” steel casing
• Production section: nominal 8” diameter
• Installation of a column comprising stainless steel wire wrapped screen and carbon steel casing connected to the 12”/8” reducer.
• Screen to be minimum Grade 304 stainless steel, wire wrapped, slot size 0.6 mm. A length of approximately 60 m to be distributed along the column.
• Casing comprising low carbon steel. A length of 80 m to be distributed along the column. • Sediment collection tube comprising a 6 m length of low carbon steel casing, which is closed at its base.
• Bow centralisers every 12 m of the column.
Final screen and casing meterage and installation depths will be determined by the …….? drilling supervisor pending the geophysical logging, geological samples and lithology description recorded at each drilled borehole.
• Supply and installation of a graded gravel filter pack. Preparation (sieving, washing, disinfection) and installation of gravel pack within the annular space inside the borehole. Gravel pack grain size is expected to be 0.5 to 2 mm and will be confirmed prior to drilling, based on previous lithological logging completed in the area.
• Installation of sanitary seal and bentonite plugs as outlined in section 4.18.
• Installation of borehole apron as outlined in section 4.19.
• Borehole development according to section 4.20 and instructions provided by the …….? Drilling Supervisor.
• Production testing, to include a minimum 4-step pumping test and a 72-hour constant rate pumping test according to section 4.21 and instructions provided by the ......? Drilling Supervisor. • Provision of all labor, equipment, fluids, materials, and water to complete the job, unless otherwise agreed and approved by the …….? Project Manager
2. General Clauses
The GAZI BORING is obliged under the terms of the contract to carry out the following:
1. Read thoroughly and understand the technical specification document. Failure to do so will NOT be considered a reasonable excuse by the CLIENT for failure to carry out the works as specified; 2. The GAZI BORING will not carry out any drilling activities without the presence or authorization of the CLIENT’s representative ‘drilling supervisor’;
3. Provide the proper machinery, implements and tools which must all be in good mechanical/working condition to carry out the contracted tasks and as per the EQUIPMENT SCHEDULE (Section 4.4); 4. Mobilize and demobilize all necessary equipment to the site under the cost of the contract; 5. Provide all skilled and unskilled labour necessary for the completion of the task(s) –; 6. Incur all costs for the whole team related to living at or near the site under the total cost of the contract; 7. Ensure that safe working practices are used at and around the site to protect both workers and members of the community from harm. The GAZI BORING will be responsible for all safety issues on site (staff and equipment), including training of personnel on safety risks, safety equipment, provision of personnel protective clothing and footwear;
8. Incur all costs related to the transport of personnel or additional equipment to and from the site under the total cost of the contract;
9. Incur all costs related to the repair of mechanical problems with any tools or machinery under the ownership of the GAZI BORING and used in the completion of tasks on this project, 10. Incur all costs related to the loss or damage to equipment, material and personnel; 11. Leave the borehole and any associated equipment in such a way as prevent any act of vandalism and delays to the completion of the project.
The CLIENT and the GAZI BORING will maintain open conversations to ensure that all permanent materials and consumables are provided for the completion of the borehole/well. All permanent items are to be approved by the CLIENT prior to purchase by the GAZI BORING, i.e., casing, screens, gravel/filter pack, bentonite pellets, cement for sanitary seal etc.
The GAZI BORING will submit to the CLIENT for review and approval the final specifications of consumables required for completion of the borehole. Notwithstanding this, it must be ensured that the materials procured meet the specifications determined by this document and that there is no compromise with quality of materials.
3. Expected Geology and Hydrogeology
Three boreholes have been previously drilled by MSF-OCA in Camp 21, which provide lithological descriptions of the underlying strata. These reports are available for review. It is expected that the GAZI BORING will fully review the geology and hydrogeology of the project area to generate a sufficient background for equipping and performing the works.
Typical geological conditions are displayed in Figure 1: Borehole summary sheet for MSF-OCA BH26, located in Camp 21, an example log of one of the pre-existing boreholes. The lithological log indicates that drilling encountered approximately 260 m of Tipam Sandstone before reaching the underlying Bokabil Formation (part of the Surma group).
The Tipam Sandstone
The Tipam Sandstone Formation typically comprises coarse grained sandstone, whose colour varies from yellowish to reddish brown, with limited presence of siltstone and mudstone (Sikder and Alam, 2001). The Tipam Sandstone is loosely to moderately consolidated (Rahman et al., 2008). Intercalations of grey shale occur particularly in the upper portion of the succession, in which current bedding and ripple marks are common features. Conglomerate horizons occur mainly in the lower part (Reimann, 2003). The thickness of this formation is about 300m in this area. This is the target aquifer.
The Bokabil Formation
Records collected at BH26 suggest that underneath the Tipam Sandstone in this area, a low permeability claystone occurs and is part of the Bokabil Formation. This Formation consists typically of grey to black mudstone and grey to yellowish siltstone, to very fine-grained sandstone. This lithology is not considered to be an aquifer. The well’s terminal depth will be determined by the …….? drilling supervisor, if this lithological unit is considered to be penetrated before the prescribed depth.
The lithology vs. Gamma Log and Sieve Analysis is shown in Figure 1: Borehole summary sheet for MSF-OCA BH26, located in Camp 21 to visualise the informatio
Photo-1
4. Scope of Works
4.1 Borehole Site Selection
• Borehole siting will be determined by ......? and will be shown to the GAZI BORING during mobilization and prior to the GAZI BORING arriving in the project area.
• Any changes to a pre-determined and validated location shall be communicated by the …….? project manager and will be provided in writing to the GAZI BORING. If the change to location is within 30 m of the original site, the change can be made onsite through agreement with the site supervisor and the change will be noted in the log book.
• If the location significantly changes, …….? must provide the updated location seven (07) days prior to the commencement of drilling that borehole, and obtain agreement with the GAZI BORING in terms of access and suitability.
• Permissions will be provided to the GAZI BORING but access may need to be improved and maintained over the drilling programme and will form part of the mobilization unit cost.
4.2 Site Preparation
• The GAZI BORING will take full responsibility for obtaining and mobilization of all required equipment and materials to the project area and site of each drilling activity.
• A site plan shall be approved by the …….? Drilling Supervisor to ensure that drainage is provided around the drilling site to ensure effective management of water, drilling cuttings and local environmental protection.
• The GAZI BORING should provide any necessary fencing for the site working area where the borehole drilling and construction works are executed. The site should be secured and fenced to limit public access and ensure children and other unauthorized people cannot access the site.
• Shelters should be constructed to protect the integrity of the site and to protect collected drill samples. • A mud pit may be excavated for circulation of drilling fluids, but its final design must ensure that any drilling fluid will drop fines before flowing back into the well.
• All electric power required on the part of the GAZI BORING during the performance of the work called for under these specifications shall be furnished by the GAZI BORING at the sole expense of the GAZI BORING. • Unless approved otherwise in writing by the Owner, the GAZI BORING shall not remove any existing trees of vegetation on the site. Topsoil removed during the site preparation, drilling, well construction or testing shall be respread over the disturbed construction area by the GAZI BORING once construction is complete.
4.3 Mud Pits
The GAZI BORING is responsible for preparing any mud-pits to circulate and settle drill cuttings. Clean mud free of excessive debris should be maintained at all times in the suction area by ensuring prior settlement. Should it be seen that the GAZI BORING is not controlling circulation and settlement, the work will be suspended until corrective action is performed. Equally, the GAZI BORING will control temporary storage and disposal of cuttings during the course of drilling.
4.4 GAZI BORING’s Drilling Rig & Associated Equipment
The GAZI BORING will provide a list of plant and equipment to be used during the course of the works. The list should comprise all necessary information to demonstrate its adequacy for the demands of the works. The GAZI BORING must ensure that the tools and equipment are in good working order and properly calibrated and maintained for the course of the drilling programme.
All equipment (drill pipes and bits) used by the GAZI BORING in the drilling and construction of the well shall be cleaned and disinfected prior to being placed in the borehole. All equipment and materials shall also be
maintained essentially free of oil, grease, or other petroleum hydrocarbons that may otherwise impact the aquifer and the well.
The cost of any lost or damaged drill bits, rods or any other part of the drilling rig and associated equipment must be covered by the GAZI BORING.
The GAZI BORING’s drilling rig and associated equipment must be capable of drilling to a depth of 300 m at a minimum diameter of 18” (457 mm). The GAZI BORING will be permitted to drill by either direct or reverse circulation methods, although preference will be given to the use of reverse circulation. The GAZI BORING will provide evidence that his equipment is capable of completing the well according to the requirements and approved by the ......? Project Manager.
4.5 Target Yields
The target production capacity of each completed well will be 50 m3/hr.
Cleaning, development and testing of the well will be carried out at higher level of production and, in this respect, development equipment (compressors etc) and test pumps will be capable of producing the well at minimum 70 m3/hr.
4.6 Failed Boreholes
A Failed Borehole, under this Contract, shall be defined as one where the well fails to achieve the target yield set out in Section 4.5. However, the following scenarios will be applied in assessing failure: i. Where the GAZI BORING has been unable to drill to the prescribed depth requirement; ii. Any equipment lost down a borehole must be removed by the GAZI BORING, or the borehole will be considered a lost bore, a replacement borehole will have to be constructed and test pumped at the GAZI BORING's expense. The GAZI BORING shall not be entitled to payment for such tools or equipment; iii. Where Screens have not been placed at prescribed horizons;
iv. Where the borehole has collapsed before casing installation or gravel emplacement due to failures of circulation equipment;
v. Where casing and screens cannot be freely run into the drilled borehole;
vi. Where the GAZI BORING is not able to demonstrate verticality of the open hole and/or alignment of casing;
vii. Inability of the GAZI BORING to properly develop the borehole;
viii. Where the GAZI BORING has used well consumables not previously approved or permitted; ix. Where the GAZI BORING has not followed specific instructions provided by ......? Drilling Supervisor.
In all cases above, the final decision to define a borehole as a Failed Borehole, shall lie with the…….? Supervisor.
The GAZI BORING shall not be paid for Failed Boreholes. Upon determination that the borehole or well has failed and should be destroyed, the GAZI BORING shall furnish all material and equipment and perform all labor to properly destroy the borehole or well. The GAZI BORING may salvage as much casing from the borehole as possible and use it in the alternative borehole upon approval of the …….? Drilling Supervisor. Any damaged casing cannot be re-used.
Failed Boreholes shall be sealed by the GAZI BORING as follows:
• The borehole shall be backfilled to a level of 8 m below ground level with inert material (e.g. drill cuttings), followed by a 6 m long plug of concrete, cement grout, or neat cement.
• The upper 2 m of borehole shall be backfilled with native topsoil. Sealing of the abandoned boreholes shall be done in such a manner as to avoid accidents and to prevent it from acting as a vertical conduit for transmitting contaminated surface or subsurface waters into the water bearing formations.
The replacement borehole shall be constructed adjacent to the lost borehole or at any site indicated by the
4.7 Drilling General
The GAZI BORING will drill a hole at an appropriate diameter in which to install a 6 m length of permanent surface protective casing. The casing will be cemented in place using a cement slurry of Specific Gravity (SG) 1.80 kg/litre from its base to ground surface.
The GAZI BORING will drill each production borehole below the protective casing at a minimum diameter of 18” (457 mm) to a depth of 985 feet (300 m) or until the final depth is instructed by the…….? drilling supervisor.
Any change in cost as the result of changes in final drilled depth will be calculated as per the unit price given by the GAZI BORING as listed in the bill of quantities (BoQ) incorporated into the Contract. The GAZI BORING shall notify the …….? Project Manager in writing of any concerns they have with regards to the drilling works as soon as they occur.
The GAZI BORING will take utmost care to avoid physical and chemical and bacteriological contamination of the well water during the construction process. Where water is polluted owing to the GAZI BORING’s neglect, they will be obliged to carry out all necessary remedial operations, at their own cost, in order to remove such pollution from the well.
During borehole construction, installation, development and test pumping, the GAZI BORING shall use all reasonable measures to prevent entry of foreign matter/objects, contaminated water, gasoline, or any other contaminant into the borehole, either through the opening or by seepage through the ground surface. The GAZI BORING shall be responsible for any objectionable materials that may fall into the borehole and any effect it may have on the water quality or quantity until completion of the Works and acceptance by the ......? Drilling Supervisor.
At all times the GAZI BORING will maintain written records of all tubulars and materials in the well. The GAZI BORING will rigorously maintain depth records for the progressing well depth at all times.
4.8 Materials and Consumables
The GAZI BORING shall be responsible for the supply, storage and delivery to site of all permament materials and consumables used in the drilling of the boreholes. The intent of this Contract is to use permanent materials readily available within Bangladesh in order to minimise the delivery schedules to the site and Contract mobilisation. Following an evaluation of local availability, Table 1 outlines the requirements for permanent materials to be installed in each borehole. The GAZI BORING is offered the opportunity to provide alternative materials meeting similar standards. In this event they should provide detailed modified specifications for each alternative.
The GAZI BORING shall also be responsible for recording accurately all permanent materials installed during the construction of each borehole. At the end of the works, all unused permanent materials (casing, screen and gravel filter) will become the property of …….? or as agreed during Contract formalities. Running lengths of gravel pack, bentonite pellet and cement grout have also been estimated. It is the GAZI BORINGs responsibility to calculate the volumes required for consumables and to ensure that the appropriate volumes are delivered to site. These volumes shall be shared with the …….? Drilling Supervisor who will confirm this is sufficient.
4.9 Rate of Penetration
The GAZI BORING shall record the rate of penetration in metres per minute of the drill bit at 3 m intervals.
4.10 Verticality and Alignment
The GAZI BORING will apply reasonable methods for control of verticality including use of suitable bottom hole assemblies and application of appropriate drilling parameters.
The GAZI BORING is responsible for ensuring that verticality and alignment are to the agreed standard. The GAZI BORING will monitor verticality and alignment by conducting tests at 80 m intervals throughout drilling, so that deviations or errors are identified as soon as possible.
If these deviations or errors cannot be corrected, then drilling shall cease and a new borehole shall be drilled at an agreed position nearby, at the GAZI BORING’s own expense. The abandoned borehole shall be backfilled and/or capped by appropriate methods at the GAZI BORING’s own expense. Verticality
The GAZI BORING will perform drift tests during drilling using a suitable drift indicator at 80 m intervals to keep the hole within 1.5o deviation. The GAZI BORING may propose alternative methods to demonstrate compliance with hole verticality requirements.
Alignment
The alignment test requires to lower a section of pipe or dummy through the total length of the pump house section of the well. The section of pipe or dummy shall have a length of 12 metres and an outside diameter of no more than 25mm smaller than the internal diameter of the casing. The GAZI BORING is expected to supply/fabricate this dummy and it should be disinfected prior to being placed within the borehole.
4.11 Formation Samples
Representative drill cutting samples (minimum 200 grams) of the strata penetrated shall be collected for each 3 m interval (or as directed by the ......? Drilling Supervisor) and at change in geological formation, by whatever method is standard for the drilling technique in use. The GAZI BORING shall take every possible precaution to guard against sample contamination. Samples shall not be washed. Every effort shall be made to ensure a representative sample is collected, stored and adequately labelled for subsequent examination. The GAZI BORING shall provide descriptions of the drill cuttings as the drilling proceeds, at 3 m intervals, along with the depth at which that material was obtained.
The GAZI BORING shall ensure samples are stored in a position where they will not be contaminated by site conditions and protected from the rain.
The samples shall be made available to the …….? Project Manager for examination, as and when they are collected. Upon completion of the drilling the GAZI BORING shall hand over the samples to the Project Manager.
4.12 Use of Drilling muds and drilling additives
If drilling additives are required to maintain borehole stability and raise cuttings to surface, the GAZI BORING must record the use of these within routine drilling reports and described in the borehole log.
Biodegradable drilling polymers are the preferred and permissible drilling mud additives to be used for either of direct or reverse circulation drilling. The polymer will be approved by the ......? Manager prior to commencement of the contract.
Bentonite will be approved only if used sparingly and at a prescribed ratio by weight to the polymer. An absolute maximum ratio, bentonite:polymer of 4:1 may be allowed but will be dictated and modified according to the prevailing site condition. This will be strictly enforced, and the working ratio will be set by the…….? Drilling Supervisor.
All drilling additives and volumes must be approved by the ......? Drilling Supervisor prior to use. All drilling fluids shall be appropriate for water well construction, designed for minimum aquifer penetration, and shall not damage the potential capacity, efficiency, or quality of the well. Should a conflict arise between drilling fluid requirements for ease in drilling and requirements for well yield and aquifer protection then the ruling requirements shall be those for well yield and aquifer protection.
The procurement of additives must be confirmed with the…….? Manager.
Circulating mud properties will be rigorously monitored and the settlement channels, settlement and suction pits will be cleaned and conditioned as necessary. Mud properties will be measured at the suction end of the surface circulation system:
🞆 The density of the drilling fluid should be kept as low as possible but sufficient to ensure stability of the borehole. Mud weight will be maintained at less than 1.08 grm/cc – denser mixes should only be prepared under specific circumstances previously agreed with the …….? supervisor,
🞆 Mud viscosity should be kept as thin as is practicable,
🞆 Mud viscosity/fluid property tests should be conducted and recorded 1) every 8 m of depth or 2) every 4 circulating hours, whichever is more frequent,
🞆 The GAZI BORING will demonstrate that circulation pumps working on the site are able to sustain adequate up-hole or descending annular velocities for efficient cleaning of the hole and hydraulic performance at the drilling bit. These data will be incorporated into the equipment list requested in Section 4.4 of this Specification
4.13 Water Supply for Drilling and Staff
The GAZI BORING shall be responsible for the collection, storage and transportation of all water required for drilling activities but also for personal use and consumption by the GAZI BORING. The GAZI BORING shall be solely responsible for the adequate functioning of its water supply system and shall be solely liable for claims or damage resulting from its use. The GAZI BORING shall furnish and install any necessary pump, piping, storage, and appurtenances to convey water from the Owner’s water system to the well site or to a water truck. The GAZI BORING is responsible for the payment of any fees or charges associated with the collection and transportation of water.
4.14 Downhole Geophysical Logs
The GAZI BORING shall provide and be able to conduct a suite of downhole geophysical logging prior to casing installation.
After drilling the borehole to the prescribed total depth, borehole fluid circulation shall continue until all drill cuttings have been removed from the borehole, the drilling fluid in the hole is uniform, and the geophysical equipment is on location. With approval from the …….? Drilling Supervisor, the drill pipe shall be removed from the hole.
The following minimum suite of downhole sondes will be run through the depth of the drilled borehole.: • Natural Gamma (NG)
• Combination Single Point Resistance (SPR), Long & Short Normal (NR) and Spontaneous Potential (SP) • 3-arm Calliper
If geophysical surveying is sub-contracted by the GAZI BORING, the GAZI BORING shall submit for review and approval by …….? Drilling Supervisor supporting information including:
1. Proposed geophysical subGAZI BORING
2. Proposed geophysical logging program details
3. Geophysical logging equipment and calibration records
The GAZI BORING shall be responsible for ensuring that the wireline winch and geophysical sondes are properly calibrated for accurate recovery of data. The GAZI BORING shall cooperate fully and assist the geophysical operator as required in conducting the geophysical testing.
In the event geophysical testing cannot be performed over the total depth drilled in the pilot borehole, the GAZI BORING shall re-drill or otherwise open the inaccessible or collapsed portion of the borehole to allow for geophysical testing of the entire borehole. All costs for re-opening the borehole, repeated geophysical logging, or additional mobilization of the geophysical subGAZI BORING shall be borne by the GAZI BORING. No additional payment shall be made for re-opening the pilot borehole to the original drilled depth or any increased geophysical testing.
4.15 Borehole Design
The …….? Project Manager shall be responsible for final design of the borehole which includes but not limited to placement of casings, screens and gravel filter. The GAZI BORING will receive instructions from the …….? Project Manager before installation of material into the borehole.
As soon as all the information is available the well design will be confirmed by the…….? Project Manager within 12 hrs. No standby time is warranted.
Depending on hole condition indicated from geophysical logs, the GAZI BORING may be required to perform a sweep of the hole to clear any settled debris or squeezing of the drilled hole.
4.16 Casings and Screen Specifications/Installation
The final specification of screen and casing to be used shall be approved in advance by the …….? Project Manager. The GAZI BORING is fully responsible for procurement and delivery of screens and casing to the site, unless stated otherwise by the CLIENT. Casing and/or screen will not be installed in the drilled borehole unless approved by the ......? Drilling Supervisor
o Pump house casing nominal 12” diameter
▪ From 0.4 m above ground surface to approximately 150 mbgl, installation of continuous column of carbon steel casing.
▪ Installation of steel reducer section between 12” and 8” steel casing
▪ Connection of individual casing joints will be by either screwed coupling or butt welded. The
GAZI BORING will clearly state his intention.
▪ In the event of screwed couplings the individual joints will be tightened to a prescribed torque depending on the final specification of casing
▪ In the event of welding. Welding will be continuous around the joint and performed using an approved welder and welding equipment
o Production section nominal 8” diameter
▪ Installation of a column comprising stainless steel wire wrapped screen and carbon steel casing connected to the 12”/8” reducer,
▪ Screen to be minimum Grade 304 stainless steel, wire wrapped, slot size 0.6mm. A length of approximately 60 m distributed along the column
▪ Casing to be low carbon steel. A length of 80 m distributed along the column
▪ Sediment collection tube comprising a 6 m length of low carbon steel casing which is closed at its base. ▪ Bow centralisers every 12 m of the column.
▪ Joint connection to be performed to minimise potential for galvanic corrosion.
The final lengths and placement of casing and screen will be determined by the ......? Drilling Supervisor and communicated to the GAZI BORING.
The production column of the installation will be centralised at approximately 12 m intervals for its entire length. The centralizer type and dimension will submitted for approval prior to delivery at the site.
The GAZI BORING will clearly state the connection type and its detail for all components of the permanent column.
The GAZI BORING is responsible for ensuring all lengths of casing and screens are straight and there is no sign of damage, corrosion or distortion due to sunlight UV or poor storage practice.
All casing lengths must be free from dirt, grease, fuel or other chemical contaminants prior to their installation in the borehole.
If for any reason, the casing/screen column cannot be landed to its full tally depth the GAZI BORING will remove the column and take appropriate corrective action. This may involve further cleaning and reaming of the hole which will be done at own expense. Any consequent damage to casing/screen
joints will be at GAZI BORING expense. In any event, the …….? Drilling Supervisor will confirm the extent of corrective action necessary,
4.17 Gravel Pack
A properly graded gravel pack shall be provided by the GAZI BORING and emplaced in the annulus between the production column and the drilled borehole. The gradation of gravel will be communicated prior to mobilisation but is expected to be within the range 0.5 to 2 mm. The gravel should be washed, relatively homogenous, siliceous and well rounded. The grains should be hard and of alluvial origin. Samples of gravel delivered to the site will be subject to gradation analysis to ensure the gravel pack is within the appropriate limits. The gravel pack shalled be delivered to the site sieved, washed, disinfected and bagged. The gravel shall be approved by the …….? drilling supervisor.
Sufficient gravel-pack shall be installed to cover the entire production column or at least 30 m above the uppermost screen.
The gravel pack material shall be placed to ensure continuity of the filter pack without bridging, voids or segregation. Gravel will be emplaced in a continous stream of water using a tremie pipe installed in the borehole/column annulus. The tremie pipe will extend, at minimum, to the uppermost screen. Any modification to this practise will be permitted only after approval from the ......? Drilling Supervisor.
The gravel pack volume will be fully recorded and compared against the expected volumetric requirement based on hole/column annulus. Wherever possible the actual level of gravel will be confirmed by tag line.
4.18 Sanitary Seals, Backfill and cementation
The gravel-pack will be capped with 100% coated bentonite pellets to form a seal minimum 30 m (or 90 feet), unless otherwise specified by the …….? drilling supervisor. The bentonite pellets must NOT contain a local clay mix. The pellets should be brought to site and approved by the ......? drilling supervisor before the commencement of drilling works.
The annular space above this seal can be back-filled with inert drill cuttings, supplied by the GAZI BORING. The fill will be brought to a level inside the 6m protective steel surface casing.
The annulus between the protective steel casing and 12” column above the inert fill will be filled with cement. The GAZI BORING may use a cement mixed with powdered bentonite at a proportion of 15% by weight. This will provide a final SG of approximately 1.5 kg/litre. This final operation will be carried out after the completion of development and test pumping described in subsequent sections.
4.19 Well Apron
On completion of all cleaning, development and testing the GAZI BORING will leave the head of the surface protective casing 1 m above ground level and sealed with a flange cap and bolts to secure the borehole from vandalism. A concrete apron will be constructed around the borehole to the following dimensions: 1.5m by 1.5m by 0.5m depth.
The apron should be built from a cement: sand: aggregate mix of 1:2:3 The cement needs to be fresh and to have been unaffected by damp conditions during storage or transportation. The sand needs to be coarse, clean and free from clay. The aggregate needs to be clean, durable, rough and made up of a mixture of sizes of stones, typically ranging from between 5 and 25 mm in size. The concrete needs to be well mixed, without adding excessive water that will weaken the concrete.
4.20 Borehole Development
Development of the borehole shall be carried out by the GAZI BORING upon completion of the drilling and construction of the borehole, in order to maximise well yield. The GAZI BORING shall ensure that the development removes any formation damage caused by the drilling, increases formation permeability around the well screen as well as stabilising the formation and gravel pack so that excessive fines do not enter the well during production.
Development shall be carried out in several stages:
• Circulation of clean water with chemical dispersant to break down any polymer fluids in the well. Dispersant will be prepared according to manufacturer specifications. Hydraulic jetting may be applied using an approved jetting tool. Jetting will require on-wall velocities of 30 m/s and at least 0.3 m3 of clean water fluid shall be jetted per linear metre of screen Jetting shall start from the top of the water bearing formation, progressing downwards through each screen.
• Airlifting of the well using an eductor pipe and internal airline set at various levels to physically agitate and settle the emplaced gravel pack in the production section of the well. The GAZI BORING will provide a compressor with an adequate pressure and volume rating to achieve an effective airlift throughout the production horizon of the well. The GAZI BORING will ensure that the development generates alternating flow directions and that flow velocities exceed operational velocities.
• Over-pumping will also be used to pump the well at higher discharges than foressen during production.
The GAZI BORING will describe his proposed methods and equipment deployed for the development process. Details of the proposed equipment and capacity will be clearly set out as required in Section 4.4 of this Specification.
Sand content and turbidity will be measured every 1 hour of development. Development shall continue until the …….? project Manager is satisfied that the water is completely free from fine particles and free of turbidity.
Upon completion of the development, any accumulation of material shall be removed from the bottom of the borehole by airlifting.
4.21 Test Pumping
Test pumping shall be performed on all completed boreholes to establish the hydraulic characteristics of the completed well. The GAZI BORING shall provide a test pumping unit for the test pumping of the borehole. The GAZI BORING must provide and install a temporary test pump to deliver
approximately 60 m3/h against a head of 160 m. The GAZI BORING will provide appropriate pump characteristic curves to confirm the pump capacity.
The pump will be installed with a non return valve, a suitable control panel, generator, rising main, electrical connections, and all other ancillary equipment required to carry out the pumping test. The GAZI BORING must ensure that the power generating capacity and necessary fuel to run the pumping equipment is on site before commencement of the tests.
A dip tube of minimum 1.25” internal diameter (ID) should be installed with the test pump In order to enable manual and automated water level data to be collected during the test pumping.
Test pumping will comprise the following:
• A 4-stage step test. The well will be pumped for fixed periods at progressively higher discharges. Each period will be for 2 hour periods. The change in discharge will be controlled and achieved through a well head control valve.
• Recovery of the water level to the original water surface or as confirmed by the ......? Drilling Supervisor. • Constant discharge test. The well will be pumped continuously at a constant discharge for a period of 72 hours. The discharge will be maintained with 10% of the starting discharge throughout the period of pumping. • Recovery measurements. The recovering water surface will be measured for a period of at least 48 hours. The GAZI BORING may remove surface equipment during this period but will not remove the down hole pump and rising main.
Discharge measurements shall be measured using at least one flowmeter, calibrated within the past 6 months. The calibration certificate/proof of calibration shall be presented to the ......? Project Manager prior to commencing of the pumping tests. A V notch calibrated weir should also be undertaken during the pumping test to provide further evidence of discharge volume and sand production. During test pumping, the discharge water shall be diverted in an appropriate manner over a distance of at least 100 m downslope from the wellhead to ensure that this water does not migrate back in the groundwater within the effects of the drawdown radius .
During all testing operations, once the flow rate has been determined and preliminary adjustments made, the measured discharge rate shall be maintained within 10 % of the required rate for the duration of the test. If persistent fluctuations beyond this tolerance occur, the …….? Project Manager may order termination of the test and a subsequent restart after recovery of water levels.
Any test, which is aborted due to the reasons stated above, shall be repeated after recovery of the water level test and restarted at the cost of the GAZI BORING.
Measurements
Dimension Test: The GAZI BORING shall conduct a short-term test (calibration) to establish the approximate yield/drawdown properties and to confirm the schedule of pumping. Rest Water Level Observations: Rest water level will be measured at least twice within 24 hours before the start of any test pumping.
Step Drawdown Test: The …….? Drilling Supervisor will determine the schedule of pumping. Water level measurements will be taken regularly (at least once a minute for the first 20 minutes of each step and then once every 5 minutes for the full duration of each step). ......? may provide an automated water level logger to supplement manual measurements.
Discharge measurements will be recorded at 10 minute intervals. EC readings will be taken at 20 minute intervals measurements
Constant Discharge Test: The pump discharge will be determined after completing the step test. Water level and discharge measurements shall be made at time intervals, approved by the ......? Project Manager. A schedule of field water quality parameters will be agreed and will comprise at least EC, pH and temperature using a multi-parameter sonde.
Water Level Observations during Test Pumping
• The GAZI BORING shall have appropriate electric contact water level gauges for measuring water levels in the borehole to the nearest 10 mm.
• The minimum length of the electrical dipper shall be 200 m. Wellhead arrangements shall permit these gauges to be inserted and passed freely. To accommodate this, the borehole may be installed with a dipping tube, minimum 1.25” inner diameter, strapped onto the rising main to a depth of 2 metres above the pump intake.
Water Quality Analysis
• A total of 4 samples should be collected by the GAZI BORING from each drilled production borehole using a DPHE recommended sampling bottles and preservatives according to the chemical constituent to be analysed: o One water sample and a duplicate collected 50% of the way through the long term constant rate test;
o One water sample and a duplicate will be taken just prior to the completion of the long term constant rate test.
• The GAZI BORING shall arrange storage of the water samples in a cooler to maintain a temperatue of about 5oC, transport of these water samples to the DPHE recommended laboratory for a full suite of water quality analysis as required for major public water supply (see Appendix 2) to be performed at a quality assured laboratory within 24 hrs of sample collection
4.22 Site Clearance
The GAZI BORING will leave the site as close to the condition that it was found before drilling operations began. All debris shall be removed from the site and the ground levelled and cleared prior to handing the borehole over to the CLIENT.
4.23 Reporting
The GAZI BORING will provide a completion report containing all relevant data collected during the course of construction.
The GAZI BORING will maintain a daily report setting out drilled depth, equipment in hole, consumables used and personnel on site. This report will be submitted to the …….? Drilling Supervisor.
A final report at the end of construction, development and testing will be provided to the…….? Drilling Supervisor. This will include:
1. Formation and lithology, including a description of type, colour and hardness;
2. Presentation of complete drill cuttings as samples for each 10 feet depth of drilling; 3. Details of any drill mud fluid or drilling additives used for drilling the borehole, e.g. mud type and viscosities (measured with Marsh funnel) or foam type and quantities;
4. The procedure of drilling – i.e. rate of penetration, any work stoppage, length of any temporary casing installed and all drilled bits and diameters used to achieve final design diameter and total depth; 5. Depths below ground level of water strikes (at each discrete aquifer);
6. A diary of issues encountered;
7. Details and timings of all well consumables installed and used in each borehole (casing, screen and riser material and diameter, casing lengths and locations, sump length, screen length, slot size and location, riser length, gravel pack type, quantities of all material used etc).
There will always be an ......? Drilling Supervisor present during all drilling operations so as to ensure that sampling is being done in accordance with …….?s wishes.
Appendix 2 – Water Quality Analysis
The full suite of water quality analysis, as required for major public water supply, shall include: • Major ions - Na+, K+, Ca2+, Mg2+, Al3+, Cl-, SO4-, NO3-, NO2-, HCO3-, CO2-
• Minor ions/Trace Metals (dissolved) - F-, NH4+, P, Sb, As, Ba, Be, Fe, Mn, Cd, Cr, Co, Cu, Pb, Hg, Mo, Ni, Se, Sn, V, Zn
• Microbiological – Total coliforms, E.coli and Clostridium perfringens.
• Other – pH, temperature, electrical conductivity, total dissolved solids, alkalinity, Total Oxidised Nitrogen, turbidity, taste, colour, odour
• Common hydrocarbon suite – Total Organic Carbon, Volatile Organic Compounds, Semi-volatile Organix Compounds
• Common pesticide suite (including Malathion and Diazinon)
Design of Production Borehole
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