Well drilling :General ...

Well drilling :General &Technical specifications.

Casing

Design Details

The basic well design is shown in the Figure (according to the Special Conditions Data Sheet).The Borehole will be drilled with bits of sufficient size to accommodate the specified casings. The estimated Borehole size and depth for each casing is according to the Special Conditions Data Sheet.

The location of the well screen - perforated casing sections - ( if any ) will be determined according to the water bearing strata as the Engineer may direct.

The Contractor may submit an alternative construction plan for the borehole, provided it permits the lowering of a diameter pump(1) to a depth of around (2) and the sealing of the layers as specified above. Such alternative shall be subject to the Engineer’s approval in writing and to be obtained prior the commencement of the work. The Contractor shall not make any changes in the borehole and the casing dimensions and specifications detailed above or in the quality or type of casing without the prior approval of the Engineer, this approval must be applied for at least one week prior the performance of the work concerned.

The casing permanent diameter will:

- be large enough to accommodate the pump, with enough clearance for

installation and efficient operation,

- be of sufficient size to ensure that the uphole velocity is not less than 1.5 m/sec

- provide an annulus between well casing pipe (protection pipe) and the permanent

pipe that is sufficient to accommodate centralizes and permit cementing with a trimie pipe if needed.

The permanent pipe diameter will be (5) and will be installed (---) m below the water level . The permanent casing shall be Grade J-55 having steel pipe schedule 40.

Three strings of casing will be provided for well production. Protection steel pipe sch. 40 to be large enough to accommodate the permanent steel pipe with enough clearance between protection pipe not less than 25 mm around for quartz installation and sufficient to accommodate centralizer.

The protection steel pipe to be installed and to a depth of about 2 meters below ground

Water level to prevent pollution and stabilize the top soil and upper soft formation.

• Permanent steel pipe sch. 40 as a pump house casing will be installed to a depth of

About ---- meters having out side diameter not less than ---- inch.

• Lower slotted casing s / steel pipe to prevent sloughing of the borehole in the lower formations if required, the perforation slots shall be made by the contractor either by mechanical cutter or by flame cutter subject to engineers approval and shall be (5-7) mm wide and (70-100) mm between ends of adjacent slots. The casing will

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be installed in the borehole to prevent caving and sloughing of loose rocks. Well screen opening to be selected to ratain about 90 percent of the filter pack after development or more. And the slot size of the filter should be accordingly to soil sieve analysis and screen diameter.

• Filter pack shall be placed between around the slotted casing and protection pipe and should be (5-8) m up the ground water level. And should be chosen to retain most of the formation material. The screen diameter is selected to satisfy a basic principle enough open area must be provided so that entrance velocity of the water generally does not exceed the design standard of 0.1 ft/sec. (0.03 m/s)

All casing shall be new, having couplings and buttress thread with a thread protection and of perfect roundness and uniform in wall thickness within detectable limits. Casing ends to be connected by welding shall be mill beveled. The welded casing joint shall develop strength equal to 100 percent of the pipe strength. Should a joint fail or break, the Contractor shall be responsible for the failure. All casings shall be butts welded by certified welders.

The Contractor shall install each type of casing in one string and to the depth selected by the Engineer. Final casing depths will be selected from information obtained during the drilling and geophysical logging.

The Contractor shall install each string of casing true and plumb to line. All casing shall be centralized in the borehole. Centralizers shall be installed as specified herein