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CASING PROBLEM IN DRILLING

INTRODUCTION:

In off shore and on shore drilling casing is very important. It overburden casing is not properly seated, further drilling can not be done due to leakage and if continuous drilling, there will be a possibility of stuck-up of string of Tools & Bit as a result whole borehole will be collapsed. In this condition, Mud drilling is needed in order to avoid silting / caving or borehole can be reamed by bit up to problematic area and large casing can be lowered in order to avoid silting and further drilling can be done without any problem.

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In off shore drilling long casing should be done in sea water up to bottom hard formation of the sea. If the casing is not properly done, Mud density will decrease due to leakage of sea water. As a result drilling can not be done and there is a possibility back firing due to ‘Mud Loss’ in oil well. That is why, the perfect casing is very essential as far as off shore drilling concerned.

CASE STUDY:  (SITE – CALICUT ( NORTH KERELA)
In Coasted Area, the overburden casing can not be done due to frequent silting /casing. That is why, further drilling is not possible. In this situation, Mud Rotary drilling is needed to arrest silting/caving formation.

As decided by Regional Director, it has been decided to construct one combination well by combination rig (DTH-RECP-88/95 Rig Unit) & suitable site was selected by site Geologist at Calicutt (Kerela). The main aim is to tape top zone & bottom zone by construct rotary well/bore well by DTH Machine. Accordingly, one combination well which consist of 200 meters have been constructed out of which 50 meters constructed by rotary drilling for overburden casing as well as, construction of rotary well to tape top zone. Cement ceiling is essential to arrest back pressure of compressor air and gravel down pressure so that hard rock terrain drilling can be done successfully and 36 hours was given for cement settling time. As soon as cement sittling time completed, normal drilling in hard rock was done successfully without disturbing rotary well which constructed at top with screen pipe as recommended by site Geologist in order to tape top zone and gravel was surrounded in order to avoid salting by proper “back washing”. If proper cement ceiling is not done, the gravel will fall into hard rock bore due to which the string of tools struck up and further drilling can not be done by DTH Drilling. The well is discharge 15 LPS     (Top zone + Bottom zone) and gravel was surrounded by back wash before develop well.
In boulder/sliding rock/caving/silting Area, odex drilling can be deployed because, the drilling, reaming and casing will be done simultaneously and silting/caving will not happened due to frequent operation of odex system.
If mud drilling is not available, to avoid silting/caving the problematic caving Area/silting Area should be reamed by 10ӯ button bit in which 7ӯ M.S. Pipe has to be inserted and sealed at bottom perfectly so that hard rock terrain Drilling can be completed smoothly. After completing drilling, the over size pipe 10ӯ which was inserted to avoid caving/silting may be pulled out if possible.

 

CONCLUSION:

1. In problematic boulder area and sliding rock area, casing can done by odex drilling system.

2. In Problematic boulder area, casing can done by odex drilling system.

3. In order to avoid silting, mud drilling can be deployed for overburden casing in Bore well.

4. Big size casing pipe can be inserted by Mud drilling in order to avoid silting.

5. Overburden casing should be straight so that, drilling can be done smoothly other wise there is
    possibility of fishing/ struck up in hole.
 
If the bore is not straight while drilling, the submersible pump will not go upto requirement depth for pump testing.
 
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