BH08 Drilling Depth and Compressor Selection
Drilling Depth & Compressor Selection
Select for the conditions expected through the drilling programme—not just the final depth printed on the enquiry.
A target depth tells an equipment supplier how far the project intends to drill. It does not establish the airflow, operating pressure or tooling arrangement needed to get there. A useful compressor enquiry turns that target into identifiable stages, supported assumptions and specific points for reassessment.
The practical question is: which operating cases must the proposed air package cover, and what changes would invalidate the selection?
This guide focuses on planning that depth-dependent review. Detailed hammer consumption, bore geometry and annular-velocity calculations belong in their respective technical assessments.
Distinguish the target from the equipment capability
A depth figure can mean several different things. Label it before using it in a selection discussion.
Depth description | What it tells the reviewer | What it does not establish |
|---|---|---|
Planned finished depth | The current project objective | A proven compressor requirement |
Possible extension | Additional work that may be requested | Approval to continue with the initial equipment selection |
Rig's published depth capability | A manufacturer specification for an identified configuration | Achievable performance in every formation or water condition |
Previously achieved depth | A historical result under particular conditions | Equivalent duty on a different project |
Depth reached so far | The current stage of the actual hole | Confirmation that all remaining stages are covered |
Keep the rig specification and the compressor assessment connected. Additional air capacity does not, by itself, approve an extension beyond the rig or drill-string limitations. The complete configuration needs to remain suitable for the programme.
Build a section schedule before asking for a compressor size
Divide the programme where the physical arrangement or expected operating conditions change. Suitable boundaries may include a casing transition, a planned diameter change, a different tooling assembly or a formation interval identified in the project information.
The schedule should identify the drill string and the air path for each stage. Increasing string length changes the delivery arrangement that must be assessed; it is not a basis for assigning the same pressure increment to every metre. Record the relevant dimensions, connections and equipment rather than using depth as their substitute.
Where a transition depth is uncertain, show a range or mark it as unconfirmed. A precise-looking schedule should not conceal uncertain geology.
An illustrative depth-stage assessment
Consider a hypothetical project planned to 180 metres, with a possible extension to 240 metres. The intervals below demonstrate how to organise a review. They are not recommended casing depths, formation predictions or validated compressor duties.
Illustrative stage | Planning assumption | Selection question | Required decision record |
|---|---|---|---|
0–30 m | Initial section with a planned casing arrangement | Does the proposed package cover this configuration and drilling method? | Confirmed initial equipment and duty |
30–100 m | Planned open-hole section | Do the selected tooling and assessed air requirement apply to this section? | Applicable hammer and return-flow assessment |
100–180 m | Continuation with greater string length | Have the delivery arrangement and expected conditions been reassessed for the later stage? | Supported late-stage operating case |
180–240 m | Optional extension only | What extra evidence is needed before accepting the extension? | Separate confirmation or an unresolved extension requirement |
Any depth | Conditions depart from the assumptions | Does the existing assessment still apply? | Review of the changed condition before a revised equipment decision |
The benefit of this table is its separation of scope. A supplier can clearly state whether an offer covers the original programme, the extension, or only specified cases awaiting further information.
A quotation saying “suitable for 240 metres” is less useful than a statement identifying the configuration and conditions on which that conclusion depends.
Keep four questions visible as the hole progresses
Does the tooling evidence still apply?
Retain the operating conditions attached to the hammer data. For example, a curve published for a lubricated tool without water injection in a shallow-hole condition should not silently become proof of performance throughout a different assignment.
If the hammer, bit, configuration or operating method changes, identify the replacement evidence. A matching nominal hammer size is not enough to transfer an earlier conclusion.
Has the delivery arrangement changed?
Review the pressure requirement at its stated location. Compressor-outlet pressure, rig-inlet pressure and conditions at the hammer are different descriptions. Identify the losses and conditions already included in the requirement so that they are neither omitted nor counted twice.
A revised string or surface arrangement should be assessed at the relevant flow. Do not convert a depth change directly into a new compressor control setting.
Have the return conditions changed?
For deep-hole DTH work, the assessment must consider encountered water and its associated operating conditions, including back pressure. Record what was anticipated and what is now observed. The total drilled depth is not, by itself, a measurement of the water column or return-path condition.
Refer changes in water, return behaviour or the drilling method to the responsible specialist. The appropriate response cannot be established from the depth log alone.
Is the offered package supported at the required duty?
For each assessed case, request the offered compressor's supported flow at the corresponding pressure and site conditions. Check the configuration actually being supplied. A maximum pressure and a maximum airflow taken from separate specifications do not establish that both are available simultaneously.
Keep conditional cases visible. Where the evidence is incomplete, describe the missing confirmation rather than treating the case as covered.
Separate the confirmed programme from contingency planning
A possible extension deserves preparation, but it should not be disguised as a fully assessed duty. Give the supplier a base programme and a clearly identified contingent scope.
Ask for the information needed to decide between retaining one package for the whole assignment and making a planned equipment change. The comparison should address the assessed operating cases, mobilisation arrangements, anticipated working period and the consequences of waiting for additional equipment. Availability and commercial terms require specific confirmation.
If a booster or combined supply is proposed, obtain a complete interface assessment. The proposal needs its own supported duty and equipment compatibility review; the word “booster” is not a substitute for those details.
Avoid an unexplained percentage added to both flow and pressure as a general depth reserve. Any provision should address a named uncertainty or operating need and remain within the applicable equipment limits.
Agree when the selection needs to be reopened
A useful planning record defines review triggers before mobilisation. These should be tied to the actual project and equipment, rather than copied as universal operating limits.
Change or observation | What to revisit |
|---|---|
Target depth extended | Remaining stages and the scope of the original confirmation |
Different bit, hammer or pipe proposed | Applicable tooling data and the revised assembly |
Casing or hole-diameter programme changed | Delivery and return-path assessment |
Water or formation conditions differ from the brief | The specialist's assumptions and operating-case assessment |
Return behaviour or drilling performance changes | Recorded conditions, equipment condition and the applicable technical review |
Replacement compressor offered | Evidence for the actual substitute at each required duty |
A review trigger does not diagnose a fault or prescribe an adjustment. The site's operating and safety procedures govern the immediate response. The selection record should identify who assesses the change and who confirms the revised equipment requirement.
Record progress in a form that improves the next decision
Link each observation to its depth, time and equipment configuration. Useful records include the hole section, installed string, operating activity, pressure readings with their measurement locations, recorded water observations and any change in tooling or supply equipment.
Separate measured facts from interpretations. “Pressure recorded at the compressor outlet” is a defined observation. “The hammer needs more pressure” is a conclusion that requires supporting assessment.
For a repeat job, retain the original duty sheet alongside the actual project record. The comparison can show which assumptions held, which changed and which equipment confirmation should be obtained earlier next time. A single final-depth figure cannot preserve that learning.
Frequently asked questions
What compressor is required for a 300-metre bore?
The depth alone is insufficient. Provide the bore-section plan, rig and tooling identities, drill-string arrangement, expected conditions and the required operating cases. The resulting duty can then be compared with supported compressor data.
Does deeper drilling always require higher compressor pressure?
There is no universal depth-to-pressure rule. The relevant requirement depends on the actual air path, tooling and downhole conditions. A deeper target warrants review; it does not specify the result of that review.
Can I reuse the compressor that completed the last bore?
It is a candidate when its condition and supported duty are suitable. Compare the previous and proposed configurations and operating conditions before treating the earlier result as evidence for the new assignment.
Is the final depth always the most demanding stage?
Do not assume so. An earlier section may use different tooling, diameter or operating conditions. Assess the relevant stages individually instead of selecting from the deepest point alone.
Should an optional extension be included in the rental enquiry?
Yes. Identify it separately so the supplier can address availability, duty confirmation and any proposed change in equipment. Do not assume the initial rental approval covers an unassessed extension.
Submit your drilling-depth programme
Send Reddy Compressors the target and optional extension depths, section schedule, rig and tooling details, and available formation and water information. Include the assessed airflow and pressure requirements wherever these have already been established.
For sales or rental enquiries, specify the project location, planned operating period and any proposed equipment change between stages. Supply and high-pressure availability remain subject to confirmation against the documented requirement.
Related pages: Borewell Compressors Parts and Lifecycle Support · DTH Compressor Sizing and Duty Confirmation · Borewell Project Enquiry Brief