Questions
8–12 questions in ONGC/OIL papers
Difficulty
Medium-Hard
Importance
Core — never skip
Overview
Drilling Engineering is the backbone of the petroleum industry, focusing on the mechanical processes required to create a borehole into the subsurface. For PSU exams, mastering this topic is non-negotiable as it forms the technical core of the ONGC and OIL exams. Candidates must focus on the interplay between fluid dynamics, mechanical integrity of the wellbore, and safety protocols.
Rotary Drilling System
The rotary drilling system involves the transmission of mechanical energy to the drill bit through the drill string and rotation. Understanding the components like the swivel, rotary table, and the power system is critical for solving questions related to torque and drilling power.
- Mechanical power = Torque * Angular velocity
- Rig power efficiency is typically 60-70% in field applications
- Hook load = Weight of string - Buoyancy force
- Drill string components: Kelly, Drill Pipe, Heavy Weight Drill Pipe (HWDP), Drill Collars
- Buoyancy factor (BF) = 1 - (Density of mud / Density of steel)
Drilling Fluids & Mud Engineering
Drilling muds serve essential functions including hole cleaning, formation pressure control, and bit lubrication. PSU exams frequently test on the rheological properties and the impact of mud density on well control.
- Hydrostatic pressure (Ph) = 0.052 * Mud Density (ppg) * True Vertical Depth (ft)
- Marsh funnel measures apparent viscosity
- Bingham Plastic model: Tau = Yield Point + Plastic Viscosity * Shear Rate
- Formation damage is often caused by excessive mud weight
- Mud weight increase is the primary method to combat influx
Casing Design & Cementing
Casing provides the structural support for the well, while cementing isolates permeable formations and protects the casing from corrosion. Calculations regarding burst pressure and collapse resistance are common in technical papers.
- Burst pressure rating depends on yield strength and wall thickness
- Collapse pressure is highest at the bottom of the casing string
- Cement slurry density is controlled by water-cement ratio
- Primary cementing involves displacement of mud by cement spacer
- API casing grades: J-55, K-55, N-80, P-110
Well Control & BOP
Well control involves preventing or safely handling kicks using Blowout Preventers (BOPs) to ensure personnel and environmental safety. Aspirants must know the procedures for identifying a kick and the basic shut-in protocols.
- Shut-in Drill Pipe Pressure (SIDPP) indicates the severity of the influx
- Wait and Weight method vs. Driller's method
- BOP Stack: Annular preventer at the top, followed by Pipe Rams and Blind Rams
- Kill Mud Weight = Original MW + (SIDPP / 0.052 * TVD)
- Primary well control is the hydrostatic head of the mud column
Formula Sheet
Ph = 0.052 * rho * TVD
BF = 1 - (rho_mud / rho_steel)
Hook Load = (Weight in Air) * BF
Kill Mud Weight = MW_orig + (SIDPP / 0.052 * TVD)
Tau = YP + PV * Gamma
Hydraulic Horsepower = (Pressure drop * Flow rate) / 1714
Exam Tip
Always convert your depth units to feet and mud density to ppg before using the 0.052 constant to avoid calculation errors in high-pressure questions.
Common Mistakes
- Confusing measured depth with true vertical depth when calculating hydrostatic pressure.
- Neglecting the buoyancy factor when calculating the hanging weight of the drill string.
- Forgetting the constant 0.052 conversion factor for oilfield units.
More Revision Notes
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