In the oil and gas industry, drilling efficiency is critical to the economic success of a project. The two primary metrics used to evaluate performance are the Rate of Penetration (ROP) and the Cost Per Foot (CPF).
What is Rate of Penetration (ROP)?
Rate of Penetration refers to the speed at which a drill bit breaks the rock to deepen the borehole. It is normally measured in feet per hour (ft/hr) or meters per hour (m/hr). A higher ROP means faster drilling, but it must be balanced against bit wear and tool durability.
The basic formula for ROP is:
ROP = Footage Drilled / Rotating Hours
Cost Per Foot (CPF) Formula
While ROP measures speed, CPF measures economic efficiency. It accounts for the cost of the drill bit, the rig's hourly operating cost, and the time spent on non-drilling activities such as tripping pipe. The goal of drilling optimization is to minimize the CPF.
The industry-standard formula used in this calculator is:
CPF = (B + R(T + t)) / F
Where:
B = Bit Cost ($)
R = Rig Rate ($/hour)
T = Rotating/Drilling Time (hours)
t = Trip/Connection Time (hours)
F = Footage Drilled (ft)
Factors Affecting Drilling Rates
Several mechanical and geological factors influence the drilling rate:
Weight on Bit (WOB): Increasing the downward force generally increases ROP up to a certain point (foundering point).
Rotary Speed (RPM): Higher RPM increases the number of times the cutters impact the rock per minute.
Hydraulic Cleaning: Efficient removal of cuttings preventing bit balling is essential for maintaining a high ROP.
Rock Compressive Strength: Harder formations naturally result in lower penetration rates.
Using the Calculator
To use the calculator above, input the length of the section drilled and the time spent actively rotating. To get a complete economic analysis, include the bit cost, rig hourly rate, and non-rotating time (trips/connections). The "Break-Even ROP" metric helps you understand the speed required to justify the cost of the specific bit configuration entered.
function calculateDrilling() {
// Get input values
var footage = parseFloat(document.getElementById('footage').value);
var rotHours = parseFloat(document.getElementById('rotHours').value);
var bitCost = parseFloat(document.getElementById('bitCost').value);
var rigRate = parseFloat(document.getElementById('rigRate').value);
var tripTime = parseFloat(document.getElementById('tripTime').value);
// Validation: Ensure essential values are present for ROP
if (isNaN(footage) || footage <= 0 || isNaN(rotHours) || rotHours 0 || rigRate > 0) {
document.getElementById('resTotalCost').innerHTML = "$" + totalCost.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('resCPF').innerHTML = "$" + cpf.toFixed(2) + " / ft";
// Simple break-even heuristic: Required ROP to cover Rig Rate
// Cost = RigRate * Hours.
// Often used to compare expensive PDC bits vs cheaper Roller Cone bits.
document.getElementById('resBreakEven').innerHTML = "N/A (Comparison requires offset data)";
if(cpf > 0 && rigRate > 0) {
// Showing the percentage of cost driven by rig time
var timeCostPercent = (totalRigCost / totalCost) * 100;
document.getElementById('resBreakEven').innerHTML = timeCostPercent.toFixed(1) + "% Rig Time Driven";
}
} else {
document.getElementById('resTotalCost').innerHTML = "Enter Costs";
document.getElementById('resCPF').innerHTML = "Enter Costs";
document.getElementById('resBreakEven').innerHTML = "-";
}
}