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Calculating net pay thickness is a crucial step in evaluating unconventional reservoirs. It helps determine the productive zone within a formation and influences development strategies. This article provides a clear, step-by-step approach to accurately measure net pay thickness in such reservoirs.
Understanding Net Pay Thickness
Net pay thickness refers to the vertical thickness of the reservoir zone that contains hydrocarbons capable of being produced. It excludes non-productive intervals such as shales or water-bearing zones. Accurate measurement is essential for reserve estimation and well planning.
Step 1: Data Collection
Gather core samples, well logs, and seismic data. Well logs, especially resistivity and gamma-ray logs, are primary tools for identifying productive zones. Core analysis provides direct measurements of reservoir properties.
Step 2: Identify the Reservoir Zone
Use well logs to delineate the reservoir interval. Look for high resistivity readings indicating hydrocarbons and low gamma-ray values suggesting clean sands or carbonates. Mark the top and bottom of the reservoir zone based on these logs.
Step 3: Measure Thickness
Calculate the thickness by subtracting the depth of the top of the reservoir from the bottom. Correct for borehole inclination if necessary. Use the following formula:
Net Pay Thickness = (Bottom Depth – Top Depth) × Cosine of Inclination Angle
Step 4: Adjust for Porosity and Saturation
Refine the net pay thickness by considering porosity and hydrocarbon saturation. Core data and logs help estimate these parameters, ensuring the measured thickness reflects the productive zone accurately.
Summary
- Collect comprehensive well and core data.
- Identify the reservoir zone using logs.
- Measure the vertical thickness accurately.
- Adjust measurements based on petrophysical properties.