Wellbore Storage & Skin — Type Curve Diagnostic
Spreadsheet
32 rows x 4 columns
| A | B | C | D | |
|---|---|---|---|---|
| 1 | WBS & Skin Type Curves | |||
| 2 | Reservoir Properties | |||
| 3 | Permeability, k | 50 | mD | |
| 4 | Porosity, φ | 0.2 | fraction | |
| 5 | Viscosity, μ | 1 | cP | |
| 6 | Total compressibility, ct | 1.5E-05 | 1/psi | |
| 7 | Wellbore radius, rw | 0.354 | ft | |
| 8 | Net pay, h | 30 | ft | |
| 9 | ||||
| 10 | WBS Scenarios | Case 1 | Case 2 | Case 3 |
| 11 | Description | Low C, no skin | Medium C, moderate skin | High C, high skin |
| 12 | C (bbl/psi) | 0.0001 | 0.001 | 0.01 |
| 13 | S | 0 | 5 | 10 |
| 14 | CD | 7.923081561 | 79.23081561 | 792.3081561 |
| 15 | CDe²ˢ | 7.923081561 | 1745174.85 | 3.844003414E+11 |
| 16 | End of WBS (h) | 0.01333333333 | 0.1733333333 | 2.133333333 |
| 17 | IARF onset (h) | 0.4216370214 | 5.481281278 | 67.46192342 |
| 18 | ||||
| 19 | Dimensionless Type Curves | |||
| 20 | tD/CD | PD (Case 1) | PD (Case 2) | PD (Case 3) |
| 21 | 0.01 | 0.009715888294 | 0.009990807725 | 0.009995463317 |
| 22 | 0.1 | 0.09018488603 | 0.09917547089 | 0.09958223696 |
| 23 | 0.5 | 0.3823455815 | 0.481658025 | 0.4902749089 |
| 24 | 1 | 0.6647987452 | 0.9314273674 | 0.9625772346 |
| 25 | 5 | 1.773594435 | 3.685440895 | 4.196917992 |
| 26 | 10 | 2.308225068 | 5.762902704 | 7.183282976 |
| 27 | 50 | 3.328209339 | 9.254183388 | 14.71540983 |
| 28 | 100 | 3.705951945 | 9.776900719 | 15.8042232 |
| 29 | 1000 | 4.888730073 | 11.03342455 | 17.17825084 |
| 30 | 10000 | 6.04403623 | 12.19467546 | 18.3453459 |
| 31 | 100000 | 7.195825158 | 13.34705178 | 19.49828257 |
| 32 | 1000000 | 8.34717695 | 14.49846295 | 20.64974947 |
Description
Dimensionless type curve display for wellbore storage and skin effects. Compares three WBS/skin scenarios showing how the CDe²ˢ grouping controls the transition from unit-slope storage to radial flow. Includes end-of-WBS time estimation and the 1.5 log-cycle rule for IARF onset.
CDe²ˢ grouping. The dimensionless pressure PD during the WBS-to-IARF transition depends only on the product CD·e²ˢ. Two wells with different (C, S) but the same CDe²ˢ will follow the same type curve. This is why type curve matching uses CDe²ˢ as the curve parameter.
Unit-slope identification. During pure WBS, PD = tD/CD exactly (45° line on log-log). Real data that follows the unit slope confirms wellbore storage dominance and allows C estimation.
1.5 log-cycle rule. IARF begins approximately 1.5 log cycles (factor of ~31.6) after the end of pure WBS. This rule of thumb helps estimate minimum test duration.
End of WBS formula: tWBS = (200000 + 12000·S) × C × μ / (k·h). The skin factor S increases WBS duration because the skin pressure drop adds to the storage response.
This blueprint works in dimensionless variables. For real-units analysis, see po.pta.drawdown.analysis or po.pta.horner.pstar.
Workflow
- Reservoir Properties (rows 3–8): Common properties for all scenarios — k, φ, μ, ct, rw, h. Used for dimensional conversions and end-of-WBS calculations.
- WBS Scenarios (rows 10–17): Three cases with different C and S. Rows 14–15 compute CD (via PO.PTA.ToDim.CD) and CDe²ˢ (via
_PO.PTA.CDe2S). Row 16 gives end-of-WBS time in hours. Row 17 estimates IARF onset using the 1.5 log-cycle rule. - Type Curves (rows 19–30): PD vs tD/CD for each case using PO.PTA.PD.VW. On a log-log plot: (1) early tD/CD — all curves follow the unit slope PD = tD/CD; (2) transition — higher CDe²ˢ shows larger hump; (3) late tD/CD — all curves merge onto the IARF trend (flat derivative at PD ≈ 0.5·ln(tD) + 0.8091).
- Key Observations: Case 1 (low C, no skin) transitions quickest. Case 3 (high C, high skin) has the longest WBS period. The CDe²ˢ grouping determines which type curve to match — this is the foundation of type curve matching in modern PTA.
How to use this blueprint
- In Excel, go to the Petroleum Office ribbon tab and click Blueprint Manager
- Search for Wellbore Storage & Skin — Type Curve Diagnostic
- Click on the blueprint to preview the spreadsheet template
- Click Insert to place it into your worksheet. Modify the input values to match your data.