| Advanced 3-D Stratigraphic Thickness Calculations in Recon | ||||
Proper thickness calculations are crucial for the accurate determination of hydrocarbon reserves. These calculations become especially challenging in the case of deviated wells penetrating dipping reservoir zones with non-uniform thickness. Traditional 2-D geological interpretation software has long used parallel bed assumptions in the calculation of true stratigraphic and true vertical thicknesses. This incorrect assumption can lead to significant errors in determining thickness values used for hydrocarbon reserve calculations. The figure below describes four most commonly used thickness definitions for the case of a deviated well penetrating a reservoir zone: |
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| The figure above shows 3-D gamma ray logs in Recon with picks showing dip & azimuth. Lines are projected perpendicular to the dip of the red top picks and intersected with the base of zone surface to obtain the most accurate 3-D stratigraphic thickness. | ||||
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To determine the thickness we need an equation that corrects for wellbore deviation, zone dip and zone thickness variation. In this case, TVT is the appropriate thickness used for accurate volumetric reserve calculations. |
Based on the angles defined in the figure above, the following thickness types can be calculated: TVDT = MDT × COS(a) TVT = MDT × {COS(a) – [SIN(a) × COS(b) × TAN(c)]} TST = TVT × COS(c) Angle a: The wellbore inclination (inclination from vertical, 90° = horizontal) obtained from the directional survey. Angle b: The azimuthal difference between the direction of the bed dip (from dip/azimuth for pick at top of zone) and the direction of the deviated wellbore (azimuth obtained from the directional survey). Angle c: Zone dip angle obtained from dip/azimuth data for pick at top of zone. |
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Notice how the depth lattices for the stratigraphically equivalent sections are stretched and compressed in this Recon cross-section. Recon enables you to correlate deviated and horizontal wells directly in TST (True Stratigraphic Thickness) mode. |
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| The scenario shown above shows how the parallel bed assumption can lead to 100% overestimation in the calculation of TVT and TST. Recon calculates more accurate TVT and TST values by using the dip and azimuth information associated with the top of zone pick. By intersecting a 3-D line perpendicular to the pick’s dip with the base of zone surface, a true 3-D stratigraphic thickness value is calculated. | Using Recon’s interactive 2-D and 3-D integrated interpretation environment will release you from your dependence on outdated 2-D calculation methods founded on incorrect assumptions. Recon’s advanced 3-D stratigraphic thickness calculations enable you to improve the quality of your interpretations and increase the accuracy of your reserve determinations. |
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| About AGM | ||||
AGM, also known as Austin GeoModeling, Inc., specializes in developing next-generation 3-D geological interpretation software deployable on a wide range of computing hardware, from low-cost desktop workstations to large-scale immersive visualization centers. Visit the company's website at www.austingeo.com. |
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