You have five (5) wells to correlate Exercise 4 Well Log Correlations You have five (5) wells to correlate Well 5 Well 4 Well 3 Well 2 Well 1 Base Map Description of main class objectives Your Task: Lithostratigraphic correlation Chronostratigraphic correlation

Well Correlation Exercise We will look at the sediments deposited above a regional unconformity Well 5 Shale Baseline Well 5 Well 4 Well 3 Well 2 Well 1 Base Map Resistivity Markers SP for lithology We have five (5) wells that define a SW-NE transect. Each well has an spontaneous potential (SP) log (left track) that we can use to differentiate shale, silt and sand. The right track has a resistivity curve shown with two gain settings. In the shale zones, the resistivity curve has a lot of ‘character’ – somewhat unique highs and lows, and transitions from highs to lows. Several unique ‘patterns’ (fingerprints) are given in well 5 9shown here) – labeled A to H. There is also a regional unconformity marked on each well log. Resistivity for time-correlation Regional Unconformity Vail et al., 1977b AAPG©1977 reprinted with permission of the AAPG whose permission is required for further use.

Well Correlation Exercise On one copy of the well log cross-section, identify the sand sitting above the regional unconformity (use the SP deflection to the left to ID sands) Correlate the logs based on lithology Use the resistivity markers (A, B, C, …) to correlate time-equivalent horizons (hint: markers G and H do not extend all the way to Well 1) QUESTION: Is the lithostratigraphic correlation and the chronostratigraphic correlation different? You are given two (2) copies of the logs laid out as a transect - one is for a lithostratigraphic correlation, the other is for a chronostratigraphic correlation. Note that the animations on Slides 5 and 6 will help the students get started.

Well Correlation Exercise This slide shows the uninterrupted log cross section. Vail et al., 1977b AAPG©1977 reprinted with permission of the AAPG whose permission is required for further use.

Lithostratigraphic Correlation Well 5 Well 4 To get started, we’ll start the correlations from well 5 to well 4. First, mark the unconformity in each well and connect (correlate) them. Use the SP curve to identify sandy zones (curve to the right), and then correlate the tops of the sands. I have marked 3 sands in each well and correlated them. Vail et al., 1977b AAPG©1977 reprinted with permission of the AAPG whose permission is required for further use.

Chronostratigraphic Correlation Well 5 Well 4 A Start with the chronostratigraphic correlations – Marker A, B, and C. I marked part of the resistivity curve near Marker B in Well 5 with magenta. I copied the magenta shape onto Well 4 at where I think it matches. Then I correlate Marker B from Well 5 to Well 4. Repeat for Markers A and C. B C Vail et al., 1977b AAPG©1977 reprinted with permission of the AAPG whose permission is required for further use.

Exercise 4 Questions?