Naturally fractured reservoirs are the most significant target for horizontal wells in the U. S. While most of the horizontal wells drilled to exploit naturally fractured reservoirs are not logged, substantial useful information can be obtained by logging such wells. A previous paper1  contrasted various logging technologies including acoustic televiewers, sonic logs, and oriented microresistivity devices. Union Pacific Resources (UPRC) has logged 42 of the 120 horizontal wells drilled to date; 38 of these wells have been logged with Schlumberger’s Formation MicroScanner (FMS), an oriented microresistivity device. Extensive analysis of these logs on UNIX-based workstations and correlation with horizontal well performance has resulted in a correlation between the horizontal well fracture index (RFI) and horizontal well fluid Productivity Index (PI). Attempts to correlate RFI with ultimate oil or oil and gas recoveries have been unsuccessful; however, a correlation with ultimate fluid (oil+water) recoveries has been developed. These correlations have been used to integrate FMS information with artificial lift, stimulation, isolation, and repair decisions as well. Example cases are used to illustrate these decisions. Further, the quantified data have been used in making development, exploitation, and spacing decisions. Geostatistical techniques used in reservoir characterization efforts have also incorporated the spatial distribution and correlation of RFI density.

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