Over the last two decades the process of drilling high-angle and horizontal (HA/HZ) wells has changed from cutting-edge to almost routine. While the industry has developed technologies to log and acquire data from these wells, it has not yet developed the technology to interpret the data quantitatively on a routine basis. Generally, hydrocarbon pore volume (HPV) is calculated from the height, porosity, and water saturation derived from logs in near-vertical wells. Case studies have shown that application of similar procedures in high-angle and horizontal wells can result in values significantly different than those calculated from near-vertical wells. As the apparent wellbore deviation angle increases, so increases the uncertainty in the log-derived properties. Using currently available technology, our observation is that in wells with a relative angle to the formation greater then 80°, HPV cannot be calculated from logs with the same confidence as from near-vertical wells. While historically this has not been a problem, the impact of increased uncertainty associated with the reliance on HA/HZ wells for reservoir assessment needs to be recognized and addressed.

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