Geological Characterization of Texas Oil Reservoirs

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Date

1982

Authors

Galloway, William E.

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Abstract

Of the approximately 153 billion barrels of oil discovered in Texas, conventional techniques and practices are estimated to recover around 33 percent, totaling about 51 billion barrels. If conventional recovery were to reach 40 percent of the original oil in place, which some consider possible, the total conventional production would be around 61 billion barrels.

This leaves between 92 and 102 billion barrels of oil as conventionally unrecoverable. Nonconventional recovery methods could potentially target this substantial volume of oil, but the extent to which it can be recovered is a subject of debate among oil professionals. Estimates for nonconventional recovery range from as little as 5 percent to as much as 40 percent.

Several factors contribute to this uncertainty, primarily concerning the spatial distribution and geologic occurrence of unrecoverable oil within known reservoirs. Historically, it was assumed that reservoirs and fluid distribution within them were uniform and homogeneous, leading to conventional field development based on a specified number of uniformly spaced wells. However, evidence suggests that many reservoirs exhibit significant geologic variations and compartmentalization, rendering uniform spacing inefficient in tapping and draining the reservoir efficiently.

Untapped oil in these areas of geologic complexity is the potential target of strategic infill drilling. Conversely, residual oil remaining in portions of reservoirs that have already been tapped and drained during conventional primary and secondary production is the focus of enhanced or tertiary recovery technologies. These technologies aim to extract additional oil from already depleted reservoirs.

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