Print this pageSimultaneous NMR T1 and T2 Acquisition Increases Understanding of Complex Lithology
The Tesnus sandstone was deposited in late-Mississipian/early Pennsylvanian time in clastic debris flows. In general, it consists of a series of sand/mudstone turbidite sequences that are deposited in thicknesses varying from a few hundred to several thousand feet overall. The uppermost Tesnus consists of amalgamated and thinly bedded sands that contain poor - good vertical connectivity and tend to have better ultimate recoveries. The lower sands are layered sands consisting of thin interbedded sandstone and shale sequences with poor vertical connectivity.
The sands in the WTO present an analysis problem with conventional open-hole logs since standard porosity interpretation is not correlative to well performance due to the clay content and poor permeability that is difficult to measure/quantify. Hydrocarbon production from the Tesnus is primarily natural gas with varying amount of CO2 content from 1% - 30% and very minor amounts of formation water. Sand and shale sequences can be as thin as 1-2 inches. These thin zones could have high permeability zones next to zones of no permeability. Even thin bed logging approaches could not adequately measure this.
Magnetic Resonance logs were added to the typical logging program in an attempt to gain a better understanding of this complexity. Utilizing T2 bin distribution permeability calculations supplied an exact understanding of where these high permeability zones occurred in the wells. The T1 response was utilized as a fluid typing measurement, increasing confidence in pay calculations. This allowed completions to be targeted in the more productive parts of the Tesnus and enhanced the calculation of net pay. We think this application could be used in many difficult reservoirs.
AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil