--> Abstract: N3LIP: A Lithology Independent Porosity Model Using Three Neutron Measurements, by M. E. T. Oraby; #90992 (1993).

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ORABY, MOUSTAFA E. T., ARCO Exploration and Production Technology, Plano, TX

ABSTRACT: N3LIP: A Lithology Independent Porosity Model Using Three Neutron Measurements

N3LIP, a lithology independent porosity model using three neutron measurements, thermal and epithermal neutron porosities, and thermal absorption cross section has been developed and was presented at the 33rd SPWLA annual logging symposium. This model considers any formation, regardless of its mineralogical composition, as two major regions. The first region is the pore space which is filled with fluid; the second region, the matrix, is the rest of the formation. N3LIP deals with the second region as a black box where it calculates its diffusion length without a need to know its lithological composition. This matrix diffusion length is calculated using two different techniques while iterating on porosity. The final solution, porosity, is determined by analyzing the solutions of the tw techniques.

N3LIP generates some nuclear parameters known as neutron-slowing-down length, diffusion length, and migration length using the neutron tool responses instead of formation composition. It uses the thermal neutron tool, epithermal neutron tool, and thermal decay time tool to calculate these parameters. N3LIP model is applied to actual reservoirs to calculate porosity in two different types of formations: shaly sandstone and carbonates. The shaly sand reservoirs are Point McIntyre in the North Slope and Long Beach in California; the carbonate reservoir is Sycamore in the Permian basin. Also N3LIP has been applied in Prudhoe Bay, a shaly sand reservoir where the early epithermal tool SNP was run.

Excellent agreement is observed between the calculated porosity using N3LIP model and the core porosity for all the studied reservoirs. N3LIP model is a very inexpensive method to have an excellent porosity estimator. Also, a lithology independent water saturation is under development.

AAPG Search and Discovery Article #90992©1993 AAPG Pacific Section Meeting, Long Beach, California, May 5-7, 1993.