Nurmi, Roy¹ 
(1) Borehole Geology & Technology, Fallbrook, CA

ABSTRACT: Sequence Analysis of Petrophysical Data for Improved Formation Evaluation

Sequence analysis of petrophysical data and minor changes in standard presentations are used to identify and quantify secondary pores and their diagenetic evolution. The identification of depositional rock types using cuttings, sidewall cores and well logs defines basic pore system populations, while petrophysical data is used to quantify the impact of diagenesis when the core is not available. Secondary pores that cause wide variations in calculations of water and hydrocarbon saturation are defined and quantified using this sequence analysis of poro/perm and poro/resistivity data. 
Sequence analysis of core porosity and permeability data is valuable for geologists and petrophysicists characterizing carbonate reservoirs. The depth relationship between samples is fundamental to defining diagenetic facies and is available in all core reports, but geological sequence variations are generally not included in Formation Evaluation or in the characterization and analysis of diagenetic overprints on the normal burial and cementation poro/perm trends of each depositional population. A sequence approach in the analysis of well log data and core petrophysical data allows geologists, especially those experienced in SEM and microscopic studies of pores, to apply their experience and rock insights to the log analysis of carbonate reservoirs, particularly Formation Factor and understanding Archie’s ‘m’ exponent. Using conductivity versus porosity rather than resistivity versus porosity also allows geologists to better conceptualize formation evaluation of log data in geological terms and make use of this data in their studies. This approach and techniques insures that more geological knowledge and experience is more fully used in petrophysical studies.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.