A novel model of predicting Archie’s cementation factor from nuclear magnetic resonance (NMR) logs in low permeability reservoirs

Abstract

The resistivity experimental measurements of core samples drilled from low permeability reservoirs of Ordos Basin, Northwest China, illustrate that the cementation factors are not agminate, but vary from 1.335 to 1.749. This leads to a challenge for the estimation of water and hydrocarbon saturation. Based on the analysis of Purcell equation and assumption that rock resistivity is determined by the parallel connection of numerous capillary resistances, a theoretical expression of cementation factor in terms of porosity and permeability is established. Then, cementation factor can be calculated if the parameters of porosity and permeability are determined. In the field application, porosity can be easily obtained by conventional logs. However, it is a tough challenge to estimate permeability due to the strong heterogeneity of low permeability reservoirs. Thus, the Schlumberger Doll Research (SDR) model derived from NMR logs has been proposed to estimate permeability. Based on the analysis of the theoretical expressions of cementation factor and SDR model, a novel cementation factor prediction model, which is relevant to porosity and logarithmic mean of NMR T ² spectrum (T _2lm), is derived. The advantage of this model is that all the input information can be acquired from NMR logs accurately. In order to confirm the credibility of the novel model, the resistivity and corresponding laboratory NMR measurements of 27 core samples are conducted. The credibility of the model is confirmed by comparing the predicted cementation factors with the core analyzed results. The absolute errors for all core samples are lower than 0.071. Once this model is extended to field application, the accuracy of water and hydrocarbon saturation estimation will be significantly improved.

Keywords

cementation factor / nuclear magnetic resonance (NMR) / low permeability reservoir / logarithmic mean of NMR T ₂ spectrum / saturation calculation

References

Abushanab M A, Hamada G M, Oraby M E. DMR Technique Improves Tight Gas Sand Porosity Estimate. Oil & Gas Journal, 2005, 103(47): 54-59.

Archie G E. The Electrical Resistivity Log as an Aid in Determining Some Reservoir Characteristics. Transactions AIME, 1942, 146: 54-62.

Borai A M. A New Correlation for the Cementation Factor in Low Porosity Carbonates. SPE Formation Evaluation, 1987, 2(4): 495-499.

Carpenter P J, Ding A Z, Cheng L R, . Apparent Formation Factor for Leachate-Saturated Waste and Sediments: Examples from the USA and China. Journal of Earth Science, 2009, 20(3): 606-617.

Chen L Q, Zou C C, Wang Z H, . Logging Evaluation Method of Low Resistivity Reservoir—A Case Study of Well Block DX12 in Junggar Basin. Journal of Earth Science, 2009, 20(6): 1003-1011.

Focke J W, Munn D. Cementation Exponents in Middle Eastern Carbonate Reservoirs. SPE Formation Evaluation, 1987, 2(2): 155-167.

Gomez C T, Dvorkin J, Vanorio T. Laboratory Measurements of Porostiy, Permeability, Resistivity, and Velocity on Fontainebleau Sandstones. Geophysics, 2010, 75(6): 191-204.

He Y D. Analysis of Conductive Characteristic and Study of Evaluation Methods of Low Porosity and Permeability Reservoirs: [Dissertation], 2005 Beijing: China University of Petroleum

Jackson P D, Taylor-Smith D, Stanford P N. Resistivity Porosity Particle Shape Relationships for Marine Sands. Geophysics, 1978, 43(6): 1250-1268.

Kenyon W E. Petrophysical Principles of Applications of NMR Logging. The Log Analyst, 1997, 38(2): 21-43.

Kenyon W E, Day P I, Straley C, . A Three-Part Study of NMR Longitudinal Relaxation Properties of Water-Saturated Sandstones. SPE Formation Evaluation, 1988, 3(3): 622-636.

Knight R, Endres A. An Introduction to Rock Physics Principles for Near-Surface Geophysics. SEG Investigations in Geophysics, 2005, 13: 31-70.

Mao Z Q. Study of Foundational Experiment, Theory and Application of Saturation Logging Interpretation on the Reservoir Condition: [Dissertation], 1995 Beijing: PetroChina Research Institute of Petroleum Exploration & Development

Olsen C, Hongdul T, Lykke-Fabricius I. Prediction of Archie’s Cementation Factor from Porostiy and Permeability Through Specific Surface. Geophysics, 2008, 73(2): 81-87.

Purcell W R. Capiliary Pressures-Their Measurement Using Mercury and the Calculation of Permeability Therefrom. Transactions AIME, 1949, 168: 39-48.

Raiga-Clemenceau J. The Cementation Exponent in the Formation Factor-Porosity Relation: The Effect of Permeability. Society of Petrophysicists and Well-Log Analysts, 1977, 13.

Ransom R. A Contribution Towards a Better Understanding of the Modified Archie Formation Resistivity Factor Relationship. The Log Analyst, 1984, 25(2): 7-12.

Saha S, Asquith G B, Drager L. A New Approach to Estimating Sw in Carbonate Reservoirs. The Log Analyst, 1993, 34(3): 20-25.

Wyllie M R J, Gregory A R. Formation Factors of Unconsolidated Porous Media: Influence of Particle Shape and Effect of Cementation. Transactions AIME, 1953, 198: 103-110.

Xiao L, Mao Z Q, Li G R, . Calculation of Porosity from Nuclear Magnetic Resonance and Conventional Logs in Gas-Bearing Reservoirs. Acta Geophysica, 2012, 60(4): 1030-1042.