Investigation of Organic Related Pores in Unconventional Reservoir and Its Quantitative Evaluation

Pores in organic matters are important for-unconventional reservoirs since a large amount of absorbed hydrocarbons reside in these spaces. An integrated method to quantify organic pores, using low field nuclear magnetic resonance (NMR) is introduced in this paper. Relationships between the organic related porosity and geochemical parameters are also discussed. Resistivity, velocity, density, and natural gamma ray spectra are measured simultaneously to investigate petrophysical responses of organic pores, aiming to predict the organic related porosity using conventional petrophysical data. Results show that the NMR signal of samples under the dry state is a good indicator of organic pores and can be calibrated to the organic related porosity. The organic related porosity is,positively correlated with total organic carbon content (TOC), absorbed free gaseous hydrocarbons (S-0), absorbed free liquid hydrocarbons (S-1), and residual petroleum potential (S-2) but negatively correlated with residual carbons (RCs). The organic related porosity is positively correlated with thorium content (Th), natural gamma intensity (GR), and resistivity (R), whereas it is negatively correlated with density (DEN), compression wave velocity (Vp), and shear wave velocity (Vs). The model achieves favorable results, which can be generalized to predict the in situ organic related porosity.