DOES PORE SPACE WITHIN BAKKEN SHALE CHANGE WITH MATURITY?

Source rock maturity of five wells from the Bakken Formation were obtained using the source rock analyzer (SRA). Core samples (one sample each from Upper and Lower Bakken shales) of various sizes and shapes were selected from the five wells with known maturity to test whether pore size distribution varies with maturity. Samples were prepared for NMR by saturating with 300,000 ppm NaCl brine solution under 100 psi of compressed air for 30 days.

Pore size distributions were obtained from NMR transverse relaxation (T2) analysis via Oxford Instruments GeoSpec2 core analyzer coupled with Green Imaging Technology software. Pore size distributions were calculated using T2 cutoff values to partition total porosity measurements into micropores (less than 0.5 microns), mesopores (0.5 to 5 microns), and macropores (greater than 5 microns). I expect that low maturity source rocks will have high porosity because pores are filled with conductive water and will become more matured as high conductive water are replaced with non-conductive hydrocarbon.