Application of high pressure mercury injection and nuclear magnetic resonance in analysis of the pore structure of dense sandstone: A case study of the Heshui area, Ordos Basin

Abstract

Pore structure restricts the reservoir capacity and flow capacity of oil and gas in the reservoir, which is the key factor of studying tight sandstone reservoir, and also the key and difficult problem of current research. Taking the Chang 7 tight reservoir of Upper Triassic Yanchang Formation in Heshui area of Ordos Basin as an example, the relationship between pore structure and movable fluid parameters was studied by combining high-pressure mercury injection and nuclear magnetic resonance (NMR) analysis techniques. The main results are as follows: ① when using the conventional method and linear least square method to convert the NMR T2 spectrum into pore radius, the pore structure can be divided into two parts, The correlation coefficient is (0.87-0.98)/0.92. The inflection point of the mercury injection curve is calculated by fractal theory, and the corresponding T2 is converted. The T2 spectrum is converted by segments. After the conversion, the curve has a high degree of overlap, and the number of phase relations is (0.97-0.99)/0.98. ② By analyzing the influencing factors of fluid mobility, it is found that there is a direct relationship between rock physical properties, in which porosity is more suitable to characterize the size of reservoir space, the correlation is 0.9, and the correlation with movable fluid saturation is better; The characteristic parameters of pore structure have a good correlation with the parameters of movable fluid, and the tight pore structure restricts the mobility of fluid. The proportion of dead pores is related to SMFS φ The negative correlation coefficients of MFS were 0.5371 and 0.3775, respectively φ MFS has little effect, but it has no effect φ MFS is more suitable to characterize the micro pore structure.

Keywords

• dense sandstone
• nmr
• high pressure mercury injection
• mercury compression fractal
• pore structure
• movable fluid