Investigation of water film thickness in tight reservoirs using an integrated experimental approach

The current method for calculating the thickness of the water film in tight reservoirs is inaccurate due to the ambiguous definitions of dead-end pore area and water film area. This ambiguity complicates the formulation of appropriate development of tight reservoirs. We propose a novel method for obtaining a more precise calculation of water film thickness that utilizes high-pressure mercury injection (HPMI), nuclear magnetic resonance (NMR), nitrogen adsorption (NA), and contact angle (CA) measurements to accurately determine both the dead-end pore area and the water film area in tight reservoirs, as well as the corresponding thickness of the water film. First, the rock wettability of a tight reservoir is obtained by a CA measurement, and then both the blind end bound water and film bound water are distinguished by using HPMI and NMR, respectively. Subsequently, the radius, total surface area, and number of dead-end pores are calculated by analyzing the mercury injection curve and the mercury withdrawal curve using HPMI. Finally, the total surface area of the tight core is obtained by NA, and the membrane-bound water can be calculated as the difference between the total surface area and the area of dead-end pores. Hence, the thickness of the water film is given by combining volume and area data. The results for the test core sample showed that the volumes of irreducible water, dead-end irreducible water, and membrane irreducible water were 2.05×10 -2 cm 3 /g, 1.57×10 -2 cm 3 /g, and 0.48×10 -2 cm 3 /g, respectively, after the core was subjected to centrifugation. Furthermore, the total surface area and the surface area of the cul-de-sac per gram core were 2.36 m 2 /g and 1.66 m 2 /g, respectively, and the water film area and average water film thickness were 0.70 m 2 /g and 6.85 nm, respectively. The proportion of pore-throat radii less than 6.85 nm was 9.88% of the total pore volume, and the oil and gas in pores less than 6.85 nm could not be produced due to the water film. • A new method for accurately calculating the thickness of boundary layer in tight gas reservoir, is proposed through the high-pressure mercury injection (HPMI), nuclear magnetic resonance (NMR), nitrogen adsorption (NA), and contact angle (CA). • The water in the wetting phase is distributed in the blind-end pores inside the rock and on the rock surface, and the mercury in the non-wetting phase is distributed in the blind-end pores inside the rock. The difference in wettability is used to distinguish the volume of membranous water distributed on the rock surface. • It is calculated that the average water film thickness is 6.85 nm, the existence of water film leads to 9.88 % of natural gas cannot be produced.