Seepage Characteristics of Single-Phase Fluids in Tight/Shale Cores

The single-phase flow characteristics are the basic problems of oil and gas seepage research. Compared with conventional reservoirs, tight reservoirs are featured by low porosity and low permeability, and when the flow pressure difference between the two ends of the core is low, the accurate measurement of the flow rate at the outlet end of the core is the key to study the flow percolation characteristics. Aiming at the characteristics of narrow pore throats and low flow rates of tight rocks, a device was designed for measuring the flow rate with a precision of 0.003 cm3. The steady-state flow experiments of 11 shale and tight sandstone cores saturated with nC12 were conducted to study single-phase flow characteristics. The results show that (1) The micro-nanoscale pores of shale reservoirs are developed, including microfractures, intergranular pores, intragranular pores, organic matter pores and intragranular pores, and the pore morphology is irregular. Organic matter mostly exists in the form of organic matter-clay mineral complexes with clay minerals. (2) for tight sandstone and shale cores with liquid-permeability of 10–3–10–5 mD, under the pressure difference of 0–18 MPa, the relationship between flow rate and pressure gradient is a straight line through the origin, which obeys the Darcy’s law. (3) The measured liquid-permeability is 1–2 orders of magnitude smaller than that of the gas-permeability in the experiment process.