Estimating the Reservoir Hydrocarbon Capacity Through Measurement of the Minimum Capillary Entry Pressure of Shale Cap-Rocks

Abstract

Shales play a major role in petroleum exploration and production because they occur both as source rocks and caprocks. Their small pore throat size means that very high capillary pressures are required to establish any hydrocarbon saturation in the shales. The minimum capillary entry pressure (trap capacity) defines the maximum height of a hydrocarbon column that can be trapped by a shale.In this paper, pressure transmission tests were used to experimentally measure capillary entry pressures of various non-wetting fluids (oil-based mud, crude oil. Decane and Nitrogen gas) through different shales. These capillary entry pressures are needed for the estimation of a shale's seal capacity (h). Results show that measured capillary entry pressure (seal capacity) of shales are correlated with other shale properties such as CEC and permeability. The effects of fluid type and interfacial tension on capillary entry pressure of shales were also investigated. Results show that the presence of a hydrocarbon phase (decane) in the shale reduces the shale capillary entry pressure (seal capacity) and significantly increases hydrocarbon flux. Also, the presence of surfactants in the hydrocarbon phase significantly reduces the capillary entry pressure and, therefore, the shale's seal capacity. Measured capillary entry pressures were also used to estimate the pore throat radius of shales.Since pressure transmission tests are so difficult to run, a quick and easy rig-site electrochemical test on shale cuttings to characterize the capillary entry pressure of drilled shale formations is suggested.

What’s Conventional and What’s Special in a Reservoir Study for Underground Gas Storage

“…A two-phase fluid flow drainage process is induced through the rock sample in a triaxial cell, which reproduces the in situ confining pressure and stress conditions acting on the rock [10]. The test can be performed and interpreted according to different experimental procedures and approaches [11][12][13]; generally, mercury-air or nitrogen-water systems are utilized in lab experiments and the results are then corrected according to the real gas-water characteristics. A detailed literature review of threshold pressure measurement can be found in [14].…”

What’s Conventional and what’s Special in a Reservoir Study for Underground Gas Storage

“…A two-phase fluid flow drainage process is induced through the rock sample in a triaxial cell, which reproduces the in situ confining pressure and stress conditions acting on the rock [8]. The test can be performed and interpreted according to different experimental procedures and approaches [9][10][11]; generally, mercury-air or nitrogen-water systems are utilized in lab experiments and the results are then corrected according to the real gas-water characteristics. A detailed literature review of threshold pressure measurement can be found in [12].…”

An evaluation of hydrocarbon deposit tightness in aspect of CO2 sequestration

“…At the initial stage, when the nonwetting fl uid pressure increases above the capillary entry pressure P c,entry , the rock is partly saturated with this fl uid. The capillary entry pressure, is a pressure above which the wetting phase is displaced from the unconnected pore canals of the largest diameter at the interface [2]. Exceeding of this characteristic pressure value allows migration of the nonwetting phase to the system of pores in the sealing rock, though the nonwetting fl uid is not observed to fl ow yet.…”