Modeling pore proximity using a modified simplified local density approach

Abstract

Unconventional oil and gas resources have gained remarkable interest, as their production is expected to grow significantly in the coming decades. However, among these resources, the shale formations feature extremely small nanopores, imposing considerable challenges in characterizing and modeling fluid pressure-volume-temperature (PVT) property and fluid phase behavior. The fluid phase behavior was reported to deviate from its bulk phase when confined in nanopores. This is often referred to as pore proximity effect. Herein, we present a systematic study using a modified simplified local density (SLD) approach to investigate the pore proximity effect. Phase envelopes have been constructed for two typical synthetic hydrocarbon mixtures representing volatile and black oils as well as two real-life crude oil samples extracted from an unconventional reservoir in Canada. This work is the first report applying the SLD model on real-life crude oil samples. With decreasing pore size, the confined fluids all exhibit shrinking two-phase envelopes, where the pore proximity effect becomes notable for pore size smaller than 10 nm. Furthermore, the SLD model has been demonstrated on the case where the crude oil sample is confined in a literature reported shale sample with a realistic pore size distribution. This work serves as an important building block towards better understanding of the pore proximity effect and practical implementaion into real-life reservoir simulators to guide production activities.