Towards the "Snap-Off" Pressure Ratio – Using 3-D Printed Pore Volumes to Better Understand Residual Seal Capacity in Hydrocarbon Exploration

Abstract

Conventional hydrocarbon exploration frequently assumes that hydrocarbon columns are sealed by capillary membrane processes in the small pore throats common to mudrocks. Once the buoyancy pressure of the predicted column exceeds the strength of the capillary membrane in the small pore throats, the seal capacity of the top seal is considered to be exceeded, and leakage begins (drainage). Once leakage is sufficient to lower the column height (and buoyancy pressure), membrane forces re-assert themselves in the pore throats and re-seal the column (imbibition). The ‘snap-off ratio’ is the ratio of the drainage to imbibition pressures for the same geological material and is also assumed to be the ratio of the initial membrane-sealed column height to the subsequent re-sealed column height. The ‘snap-off ratio’ is thus an important number for practical hydrocarbon exploration, as it indicates what a post-leakage remaining hydrocarbon column would be. The ‘snap-off ratio’ is widely assumed to be about ½ the initial column height, but has rarely been measured directly.

We present results of initial experiments in a simple air-water system to measure the ‘snap-off ratio’ directly using 3D-printed pore volumes with a variety of pore geometries and sizes. 3D printing allows for printing pore networks with controlled pore shapes and geometries in a system where the pore throat size, pore wall wettability, and system interfacial tension are all known, allowing for direct testing of assumption about hydrocarbon seal that go back to the 1920’s and Washburn’s initial equation.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018