3-D Printed Reservoir Sandstone: How Accurate Are Pore System Copies?

Abstract

Recent advances in pore-scale imaging and modeling have allowed these techniques to be more commonly used to test hypothesis about petroleum reservoir rocks. The current challenge of this so-called “digital core analysis” is to integrate data with different resolutions, from nanometer in microscopy images to centimeter or larger in well logs. High-resolution x-ray computed micro-tomography (CT) is one route to build accurate digital pore network models. Three-dimensional (3-D) printing is a novel technique that transforms digital pore models into tangible rock samples, which are analyzed using traditional laboratory methods and compared to petrophysical measurements of conventional core analysis. This study uses a combination of CT and petrography data from Fontainebleau sandstone samples and 3-D printing to characterize heterogeneity, pore classes, and porosity types at different scales. CT data of sandstone samples represent cubes with three millimeters on each side. Conventional core analysis for Fontainebleau sandstone gives porosities of 13–28%, whereas pore sizes range from 3 to 100 microns. The mean grain size of Fontainebleau sandstone is 250 microns. The resolution of CT imaging varies from 5 to 40 microns; the resolution of 3-D printing used in the study varies from 2.5 to 300 microns. Increasing the scale of the pore systems ten-fold (e.g., from 5 micron in reality to 50 microns in a 3-D printed model) helps better determine porosity-permeability relationships because connectivity of small pores that is not observed at the original scale becomes distinguishable after up-scaling. Moreover, the digitally up-scaled pore network is quantitatively analyzed taking into account the up-scaling factor that influences changes in properties like fluid pressure, flow velocity, and viscosity. Preliminary results show that porosity, pore size distribution, and permeability can be measured on 3-D printed copies of Fontainebleau sandstone. Mercury injection tests conducted on replicated samples manufactured from silica and polymer powders reveal discrepancies in pore network replication that can be eliminated in the course of digital modeling. CT images of clean and brine-impregnated 3-D printed models help comparing contact angles and wettability with original samples and deriving conclusions on accuracy of pore geometry and topology in 3-D printing materials used for manufacturing.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015