Improving the Interpretation of Formation-Damage Laboratory Tests

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 165110, ’Use of Micro-CT-Scanning Visualizations To Improve Interpretation of Formation-Damage Laboratory Tests Including a Case Study From the South Morecambe Field,’ by Justin Green, Ruaridh Cameron, and Ian Patey, Corex, and Vishal Nagassar and Mark Quine, Centrica, prepared for the 2013 SPE European Formation Damage Conference and Exhibition, Noordwijk, The Netherlands, 5-7 June. The paper has not been peer reviewed. The paper presents a new approach that uses X-ray-microcomputed-tomography (micro-CT) scanning to produce high-resolution data of entire core samples. The images of core produced are superior to those produced by commonly used medical scanners and give insight into core properties as well as issues such as drilling-mud-constituent infiltration, mudcake structure and thickness, and alterations in the pore network. Through a technique that the authors refer to as “difference mapping,” data sets captured before and after laboratory testing are compared to reveal the distribution of changes within samples. Introduction Formation-damage laboratory studies aid in risk reduction when making important well-design decisions, so reducing uncertainty surrounding test results is an important effort. The major areas in which laboratory testing can be influenced to provide the most meaningful (and therefore more valuable) information include the following: Performing tests at reservoir conditions of temperature and pressure by use of reservoir overbalance and underbalance pressures and real/representative fluids and exposure periods Ensuring that the equipment and procedures used have minimal or no effect on the results of testing Understanding test results through interpretive analysis to put laboratory-test results into a field context For a discussion of current techniques used to aid in core-sample interpretation, such as scanning electron microscopy (SEM), thin-section analysis, X-ray diffraction (XRD), and computed- tomography scanning, please see the complete paper. Micro-CT Scanning Micro-CT scanning uses a class of scanner that can rapidly capture a series of scans at high resolution; these scans can be reconstructed with software to create a 3D model of the object scanned. Resolution of significantly less than 1 Μm can be achieved on smaller subsamples, reducing as the sample size and length increases. The time taken to capture a data set also decreases as the resolution lowers, so the selection of operational settings is a balance of resolution vs. sampling times and data-set sizes. For scans of intact core samples, a maximum resolution of 10–15 Μm is achievable after taking into account sample size and sampling time.