Formation damage

Improving the Interpretation of Formation-Damage Laboratory Tests

The paper presents a new approach that uses X-ray-microcomputed-tomography (micro-CT) scanning to produce high-resolution data of entire core samples.

jpt-2015-02-fig2improvinginterpret1.jpg
Fig. 2—Example of the difference-mapping technique applied to a tested core sample. The post-test image (A) shows a mudcake attached at the top, which is not present in the pretest image (B). Image B is subtracted from Image A, leaving behind the change (C).

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.

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