These core holders are designed to allow the flow of a drilling fluid across the
core face. The direction of the flow is perpendicular to the core face. The flow
paths prior to and after the core face are designed to allow uniform fluid flow.
The design allows for shear rates to 200 sec-1. These core holders generally also
have pressure taps along the core holder to characterize the damage at the core
face versus the damage along the length of the core sample.
The key element of the design is the ability to flow across the core face, without
inducing a change in the flow direction. In other words, the fluid needs to flow
directly across the core face. A channel had to be provided prior to and after the
core face for the fluid to flow without a significant restriction. The picture above
shows that the fluid flow is directly past the core face, without the introduction
of a changing flow pattern caused by a rapid turn at the core face. During a test,
the test fluid is circulated through this channel at a fixed pressure. A second
pressure is set at the core outlet with the use of a back pressure regulator. This
establishes a leak-off pressure that can be varied by the customer. During the test,
a filter cake will build up at the core face and the damage to the various sections
of the core sample can be observed with the use of pressure taps along the core
sleeve and a series of pressure transducers.