BAKER HUGHES - Drilling Fluids Reference Manual

HORIZONTAL AND EXTENDED REACH DRILLING
The examination of a core from the formation should include a petrographic analysis and mineral
composition by X-ray diffraction and scanning electron microscope. This information can be
coupled with data from return permeability tests of core plugs to choose the least damaging fluid.
Droddy, et al, utilized these analytical procedures for fluid selection on an argillaceous sandstone
from the Wilcox Formation, for example. By combining the findings of the petrological and
mineralogical analyses with return oil-permeability tests, it was possible to make a comprehensive
selection of the drilling fluid for this formation.
Core Permeability Testing
The formation damage test involves a sequence of flow tests in a liquid permeameter as shown
schematically in Figure 11-10.
Figure 11 - 10
Permeameter Schematic Diagram
The core is mounted in a Hassler-type cell, evacuated, and then saturated with simulated formation
water. The initial oil permeability, K (i, oil), is determined by flowing a filtered mineral oil through
the core under constant pressure until irreducible water content is obtained. This state is indicated
by a constant flow rate and stabilized differential pressure. The downstream or borehole face of the
core is then exposed to the test fluid under pressure for a period of time. Oil flow is then initiated in
the original direction of flow (formation to borehole) under the same initial pressure until the flow
rate and differential pressure stabilize. The permeability to oil at this point is the return oil
permeability, K (r, oil).
The ratio of K (r, oil) to K (i, oil) is expressed as the percent return permeability, % K (r, oil). A
return permeability of 90% is considered good, since a permeability loss after fluid off of 10% or
more is commonly experienced, even with the least damaging fluids.
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006. 11-22