Mr. Erik Milito - The House Committee on Natural Resources ...

ISOLATING POTENTIAL FLOW ZONES DURING WELL CONSTRUCTION 25
fluid viscosity. <strong>The</strong> process of foaming cement also produces a higher effective fluid rate in the wellbore compared to
the base cement fluid rate that will affect ECD.
5.7 Slurry Design and Testing
5.7.1 General
<strong>The</strong> primary goal of cementing is to maintain the required hydraulic isolation for the life of the well. This may include
placing competent cement between pipe and openhole or between pipe and pipe. Cement also serves to protect the
casing from corrosive fluids and provides mechanical support of the casing. Cement slurries are designed to function
under the expected downhole conditions while meeting the well construction objectives. Various performance
parameters are considered in the design process, these include the following:
— rheological properties,
— hydrostatic pressure control,
— fluid loss control,
— free fluid and sedimentation control,
— static gel strength development,
— resistance to invasion of gas or fluid,
— compressive or sonic strength development,
— shrinkage/expansion,
— long-term cement sheath integrity.
<strong>The</strong> relative importance of each of these factors to cement performance over the life of the well will vary with the
application. In some cases they are even competing priorities. <strong>The</strong>re may also be specific well conditions that require
other attributes to be prioritized in the cement design. While computer modeling may aid the designer in conducting
sensitivity analysis across a range of possible designs, it will still be necessary to use judgment and compromise
between competing priorities.
<strong>The</strong> specific slurry performance properties required to isolate flow zones will vary depending upon the severity of the
flow potential and the formation fluids contained in the potential flow zone.
Test methods for determining the performance of cement are described in API RP 10B-2/ISO 10426-2, API RP 10B-
3/ISO 10426-3, API RP 10B-4/ISO 10426-4, API RP 10B-5/ISO 10426-5 and API RP 10B-6/ISO 10426-6. <strong>The</strong>se test
methods should be adapted, as closely as possible, to simulate the conditions to which the cement will be exposed
during placement across any potential flowing zones requiring isolation. <strong>The</strong> conditioning schedule and test
conditions of the slurry will typically reflect the temperature and pressure found at the potential flow zone.
5.7.2 Lead and Tail Cement
Lead and tail cements are routinely placed in the annulus during primary casing cementing. Lead cements can be
formulated to meet various requirements ranging from economical filler systems to high performance designs. Low
density lead cements are used to lower the hydrostatic pressures to avoid or minimize losses of the cement to the
formations. Tail cements are typically mixed without extending components and thus have a higher density.