Page 126 - Shale Shakers Drilling Fluid Systems
P. 126
CHAPTE R FOU R
Shaker Applications
Most drilling rigs are equipped with at least one probably be processed through a 200-mesh screen
shale shaker. The purpose of a shale shaker, as on most linear motion shale shakers.
with all drilled solids removal equipment, is to
reduce the drilling cost. Most drilling conditions
require limiting the quantity and size of drilled SELECTION OF SHAKER SCREENS
solids in the drilling fluid. Shale shakers remove
the largest drilled solids that reach the surface, Proprietary computer programs are available
which are the ones that create many wellbore that reportedly allow estimating screen sizes used
problems if they remain in the drilling fluid. on specific shale shakers. Most of these computer
programs are verified with data obtained from
laboratory-prepared drilling fluid with limited prop-
SELECTION OF SHALE SHAKERS erty variation. Different drilling fluid ingredients
can reduce the capacity of a shaker system and,
The first consideration in selecting a shale shaker therefore, predicting screen-mesh sizes that will
is to decide whether or not a gumbo slide, or handle certain flow rates is very difficult. For ex-
gumbo-removal device, will be needed. This is ample, a drilling fluid containing starch is difficult
often necessary when drilling recent sediments. to screen because starch, acting as a good fil-
A scalping shaker must be considered next. tration control additive, tends to plug fine mesh
Scalping shakers are usually needed when large screens. Drilling fluids with high gel strengths are
quantities of drilled solids or gumbo reach the also difficult to screen through fine meshes. For
surface. Usually, long intervals of 17 -j-in.-diameter these reasons, screen selection for various shale
holes, with flow rates above 1000 gpm, require shakers is primarily a trial and error evaluation.
scalping shakers in front of fine mesh screens (see The best advice is to contact the manufacturer for
Chapter 7). recommendations for various geographic areas.
The final consideration is to decide on the type
and quantity of main shakers necessary for pro-
cessing all the drilling fluid. The goal should be to Cost of Removing Drilled Solids
sieve an unweighted drilling fluid through the fin-
est mesh screen possible. For weighted drilling Few wells can be drilled without removing drilled
fluids, the goal should be to screen all drilling fluid solids (see Chapter 1). Even for 3,000- to 4,000-
through 200-mesh screens (finer screens may re- foot wells, problems created by drilled solids, such
move too much weighting material). as lost circulation, stuck pipe, or well control, are
Many factors affect the liquid capacity of spe- more than enough reason to properly process the
cific shale shaker and screen combinations. While drilling fluid. In expensive drilling operations, the
no publication accounts for all of these variables, proper use of solids removal equipment will sig-
some manufacturers publish curves relating the nificantly reduce costs.
fluid flow capacity to screen sizes as a function Although drilled solids can be maintained by
of one or two parameters. These curves are usu- simply diluting the drilling fluid to control their ac-
ally generated without a comprehensive testing ceptable levels or concentrations of drilled solids,
program. Many manufacturers use generalizations the expense and impracticality of this approach
to gauge the number of shakers needed based on are evident using the following example. A \2\-
the maximum flow rate anticipated. For example, in.-diameter hole, 1,000 feet deep, will contain ap-
flow rates between 300 gpm and 500 gpm can proximately 146 bbls of solids. If these solids are
109
