BAKER HUGHES - Drilling Fluids Reference Manual

FLUIDS ENVIRONMENTAL SERVICES
Fluid Analysis
Analysis of oilfield completion fluids is performed using a variety of equipment including turbidity
meters, laboratory centrifuges, laser particle counters and infra-red spectrophotometers. BHDF FES
offshore filtration engineers are all trained in the operation of the above equipment and prepare
reports required by the operation.
Waste Water Treatment
BHDF FES is developing a method for removing solids, hydrocarbons and chemicals from waste
water contaminated with oil based drilling fluid water so that the water quality will satisfy regulatory
discharge levels for disposal. The process involves the use of a decanter centrifuge, a high speed disk
stack centrifuge, settling tanks and fine filtration, whilst testing will include solids, hydrocarbons,
chemical oxygen demand and pH.
Filtration Equipment Technical Information
Diatomaceous Earth Filtration Filter Press Systems
A diatomaceous earth filter press works on the principle of starting with a significantly large surface
area onto which a permeable filter cake is built until the internal plate recesses are completely filled
with the filter cake, at which point the plates are then opened for cleaning of fluids.
A diatomaceous earth unit usually requires two filtration engineers on any shift to operate but has the
advantage of being able to filter large volumes of fluids with a high solids loading. The surface areas
of typical diatomaceous earth units range from 600 sq. ft. to 1200 sq. ft. and in many cases two units
are used in order to maintain a constant supply of filtered completion fluid.
The process starts with the filter plate screens being pre-coated in order to build the initial filtration
surface. The function of the screens is not to act as a filter, but rather to provide a surface onto which
a pre-coat cake of diatomaceous earth may be built. The pre-coat, consisting of a diatomaceous earth
slurry is circulated through the filter press via a separate tank (slurry tank) until the diatomaceous
earth is retained on the screens and the base fluid begins to return to the slurry tank in a clear state.
Once complete (usually around 5-10 minutes), the filter press is ready to receive the feed of dirty
fluid for filtration.
The solids typically found in completion fluids are barite and clay which can build up a nonpermeable
cake and blind the filter press screens very quickly. In order to counter this effect, a
volume of body feed or diatomaceous earth slurry is also injected into the dirty fluid upstream of the
filter press so that the filter cake maintains a level of permeability. The quantity of body feed is
adjusted according to the level of solids in the feed fluid.
The higher the solids in the feed, the more body feed required to maintain the permeability. The
importance of a good pre-coat and body feed cannot be over emphasized, and becomes very apparent
when a badly prepared filter press is prematurely blocked at a critical time during a gravel pack or
wellbore clean-up job. A good pre-coat prevents the barite and clays from coming into contact with
the screens, and enables the cake to be removed easily when cleaning. When used correctly,
diatomaceous earth filtration systems are the best choice for wellbore clean-up and gravel packing
jobs.
• Used for brine filtration with heavy barite or clay solids loadings.
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 14-54