The Use of Filtration Theory in Developing a Mechanism for Filter-Cake Deposition by Drilling Fluids in Laminar Flow
- J.V. Fisk (Baroid Drilling Fluids Inc.) | S.S. Shaffer (Baroid Drilling Fluids Inc.) | Samy Helmy (Baroid Drilling Fluids Ltd.)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling Engineering
- Publication Date
- September 1991
- Document Type
- Journal Paper
- 196 - 202
- 1991. Society of Petroleum Engineers
- 1.6.9 Coring, Fishing, 1.11.2 Drilling Fluid Selection and Formulation (Chemistry, Properties), 4.1.5 Processing Equipment, 4.3.1 Hydrates, 4.5 Offshore Facilities and Subsea Systems, 1.6 Drilling Operations, 1.11 Drilling Fluids and Materials, 1.6.1 Drilling Operation Management, 2.4.3 Sand/Solids Control, 4.1.2 Separation and Treating, 4.3.4 Scale, 5.1 Reservoir Characterisation, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc)
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This paper presents a mechanism for filter-cake deposition by drilling fluids in laminar flow. The mechanism evolved from analysis of filtration-data plots obtained from two linear equations derived from filtration theory. With these plots, various fluid-loss additives were evaluated on their ability to form a low-permeability filter-cake that can be eroded by a fluid in laminar flow. The mechanism was tested on two wells with high torque and drag, and the static API high-temperature/high-pressure (HTHP) values were minimized.
High-permeability formations are at times drilled highly overbalanced, with differential pressures is greater than 6.89 MPa [1,000 psi] when gas pockets are encountered. When these formations are drilled psi] when gas pockets are encountered. When these formations are drilled with high differential pressures, tight hole, excessive drag during tripping, and low production rates are observed. This paper presents a mechanism for filter-cake deposition determined from the dynamic filtration of fluids through porous media and recommends fluid treatments to minimize torque and drag. The mechanism evolved from linear-regression analysis of filtration-data plots obtained from two linear equations that define constant-pressure filtration through porous media. Eq. 1, which is described in Refs. 1 through 4, is porous media. Eq. 1, which is described in Refs. 1 through 4, is the design equation for constant-pressure batch filters. Eq. 1 relates the volume of filtrate to the differential pressure, filter-cake resistance, filtrate viscosity, filter-medium resistance, and filtercake compressibility. Eq. 3 was developed by Hermans and Bredee to describe particle plugging in porous filter media. Both cake filtration and particle plugging occur during drilling. It is possible to separate particle plugging from cake formation and to possible to separate particle plugging from cake formation and to evaluate fluid-loss additives on their ability to block pore space and to form highly compressible low-permeability filter cakes.
To verify the mechanism, data were obtained from several south Texas and Gulf of Mexico wells that were experiencing tight hole and drag. Three field mud systems-a hematite oil-based mud, a seawater-based partially hydrolyzed polyacrylamide (PHPA) mud. and a seawater-based dispersed mud-were examined. Filtration tests were conducted in the laboratory to find a treatment that would lower the dynamic and static fluid-loss rates. The wellsite fluid-loss-additive treatments were based on treatment levels that minimized the laboratory dynamic filtration rate. In most cases, the static HTHP values were lowered before the samples were submitted to the laboratory without causing much change in drag problems. Such fluid-loss additives as lignite, carboxymethyl cellulose (CMC), Gilsonites, asphalt, sized calcium carbonate, and wood fiber were tested to determine how they reduce static and dynamic filtration rates.
The dynamic filtration data presented in this paper were obtained by flowing fluids radially through ceramic cylindrical filter media with known average pore sizes. The filter medium is placed inside a metal holder as shown in Fig. 1. The medium is sealed at both ends within the holder, and the entire assembly is placed within a standard 500-mL API HTHP cell. A solid cylindrical shaft coaxial to the inner surface of the cylindrical filter medium is rotated to apply a shear force on the filter-medium surface. Filtrate flows radially from the inner surface through the filter medium to a collection cylinder. The collection cylinder contains a movable piston that separates the liquid filtrate from the nitrogen gas used to maintain the low-pressure side of the filter. Filtrate volume is determined by measuring the linear displacement of the piston within the collection cell. A standard API heating jacket designed for the 500- mL filtration cell was used to heat the fluids. The standard API filter can be used to a maximum temperature of 505 K [450 degrees F] and a maximum pressure of 6.89 MPa [1,000 psi].
The filter media were ceramically bonded alumina cylinders with dimensions of 3.8-cm OD X 2.5-cm ID x 1.9-cm length [1.5 x 1 x 3/4 in.]. The pore sizes and permeabilities of the filter media used in the tests were selected to match those of core samples collected from the formations being drilled.
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