API RP 13D:2003 pdf download
API RP 13D:2003 pdf download.Recommended Practice on the Rheology and Hydraulics ofOil-well Drilling Fluids.
6.5 PORTABLE CAPILLARY VISCOMETER
6.5.1 Description
A portable capillary viscometer Consists of a fluid reservoir. heating jacket. pressure gauge. three-port valve, coiled capillazy tube and two interchangeable straight capillary tubes. A drilling fluid sample is placed in the reservoir and pressured by nitrogen from a portable souree. The nitrogen h)rces the drilling fluid out through either the coiled capillary tube or one of the two interchangeable straight capillary tubes. depending upon the positioning of the port valve. The coiled tube is used in the low shear rate range (10 — 10.000 I) The two straight tubes arc used in the higher shear rate range (1.000 — 100,000 see:1). No matter which tube is in use, the length must be sufficient to insure that flow is fully developed before entering the test section. During each measurement, the pressure drop. indicated by the gauge. and the flow rate are recorded. The reservoir pressure is varied to cover the desired range of shear rates. The gel strength of the fluid is measured in the coiled tube. The pressure required to begin flow is measured after the drilling fluid has remained stationary for the desired gelation time.
6.5.2 Calculation
Equations for determining shear stress, shear rate and viscosity from such in’4nlrncnts arc discussed in Sections 4 and 7.
6.5.3 Operating Procedures
Specific operating procedures for this instrument should be obtained from the manufactarer.
7 Data Analysis
7.1 DESCRIPTiON
This section describes nwthods for analyting drilling fluid theological data and presents a way for estimating the effects of temperature and pressure.
The pressure conslani. Ct. must be determined for each drilling fluid. For water-based fluids, the presire effect on shear stress is extremely small and can be neglected. however, for oil-based fluids the pressure has an appreciable effect on the effective viscosity. As a general rule, the pressure effect is greater for oil-based fluids with asphaltic viscosifiers than for those that use oil-wet inorganic solids as viscosifiers.
Note: Absolute temperature is in degrees Rankine t46() + Ff. Pressure is in psig.
7.6.3 Application
The use of viscosity measurements at surface conditions 11r calculating hydraulics may give erroneous resulis.’5 For accurate work, the viscosity of the drilling fluid should be determined at the temperatures and pressures encountered in the well. To do this requires a high-temperature. high-pressure viscometer for data collection and a computer to analyze the data. I-f ossrever, corrections can be made to surface conditions. Ibese correction factors are average values obtained from measurements on various types of drilling fluids under conditions of high temperature and high pressure. Although the u-sc of these correction factors will give good estimates, they are not as accurate as downholc viscosities that can be obtained by measurement under downholc conditions. Figures I 8, 19 and 20 show the correction factor to he used with wacr-hascd fluids, oil-based fluids containing asphalt, and oil-based fluids containing oil-wet inorganic viscosifiers, respectively. To obtain the correction factor:
a. Select the proper graph to he used.
b. At the Iernpcrawrc of interest, draw a line to the proper pressure curve.
c. From the intersection of the temperature-pressure lines, draw a line to the correction factor axis and read the correction factor.
d. Multiply the effective viscosity by the correction factor.
