OFITE offers equipment for testing water-based drilling fluids based on this document. The rugged, stainless steel design is perfect for field or laboratory use. Section 5 of the document details the procedure for measuring the density of a drilling fluid under pressure. Section 6.
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Particle-size distribution PSD Toxicity The environmental and toxicity standards of the region in which the fluid is being used will require testing either of the whole drilling fluid or of its individual components. Toxicity tests generally are used for offshore applications. An approved laboratory can perform the proper testing to ensure compliance of the fluid or its components.
Fluid rheology Fluid rheology is an important parameter of drilling-fluid performance. For critical offshore applications with extreme temperature and pressure requirements, the viscosity profile of the fluid often is measured with a controlled-temperature and -pressure viscometer e. Cold-fluid rheology is important because of the low temperatures that the fluid is exposed to in deepwater risers. High temperatures can be encountered in deep wells or in geothermally heated wells. The fluid can be under tremendous pressure downhole, and its viscosity profile can change accordingly.
Fluid loss also can be measured under dynamic conditions using the Fann Model 90 Dynamic Filtration System, which incorporates a rotating bob to provide fluid shear in the center of a ceramic-filter core. The fluid is heated and pressurized. Fluid loss is measured radially through the entire core, giving a sophisticated simulation of the drilling fluid circulating in the wellbore.
Particle plugging The particle-plugging test PPT often is used to evaluate the ability of plugging particles added to a fluid to mitigate formation damage by stopping or slowing filtrate invasion into a core. Ceramic disks with different mean pore-throat diameters are used to simulate a wellbore wall. A PPT typically is run with a 2,psi or higher differential pressure. The spurt loss and total fluid loss are measured over a minute period.
The cell is inverted, and fluid loss is measured from the top of the cell to eliminate the effects of fluid settling. High-angle sag and dynamic high-angle sag The weighting material used to increase the density of the drilling fluid can settle at a faster rate in an angled well than in a vertical well.
The HAST is used with fluids under static conditions, whereas the DHAST is used under dynamic conditions, in which the fluid can be subjected to shear or observed statically. High-temperature fluid aging Over time, high temperatures can degrade the components of a drilling fluid, and alter its performance.
Fluid can be aged statically and dynamically. This simulates the stress the fluid might be subjected to during static periods in the wellbore e. In dynamic aging, the fluid is rolled in a pressurized cell at the desired test temperature to simulate the fluid under drilling conditions. After undergoing aging, the fluid can be evaluated using the same tests that are applied to non-aged fluid. Also, cuttings erosion usually is accompanied by wellbore erosion, which leads to hole washout.
Two tests are available to aid in designing fluids that reduce cuttings erosion. One is an API-approved method in which the user measures out a known amount of shale material that is representative of the formation to be drilled, and that has been broken and sized between No.
After aging, the shale is collected on the No. The percent recovery is calculated on the basis of the weight of the recovered shale vs. Variations of this method are used for individual component testing. The aging time is varied to determine the erosion rate. The second available test is the slake-durability tester, which measures chemical and mechanical erosion to the shale.
This tester resembles the API-approved method in that it uses a known amount of test shale and in that recovery is calculated in the same way.
It differs in that the shale sample is placed inside a mesh-screen cage that is immersed in the drilling fluid and rolled continually throughout the test. Fluids should be designed to mitigate these shale problems.
Along with erosion testing, four other distinct tests are used to assess the interaction between the drilling fluid and shale: capillary suction time CST , return permeability, X-ray diffraction and particle-size distribution PSD. CST The CST test investigates the chemical effects of the drilling fluid on the dispersive properties of shale and active clays. The CST test measures filter-cake permeability by timing the capillary action of filtrate onto a paper medium. Changes in permeability then can be related to the inhibitive characteristics of the fluid.
A return-permeability test can reveal formation damage, and can be conducted using a return permeameter. The porosity and conductivity of a core sample are determined by flowing a refined mineral oil through the core. To simulate fluid and filtrate invasion into the core, drilling fluid is placed against the outflow side of the core, and differential pressure is applied in the direction opposite that of the previous flow measurement. After contamination, mineral oil is flowed through the core in the original direction, and the resultant porosity is compared to the original porosity to determine whether a reduction in permeability has occurred.
X-ray diffraction Knowing the mineral composition of a formation to be drilled is important for determining how the drilling fluid will react with the formation, and how to prevent potential drilling problems.
Fluid labs use X-ray diffraction to determine the mineralogical composition of shale or cuttings. They expose a crystalline mineral sample to X-ray radiation, and compare the resultant diffraction pattern to known standards to determine which minerals are present in the sample. A particle-size analyzer determines PSD by measuring laser-light diffraction, which can be related to particle size. SPE Drill Eng 2 2 :
Particle-size distribution PSD Toxicity The environmental and toxicity standards of the region in which the fluid is being used will require testing either of the whole drilling fluid or of its individual components. Toxicity tests generally are used for offshore applications. An approved laboratory can perform the proper testing to ensure compliance of the fluid or its components. Fluid rheology Fluid rheology is an important parameter of drilling-fluid performance.
API RP 13C.pdf