Tor Henry Omland

Automatic Measurement of Drilling Fluid and Drill-Cuttings Properties

Abstract In order to remotely control the drilling process it is necessary to measure several drilling fluid parameters automatically. This will increase objectivity of the measurements as well as make it possible to immediately react to changes. The current paper describes in detail the design for an integrated tool combination and the results of a full size yard test of such a combined s et of tools for measuring drilling fluid parameters and formation properties automatically. Some of the automated tools have been tested on rig site operations. Results from these individual tests are also presented. The automatic drilling fluid analysis includes viscosity, fluid loss, electric stability measurements and chemical properties like pH. Full viscosity curves for the drilling fluid are measured using configurations and shear rates similar to those suggested by API procedures. Since gel formation curves and fluid loss properties require some sort of controlled static periods, these measurements are made semi-continuous. However, they are automatic and are measured as frequently as possible. An automatic system is included to measure the particle size distribution, concentration and morphology. Knowledge of these parameters is necessary, especially when drilling in depleted reservoirs where particles are added for increasing the wellbore strength. The produced cuttings volume is measured. An automatic system is adapted that determines, with accuracy comparable to that of visual analysis, whether the particles separated at the shaker screens are drill cuttings or cavings produced by an unstable formation. The mineralogy of the cuttings is analysed automatically using Raman spectroscopy, making it possible to evaluate continuously the different formations being drilled.

Particulate-Based Loss-Prevention Material--The Secrets of Fracture Sealing Revealed!

Owing to the narrow drilling margin that exists between th e pore pressure and fracture pressure gradients, drilling in depleted reservoir, HPHT and deep water environments is univer sally recognized as being technically challenging. A number of field techniques are available for mitigating against many of the drilling problems encountered. Included amongst these are specialized fluid engineering that involve use of chemical- and particulate-based treatments for minimi zing or preventing losses. In many instances these techniques can be used to strengthen or stabilize the wellbore when drillin g on or near the fracture gradient thereby potentially eliminating the need for intermediate casing strings. This paper discusses particulate-based treatment design for sealing fractures. Substantial experience gained from innovative laboratory testing has highlighted the mechanisms and many factors that determine the effectiveness of the fracture seal. The particle size distribution relative to the fr acture aperture, particle morphology, volumetric concentration, fluid rheology and fluid-loss-control influence whether the seal is established within the fracture or at the fracture mo uth. Understanding this distinction is important with respect to selecting the optimum treatment and its application for giv en field conditions. Parameters critical for optimizing the treatment h ave been identified and are discussed in the context of laboratory and field experience.