The Shielding Effect of Drilling Fluids on Measurement While Drilling Tool Downhole Compasses—The Effect of Drilling Fluid Composition, Contaminants, and Rheology

Abstract

Materials such as added clays, weight materials, drill solids, and metallic wear products in the drilling fluid are known to distort the geomagnetic field at the location of the measurement while drilling (MWD) tool magnetometers that are used to measure the direction of well path. This distortion contributes to substantial errors in determination of azimuth while drilling deviated wells. These errors may result in missing the target of a long deviated 12 ¼ in. section in the range of 1–200 m, representing a significant cost to be mitigated. The error becomes even more pronounced if drilling occurs in arctic regions close to the magnetic north pole (or south pole). The effect on the magnetometer readings is obviously linked to the kinds and amounts of magnetic materials in the drilling fluid. The problem has recently been studied by laboratory experiments and analyses of downhole survey data. A series of experiments has been carried out to understand how some drilling fluid additives relate to the magnetic distortion. Experiments with free iron ions show that presence of iron ions does not contribute to magnetic distortion, while experiments with bentonite-based fluids show a strong effect of bentonite on magnetic shielding. Albeit earlier measurements showing a strong dependency of the content of organophilic clay, clean laboratory prepared oil-based drilling fluids show no increased shielding when adding organophilic hectorite clays. The anticipated difference between these two cases is outlined in the paper. When eroded steel from an offshore drilling site is added into the oil-based drilling fluid, it is found that these swarf and steel fines significantly increase the magnetic shielding of the drilling fluid. The paper outlines how the drilling direction may be distorted by the presence of these additives and contaminants and how this relates to the rheological properties of the drilling fluid.

Damage Mechanism of Oil-Based Drilling Fluid Flow in Seepage Channels for Fractured Tight Sandstone Gas Reservoirs

“…A previous study has shown that the elastic deformation of rock soaked in alkaline liquid is decreased and plastic deformation occurs earlier after soaking in alkaline liquid [37]. This is due to the high pH fluid immersion; the asperities of the fracture wall surface and other structures will be destroyed, and the pore structures of wall interior are damaged.…”

“…Then, the rock can adsorb the accumulation of the lipophilic substance in the OBDF on the surface, which influences the strength change of the rock to a certain extent. The adsorption of the treatment agent on the rock also includes the polymer or macromolecule treatment agents in the OBDF [37] (Figure 10), which adsorbs and retains at the pore or fracture wall and blocks the seepage channel with its macromolecular size, resulting in reservoir damage.…”

Efficient Removal of Magnetic Contamination From Drilling Fluids: The Effect on Directional Drilling

“…Contamination of the drilling fluid by iron and steel particles resulting from erosion or wear from casing, drill pipe and BHA components during drilling and well operations and following fluid additives has earlier been found to be a source for errors in magnetic directional surveying [7,8]. Both from laboratory tests and field experience, it is observed as having a non-trivial effect of magnetic and paramagnetic contamination of the drilling fluid on wellbore position accuracy [9,10,11].…”