Magnetic contamination of drilling fluid can impact the accuracy of a directional survey by shielding the magnetic field. Additionally, this contamination, such as swarf or finer magnetic particles, can agglomerate on the downhole tool or BOP and cause tool failure in the worst-case scenario. Thus, it is necessary to measure the magnetic content of drilling fluid. However, there is no recommended practice in API or ISO for this purpose. A simple experimental setup and measurement system was developed that can be easily deployed in the rig site to measure the magnetic contamination of drilling fluid. 47 drilling fluid samples were collected from a multilateral production well drilled with a semi-submersible drilling rig located in one of the North Sea's fields. The magnetic content of these samples was measured using the established method, and the microstructure of the collected content was analyzed using a scanning electron microscope (SEM) and x-ray diffraction analysis (XRD). Ditch magnets are commonly installed in the flowline on the rig to remove the swarf and finer magnetic particles, if the design is optimized. Ditch magnet measurement data of the well that the drilling fluid samples were collected from is presented. Operational details and common factors that might increase the production of the magnetic content were also investigated. By comparing the measured magnetic contamination of the drilling fluid samples and ditch magnet measurement data, it was possible to evaluate the efficiency of the ditch magnet system.

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Providing zonal isolation and ensuring long-term integrity are among the highest priorities in primary cementing during well construction. There are several factors that compromise a successful cementing job. One of them is contamination with drilling fluid. Since there is drilling fluid in the wellbore prior to pumping the cementitious material, it is highly likely that intermixing between these fluids occurs in the downhole, which in turn can lead to several effects on mechanical properties and rheological behavior of the Portland cement or alternative materials such as geopolymer. In the placement process of the cement slurry, spacer fluids and prewashes are pumped ahead of the cementitious slurry to minimize the intrusion of drilling fluid into the slurry and consequently improving bonding to the casing and formation. In designing spacer fluids that can efficiently displace the drilling fluid, it is necessary stress test the cementitious material. The rheological properties and density of both cementitious slurries and drilling fluids and must be evaluated. Failing to properly characterize the fluids in the wellbore may lead to developing a spacer or displacing fluid that can cause viscous fingering and leave a static mud layer in the annulus. In the present work, rotational test with controlled shear rate and oscillatory test were conducted on drilling fluid (water-based and oil-based) and geopolymer to identify rheological behaviors. Based on the mentioned tests, storage and loss modulus, yield stress, and flow curve of the slurries were also measured. For completeness of measurements and comparison purposes, the flow curve was measured with both an API viscometer and a proper rheometer. Obtained parameters can give us a good understanding of the flow behavior of the fluids when pumped downhole under certain shear conditions and, as a result, establish a good basis for spacer design for geopolymer as a new under-development cementitious material.

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