Sriramya Nair

Real time control of fresh cement paste stiffening: Smart cement-based materials via a magnetorheological approach

A smart cement-based magnetorheological (MR) fluid, one that could be tailor-designed to yield the desired rheological properties of cement paste, in real time is presented. By incorporating magnetic particles inside the cement paste and by varying the magnitude of the magnetic field strength, the rheological response of the sample is altered significantly. This cement-based MR fluid would allow for better control over stiffening/setting behavior of concrete and can be useful in applications in which controlling the fresh-state behavior of concrete is critical. In this work, magnetic fields were altered in a low-high-low and high-low-high pattern to assess the effect of cyclic variations of the magnetic field on the rheological behavior. It was found that a cement-based MR fluid does exhibit field sensitivity in its rheological behavior when the magnetic field is varied. At early ages, when the magnetic field is varied, the rheological behavior was seen to be less dependent on the time frame at which the magnetic field is applied and more related to the magnitude of the magnetic field. At later ages, in the presence of a cyclic magnetic field, the rheological response will be influenced by the magnetorheological response and by aging mechanisms (e.g., hydration and thixotropy) that impact the stiffening of cement paste.

Detecting Poor Cement Bonding and Zonal Isolation Problems Using Magnetic Cement Slurries

There has been growing interest in the use of magnetorheological fluids to improve displacement efficiency of fluids (drilling fluids, spacer fluids, cement slurries) in the eccentric casing annuli. When magnetic particles are mixed with the cement slurry for improved displacement, they provide an excellent opportunity for sensing the presence and quality of cement in the annulus. This work focuses on using sophisticated 3D computational electromagnetics to simulate the use of a magnetic cement slurry for well cement monitoring. The main goal is to develop a new tool, which is capable of locating magnetic cement slurry that is placed behind a stainless steel casing. An electromagnetic coil was used to generate a magnetic field inside the borehole. It was found that when a current was passed through the electric coils, magnetic field lines passed through the stainless steel casing, the cement annulus and the rock formation. Three sensors were placed inside the cased borehole and the magnetic field strength variations were observed at these locations. Various factors that have a significant influence on zonal isolation were considered. These include, effect of debonding between casing and cement annulus, effect of changing annuli thickness, influence of a fracture in the rock formation, effect of changing magnetic permeability of cement and finally influence of annuli eccentricity. Based on the results shown in the paper along with the next generation of supersensitive magnetic sensors that are being developed, the magnetic approach appears to be a viable alternative for evaluating the quality of the cement annulus to ensure good zonal isolation. Introduction The main goal of a cement job is to provide a complete and durable zonal isolation from when the cement is placed, up until the well is abandoned. Zonal isolation is extremely important in the oil and gas industry since it prevents fluids (such as water or gas) in one zone from mixing with oil in another zone. The ability of the cement sheath to provide zonal isolation depends on the cement/casing interface, the bulk cement and the cement/formation interface (Nelson and Guillot 2006). The bulk cement layer could be affected, for example, if there is gas or liquid migration into the cement during placing or if there are regions without any cement. Cementing problems were associated with 18 of 39 blowouts between 1992 and 2006 (Izon et al. 2004), and based on a survey conducted in 1997, it was found that on average 5% of total well costs were spent on cementing and that 15% of the cementing jobs ended up in failure costing the industry

Contamination of deepwater well cementations by synthetic-based drilling fluids

470 million/year in repairs (Sabins 2002). Failure of a cementing job could lead to oil spills (e.g., BP oil spill, 2010) that result in both