During well construction, the purpose of zonal isolation is to protect casing strings, the environment, and aquifers. The overall objective is simple; however, numerous well conditions exist that can hinder successful zonal isolation. In many areas, it is common practice to use water-based mud (WBM) to drill the surface and intermediate sections of the wellbore. WBM is usually preferred because of its low cost per barrel and ease of handling at the drilling location. In many cases, cement cannot be brought to surface. In these instances, OBM may be left in the hole, thus causing additional cost. Common industry practice is to use WBM to displace and recover the expensive OBM. However, there are inherent problems leaving WBM in the annulus. The microparticulate fluid is an effective replacement for the WBM and helps achieve improved zonal isolation.
This paper discusses a technically effective fluid system using a microparticulate with a high surface area to remove OBM from the annulus and effectively clean the wellbore. The microparticulate fluid can be placed in the wellbore at volumes similar to WBMs and may be designed to exhibit long-term bonding (or setting) behavior, which reduces the possibility of casing corrosion. The tunable rheology and density of this microparticulate fluid system provides improved displacement efficiency, and thus improved zonal isolation. The objective of this system is to achieve optimum displacement and place a settable spacer that promotes increased protection and isolation behind any casing string from top to bottom. A successful case history and proven design is presented.
To achieve optimal cement placement and bonding for zonal isolation integrity, wellbore preparation is fundamental. For the past several decades, research and development resources have focused on understanding barriers related to incomplete cement placement and inadequate zonal isolation (Benkley and Brenneis 2013). By the late 1920s, it was determined that many cementing failures were caused by inefficient wellbore fluid displacement (Wilde 1930). Uncemented wellbore fluid channels resulting from poor mud displacement provide a permeable conduit for reservoir fluids to migrate, causing loss of production and/or corroded casing over time.
While the study of fluid-flow interactions and displacement phenomena remain imperative, fluid-displacement efficiency has been well-documented within the oil and gas industry (Benkley and Brenneis 2013). Highlights of such research include the following.
URTeC 1579711
