Reverse Circulation of Primary Cementing Jobs-Evaluation and Case History

Abstract

Proposal Conventional means of primary cement placement pump the cementing fluids down the casing and well returns are taken from the annulus. This is the most common way of cement placement for the industry and has been used for more than 80 years. Much less commonly used by the industry, but recently gaining in use is the Reverse Circulation of Cement (RCC) technique. When using the RCC technique, the cementing fluids are pumped into the annulus of the well and returns are taken through the casing. The recent acceptance of the RCC technique is mainly driven by economics and state-of-the-art technology bringing an alternative technique. Benefits of the RCC technique can include lowering bottom-hole placement pressure, reducing cement retarder concentration, lowering the time for cement placement, and increasing location safety. The main drawback to the technique is determining when uncontaminated cement is at and around the casing shoe. This paper discusses the benefits and shortcomings of the RCC technique in relation to fluid friction, cement slurry design, location safety, and zonal isolation. The paper illustrates, through a case history, how RCC technique's strengths are obtained while shortcomings are minimized. Field data from a recent job using the RCC technique on a 3100-m gas well in Alberta, Canada, as well as lessons learned from the job, are presented. Introduction One of the common concerns in the industry when it comes to cementing is the potential for lost circulation. While a few different approaches can be taken to address this problem, a viable alternative in reducing equivalent circulating density (ECD) is reverse cementing.1 RCC is a process in which spacer(s) and cement slurries are pumped down the annulus and returns are taken through to the surface casing string (Fig. 1). Cement slurry's location can be determined by two common methods:Utilizing a logging tool and radioactive tracersFluid markers Fluid markers have been the favorite system because no environmental issues are involved and it is more economical. Logging tools and radioactive tracers are more attractive when top of cement (TOC) inside the casing needs to be limited; i.e., when foamed cement systems are used in conjunction with RCC. However, not every well is a prime candidate for RCC. Certain conditions should be present to indicate the necessity of this method. RCC is not an entirely trouble free system. Some disadvantages exist in this system just like any other system that is in use. In the remainder of this paper, the advantages and disadvantages of RCC are discussed in detail. Also, a process is examined to aid with the decision-making when an operator is evaluating the options available to cement a string of casing. Evaluation The following sections detail important advantages, disadvantages, and challenges of using the RCC method. Advantages of RCC RCC can provide the following advantages in wells meeting the requirements for the method:Reduced EDCsImproved mud displacementShorter slurry thickening timesImproved compressive strength developmentImproved safety and environmental managementEasier cement slurry selectionImproved formation production due to less risk of cement invasion into the producing zone