16 Journal of Canadian Petroleum Technology Reverse Circulation Placement Technique vs. Conventional Placement Technique: A Comparative Study of Cement Job Hydraulics Design E. KURU, S. SEATTER University of Alberta THIS PAPER IS BEING PUBLISHED AS A TECHNICAL NOTE AND HAS NOT BEEN PEER REVIEWED. Introduction Lost circulation is one of the most common problems encoun- tered when cementing a well. The problem becomes increasingly critical, particularly when cementing fractured formations such as the ones encountered in geothermal wells, and coal bed methane wells, or low fracture gradient zones near sea beds in offshore wells. Primary cementing of these zones using the conventional cement circulation placement technique (CCCPT) has been very difficult, even with lightweight and foamed cement. Reverse circulation of cement placement technique (RCCPT) has been offered as an alternative to eliminate some of the prob- lems experienced when cementing potential lost circulation zones (1-5) . Marquarie and Brisac (1) reported successful applications of RCCPT in the North-Hassi-Messaoud Field in Algeria. Using RCCPT, they were able to cement a weak Triassic formation above the casing shoe without allowing the plastic clays (above the weak zone) to extrude and salt water to enter the well. Griffith et al. (2) conducted large scale experimental tests to in- vestigate the advantages of RCCPT. They have suggested that RCCPT is a viable option to lower equivalent circulating densities during the cementing process. They have also found that reverse circulation of cement on primary cementation neither increases nor decreases the displacement efficiency. Griffith et al. (2) also outlined a procedure for a typical reverse circulation cementing operation conducted by coal bed methane producers in the area of Trinidad, CO, in the U.S. Abstract Reverse circulation cement placement technique (RCCPT) has been suggested as an alternative for providing proper annular coverage for lost circulation zones. It is generally believed that RCCPT helps minimize the circulation pressure and hence, al- lows cement placement with no apparent losses. A basic hydraulic design study is conducted to determine the anticipated pressure losses during the cement jobs run by using both the RCCPT and the conventional cement circulation place- ment technique (CCCPT). Results have shown that, for each design case (i.e., wellbore geometry and the rheology of cement slurry), there is a critical depth above which the equivalent circulating pressure (ECD) with RCCPT can be higher than ECD with CCCPT. Examples of typical cement job design calculations are pro- vided to illustrate the changing ECDs as a function of depth during both RCCPT and CCCPT. Moore et al. (3) presented case studies of reverse circulation cementing in geothermal wells. Based on the work and analysis performed for the two reverse circulation cement job case histo- ries, they have concluded that the RCCPT has several major ad- vantages, including the minimizing pressures on formation during cement placement and the minimizing of excess cement pumped in the well. Virginillo et al. (4) discussed the advantages and disadvantages of RCCPT. They have also presented a flow chart to aid de- cision making when the options available to cement a string of casing are being evaluated. In a recent paper, Davies et al. (5) also discussed the benefits and shortcomings of RCCPT in relation to fluid friction, cement slurry design, location safety, and zonal isolation. They presented a case history to show how RCCPT’s strengths are obtained, while short- comings are minimized. Reverse Circulation Cement Placement Technique (RCCPT) Figure 1A shows a sketch of the conventional circulation ce- ment placement technique (CCCPT) where cement slurry is pumped down through the casing and returned up to the surface through the annular space between the casing and the wellbore. In the reverse circulation cement placement technique (RCCPT), however, spacer(s) and cement slurries are pumped down the an- nulus, and returns are taken through the casing string (Figure 1B). Location of cement slurry top can be assessed by two methods (5) : TECHNICAL NOTE TECHNICAL NOTE A B FIGURE 1: Primary cement placement techniques: a) conventional; and, b) reverse circulation.