Evaluation Of Foam Cement Squeeze Treatments For Low-Pressure Highly Permeable Reservoirs

Abstract

Abstract Squeeze cementing is a well established remedial technique that relies upon controlled slurry placement and pressure as the key to success. Formations with low reservoir pore pressure and high permeability can create severe challenges/or proper cement placement, especially if the high permeability is due to naturally occurring formation vugs and fractures. Recently. a novel technique utilizing low density foam cement has proven to be successful in providing a squeeze cementing method offering a much higher probability of success, as com? pared with more conventional cement systems. This paper will evaluate the use of foam cement vs other conventional squeeze cementing techniques and also the design criteria used for treatment of wells producing from the Keg River formation in the Rainbow Lake area of northwestern Alberta. Seventy-nine individual well case histories involving 129 remedial cementing operations were evaluated to determine their success. Introduction The Keg River reefs in the Rainbow Lake area were, for the most part, discovered during the 19605. There are 19 such reefal structures which are presently on production (Fig. I). For many years, the Keg River formation produced oil with very few production problems. However, it eventually became necessary to implement various secondary and tertiary schemes to improve the recovery factor and maintain production. These recovery schemes required periodic well servicing operations to reduce excess water and gas production. In 1980, the number of well servicing operations increased dramatically. Cement was used in most cases to shut off unwanted production intervals. It was discovered early that normal density Class "G" cement systems would not perform adequately in highly permeable areas of these reefs. The search for a better cementing technology eventually evolved to the use of foam cement to reduce the number of repeat cement squeezes required to achieve hydraulic isolation. This paper evaluates 129 cementing operations in which four different cement systems were applied to the Keg River formation at 79 wells. Geological and Reservoir Overview Langton et al(1,2,3) have described the Rainbow member of the Keg River formation as a generally dolomitized pinnacle or atoll like reefal structure. These reefs are heterogeneous in nature, both horizontally and vertically. Presently, there are five reefs under primary recovery, six under secondary waterflood and eight under miscible production. The reefs, in general, are slightly under pressured with respect to a produced water gradient. Permeability in each of the reefs varies from less than one millidarcy to greater than 10 darcies. The area of reefs which contain many darcies of permeability are characterized by vugs and fractures of all shapes and sizes. It is these reef areas which present the greatest challenge for cement squeezing. Evolution of Cement Squeezing Techniques The primary reason for cement squeezing has been to shut off undesired water or gas production and to ensure hydraulic isolation between multiple perforated intervals. These procedures along with a specialized application of downhole tools (Fig. 2) provide control over how the reef is exploited.