Controlling Cement Circulation Loss to Both High-Permeability and Fractured Formations

Abstract

Abstract A polymeric material is described which has been developed for controlling lost circulation during cementing. The morphology of the material permits sufficient particle deformation to permits sufficient particle deformation to optimize plugging of high permeability matrices, while the particle size of the material is precisely sized so as to optimize sealing of precisely sized so as to optimize sealing of fractures. This optimization of morphology and particle size distribution enables the material to particle size distribution enables the material to effectively control cement circulation loss to both high permeability and fractured formations. Laboratory data are presented comparing the relative effectiveness of the new material, gilsonite, gilsonite plus cellophane flakes, crushed coal and a graded plastic material in controlling cement slurry loss to simulated high permeability and fractured formations. In permeability and fractured formations. In simulated high permeability formations the new material outperforms gilsonite and gilsonite plus cellophane flakes, and is slightly better than crushed coal. In simulated fractured formations this material outperforms a graded plastic material. It is shown that the new material does not appreciably affect thickening time or compressive strength of the cement slurries. Free water data for the cement systems tested with this material are satisfactory, but gel should be added to some systems to optimize this slurry property. Wyoming Overthrust, Williston Basin and Powder River Basin case histories are presented Powder River Basin case histories are presented which demonstrate the effectiveness of this new material in areas where severe lost circulation problems have been encountered. It has been used problems have been encountered. It has been used to control cement circulation loss in wells with both high permeability and fractured formations, in wells with high bottomhole static temperatures and in applications requiring flow through downhole tools. Introduction Lost circulation is one of the most troublesome and costly problems encountered in drilling and cementing a well. Lost circulation, or lost returns, is defined as the loss of the drilling fluids or cement slurries into formation voids. This loss may vary from a gradual lowering of the mud level in the pits to a complete loss of returns. The loss of drilling mud or cement slurry results in loss of drilling time, plugging of productive formations, and/or loss of well control. In general, four types of formations are responsible for lost circulation:Natural fractures and induced (or created) fractures,Unconsolidated formations,Highly permeable formations, andVugular formations. There is a long list of references that describe how to combat lost circulation while drilling an oil well. The reason is that it is less costly to prevent or cure lost circulation before cementing, and also, during drilling a wide range of lost circulation materials (LCM) and different types of pills are available for use. Despite the best efforts to control lost circulation during drilling, these problems may take place after the drilling is completed. The operator can encounter lost circulation any time fluid is circulated in an uncased hole. When this fluid is a cement slurry, lost circulation can occur even more often than during drilling, because of the cement slurry's higher density. Basically, there are two approaches for solving lost circulation problems in cementing. One is to reduce the density of the cement slurry, and the other is to add a bridging or plugging material. plugging material. p. 121