An Innovative Cement Formula To Prevent Gas-Migration Problems in HT/HP Wells

Abstract

Abstract Gas Migration through cement columns has been an industry problem for many years. The most problematic areas for gas migrations occur in deep gas wells. To control gas migration, cement densities required to successfully cement the zone could be as high as 170 pcf (Pounds per Cubic Foot). As cement slurry sets, hydrostatic pressure is reduced on the formation. During this transition, reservoir gases can travel up through the cement column resulting in gas being present at the surface. The permeable channels, from which gas flows, cause operational and safety problems at the well site. Current high density cement formulations do not provide good gas migration prevention due to settling and subsequent increase in permeability. To address the settling problem and reduce permeability of cement, a formula that resulted in great gas prevention was developed. A gas migration set-up helped in testing and optimizing cement formulations to measure gas flow through cement columns. The gas migration set up consisted of the following components: computer, data acquisition, full-length permeability determination, two partial length permeability determinations, cement volume change measurement, gas flow meter, and electronic filtrate weight determination. The pressure and temperature limitations are 2,000 psi maximum and 350°F. Different chemicals for gas migration prevention were evaluated. Special types of cements were designed and evaluated for possible use for cementing gas wells. Addition of inert particles to cement and their effect on gas migration prevention was investigated. In this paper, a new cement system was developed and resulted in significant gas prevention. The performance of this system outperforms available formulations and has great potential to improve wellbore isolation in deep gas wells. Introduction Gas migration through cement columns has been an industry problem for many years, Jennings et al. (2003). Approximately 80% of wells in the Gulf of Mexico have gas transmitted to surface through cemented casings. The most problematic area in Saudi Aramco operations for gas migration is encountered in deep gas wells. The most problematic gas migration problems occur in deep gas wells when drilling through the base of Jilh Dolomite. Drilling fluid densities as high as 163 pcf are needed to control gas or formation fluid influx, Ezzat et al. (2000). Soran et al. (1993) mentioned that gas channeling reasons can be categorized as follows:Bad mud/spacer/cement design that results in a passage of water and gas, resulting to failures in cementing operations,High fluid loss from cement slurries, which causes water accumulation, resulting in micro-fractures within the cement body, andCements not providing enough hydrostatic to control the high pressure formation.