Richard F. Vargo

Value Created Through Versatile Additive Technology and Innovation for Zonal Isolation in Deepwater Environments

Value may be created by applying innovative technology in challenging zonal isolation applications. Risk minimization in deepwater cementing can be accomplished without jeopardizing environmental impact and cost-effectiveness. Some of the highest risks encountered in deepwater cementing operations are related to low temperatures and the existence of shallow water flows (SWF). Generally, for cementing lowtemperature zones, high early strength blends with set accelerators are used. At normal temperatures, Class A or Class H Portland cements are normally preferred in Gulf of Mexico (GOM) operations. The cement system for SWF zones should have a relatively low density and a short transition time to help maintain well control. Presented in this paper are examples of how a single cement system has been used to meet all design criteria for delivery of deepwater well cementing. A disadvantage in using a variety of cement types and blends for cementing in an offshore environment is that the unused preblended materials designed for a given depth are often discarded, and new blends are made up for subsequent cementing operations. This can result in increased material costs and repeated trips to shore. It is desirable, both economically and environmentally, to be able to use the same neat cement for cementing wells at multiple depths. This paper presents details of an innovation that involves cementing offshore wells with SWF problems with only one neat cement by using versatile additive technology. Case histories for cementing several wells in the GOM in water depths greater than 2,000 ft are presented. In all cases, flowable salt-water zones were encountered while drilling. The operator’s risk assessment of the problem was uncertain at the time of well design and planning because of the exploratory nature of the wells drilled. The liquid additive system for flow control gave the operator the flexibility of having the additives on the rig at the time the holes were drilled. The operator could evaluate the flow potential before deciding to use the system or use other options. The foamed cement system used in these case studies used a liquid additive for SWF control. The remaining portions of the wells were cemented with the same neat cement by using different liquid additives. This in turn helped reduce environmental impact of wasted cement and saved the operator considerable capital for the wells drilled.