Hydrates: State of the Art Inside and Outside Flowlines

Abstract

Distinguished Author Series articles are general, descriptive representations that summarize the state of the art in an area of technology by describing recent developments for readers who are not specialists in the topics discussed. Written by individuals recognized as experts in the area, these articles provide key references to more definitive work and present specific details only to illustrate the technology. Purpose: to inform the general readership of recent advances in various areas of petroleum engineering. Abstract The state of the art of three hydrate applications in petroleum engineering is presented in order of decreasing importance:flow assurance,energy resource, andclimate change. In flow assurance, there is a hydrate-plug-prevention shift under way: from avoidance to management of hydrate formation. In addition to avoiding the region of hydrate stability by injecting thermodynamic inhibitors, time-dependent studies enable flow-assurance engineers to better address such concerns as flowline restarts, cold (stabilized) flow, low-dosage hydrate inhibitors, and plug remediation. These applications are related to conceptual ideas of hydrate-plug formation in oil and condensate systems. The second area, energy resources, is marked by a transition to an extended production test in the permafrost, and to characterizing resources and economics in the marine environment. The third area, climate change caused by hydrates, is an area of current research. Preliminary estimates suggest no abrupt methane contribution to the environment from hydrates in the immediate future. Introduction Natural-gas hydrates (clathrates) are crystalline, ice-like solids that form when small (<9 Å) molecules contact water at low temperature and high pressure (Sloan and Koh 2008). Because hydrates are solids, they can block oil and gas flowlines; flow assurance involves considerable effort and expense to ensure that this blockage does not happen. Also, hydrates concentrate hydrocarbon gases by a volumetric factor of 164 (at standard temperature/pressure), such that large deposits of natural hydrates are becoming factors in energy resources and climate concerns in marine and permafrost deposits. A combination of applications, principally in flow assurance, energy, and, more recently, climate change, has driven hydrate engineering and science for 75 years. The number of published hydrate-related papers is an exponential function of time, extrapolating to more than two refereed publications per day in this decade. As Table 1 summarizes, triennial international hydrate conferences have been held since 1993; the most recent conference, in July 2008, presented more than 400 manuscripts.