The Performance of Class 2 and Class 3 Hydrate Deposits during Co-Production with Conventional Gas (OTC 19435)

Authors: George J. Moridis (speaker), Matthew T. Reagan, and Keni Zhang

Venue: 2008 Offshore Technology Conference, Houston, Texas, May 5-8, 2008 ( http://www.spe.org and http://www.smenet.org [external sites] )

Abstract: Recent numerical studies have provided strong indications that it is possible to produce large volumes of gas from natural hydrate deposits at high rates (in excess of 10 MMSCFD) for long times by depressurization-induced dissociation of hydrates. Of the various factors that can adversely affect the production potential of hydrates, low temperatures have one of the strongest negative impacts. These can be caused by low initial temperatures, increasing stability of the hydrate (as defined by the deviation between the temperature of the deposit and the equilibrium temperature at the reservoir pressure), and by an advanced stage of dissociation (a strongly endothermic reaction) when substantial amounts of hydrates remain. The reasons for the production decline include a reduction in the rate of the hydrate dissociation at lower temperatures and the evolution of flow restrictions in the vicinity of the well caused by the formation of hydrate and/or ice in the vicinity of the wellbore. The latter is caused by continuous cooling, and is the reason why large amounts of gas that may have been released in the reservoir in the course of earlier dissociation cannot be easily recovered.

The project investigated the possibility of alleviating the problem of low production at low temperatures in Class 2 and Class 3 deposits by means of co-production with gas from conventional reservoirs. Large-scale numerical simulations involving injection-production multi-well systems indicate that, by routing some of the pressurized hot conventional gas through Class 2 hydrate reservoirs at rates that do not exceed 50% of the total production rate, it is possible to achieve a significant increase in hydrate dissociation and gas production when horizontal wells are used., Results indicate increases up to an additional 30 MMSCFD, when the total net production rate reaches 58 MMSCFD. This occurs mainly because of the enhanced relative permeability of the gas phase and the increased effective permeability of the hydrate interval, which facilitates gas flow and further dissociation. The thermal effect on dissociation appears to be limited. Co-production appears to confer no benefits to the performance of Class 3 deposits, when the production well is kept at a constant pressure, but yields significant production increases when the well is produced at a constant rate following an initial period of constant-pressure production.

Related NETL Project:
This presentation is related to the NETL project G308-01, “Numerical Studies for the Characterization of Recoverable Resources from Methane Hydrate Deposits.” The objective of this project is to develop a reservoir model that simulates the behavior of hydrate-bearing geologic systems and evaluates appropriate hydrate production strategies for both permafrost and marine environments, including thermal stimulation, depressurization and dissociation induced and/or enhanced by inhibitors (such as brines and alcohols). This research will enhance natural gas hydrate research and development activities by bringing new numerical simulation capabilities and laboratory measurements to bear on the difficult problems of characterization and gas recovery of methane hydrate deposits.

Project Contacts
NETL – Richard Baker (Richard.Baker@netl.doe.gov or 304-285-4714)
LBNL – George Moridia (GJMoridis@lbl.gov or 510-486-4414)