The Use of Horizontal Wells in Gas Production from Hydrate Accumulations

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

Venue: 6th International Conference on Gas Hydrates 2008, Vancouver, British Columbia, July 9-12, 2008. (http://www.icgh.org [external site]).

Abstract: The amounts of hydrocarbon gases trapped in natural hydrate accumulations are enormous, leading to a recent interest in the evaluation of their potential as an energy source. Large volumes of gas can be readily produced at high rates for long times from Class 1 to 3 gas hydrate accumulations by means of depressurization-induced dissociation using conventional technology and vertical wells. The results of this numerical study indicate that, because hydrate dissociation proceeds in a horizontally dominant direction and is uniform along the length of the reservoir, the use of horizontal wells placed below the base of the HBL does not lead to long-term increases in the rate of gas production or in the total volume of recoverable gas. Additionally, this well configuration does not appear to offer any of the advantages that are usually associated with horizontal wells in conventional gas systems. Thus, the easier-to-install vertical wells are just as effective, as the much more expensive horizontal wells.

The effectiveness of a horizontal well increases significantly, if it is placed near the top of the HBL, and is produced at a constant pressure higher than that at the quadruple point. This approach eliminates the possibility of ice evolution and its adverse effects on permeability. The approach is necessitated by the initially low effective permeability within the HBL, and results in a continuously increasing production rate as the hydrate dissociates and the permeability increases. Constant-pressure production continues until the dissociation front reaches the base of the HBL. Depending on the class of the deposit, production then continues either by following a constant-pressure regime at a pressure higher than the original, or by switching to a constant-rate regime. This production approach involves conventional technologies, and leads to higher production rates and cumulative volumes of produced gas.

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 304-285-2714)
LBNL – George Moridis (GJMoridis@lbl.gov or 510 486-6709)