This article, written by Technology Editor Dennis Denney, contains highlights of paper IPTC 11651, "Getting the Last Gasp: Deliquification of Challenging Gas Wells," by A.V. Bondurant, SPE, B.D. Dotson, SPE, and P.O. Oyewole, SPE, BP plc, prepared for the 2007 International Petroleum Technology Conference, Dubai, 4–6 December. The paper has not been peer reviewed.
A common characteristic of "challenging" unconventional gas resources—namely, low-permeability sands, shale, and coalbed methane (CBM)—is that the ultimate recovery depends on economic removal of liquids accumulation, generally termed "deliquification." The problem affects thousands of wells, and the solution involves not only technology development but also knowledge management and building resource capability. Industry is working on a variety of deliquification technologies for challenging gas, with developments ranging from adapting existing oilfield technologies to developing gas-specific technologies to developing "on the horizon" technologies. Examples in each stage of development are presented.
A distinguishing characteristic of North American land-based gas production is the large number of low-rate wells. In the continental US, the majority of gas wells produce less than 100 Mscf/D. The low rates reflect the maturity of North American gas production and the predominance of challenging production from low-permeability-sand (<0.1 md), shale, and CBM reservoirs.
Low-rate gas wells almost always cease production because of liquid accumulation in the wellbore. Consequently, deliquification is of great importance. From a worldwide perspective, the current need for deliquification of low-rate wells is more modest. As production from high-rate wells declines, similar technical and economic challenges will be faced outside North America and will benefit from the solutions developed there.
For this study, a gas well is any well making 50 bbl/MMscf or less of stock-tank hydrocarbon liquids. An actively producing well is one having production reported in the second half of 2005. Production data from several eastern states, which tend to have very-low-rate gas wells, were not readily available and, therefore, were not included in this analysis. With these definitions, data were collected on 235,000 active producing gas wells in the major producing states for the second half of 2005.
Approximately 150,000 wells that produce less than 100 Mscf/D/well pro-duce approximately 7.5 Bcf/D collectively, 10% of the North American gas consumption. Most of these wells either are impaired by liquid accumulation or are producing with some form of artificial lift for deliquification. Deliquification in North America involves a very large well count, with generally a small incremental effect on each well.