Selecting Drilling Technologies and Methods for Tight Gas Sand Reservoirs

Unconventional Gas Reservoirs are playing an important role as an energy source in the U.S. According to the Energy Information Administration in 2009, around 50% of the natural gas used presently in the U.S. comes from unconventional reservoirs. Also, tight gas sand reservoirs in the U.S. account for over 60% of the gas production from all unconventional gas resources. These percentages have all increased in the past 5 years and are projected to increase even more in the near future due to the contribution of new gas shale plays. A similar trend can be observed on a worldwide scale with unconventional gas resources being present and currently under investigation and development on every continent.

As compared to a well in a conventional gas reservoir, a tight gas sand reservoir well will have a lower productivity index and a smaller drainage area. Because of high risk and uncertainties associated with unconventional tight gas sand reservoirs, profitable development requires experts to be involved in the most critical development stages, such as drilling, completion, stimulation, and production. However, most of the oil and gas operating companies outside North America have little or no experience in the development of unconventional gas reservoirs.

Tight gas reservoirs production dates back to the 1940’s in the San Juan Basin in New Mexico. Until the mid 1990’s, mostly in the U.S., most wells drilled in tight gas sand reservoirs were drilled conventionally, with an overbalanced mud weight and using a conventional drilling rig. By implementing in the computer program the latest drilling technologies such as drilling with casing, underbalanced drilling, managed pressure drilling, horizontal drilling, directional S-shaped drilling (well clusters) and coiled tubing drilling, this paper shows that these new drilling technologies can be valid alternatives to conventional drilling using overbalanced mud weight and therefore have a significant impact to economically develop tight gas sand reservoirs.

The computer program discussed in this paper can be described as an ‘Advisory System’. An advisory system is a program that can be used to provide advice in a general topic such as drilling, completion, or stimulation of wells drilled in tight gas sand reservoirs. Such an advisory system for the development of tight gas sand reservoirs will not only be valuable for operators outside of North America, but even in North America, many companies need to be doing a better job of applying best practices when they are developing unconventional gas reservoirs.