Overview: Tight Reservoirs (October 2005)

Abstract

The first thing that struck me while reviewing the list of papers for this feature was the broad range of what is considered to be a tight reservoir. Engineers working in the Barnett shale in North Texas deal with “supertight” matrix permeabilities of less than 1 µd (or nanodarcies). Engineers working in the Middle East may consider permeabilities of 30 to 50 md as tight. This is a range of more than six orders of magnitude. Of course, each environment has its own challenges and reasons for being considered tight. In my opinion, there are three main challenges in the development of tight reservoirs. - Quantifying the recoverable reserves and deliverability with the uncertainty of formation evaluation and reservoir characterization. - Implementing the best well-completion, stimulation, and infill-drilling strategies to accelerate and increase ultimate field productivity. - Combining the above issues must lead to economic success. Certainly, the emergence of new technologies has improved reservoir-characterization, completion, and stimulation technologies. These technologies include better well-logging, well-testing, and core-analysis techniques; seismic interpretation; horizontal-well technologies; fracturing fluids and proppants; hydraulic-fracture diagnostics; and mapping technologies. High oil and gas prices of course, along with cost-reducing measures, contribute their part to the economic success. The move toward more marginal and unconventional reservoirs presents significant challenges to technology, some of which have been overcome successfully. The Barnett shale, for example, has moved from a “curiosity” 10 years ago to the fifth-largest gas-producing reservoir in the U.S., and there is a feverish “hunt” for more Barnett-type analogs. Many tight reservoirs are in high-pressure/high-temperature (HP/HT) environments, which pose significant challenges for drilling, formation evaluation, and well completion. The fact that only a very small percentage of wells are drilled in HP/HT environments illustrates the significant economic hurdles. However, this resource base could be significant for meeting future natural gas demand in the U.S. and abroad. Tight Reservoirs additional reading available from the SPE eLibrary: www.spe.org SPE 94249 - “Development of a Low-Permeability Carbonate Reservoir by Use of Horizontal Wells in Mature South Umm Gudair Field in the Neutral Zone—A New Approach,” by Jha, M., SPE, Saudi Arabian Texaco/Kuwait Oil Co., et al. SPE 94354 - “Adding Value Through Integrated Research To Unlock the Tight Gas Potential in the Rotliegendes Formation of North Germany,” by Gaupp, R., U. of Jena, et al. SPE 94106 - “Developing the Obaiyed Tight Gas/Condensate Field, Egypt—A Case Study,” by Strating, E.H.H., SPE, Shell Intl. E&P, et al.