Survey Of Horizontal Gas Well Activity
Authors: Jochen John E. , Robinson Bradley M. 
Published: December 2007

Abstract
This paper presents the results of a survey on horizontal gas well activity throughout the world. The survey was conducted for the Gas Research Institute (GRI) in 1993 and focused on cataloguing the number of horizontal gas well completions and the type of formations in which they were completed. A secondary objective of the survey was to determine whether each horizontal gas well could be considered an economic success. As of mid-1993, there are 218 horizontal gas wells included in our database, of which 159 are in the United States and 35 are in Canada. Because of the lack of public information available for most of the world, much of the discussion and analysis of the horizontal gas wells presented in this paper is for the United States.
From this study, we found that naturally fractured carbonate formations have been the most actively developed and the most successful type of reservoir for the application of horizontal wells. Almost one-half of the total horizontal wells drilled in the U.S. have been in fractured carbonates with an estimated success rate of 67%. More specifically, the Austin Chalk in Texas has been the most economically successful reservoir in which to drill horizontal gas wells. This success is supported by 21 operators who have drilled 60 wells achieving a 74% success rate. Overall, we estimate that 52% of all horizontal gas wells drilled in the United States are successful; however, without the success of the Austin Chalk, horizontal drain holes drilled from within coal mine shafts, and offshore wells, the success rate of onshore horizontal gas wells completed in the United States is estimated to be 20%.

Introduction
The horizontal gas well database presented in this paper is an update of a survey presented by Maurer Engineering Inc. in a 1991 report to GRI which contained 76 horizontal gas wells throughout the world. We have 218 horizontal gas wells included in our database. We began our update of the survey by obtaining data on all horizontal gas wells that are included in the Petroleum Information (P.I.) database. Based on these data, we contacted operators via telephone to request additional data on these and other wells that were not available through public sources. In some instances, due to reservoir thickness and/or reservoir characteristics, it made more sense for operators to drill high-angle wells rather than horizontal wells. For these cases, if it appeared that the objectives of a high-angle well were similar to horizontal wells, we included them in the horizontal gas well database.
For analysis purposes, we categorized each well as being in either the United States (159 wells), Canada (35 wells), or an international well (24 wells). Information on Canadian wells were obtained from P.I.; however, information from Maurer's report and P.I. for many wells were not complete and we could not draw any conclusions concerning the types of formations being targeted in Canada or their success rate. Likewise, information on international wells was sparse. We obtained much of our information from a survey conducted by the Oil & Gas Journal but also from other SPE papers and trade journal articles.

Background for the United States
A total of 159 wells are included in our database of horizontal gas wells drilled in the United States. To simplify the analysis of the database, we divided the wells into groups based on the type of formation in which they were completed. Those groups are (1) sandstones, (2) carbonates, (3) coals, and (4) shales. In addition, we felt that it would be beneficial to keep the offshore wells in a separate group; so, we included all of the offshore wells in a fifth group. The geographic areas of horizontal gas well activity are illustrated in Fig. 1.
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