Focusing on case histories of recent horizontal wells in Oklahoma, this paper provides an overview of horizontal drilling activity in a region where, currently, horizontal drilling applications are still being defined. Consequently, the paper provides information - including successes and failures - of provides information - including successes and failures - of the various target applications, drilling and completion techniques, reservoir characteristics and production histories of these case history wells.
With particular focus on one of the first proposed multiwell horizontal drilling programs in the region, the paper provides specific comparisons of two different target intervals, as well as the actual drilling applications, drilling fluid types, survey techniques, and well designs. Results of the different drilling techniques are documented, including specific drilling assemblies used and production techniques employed. In addition, specific formations are documented according to their success as horizontal drilling applications.
In the past two years, the number of horizontal wells permitted in Oklahoma has increased more than 100% in 1990, fewer than ten horizontal wells had been drilled in the state; by mid-1991, more than 20 horizontal wells had been drilled or were in progress.
According to traditional definitions of horizontal applications, the fractured geology of various reservoir formations in Oklahoma maker them prime candidates for horizontal drilling programs. Oklahoma has been found to have a number of programs. Oklahoma has been found to have a number of fields with fracture characteristics, as well as a large percentage of carbonates; a heavy structural overprint which percentage of carbonates; a heavy structural overprint which causes extensive fracturing; many unconformities, and at least one major source rock, the Woodford Shale.
However, as the following case histories document, the transfer of horizontal drilling technology from one geologic application — such as the Austin Chalk or Bakken Shale — to another, such as Southern Oklahoma's Viola or Woodford-Sycamore, does not necessarily guarantee success of a horizontal well.
As is evident in the two Southern Oklahoma wells documented, horizontal applications can vary from well to well over as little as three miles of Oklahoma's complex geology. Clearly, the successful application of horizontal technology in Oklahoma — or anywhere, for that matter — depends on the geology to be encountered, and specifically, on the extent of knowledge available concerning the target application.
A summary of horizontal wells drilled or in progress in Oklahoma as of May 1, 1991 is presented in Table 1. At the time of the survey, 20 horizontal wells had been drilled in the state, with three others in progress. Of these, major operators and larger independents account for only four wells, or 17% of the total number of horizontal wells drilled in Oklahoma.
Various geographical locations of the horizontal well activity throughout the state are shown in Figure 1. All regions, except southeastern Oklahoma, have seen some horizontal activity. Of the 23 wells included in the survey, 14 are located in north central and northeastern Oklahoma. Two of the three case history wells documented were drilled in southern Oklahoma's Love and Carter Counties, with the third in Beaver County in the northwest.
Table 2 is a breakdown of Oklahoma horizontal wells by type, including wells in progress at this writing. As shown, medium radius wellbores account for the majority of horizontal wells drilled in the state, with a total of 16 medium radius wells drilled to date. Only seven wells have utilized a short radius well trajectory, with no long radius horizontal wells reported.