Several major developmental programs in the Rocky Mountain region of the United States are in fields where zones of several hundred to several thousand feet of stacked, tight (<0.05 md) lenticular gas sands exist. In order to be productive, these wells require multiple fracture treatments over the pay interval. Since field development has been ongoing, the drilling programs are extending into more marginal production areas. Infill programs are downsizing spacing, and also, successful refracturing programs are being conducted in some fields. Before 1998, traditional methods were being used to isolate fracture treatments. These methods usually required killing the well between fracture treatments or during cleanout operations. Unfortunately, field studies have determined that the traditional isolation methods have negatively impacted well productivity.
In view of the costs involved and the lower productivity experienced with the new drilling programs, it became apparent that either well costs had to be reduced or well productivity had to be improved!
This paper will discuss the application of flow-thru composite frac plugs (FTCFP) and how they were capable of addressing the current needs to reduce operational costs and improve productivity. These plugs can be used as an alternative to traditional isolation methods, or induced stress diversion. Through June 2002, there have been over 3,200 FTCFPs run in the Rocky Mountain region. The benefits gained from FTCFP usage are derived from the following:Well drill-out costs are reducedPositive isolation is allowedAll zones can be produced during completion.
Their use has now become a "best practice" in stacked-pay completions.
Introduction
Six states make up the Rocky Mountain region in the Western United States (Fig. 1). Hundreds of different formations are productive in this region with the vast majority of these formations being classified as tight gas sands with permeabilities of less than 0.05 md. Some formations may consist of one significant sand or a couple of sands and are economic by themselves, such as the Almond in the Wamsutter area of south west Wyoming. However, as shown in Fig. 2, formations like the Mesaverde, found throughout Colorado, Utah and Wyoming, may consist of 20 to 50 individual sands spread over 1,000 to 5,000 ft of gross interval. This later scenario is the more common in the wells currently being drilled.
To economically produce these formations, the majority of these tight gas sands require hydraulic fracturing. For the formations consisting of only one or two sands, the process is straight forward. The sands are perforated, fractured, and then placed on production. For formations consisting of multiple sands and those that cover a long interval, the fracturing process is more complicated, since these formations require multiple fracturing treatments.
A significant portion of the current activity in the Rocky Mountain region is in fields that were uneconomic prior to the 1990's. Throughout the 1990's, a variety of different techniques were tried to effectively stimulate multiple-sand formations. The most common technique was to break up a well into several fracture treatments with each treatment consisting of several sands. For each treatment, the sands were perforated using limited-entry perforating1 to help ensure that each sand would be treated. The interval sizes varied throughout this time period from 200- to over 500-ft per fracture treatment. In the Piceance basin, however, it was found that longer gross intervals for each treatment significantly reduced completion coverage.2 This study also showed that as the number of sands per treatment increased, the completion coverage decreased.
