The horizontal recompletion of the Ryckman Creek Well #21 was the first to be attempted in a Thrust Belt Nugget field. The horizontal completion is significant because of the potential to substantially increase oil reserves over what can be produced with conventional methods. A horizontal wellbore has the ability to penetrate long intervals of an oil zone and expand the well's drainage area. The greater open productive interval permits lower drawdown pressures, alleviating the stratigraphic gas/water coning tendencies that have plagued many Nugget fields.
To recomplete the Ryckman Creek #21 as a horizontal wellbore, a directional program was designed to incorporate industry proven tools and techniques. A section was milled in the 7 in (17.7 cm) production casing at a predetermined elevation above the desired horizontal target zone. Medium radius of curvature (20 degrees/100 ft [30.5 m]) tools were utilized to drill the curved portion of the wellbore. A total of 534 ft (162.8 m) of lateral hole was drilled with a steerable bottomhole assembly. The amount of open productive interval was a five-fold increase over the vertical completion originally performed in the Ryckman Creek #21 well.
Ryckman Creek field is the northernmost Nugget oil and gas reservoir on the hanging wall of the Absaroka thrust plate in southwestern Wyoming (Figure 1). Nugget production is structurally controlled by a northeast trending truncation anticline (Figure 2) and has been developed by 37 wells on 40- to 20-acre spacing. Ryckman Creek Nugget reservoir characteristics are similar to those previously described at nearby fields therefore they will not be discussed in detail here. The heterogeneous, anisotropic nature of the Nugget, attributable to its eolian origin, reduces oil recoveries because gas or water is preferentially coned through high permeability channels. Nugget coning problems are considered analogous to coning problems observed at other fields which have been exploited by horizontal drilling. Nugget gas/oil ratios are also elevated by the pressure sensitive phase behavior of the high volatility oil. Enhanced oil recovery techniques have been successfully employed at Ryckman Creek which include reservoir pressure maintenance (nitrogen and hydrocarbon gas injection) and reducing bottomhole pressure drawdown.
Ryckman Creek field was selected for the initial horizontal completion attempt because it is the shallowest Nugget reservoir in the Overthrust Belt with an average depth to the Nugget top of about 7,500 ft (2,286 m) MD. The Ryckman Creek #21 well (Figure 2) was selected as the recompletion candidate because 1) the use of an existing wellbore minimized the upfront drilling costs that would have been incurred drilling a grass roots well prior to kicking off the curved and lateral sections of the horizontal wellbore; 2) the poor current and historical production performance of the well reduced the risks of losing significant reserves, and; 3) the well was located outside of the original Nugget gas cap area, eliminating the need to run a liner through the curved portion of the wellbore to isolate the gas.
The target zone and orientation of the horizontal completion was determined by a detailed stratigraphic analysis of the Nugget in the Ryckman Creek #21 well and its offsets. The Nugget was subdivided into four zones, "A through D" as shown on Figure 3, and Zone B was targeted because it consisted of the best reservoir quality rock in the vicinity of the candidate well.