Due to the current marginal economic status of the petroleum industry, drilling a new well is more difficult to justify than ever before. Many Operators have adjusted by recompleting old wells whenever possible. While the use of old wells reduces up front capital investment and alleviates some environmental concerns, the risk to formation damage can be much higher than drilling a new well. Although there are many methods of recompleting old wells, the experience at Mt. Poso indicates that none can provide a cleaner wellbore than a sidetrack completion.
This paper discusses sidetrack operations using redesigned staged mill and mechanical whipstock. These sidetracks were performed in 1800' wells located at the Mt. Poso field, CA. The staged mill and mechanical whipstock system, called the Sidewinder, and is jointly invented by B&G Machine & Welding shop and Shell Western E&P Inc. The Sidewinder Is an enhanced version of the existing whipstock and staged mill technology that is currently overshadowed by the casing section mill. The initial result indicates the new method can reduce both time and cost by as much as 50% over the conventional casing section mill method. The margin of savings is even greater in wells with multiple casing strings.
Thus far, the Sidewinder has been used to sidetrack single and dual casing wells with standard casing sizes. The Sidewinder can be modified to accommodate any non-standard casing sizes also. The greatest benefit thus far has been superior economic success rate due to reduced number of tools and less milling time from sidetracking wells with multiple casing strings. The superior economics have also allowed wells to be recompleted that would have been uneconomic using the conventional casing section mill.
Mt. Poso field is located 35 miles north of Bakersfield, Ca. The main producing formations are the Pyramid Hill, the Upper Vedder and the Lower Vedder arranged from top to bottom. Both the Upper and Lower Vedder zones are steam flooded and consist of desaturated 5 - 6 darcy sands. As the Upper Vedder wells are depleted and become uneconomical, they are selected for up hole recompletion into the Pyramid Hill zone. The Pyramid Hill formation contains Montmorillonite (80%) / Illite (40%) mixed layer (5% weighted). This mixed layer clay is extremely sensitive with porosity and permeability easily damaged by fresh water mud systems.
The typical original permeability of the Pyramid Hill formation is 0.02 - 0.1 darcy.