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PFS News

Legal Drilling Windows in the GWA At PFS we are often asked to compute the legal drilling windows for proper well placement in the Greater Wattenburg Area (GWA). Many times we may need to see if an existing well is actually within these “windows”. The Colorado Oil and Gas Conservation Commission (COGCC) have defined these windows in Rule No. 318A.1 and 318A.2. I have heard of several different methods used by our clients in determining these windows. Below, I will define the process PFS uses.

The method defined by the COGCC is based on a “perfect section”, whereas the section is exactly 1 mile square, with the interior angles of the section being 90° and each side being 5,280 feet long. This is somewhat evident in that we are to tie well locations to the exterior section lines at right angles. In actuality, a section of land is never a perfect square. The exterior lines of a typical section can be just about any bearing near the four cardinal directions, and just about any distance near 1 mile long, give or take several hundred feet. The COGCC states in their rules the window be a square with sides 400’ in length, the center of which is the center of any ¼ section; or the square be with sides 800’ in length, the center of which is the center of any ¼ section. The key word here is “a square”. The rules do not say a parallelogram, only a square. Since sections are never a square, the question arises: To which line of a section does the drilling window need to be parallel? Given the current system of well window locations, there are 5 windows in each quarter section. The orientation of the 5 windows in any particular quarter section should be the same for each window. We should not have one window within the quarter section tilted (oriented) one direction and another in the same quarter section tilted another direction.

Before I move on to the questions before us, we should understand what the center of a section, a quarter-section, or a quarter-quarter section is exactly. According to the BLM Manual of Surveying Instructions: a. The centers of these aliquot parts of a section were never set in the original surveys (unless indicated by special exception on the original plat). b. The center of a section is defined as the point that is established by the intersection of two straight lines running from the controlling quarter corners. This means that the quarter corners must actually, physically exist and be surveyed in the field. You may notice that some well certificates by surveying companies other than PFS do not show the quarter corners on there well certifications which has been deemed as unacceptable by the Colorado State Board of Architects, Professional Engineers and Professional Land Surveyors and contrary to the state laws set forth in the Colorado Revised Statutes. c. The centers of quarter sections and quarter-quarter sections are established in the same manner as the center of a section: at the intersection of two straight lines from the mid-points of the exteriors of the quarter or quarter-quarter sections. With the BLM rules show above, we now know the locations of the centers of the 400’ and 800’ windows. As for the orientation of the windows (the tilt or the rotation of the square), the solution is fairly simple: the azimuth of diagonal line across a drilling window would be the same as the bisection of the angle at any particular section corner between the controlling quarter corners. Here is an example: The diagonal line across a 400’ square for example would be 565.69’ long, and with the sides being set at true north, the diagonal line would have an azimuth of 45°. Let us say that we are determining the windows in the SW ¼ of a section, the azimuth from the SW corner to the West ¼ corner is 2° and the azimuth from the SW corner to the South ¼ corner is 87°. The difference between the two lines gives an interior angle of 85°, half of this would be the azimuth of the bisection of the angle: 42 ½ degrees or 42°30’. Now we would rotate the square, with the diagonal at 45° to the left (counter clockwise) 2 ½° or 2°30’ so it will equal the azimuth of the bisection angle. As you can most likely see by now, all 5 windows (and possibly more in the future) within the SW ¼ will be oriented the same direction. This solution in our opinion makes much more sense than any other solution where the square would be parallel to the West line or to the South line of the quarter section, at cardinal directions (true north), or be a parallelogram (not a square).

If you have any questions regarding this topic, please feel free to contact Dan Corriell at dan@petro-fs.com.