Computer Graphical Analysis Method Proves Beneficial in Lost Soldier Field Deviated Well Application
Authors: Smith David L. 
Published: December 2007

Summary
This paper presents results of using computer-generated plots of directional drilling data as a tool in planning the directional and normal drilling operations in a test at Lost Soldier Field, WY. Emphasis is placed on their application to deviation-controlled wells in areas experiencing crooked-hole drilling, Results have shown that their use in conjunction with dipmeter data and structural contour maps of shallow horizons penetrated is effective in projecting wellbore trajectory. With these data, surface locations can be engineered to minimize corrective mud motor runs and to allow for optimal bit conditions. Our computer-generated plots have contributed greatly to cutting average drilling time in the field from 62 days in 1978 and the first half of 1979 to 32 days for the last half of 1979. Drilling costs were reduced 44% during this time, even though the daily rig costs increased 37 %.

Introduction
Lost Soldier field, located in Sweetwater County, WY, produces from the Pennsylvanian Tensleep sandstone (average depth 5,000 ft), and the Mississippian Madison carbonate (average depth 5,700 ft). The two reservoirs are asymmetric anticlines overlying each other with dips of 40 deg. on the west and 60 deg. on the east. Increased waterflood activity in both reservoirs has led to drilling infill wells to accommodate pattern flood operations. Because wells in the area normally deviate substantially and well spacing is 10 acres per well, targets of 100-ft radius at the formation top have been specified by the reservoir engineers to ensure optimal depletion of maximum reserves. Until the summer of 1978, the surface locations were chosen about 200 to 300 ft downdip of the Tensleep structure (Fig. 1). This decision required that the directional driller pay close attention to inclination because of the tendency to drill at higher angles than could be tolerated. Drilling with light weight on bit (WOB) or "fanning" the well to control inclination slowed penetration rate and increased days and costs. Distances increased gradually between target and surface locations to allow for more WOB, but this met with only limited success. Many times the direction was off considerably, and, at the higher inclination, this resulted in longer mud motor runs to correct azimuth. This was undesirable because the dogleg caused additional drilling, completion, and operational problems. In May 1979 it became obvious that the unpredictable nature of Lost Soldier drilling needed to be understood to minimize drilling costs and hazardous doglegs that are troublesome throughout the life of the well.

Computer Graphical Analysis Method Application
To alleviate directional problems, a postappraisal of drilled wells was initiated. To accomplish this, a computer graphical analysis method was used. Fig. 2 is the computer graph for Lost Soldier Unit (LSU) Well 130. Depth is plotted on the ordinate scale vs. eight different parameters across the abscissa:WOB in 1,000 lbm,rotary speed in rpm,average penetration rate in ft/hr,bit number, size, and type,measured inclination in degrees,measured direction in degrees,dogleg severity in degrees per 100 ft, andbottomhole assembly (BHA) description.
Lithology with formation tops also can be included in the computer presentation. With these data presented simultaneously, graphic relationships between inclination, formation drilled, and drilling assembly became apparent. Bit walk, or measured direction (in degrees), had no apparent relationship with other drilling parameters. An updip tendency of a drilling-bit was noted, so formation dip data from service-company calculated dipmeters were converted to updip direction and hand-plotted on the bit-walk curve in Fig. 2.
JPT
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