GIS data modeling for well spot planning
Dr. Robert C. Maggio
Manager, GIS Operations
Petris Technology, Inc.
1900 St. James Place, Suite 700
Houston, TX 77056
713-403-8451
Emailt: maggio@petris.com
Introduction
Oil and gas exploration uses considerable data regarding underground geologic structure to
determine the placement of wells. There are sophisticated software systems that aid the geologist
in the placement of oil wells. These software systems depend on the geologist's interpretation of
the geologic strata, production figures from existing wells, as well as a vast amount of experience.
The result is the placement of the bottom of a new well. The exploration software systems locate
new wells by assigning them a world coordinate; most often, this coordinate reference is in
degrees of latitude and longitude. This method effectively locates the well. However, this is only
a coordinate. Most exploration software systems do not reference this new coordinate to
landcover features at the surface.
The geographic information system (GIS) is an integrated system of software tools that capture,
store, analyze, portray, and output spatially referenced data. The GIS is based on coordinate
systems; and much like the software system used by the exploration geologist, it represents data
in two or three dimensional space. Each system has its strengths and weaknesses. The
exploration system is designed to aid the geologist in finding oil. The GIS is an analytical tool
whose forte is the representation of many data types in a single view. An integration of these two
capabilities could equip the exploration geologist with a very powerful decision making tool.
One of the challenges to a geologist when a new well has been spotted, is the placement of the
surface location of the well. The decision to drill the well vertically or horizontally is based both
on geologic evidence and surficial landcover type. Placing oil wells at the surface in residential
areas, on highways, in rivers, or on highly rugged terrain is not practical. For this reason, it is
prudent to integrate the well spots with detailed landcover data. This landcover Therefore, the
final decision as to where to place the well may depend on the landcover at the surface. data is
often depicted on aerial photographs or satellite imagery.
Another key factor in the placement of the surface location of oil wells is the density of the wells
in a production unit or field. The GIS has a sophisticated set of spatial analysis tools that will aid
the geologist is the grouping of wells according to criteria set forth by regulatory agencies.
Grouping of wells into units and fields is a service the GIS can provide. Additionally, since the
GIS integrates both mapped data and remotely sensed imagery, it will allow the geologist to plan
well densities, while at the same time, use good judgement in their placement with reference to
landscape elements.
The data
Well Location Data
A portion of the data used in this analysis is extracted from the geologic exploration software
system Geographix. The system yields coordinate pairs that reference the location most likely to
produce oil. No effort will be made to explain the operation of the system or its use. For this
presentation, it merely produces a location to drill a well. The coordinates from Geographix are
integrated into the GIS using a process known as geocoding. This function takes an X,Y
coordinate pair listing and generates a map. The map may contain one to any number of
positional locations. In addition to the locational information for each well, data describing the
well such as depth, operator, owner, etc. is also stored with its location.
Aerial Photography
The landcover data stored in the GIS is digital, color aerial photography. The photography was
imaged using a conventional aerial camera that produced a 9" X 9", true color photograph. The
negative scale was 1:24,000 or 1" = 2000'. This is a common scale used for landuse/landcover
mapping. The photographs were then scanned at a resolution of 400 dots per inch to produce 1-
meter pixel resolution digital images. Due to time constraints and equipment available to image
the photographs, there was no attempt to geo-reference the images using aerial Global Positioning
Systems (GPS) equipment.
The geo-referencing of the aerial photographs was developed manually. Ground control points
that appear both on the photographs and on the ground were visited in the field using GPS
equipment. Features visited in the field included road intersections, stock tank dams, fence
corners, oil tank batteries, and other man made features. Using the GPS equipment, coordinates
were collected for four to eight points per photograph. A digital image processing system was
used to geo-reference each photograph. The result of this process was a coordinate location for
each pixel on each aerial photograph.
Each individual, geo-referenced aerial photograph was of great value and could be loaded directly
into the GIS. However, an additional step of mosaicing all of the geo-referenced aerial
photographs into a single, seamless image greatly enhanced its utility. The digital image
processing system, ER Mapper was used to mosaic each of the individual geo-referenced images
into a single image. The process of mosaicing multiple, large-scale images into a single, large-
scale image produced an image that was seamless, and yet preserved the 1-meter pixel resolution
of the original photography. The ER Mapper image mosaicing process also conducted edge
matching, color balancing, edge feathering among images, and image compression. The original,
seamless image exceeded 108 gigabytes, but was compressed to 482 megabytes. This
compression is very important when displaying large images in the GIS. The ER Mapper
software provides a "plugin" to most GIS packages that display imagery.
