Rodney S. Stoa, Scott A. Bassingthwaite, James A. Sorensen
Energy & Environmental Research Center
Grand Forks, N.D.
PC-based geographic information systems (GIS) software allows casual users to quickly and intuitively visualize oil and gas data bases.
No longer is it necessary for a company to have specially trained personnel to effectively access and use GIS capabilities, although a thorough understanding of GIS techniques can enhance the analysis.
GIS is a versatile and effective tool for oil and gas data management. It has a proven track record, although in the past, the investment in both cost and training precluded its use by many operators.
The relatively recent availability of affordable yet powerful PC-based GIS software has virtually eliminated these limiting factors.
From the standpoint of any industry, GIS use depends foremost on its practical applications such as working with information from a visual rather than numeric perspective. This allows information to be communicated to a diverse work force in an easily understood manner.
The notion that a picture is worth a thousand words, although a cliche, is certainly true when comparing a map generated by a GIS to the extensive data tables represented by that map.
GIS application
This article is partially based on work performed at the Energy & Environmental Research Center (EERC) for the Gas Research Institute (GRI) and the U.S. Department of Energy (DOE) related to produced water and drilling waste management.(1 2)Nearly 300 players in the oil and gas industry were surveyed on various operational aspects, such as waste management practices, production characteristics, and drilling problems. In conducting this telephone survey, it became apparent that a relatively inexpensive, PC-based GIS would be useful for oil and gas operators.
This study extensively used Atlas GIS software, which proved to be user-friendly and served our purposes for data manipulation, interpretation, and display.
Several other mapping programs were previewed with various degrees of success. These other programs could not analyze the large data bases that had been developed. Also, they lacked the capability to overlay and extract information.
The criteria for choosing a system were simple and straightforward. The software had to be output-oriented, while containing the necessary data management capability and possessing the basic functionality of a more sophisticated workstation-based GIS software.
The produced water and drilling waste management project aimed to provide the gas industry with a broad-based view of practices and activities related to produced water and drilling waste management and associated regulations affecting these activities.
The project involved construction of a quantity and quality data base for visually relating the data through GIS output. This information gave the gas industry focal points upon which to base decisions for developing proactive responses to environmental regulations. Such decisions require knowledge of the oil and gas exploration and production activities in specific regions of the country, as well as the federal and state regulations that apply to each of those regions.
To determine the effects of regulations on oil and gas activity in the various regions of the country, data were collected at various levels of spatial resolution (state, geologic province, state-province, county or parish levels). This allowed for the flexibility of developing different information with regard to the areal distribution within these spatial boundaries.
Development of the information at the field level and even the well level exists, but was deemed impractical for the waste management study.
Data analysis
A GIS is a unique combination of spatial feature representation and analysis in digital format and the more traditional data base information that describes or quantifies the spatial feature or features.The spatial features are located with respect to a known coordinate system and are represented as one of the following: point, line, or polygon. These spatial features are further described by a record in a data base.
A point feature might represent the location of an oil or gas well that can be associated to a data base record containing information on well installations related to production and servicing. A line feature might represent a gas, oil, or produced-water pipeline or a road. A polygon is an enclosed area of any size or shape that could represent the extent of a political boundary, such as a lease area or county.
These spatial features are typically managed in layers of related features. The capability of GIS to portray complex interactions in and between spatial features in layers through GIS spatial analysis techniques is the true power of GIS.
Acquisition of both spatial and nonspatial data is the greatest cost associated with the development of GIS capability. With the PC-based system, nonspatial data developed in a PC data base can easily be integrated into a GIS system through geocoding.
Geocoding is a technique where each data element is assigned a geographically corresponding identification code, which is used by the GIS. When balanced with the ability to query, analyze, and view information in a spatial context, the cost-effectiveness of data acquisition and development will clearly be shown through the advantages of visual information display.
Several paths can be followed for data development. The only requisite is that the final file format is saved with a .dbf extension, which is associated with data base files. Data are easily imported from a number of sources, including spreadsheets, relational data bases, and files in Ascii format.
The produced-water and drilling waste management project used all three types of sources. These were reduced and saved with the necessary .dbf file extension for use by the GIS. Data can also be changed or added directly to the GIS through editing of the data base.
Project example
The Louisiana portion of the Gulf Coast basin, which has excellent data coverage and is large enough in areal extent, provides a useful example.Data on natural gas and water produced from the Louisiana Gulf Coast basin in 1990 were obtained from Petroleum Information Corp.3 The basic data, on a parish level, included the number of active wells and fields, annual nonassociated gas and water production, and average producing depth.
Although these data were developed at the parish level, geology is obviously not constrained by political boundaries. In light of this, the Geologic Provinces Code Map from AAPG committee on statistics of drilling (AAPG-CSD)4 was used to establish province boundaries.
We also added a state-geologic province delineation from our previous work for GRI and DOE. This adds a component to the province that allows one to consider factors that vary from state to state, such as regulatory differences.
Thematic maps graphically display and enable comparison of data base information, illustrating the relationship between geographic features and particular information. The theme of the map is constituted by the kind of data base information it represents. Although this information could be examined in tables or graphs, the visual impact of the thematic maps is immediate, as can be seen by Figs. 1a and b. (226382 bytes)
These figures are graphical representations of 1990 annual water and gas production rates at the state-province level. With the thematic map providing a geographic reference, any anomalous areas are immediately evident. The thematic criteria can be set to indicate only those areas that fall outside the user-defined limit.
The subsurface geology of the Louisiana Gulf Coast basin is highly complex. The province is a classic example of a marginal sedimentary basin in which the subsidence rate is approximately equal to the deposition rate.
The sediments of the South Louisiana portion of the basin are a mix of terrestrial and marine sediments deposited in a deltaic environment. The deposits are predominantly sands, silts, and shales, with transgressive and regressive sequences.
Further complicating the stratigraphy are numerous growth faults and salt intrusions. Most of the gas reservoirs are found in structural traps created by the growth faults and salt intrusions. These structural features prevent making general statements about the producing depth for most of the gas-producing formations.
Much of the natural gas produced in South Louisiana is from water-drive reservoirs in Tertiary sand units.
From the state-province level map of the U.S. (Fig. 1a (226382 bytes)), one would think that the entire Louisiana portion of the Gulf Coast basin has high water production rates, but when the parish-level map is examined (Fig. 1c (226382 bytes)), it is readily apparent that the high water production rates are confined essentially to the southern portions of the Louisiana Gulf Coast basin. The application of the annual water production rates to the state-province level presents a less-than-accurate portrayal of the water production in the area.
Water production per well on a daily basis is variable, with high water production rates, in b/d or b/Mcf, seeming to correlate with high gas production rates. No correlation between water production rates and depth of production was evident.
Water production ranged from less than 1 to 384 bbl/well/day (Fig. 1c (226382 bytes)). While the high water production rates might be alarming at first glance, when they are examined in the context of the corresponding gas production rates (Fig. 1d (226382 bytes)), it is evident that high water production correlates with high gas production rates.
The water-to-gas-ratios can be quite high (Fig. 1e (226382 bytes)), with most parishes much greater than the 0.015 bbl/Mcf reported as the average for the U.S.5
With produced water being an important management concern, this may be a useful relationship for planning exploration, production, and corresponding management activities.
References
1.Daly, D.J., Stoa, R.S., Bassingthwaite, S.B., Sorenson, J.A., Mesing, C.E., Fillo, J.P., Pemmaraju, S., Martz, K.D., and Tallon, J.T., Atlas of Gas-Related Produced Water for 1990, Topical Report No. GRI-95/0016, Gas Research Institute, 1995.
2.Daly, D.J., Stoa, R.S., Bassingthwaite, S.B., Sorenson, J.A., Atlas of Gas-Related Drilling Waste for 1990, Topical Report No. GRI-95/0017, Gas Research Institute, 1995.
3.Petroleum Information Corp., Gas Production, Gas-Producing Well Populations, and Gas-Related Water Production (selected areas) by County, for the U.S. in 1990, customized report, 1992.
4.Meyer, R.F., Wallace, L.G., and Wagner, F.J., Jr., AAPG-CSD Geologic Provinces Code Map, AAPG Bulletin, October 1991, pp. 1,644-51.
5.Gruy Engineering Corp., Estimates of RCRA Reauthorization Economic Impacts on the Petroleum Extraction Industry, unpublished API report, 1991.
