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A GIS Approach to the Geology, Production, and Growth of the Barnett Shale Play in Newark East Field, North Texas*
By
Rick Gonzalez1
Search and Discovery Article #40147 (2005)
Posted March 27, 2005
*Adapted for online presentation from the Master of Science Project by the author at the University of Texas at Dallas. Mr. Gonzalez’s work (2004) at UT Dallas is posted at http://charlotte.utdallas.edu/mgis/prj_mstrs/2004/Summer/Gonzalez/jegonzalez.htm.
1University of Texas at Dallas; present residence, Grand Prairie, TX ([email protected]).
Introduction
This paper is a
study of the gas-bearing Mississippian Barnett Shale in Newark East Field
located northwest of Fort Worth, Texas. Newark East Field straddles most of Wise
County, western Denton County, and northwestern Tarrant County. Because it is
located near the major urban centers of Dallas and Fort Worth (DFW), it is
important to know and understand the developmental state and geology of the most
active gas play in the United States. The aim of this study is to gain an
insight, by using 
well
data, into the structural geology and its relationship to
production patterns. Additionally, the field growth in Newark East is mapped so
as to examine its spatial relationship with the surrounding culture and to see
the field’s growth in relation to the surrounding urban centers. An analysis of
surface lineament trends and their possible relation to the subsurface faulting
trends is also discussed.
Figure 1 shows the regional setting in North Texas
and the major geologic structures as well as cultural elements that have
influenced gas production in Newark East Field. To the northeast the limit is
imposed by the Muenster Arch; to the east and south the limits are the urban
centers of the DFW area; and to the west the limit until recently had been the
Viola Limestone erosional limit (or pinchout) (Figure 2).
However, recent improvements in fracturing (stimulation) techniques and drilling
methods have begun to allow field expansion west of the edge of the Viola.
The Fort Worth Basin, where the Barnett Shale play is located, encompasses the counties of Clay, Montague, Young, Jack, Wise, Denton, Stephens, Palo Pinto, Parker, Tarrant, Eastland, Erath, Hood, Somervell, Johnson, Comanche, Hamilton, Bosque, Mills, Lampasas, and Coryell in Central and North-central Texas (Figure 1). The aim in this study is to map the formations above and below the Barnett Shale and the growth of the main drilling area where most of the field development has taken place--within Wise, Denton, and Tarrant counties. As of 2003 there have been more than 2800 wells drilled in these counties.
It is worthwhile to mention that the Barnett Shale produces some oil in addition to the gas. This oil is more prevalent in the northern and western parts of Newark East Field, and its production is marginal compared to gas production in the field. Both gas and oil production is mapped in this study.
The Barnett Shale wells require stimulation by fracturing (fracing) in order to obtain commercial (economic) volumes of gas. Early in the existence of the field (1980’s), the stimulation technology did not yet exist for completion of economically successful wells. Through trial and error, Mitchell Energy persisted until they succeeded in developing a technique for fracturing, gel frac, that made the Barnett economically productive. The caveat at the time and up until recently was to keep the fracture stimulation contained within the Barnett. This could be achieved by having the dense Ordovician Viola Limestone below and the dense Pennsylvanian Marble Falls Limestone above. Eventually, in the mid to late 1990’s Mitchell Energy developed a better and less expensive replacement for a gel frac--the slick water frac, which at the time was unconventional for shale stimulation. It became apparent that because of increased interference with neighboring wells water fracs cause a much different fracture pattern than the gel fracs did. Also, wells that were re-stimulated with a water frac produced at even higher rates than when they were initially fraced. Subsequent re-fracturing actually propagated into rock not affected by the first frac, and thereby causing production to increase to rates even higher than obtained after the first stimulation (Bowker, 2002). Once Mitchell perfected the technique and word leaked out to the industry, the play rapidly expanded in the late 1990’s.
The Barnett was deposited over a regional unconformity (Figure 2); the Viola pinches out, or is truncated, below this unconformity just west of Fort Worth and in western Wise County. Because of the missing Viola Limestone, wells drilled on the western part of the main (core) area tend to produce considerable water because the fracture stimulation is not contained extends into the water-bearing Ellenburger Limestone. Until recently drilling had been restricted to east of the Viola erosional limit because it was thought the fracture barriers needed to be present, but drilling and stimulation technology is catching up to the western part of the play. Eventually it will not matter if the fracture barriers above and below the Barnett are present.
This study arose from curiosity about the productive history and geology of the Barnett Shale productive area. Because this is an active and rapidly expanding play, there is the reluctance on the part of some operators to share their data. Most of the work on this play involves geophysical, geochemical data, stimulation techniques, core studies, and thermal maturation history. There have been limited studies related to production and comprehensive geologic maps. Geologic maps submitted to the Texas Railroad Commission are only general in nature; other available maps are broad, regional in nature, encompassing the Fort Worth Basin. The focus of this study is on the Newark East Field area northwest of the DFW Metroplex.
The data
obtained for this study are noted, including their format and subsequent
manipulation of them. Analysis and methodology applied to the data are explained
with the results and discussion.
The
stratigraphic units mapped for structural purposes are the Marble Falls
Limestone, Barnett Shale, Lower Barnett Shale, and Viola Limestone. A lack of
data on the Ellenburger Limestone prevented mapping it. Additionally,
lineaments, digitized using DEM data, are compared to subsurface faulting and
known studies of fracture orientations to determine if a relationship exists. An
isopach map of the gross thickness of the Barnett Shale and three cross-sections
have been prepared from well data. ArcScene is used to obtain a 3D model of the
subsurface by using the interpolated grids.
Production data are mapped in order to understand where the most productive areas are located, to determine if there are any differences or anomalies in production for different areas of the play, and how the production is related to structure. In this study, Cumulative Gas Production, Cumulative Oil Production, and Practical IP (Initial Potential) are mapped.
Maps were prepared showing the growth of the field since the early 1980’s and how it has expanded near or into some of the surrounding municipalities north and northwest of Fort Worth. The cultural data have been incorporated to illustrate the urban and cultural limits facing operators as field expansion continues. Also, the stake of the main operators in Newark East Field is mapped by showing which wells are operated by whom.
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Previous WorkDuring
the course of this current study, updated information was obtained at
the AAPG annual meeting in Dallas (April, 2004) and the Barnett Shale
Symposium (June, 2004). Old geologic maps submitted to the Texas
Railroad Commission by Mitchell Energy are outdated and general in
detail, yet useful; they were used as a check for elements of this
study. Additionally, a copy of one of the posters presented at the AAPG
meeting, “The Barnett Shale: Not So Simple After All” (Zhao and
Givens, 2004), describes the history of the Barnett play since the
1980’s by describing the advancement of stimulation techniques and
geologic knowledge. It contains isopach maps of Barnett Shale, formation
trends, Fort Worth Basin limits/trends, and major structural elements.
Another presentation by Zhao (2004) described the maturation and
physical properties of the Barnett shale. “Fractured Shale-gas Systems”
(Curtis, 2002) discusses a number of organic shale formations in the
United States and focuses on formation lithology, geologic framework,
and properties. “
DataThe
data collected for this study included The Oil
Information Library of Fort Worth provided its computer libraries and
microfiche Cultural shape files such as roads, rivers, municipality outlines, county outlines, and freeways were obtained from the 2002 ESRI Data CD’s that come with ArcGIS software. Other shape files, such as the Viola erosional limit, faults, regional structural elements, and lineaments, were generated in ESRI’s ArcCatalog software and digitized in ArcMap. A shape file, named “mask.shp,” was created and used as a mask during raster interpolation of structures. Additionally, DEM and Hillshade grids, from the Texas Natural Resources Information System website, were downloaded for use in the study area. Also,
electric After a personal geodatabase was created in
ArcMap, the project’s database in Access, the HeaderData and the
Tops spreadsheet, was imported as separate tables. Once this was
accomplished, the HeaderData table was added as an X-Y event
table in ArcMap. Because this table had each In order to map the tops, a “query by
attribute” was performed for each of the formation tops on the joined
tables. Once the queries were performed, a table was exported with the
selected records into the geodatabase. The same process of querying was
performed for the following attributes and saved to the geodatabase:
Practical IP, Cumulative Oil, Cumulative Gas, Operator Name, and First
Production Date. Thus, the exported tables contained latitude-longitude
for each For each table for a formation, the
preliminary interpolation was done using the Inverse Distance Weighted (IDW)
method and the Spatial Analyst with the mask shape file to keep
from rasterizing beyond the area where sparse Before finalizing the interpolated structure
map for each formation, three cross-sections were made across Newark
East Field: Section A-A’, West to East (Figure 3);
Section B-B’, Northwest to Southeast (Figure 4);
and Section C-C’, North to South (Figure 5).
As noted above, the cross-sections allow for verification of the general
structure and for the detection of structural and/or stratigraphic
changes over the field. Based on the information from cross-sections,
the Practical IP map, and To compensate for the problem due to limited
control near faults, especially for the Viola, Marble Falls, and Lower
Barnett, some “ghost” wells with tops were created that conform to the
anticipated structure in those sparsely controlled areas. This was
accomplished by placing the cursor over the desired spot, noting the x-y
values, then creating the new ghost The Barnett Shale thickness (isopach) map was constructed by substracting the Barnett Shale interpolated structure from the Viola Limestone interpolated structure, using the map calculator. Data from the HeaderData table in the geodatabase includes the field Operators. Using these data, the main Operators were mapped in order to show the areas where they operate and have the most acreage. The HeaderData table was queried for Operator. The records of each Operator were saved to a table in the geodatabase. Then, each was loaded as an x-y table event theme in ArcMap and symbolized. Also, Dates of First Production were queried from the HeaderData table to obtain a sense of how the field has expanded since the early 1980’s. These were queried by time intervals: 1982-85, 1986-90, 1991-95, 1996-98, 1999-2000, and 2001-2004. Each interval was saved as a table to the geodatabase and loaded as an x-y table event theme in ArcMap and symbolized. Finally, an
The Figure 13 shows
the wells and their encroachment on the urban area of the greater DFW
Metroplex. What is evident is that
Each formation dips to the northeast (Figures 14, 15, 16, and 17) toward the prominent Muenster Arch, which trends northwest to southeast. Specifically, the Barnett Shale subsea depths range from -5720 to -7628 feet; the highest elevations occur in southeastern Wise County, with elevations decreasing toward the center of Denton County. The cross-sections demonstrate the overall formation dip and faults, represented by blue lines in Figures 14, 15, 16, and 17. Less drilling has occurred in these zones characterized by production of significant volumes of water and little gas. The fractures and faults are thought to be in communication with the water-bearing Ellenburger below the Viola-Simpson rocks. A layered-cake model is illustrated by the 3-D representation of structure (Figure 18). Because the faults are nearly vertical (> 70 degrees--Steward, 2004, personal communication), the structural offsets across a fault can be seen clearly in the 3-D view. Inspection of Cross-section C-C’ (Figure 5) demonstrates that the Forestburg Limestone, between the Upper Barnett and the Lower Barnett, locally is as much as 200 feet thick; it thins to the south and finally pinches out in the southern part of the field. In Tarrant County the Upper Barnett and Lower Barnett merge into one unit. The Barnett Shale also thins from north to south (Figure 19). It ranges in thickness from about 240 feet in southern Newark East to greater than 1100 feet in the northern area. It is thought that in Mississippian time the shoreline lay to the north relative to Newark East Field, with the limestones, such as the Forestburg, having been deposited in shelf areas and shales deposited in deeper waters.
Lineaments, Faults, and Surface Topography Average strike of natural fractures is 114o;
average dip is 74o SW (Hill, 1992). The drilling-induced
fractures measured on the FMS In this study DEM’s were used to map 65
lineaments as line shape files. Figure 20
shows the various lineaments mapped (red lines) over the DEM topography.
The subsurface faults have been included on the map to compare with the
lineaments. In this study the NE-trending lineaments average 55o
(standard deviation 20, variance 402). SE-trending lineaments average
133o (standard deviation 34, variance 1172). The subsurface
faults, which average 65o (standard deviation 18, variance
307), may be related to the same stress field; however, the large
standard deviation and variance (Table 2)
show why this finding is not quite conclusive. On the surface, the
SE-trending lineaments would seem to be related to the natural fractures
striking 114o. The NE-trending lineaments would seem to be
related to the changed stress field (55o) noted by Hill
(1992). One must keep in mind that Hill’s work was done on one
Three interpolated maps were produced from
the production data: Practical IP, Cumulative Gas, and Cumulative Oil.
Practical IP is the 24-hour rate (Mcd/day) for a Cumulative Gas (Figures 22 and 23) and Cumulative Oil (Figures 24 and 25) maps, respectively, show that most gas and oil production occurs away from the major faulting. It is known that most of the gas produced has come from the core area where Wise, Denton, and Tarrant counties intersect. For the Cumulative Oil map, it is known that crude has been produced in the northern part of the core area. The northern part of the core area is near the edge of the oil-generating window that extends over Clay, Montague, Cooke, and Jack counties (Zhao and Givens, 2004). South of this area is the transition to the gas-generation window, where in Newark East Field the Barnett produces more gas than oil.
As Newark East Field expands, it is encroaching on the DFW area and municipalities. It is evident from the mapping that further growth is being complicated by the urban centers. Producers will have to deal with land-use issues, right-of-way issues, mineral-rights issues, and local ordinances. Expansion of the field appears to be limited to the south and southeast by the population centers. Mapping and an ArcMap 3-D model show that the Barnett Shale and associated strata dip in the same direction and show a layered-cake-like stratigraphy. The cross-sections aided in determining where the major faulting occurs in Newark East. Production maps show that the best production is away from the faults. The more heavily faulted areas tend to contain poor gas producers but substantial water production. There may be some relationship between the surface lineaments and subsurface fracturing and faulting. However, based on the statistics, the relationship is not conclusive. The SE-trending lineaments may be related to the natural fracture orientation of 114o. The NE-trending lineaments may be related to the induced fracturing of 55o. Subsurface faults, with the same 55o orientation, may reflect the same stress field.
Adams, G., 2004, Challenges of urban drilling [abs]: Barnett Shale Symposium II, Brookhaven College, Richardson, Texas. Bowker, K., 2002, Recent developments of the Barnett Shale play, Fort Worth Basin, in Law, B.E., and M. Wilson, eds., Innovative Gas Exploration Concepts Symposium: Rocky Mountain Association of Geologists and Petroleum Technology Transfer Council, October, 2002, Denver, CO, 16 p. Gonzalez, Rick, 2004, A GIS Approach to the Geology, Production, and Growth of the Barnett Shale Play in Newark East Field: GIS Masters Project: POEC 6386, University of Texas at Dallas (instructor: Instructor: Dr. Ron Brigg) (http://charlotte.utdallas.edu/mgis/prj_mstrs/2004/Summer/Gonzalez/jegonzalez.htm). Henry, J.D., 1982, Stratigraphy of the Barnett Shale (Mississippian) and associated reefs in the northern Fort Worth basin: Dallas Geological Society paper, 21 p.
Hill, R.E., 1992, Jarvie, D.M., B.L. Claxton, F. Henk, and J.T. Breyer, 2001, Oil and shale gas from the Barnett Shale, Fort Worth Basin, Texas [abs]: AAPG Annual Meeting, Program and Abstracts, p. A100. Jarvie, D.M., and B.L. Claxton, 2002, Barnett Shale oil and gas as an analog for other black shales [abs]: AAPG Southwest Section Meeting, Ruidoso, New Mexico. Jarvie, D. M.,2003, The Barnett shale as a model for unconventional shale gas exploration, presentation for AAPG meeting: Accessed June 2004 at URL http://www.humble-inc.com Kuuskraa, V.A., G. Koperna, J.W. Schmoker, and J.C Quinn, 1998, Barnett Shale rising star in Fort Worth basin: Oil & Gas Journal, v. 96, no. 21, p. 67-68, 71-76. Lancaster, D.E. et al, 1992, Reservoir evaluation, completion techniques, and recent results from Barnett Shale development in the Fort Worth basin; Society of Petroleum Engineers, SPE paper 24884, 12 p. Pollastro, R.M., et al, 2003. Assessing undiscovered resources of the Barnett-Paleozoic total petroleum system, Bend Arch-Fort Worth basin province, Texas: Search and Discovery Article #10034; AAPG Southwest Section Meeting, Fort Worth, Texas. 17 p. Steward, D.B., 2004, Personal communication: discussion on the Barnett play.
Thomas, J.D., 2003, Integrating synsedimentary tectonics
with Williams, P., 2002, The Barnett Shale: Oil and Gas Investor, v. 22, no 3, p34-45. Zhao, H., 2004, Thermal maturation and physical properties of Barnett Shale in Fort Worth Basin, North Texas (abs.): AAPG annual convention Dallas (Search and Discovery Article #90026 (http://www.searchanddiscovery.net/documents/abstracts/annual2004/Dallas/Zhao.htm). Zhao, H., and N. Givens, 2004, The Barnett Shale: not so simple after all: AAPG annual convention Dallas (poster)--Republic Energy Inc. website (http://www.republicenergy.com/Articles/Barnett_Shale/Barnettaspx).
I would like to thank the following individuals and/or companies who made this study possible either by donation of their digital data or access to their hard copy files. Their contributions to this project are very much appreciated: The Oil Information Library in Fort Worth and Mr. Roy English for his help while researching at the library; DrillingInfo.com and Charles Hopkins for the production data; Dan B. Steward and Natalie B. Givens at Republic Energy Inc. in Dallas for taking the time to discuss the Barnett Shale and providing material for research; and Bill Harrison, Geoff Ice, Yvette Chovanec, Steve Vonfeldt, Martin Selznick, and Debbie Fierros at Rosewood Resources, Incorporated for their support and encouragement on this project. Also, to my advisor and instructor, Dr. Ron Briggs, University of Texas at Dallas, and to my wife Alicia for “putting up with me” while engrossed in this work. |
