UNCONVENTIONAL GAS RESOURCES IN KANSAS

Based on a workshop sponsored by PTTC's North Midcontinent Region in Wichita, Kansas on January 19, 2005.

BOTTOM LINE

Unconventional gas resources have become an increasingly important part of natural gas production from the domestic United States. Coalbed methane gas, alone represented 9% of all natural gas produced in 2003 and 2004. Opportunities to reap the benefits of unconventional gas plays exist in Kansas and the adjoining areas of Colorado, Missouri and Oklahoma. This workshop provides an overall prospective of unconventional gas resources in Kansas by the Survey. Companies involved in the development also shared their expertise with fellow operators. One challenge is to scale down new technologies to make them available and economic to the small independent operators working in the Midcontinent.

PROBLEM ADDRESSED

The need for increased unconventional natural gas production in the next 10 to 20 years has created a market, which independent operators in Kansas want to share in. However, information on the resources and techniques to evaluate them has been minimal. The Kansas Geological Survey has a responsibility to the people of Kansas to provide information on the development and economic production of resources vital to Kansas' economy.

KEY WORDS:

Central Kansas Uplift, Coalbed Methane, Niobrara Chalk, Gas Processing, Hugoton Field, Low BTU Gas, Niobrara Chalk, Pratt Anticline

SPEAKERS:

Speakers from PTTC and Kansas Geological Survey:

Introduction, PTTC,
Rodney Reynolds & Dwayne McCune, PTTC

Geologic Overview of Niobrara Chalk Natural Gas Play,
Lynn Watney, KGS

Petrophysical Rock Properties of Niobrara Chalk,
Alan Byrnes, KGS

General Survey of Low - BTU gas reservoirs, KGS, David Newell
Production characteristics of Cherokee Basin Coals in Kansas and Oklahoma,
Dwayne McCune, PTTC


Industry Speakers:

Micro-scale Gas Processing:Low-pressure, Low-volume CO2 and N2 Rejection and Helium Extraction Utilizing Pressure Swing Adsorption,
Scott Sears, Inter-American Corp.

Log Analysis Techniques of Permian and Pennsylvanian Low-BTU Gas Reservoirs in Central Kansas,
Richard Leeth, ELI Wireline Services

Optimizing Artificial Lift Systems In A Gas Producing Environment,
Anthony Crivello, eProduction Solutions

Geologic Characteristics of Coalbed Methane in the Cherokee and Forest City Basins in Eastern Kansas,
Jim Stegeman, Colt Energy Inc.
 

TECHNOLOGY OVERVIEW

Kansas has two active but underexploited plays and one undeveloped play that fit the unconventional gas definition. The shallow chalk tight gas play of western Kansas and eastern Colorado and the coalbed methane play of eastern Kansas and Oklahoma are active natural gas producers. Low BTU gas, having a heating valve of less than 950 BTU is classified as unconventional gas, but has seen little development. The Energy Information Agency of DOE currently estimates onshore natural gas reserves in the U. S. at 260 Tcf. Reserves in the Midcontinent are estimated at 13 Tcf contained in low BTU reservoirs, providing a significant target if technologies can make low BTU gas economic to produce.

Niobrara Chalk Natural Gas Play
The Niobrara Chalk is an upper Cretaceous shallow carbonate deposit outcropping across west-central Kansas and eastern Nebraska. The Niobrara natural gas reservoirs are located in western Kansas, Nebraska and north-eastern Colorado (Denver Basin). The Niobrara natural gas play is from shallow zones that can be correlated on logs by the Fort Hays limestone, which forms a regional marker.

The geological setting in the Niobrara area in the late Cretaceous was a side shallow inter-continental sea where black shale and chalk deposits formed. Volcanism and tectonic activities along the Cordilleran provided wind blown ash, which settled into the shallow interior sea mixing with the microscopic marine sediments from planktonic foraminifera. Chalk is a fine-grained muddy textured rock formed from these marine and terrigenous sediments. Chalk represents 70% of the total carbonate sediments worldwide over the past 100 million years.

The Niobrara Chalk has high porosity (40-50%) and low permeability (0 to 1-3 md), making it a very tight reservoir. Biogenic gas formed from thermally immature organic-rich chalk. Chalk is brittle and fractures easily, which caused enhanced porosity along fractures and local faults. Local natural gas accumulations are controlled by the faulting and structural features, such as shallow domes and noses. Local diagenetic action alters porosity through dewatering sediments, and reactions between organic and inorganic constituents. Such chemical alteration forms pyrite and kaolinite (authigenic clays). The clay content has an effect on the heating values in the chalk, resulting in natural gas with a BTU content ranging from 965 to 1025.

Mapping the Niobrara with wireline logs is the best method to locate the shallow gas pay zones. Cross sections and isopach maps illustrate the changes in depth and range in thickness of the Niobrara Chalk in western Kansas and into the Denver Basin in Colorado. The pay zones in the Niobrara typically have higher neutron porosity and low density porosity, reflecting the pressure of natural gas on wireline logs. To make the unconventional Niobrara gas play produce, it is necessary to use fracture stimulation. Currently the most effective stimulation is a sand nitrogen foam, sand-CO₂ and methanol-water treatment.

Petrophysical Properties of the Niobrara Chalk NW Kansas, NE Colorado
Reservoir characterization of the Niobrara Chalk attempts to model porosity, permeability and saturation and relate these properties to economically recoverable natural gas accumulations. Basin models include architectural properties of structural tops, thickness and reservoir connectivity; reservoir properties of porosity, permeability and saturations; and fluid properties of pressure, viscosity, bubble point and formation volume factors. Core analysis is the most effective way to obtain these values and provides data for reservoir models of the Niobrara Chalk.

Initially Niobrara porosities were as high as 60-80%, but as burial compacted and dewatered the marine cocoliths porosity dropped to 40-50%. Compaction caused breakage of shells and reorientation of grains reducing porosity. Porosity was further reduced by the volcanic ash content, which altered the ash to clay and shales. Wireline log porosity values reflected on Neutron and Sonic logs are influenced by shale content in the chalk.

Permeability in the Niobrara Chalk is very tight, reflecting the degree of diagenetic alteration of the sediments and the fluid saturation. Core analysis for permeability measurement relies on full diameter cores, plugs, sidewall cores, ships/cuttings and mini-permeameter probe analysis. Plots of the relationship between pore throat diameter and permeability reflect lithologic changes and compositions.

Determination of the water saturation of the chalk is important prior to drilling since the Niobrara tends to absorb the water in drilling muds. The primary means to determine water saturation are wireline logs, fluid saturations from cores and capillary pressure measurements from core samples. Saturation is dependent on wettability of the chalk. The presence of methane gas can be mapped in relationship to pressure gradients and temperatures.

Conclusions based on the petrophysical analysis of the Niobrara indicate that it is fairly incompressible. Porosity is influenced by original content and matrix density, which varies with porosity changes. Permeability of the Niobrara is predictable based on porosity measurement, and does not change greatly with confining pressure unless the rock is fractured. Capillary pressures and permeability have a high correlation. Saturations are consistent with capillary pressure, permeability and height above the free water level. In the Niobrara chalk the relative permeability changes consistently with absolute permeability. Saturation, based on Archie cementation equations, is not highly sensitive to differences at the high porosities in the Niobrara Chalk.

Survey of Low BTU Gas Reservoirs
Low BTU (less than 950 BTU) gas reservoirs contain 13 Tcf of natural gas reserves in the Midcontinent. Much of this resource is unavailable, shut in behind pipe, uneconomical or abandoned because it can't be blended with higher BTU content gas. New technologies can be combined to make recovery of low BTU gas economic in the near future.

Low BTU reservoirs result from noncombustible gases (nitrogen, helium, argon and carbon dioxide) that reduce BTU content to less than 950. If the noncombustible gas content is 15% or higher, the heating value will be less than 950 BTU. As estimated, one-third of the gas reservoirs in Kansas have values below 950 BTU. Helium is normally associated with high nitrogen content. Low BTU reservoirs rim the Hugoton field with nitrogen to helium ratios even higher than those at Hugoton (48:1).

A databank of BTU content can be collected from Bureau of Mines and state data, but doing so is a labor intensive task. Geological information, location, formation and depth information should be incorporated as well as BTU values. Preliminary analysis of Kansas gas quality is underway at the Kansas Geological Survey, but as yet no comprehensive maps have been published.

Gas quality curves typically are expressed as bimodal; reservoirs range from 950 to 1050 BTU (two-thirds of Kansas reservoirs) and those less than 950 BTU. Associating gas heating valves to formations is the key to mapping gas quality across the state. Most low BTU reservoirs are in geological strata above the basal Pennsylvanian-Permian unconformity. Mapping associated noncombustible gases (N₂, He, CO₂ and Ar) corresponds to the 950 BTU cut-off value for low BTU gas reservoirs.

Mapping low BTU trends in Kansas shows that the Central Kansas Uplift and the Pratt Anticline (south-central Kansas) have high numbers of low BTU gas analyses. Low BTU gas content increases northward on the Central Kansas Uplift. Pennsylvanian-age formations on the Uplift may contain low BTU reservoirs, while west of the Uplift low BTU reservoirs may be present in Permian age formations. Low BTU analysis indicates potential reservoirs in the southern portion of the Central Kansas uplift and the northern portion of the Pratt Anticline.

Low BTU gas reservoirs represent a third type of natural gas play in Kansas. Mapping gas quality and predicting the distribution will assist in developing this play.

Log Analysis of Permian-Pennsylvanian Low BTU gas reservoirs
Low BTU gas reservoirs have been identified in the Permian Chase Group (Hugoton field play), Council Grove Group and Admire Group, and in the Pennsylvanian Wabaunsee Group in central Kansas. Log analysis of the lithologies helps to identify the potential areas for low BTU gas reservoirs within these formations.

Micro-Scale Gas Processing
New technologies for gas separation can economically make use of noncombustible gases from low BTU reservoirs feasible. This would provide additional income and make producing natural gas from low BTU reservoirs economic as well. Micro-scale processing of CO₂ and N₂ for reinjection in enhanced oil recovery, and helium extraction for resale is possible using pressure swing adsorption (PSA) technology. PSA is commonly used for hydrogen generation and purification, nitrogen generation from ambient air, and specially designed brake systems.

Large scale facilities (5 to 15 MM/D) for processing low BTU gases have been developed, but well identified reserves were lacking to make them profitable. Current mapping of low BTU reserves indicates that areas in south-central Kansas and the Denver Basin of Colorado and western Kansas have potential for micro-scale gas PSA processing systems.

PSA units are designed as small, mobile processing units. Scalability of these units is from 500 Mcf/d to over 7 MMscf/d. For CO₂ rejection processing, steps include: reducing gas levels to pipeline specifications, maintaining operating pressure between 50-175 psig, and recovering 95% of CH₄, 96% of C₂, 98% of C₃ and 99% of C₂. The difficulty with using PSA units is to establish the best operating costs versus rejection rates for optimum economic return. Current CO₂ rejection units pay out over a seven-year life of the project. Similar PSA units are designed for nitrogen rejection.

Helium extraction and purification units are designed to process He at 99.9997% purity. For resale the He is stored in tanks at 3,000 psi. With current He prices up to $50 per Mcf, helium recovery from low BTU reservoirs in Kansas is a good economic opportunity, and will encourage natural gas recovery from these reservoirs as well. Helium demand is expected to grow at a rate of 4% per year in the U. S. The cost of supply is expected to increase 50% over the next decade to meet demand.

Advantages of PSA units include: mobile highly flexible units, unattended operation reduces labor costs, high BTU recovery, units work on a low pressure system and processing can perform to specifications.

Coalbed Methane (CBM) in the Cherokee and Forest City Basins
The Western Interior Coal region has prime producing coal seams in eastern Kansas. For evaluation of coal seams for CBM potential, coal properties of thickness, rank, gas content and composition, ash content, and permeability must be analyzed. Coal is ranked with increasing hardness and carbon content and decreasing water content from: peat through lignite, sub-bituminous, bituminous, semi-anthracite, and anthracite to graphite. The BTU value per pound in lignite is 7500, 10,000 for sub-bituminous, 15,500 for bituminous and 15,500 for semi-anthracite. Water content ranges from 75% in peat to 2% in graphite and 1% in anthracite and semi-anthracite.

CBM origin can be biogenic (produced by microbes) or thermogenic (generated from temperature and pressure) with low ash content and up to 100% absorption or gas saturation. In the Cherokee Basin gas saturation reaches 100%, but typical coals in the Forest City are undersaturated. Sources of gas migration into coalbeds are an important factor for CBM development. Biogenic gas comes from organic shale, while thermogenic gases come from other mature source beds. Gas results from degassing of mantle or intrusive igneous rocks.

CBM gases are high in methane and have less than 5% nitrogen and less than 5% CO₂ with minor amounts of hydrocarbons. Isotopic analysis of the coals from the Cherokee and Forest City basins indicates mixed biogenic and thermogenic origins. Closer to outcrop areas in eastern Kansas, the biogenic content is highest with limited or no thermogenic gas content in a 25- to 40-mile radius. The biogenic gas in the northern Forest City Basin is similar to that found in the Illinois Basin.

Ash content in coal is mainly sulfur and clay minerals and forms the noncombustible portion of coal. High ash content is associated with increased bound H₂O. Coals from fresh water swamps have higher ash content than coals from marine-influenced shales.

Permeability is the key to CBM development. Permeability is related to fracturing and migration along cleats, which relates to coal rank. Tests for permeability are somewhat difficult due to the need to capture samples and bring them to the surface to preserve and measure the true permeability at depth while avoiding gas loss from the samples.

In the Forest City and Cherokee basins the most productive coal seams are in the Mulky, Weir-Pittsburg and Riverton formations. A number of other coals have potential for CBM production, but may not have been fully characterized for gas content. The Mulberry, Croweburg, Mineral Coal, Mulky and others all produce coal in eastern Kansas and western Missouri.

The Weir-Pittsburg coals have a long history of coal mining and have produced CBM since 1982. Coals from the Riverton formation have tested with the highest gas content of all Pennsylvanian coal deposits in Kansas. Selection of drilling locations for CBM production is based on thickness of coal seams, high gas content, low ash content, low moisture content, permeability, high coal rank (bituminous) and depths ranging from 500 to 2000+ ft.

Production Characteristics of Cherokee Basin Coals
Production data come from public records that give monthly gas sales, but don't have data on water production or pressure. Information on well spacing, completion techniques and other limitations are also unavailable from public records. Production records can assist with defining typical CBM properties by combining public data with geologic data and stratigraphic position. Data plots show typical production curves with steep declines for individual wells and the steady rise in CBM production for the Cherokee Basin as a whole.

Plots show that gas and water production have a similar curve for all CBM wells over time. Initial water production is high, but as gas production increases water production declines steeply. Gas production peaks and declines slowly as water production plateaus out at a much lower level than initial rates. Permeability-enhancing technologies can change the curve by greatly extending and even increasing gas production after the initial gas peak, while water production declines slowly after reaching its low plateau.

CONCLUSIONS

Three distinct unconventional gas plays are important in Kansas and the Midcontinent. The tight gas Niobrara gas play in western Kansas has been producing for several decades, but can benefit by better prediction capabilities. The coalbed methane play in eastern Kansas was initiated in the 1980s, and has moved into prominence in the past five years. The low BTU gas play in central and western Kansas can be made economical with the use of new technologies, and the resale benefits of processing noncombustible gases such as helium by separation technologies. New technologies and methodologies and prediction capabilities can allow the small independent operators in Kansas to participate in economic recovery from unconventional gas plays.

 

CONNECTIONS:

Kansas Geological Survey

Lynn Watney
Ph 785-864-2184
E-mail: lwatney@kgs.ku.edu

Alan Byrnes
Ph 785-864-2177
E-mail: abyrnes@kgs.ku.edu

David Newell
Ph 785-864-2183
E-mail: dnewell@kgs.ku.edu

Industry Speakers

Scott Sears
Inter-American Corp.
One Energy Square
4925 Greenville Ave., Ste. 717
Dallas, TX 75206
Ph: 214-696-6700
E-mail: scottsears@iacx.com

Richard Leeth
ELI Wireline Services
225 N. Market, Ste. 340
Wichita, KS 67202
Ph: 316-262-5963
E-mail: rhleeth@swbell.net

Anthony Crivello
eProduction Solutions
22001 N. Park Drive
Kingwood, TX 77339
Ph: 281-348-1008

Jim Stegeman
Colt Energy Inc.
4350 Shawnee Mission Parkway, Ste. 280
Fairway, KS 66205
Ph: 913-236-0016
E-mail: jstegeman@coltenergy.com

For information on PTTC’s North Midcontinent Region and its activities contact:

Rodney R. Reynolds, Project Manager, Kansas University Energy Research Center
1930 Constant Ave., Lawrence, KS. 66047-3726
Phone: 785-864-7398, Fax: 785-864-7399, Email: rreynolds@ku.edu

Disclaimer: No specific application of products or services is endorsed by PTTC. Reasonable steps are taken to ensure the reliability of sources for information that PTTC disseminates; individuals and institutions are solely responsible for the consequences of its use.

The not-for-profit Petroleum Technology Transfer Council is funded primarily by the US Department of Energy’s Office of Fossil Energy, with additional funding from universities, state geological surveys, several state governments, and industry donations.

Petroleum Technology Transfer Council, 16010 Barkers Point Lane, Ste 220, Houston, TX 77079
toll-free 1-888-THE-PTTC; fax 281-921-1723; Email hq@pttc.org; web www.pttc.org