OIL AND GAS FIELDS HAVE POTENTIAL IN SOUTHEASTERN NEW MEXICO

Based on a workshop cosponsored by PTTC's Southwest Region from September 15-17, 1999, in Roswell, NM.

BOTTOM LINE

Significant reserves have been located during the past 20 years in the Pennsylvanian Morrow of southeastern New Mexico and, with the aid of sound characterization schemes, more discoveries are expected.

PROBLEM ADDRESSED

The Pennsylvanian-age Morrow has been a primary exploration target in southeastern New Mexico. Characterization of older reservoirs has led to significant new reserves, as well as the discovery of reserves in shallower stratigraphic zones. Regional and field-wide stratigraphic, depositional, and tectonic characterization studies followed up with carefully designed drilling, completion and stimulation (e. g. binary foam) programs will continue to lead the way for future discoveries and field expansions.

KEY WORDS:

Morrow Formation, Atoka Formation, Permian Basin, Southeast New Mexico, Tight Gas Reservoirs

SPEAKERS

Logan Draw/ Crow Flats Morrow Gas Play
Curtis Anderson, Chi Energy, Inc.

Basement Tectonics: Insights from White City Penn Field
Robert Casavant, University of Arizona

Facies and Reservoir Characterization of Morrow Sandstones, White City Penn Gas Pool
Robert Casavant and Kenneth Mallon, University of Arizona

Tight Gas Sand Fracture Stimulation With Binary Foam
Michael Gerstner and Mark Malone, BJ Services

Petrophysics of Morrow Formation, SE New Mexico
George Hillis, Bass Enterprise Production Company

Morrow of SE New Mexico, the Big Picture
Kevin Kohles and John Roberts, Geological Data Services

Gas Reservoirs in the Shugart & North Sugart Field Areas
Ralph Worthington, TRW Exploration Inc.

TECHNOLOGY OVERVIEW

The Morrow sandstones constitute a primary exploration and development play in southeastern New Mexico. Examining several recent case studies can help operators make future discoveries and field expansions:

Logan Draw/ Crow Flats Morrow Gas Play
Morrow gas production in the Logan Draw/ Crow Flats area of Eddy County dates back to the early 1950s. Drilling accelerated through the 1960s and 1970s, and much of the information has been summarized in Roswell Geological Society Symposiums. The earlier data set the stage for more than 30 wells drilled recently by several operators. The play is based on a Morrowanage paleotopography consisting of hills and valleys. Erosion of underlying Mississippian-age rocks resulted in widespread sand deposition in the paleovalleys.

Regionally, the Morrow Clastics Interval is subdivided into upper and lower units. In the Logan Draw/ Crow Flats field area, the upper unit is locally called the “A” sand. The lower unit is subdivided into “B,” “C,” and “D” sands. Important channel sands are developed in the “B” interval, making it the primary target. Average perwell reserves of natural gas are 3.0 bcf, with maximums of 20 bcf. With relatively shallow depths, even the secondary objectives can be economic.

Characterization of the White City Penn Gas Field
The White City Penn Gas Pool is located in the northwest portion of the Delaware Basin, slightly basinward of the edge of the Permian-age Capitan Reef shelf margin. This combination structural-stratigraphic trap pool encompasses 29 sections (18,560 acres) and produces primarily from stacked deltaic and nearshore marine sandstone units of Morrowan (early Pennsylvanian) age at depths between 10,500-11,800 ft.

Gas and gas condensate are trapped within a complex northwest-oriented anticlinal structure that has been further partitioned into discrete northeast-trending structural blocks in an en echelon pattern. The blocks are bounded to the north, west, and south by strike-slip faults of minimal throw. The general architecture of the field is suggestive of a wrench-fault model. Analysis of subsurface and geomorphic features such as drainage patterns, topographic relief, and distribution of natural springs indicate that basement reactivation may influence present-day depositional and structural systems. This tectonic model may have ramifications for both the petroleum industry and nuclear waste disposal enterprises because basement faulting has played a key role in the depositional and structural history of the Morrow sands.

Detailed analysis of the lower half of the Morrow Formation revealed two coarsening-upward sandstone intervals that represented southeastward progradation of fluvial-deltaic deposits during early Pennsylvanian time. Periodic delta lobe abandonment, compaction, and syndepositional faulting led to numerous local marine incursions and shale deposition. Upper portions of many sandstone parasequences within these intervals contain reworked channel-mouth bars, and beach and barrier-bar deposits. These, in turn, are capped by transgressive marine shales and thin carbonates. Oolitic limestone is the dominant grainstone, forming on shoals developed across tops and seaward flanks of isolated paleotopographic highs on a shallow marine shelf. Carbonate wackestone and mudstone formed on lower-energy interbar and shelfward flank settings.

All Morrow sandstones have significant variations in thickness, distribution, and reservoir quality (which usually correlates to the type and quantity of clays and authigenic cements in the sandstones). Drilling issues that must be dealt with in Morrow sandstone production include: using high-pressure in the overlying Atoka, using lightweight drilling fluids to prevent formation damage, using treated drilling fluids to prevent formation damage, low water loss (< 7.5%) to prevent clay swelling, and possibly damaging the formation when Drillstem Test (DST) tools are released.

Completion issues that must be dealt with include: carefullyselecting completion fluid to minimize near-borehole and skin damage, selecting proper production rate to eliminate clay (and other) fines dislodgment and migration, and using proper treating fluids that avoid precipitation of solids which block pores.

After a 1980 reservoir characterization study by Gulf Oil Exploration and Production Company, the number of wells was increased from 23 to 44. Of this total, 38 were still producing in April 1999, when total field production was 166 bcf gas, 51,000 bbl condensate, and only 332,000 bbl water from the Morrow sandstones. The infill/ expansion program added about 30% more gas, 40% more condensate, and 38% more water to the total field production. Additional field characterizations in this region were encouraged, noting that they could be used as important guides for further exploration and field development in the Permian Basin and elsewhere.

Database for the Morrow and Atoka Formations
A subsurface database is under development by Geological Data Services (GDS) for the Morrow and Atoka formations of southeast New Mexico. The database will contain correlated stratigraphic tops and markers for over 3,000 digitized wells. The thickness for total net sand, as well as sand attributes for the productive intervals, are also included. The data will mainly be used to generate isopach, structure, and trend residual maps to view the “big picture” of Morrow deposition. It is anticipated that comparison of these maps should provide insights into the geometry of producing trends and delineate prospective areas for additional drilling.

Morrow/ Atoka Gas Reservoirs, Shugart and North Shugart Field Areas
Gas production from Pennsylvanian age Atoka and Morrow sandstones was first established in the Shugart area of northeastern Eddy County in 1958. During the “boom years” of 1977-1984, 29 completions extended the Shugart and North Shugart Morrow and Atoka production to 16 sections and over 10,000 acres. Recent drilling has proven production potential exists on the downthrown side of a regional fault that previously defined the field area several miles from the nearest well control in a geologically complex area. This fault forms a ridge that controls the production from the Siluro-Devonian and enhances production from most other reservoir zones. This structure is important for enhancing gas production from otherwise thin sands, especially at Shugart Field where the structural relief is greatest.

As a result of deep drilling for Pennsylvanian targets, additional oil discoveries have been made in the Delaware, Bone Spring, and Wolfcamp formations. In this area, there are at least 19 separate pay zones from the Yates Formation down through the Siluro-Devonian. Thus the cost of drilling 12,000 ft or deeper Morrow wells can be partly offset by the chance of additional discovery in the intermediate pay horizons. In much of the Morrow play it is important to drill into the Mississippian because of the down-cutting nature of the Lower Morrow channels. As a rule, drilling into Mississippian limestone deep enough to be able to see it on the open-hole logs will ensure a complete penetration of the Lower Morrow.

Total Atoka and Morrow production for Shugart and North Shugart pools has reached 50 bcf of natural gas and 1 million bbl of oil. The average well production in the area has averaged almost 1.7 bcf and over 30,000 bbl of oil. With additional development in known producing zones, the area will continue to be a significant oil and gas producing area.

The greatest hurdle for exploration in this area is the leasing situation, where almost all of the acreage in the township is held by production. Primary term leases that are undeveloped account for only about 2% of the acreage.

Binary Foams for Fracture Stimulation
Successful binary foam treatments in most formations in southeast New Mexico are classified as “tight gas sands.” Previous studies have outlined the benefits of fracture stimulating the Morrow and Atoka formations with binary foams, which were first introduced in 1989. During 1998, approximately 42 binary foam fracture stimulations were successfully pumped in Lea, Eddy, and Chaves counties in the Morrow, Atoka, Abo, Strawn, and Eumont (Queen, Seven Rivers, and Yates formations).

Binary foams are a combination of carbon dioxide and nitrogen dispersed in liquid and stabilized by a surfactant. The surfactants are referred to as “foamers.” The liquid phase for foamed fracturing fluids is typically gelled water. Foams are generally between 60 and 85 "quality," where quality refers to the percentage of gas (CO2 and N2) in the system. Below 60%, there is not enough gas to foam the fluid phase, above 85%, there is too much gas and not enough fluid to foam the system.

Carbon dioxide and nitrogen are mixed in foams to hasten cleanup and do it more completely than straight carbon dioxide foams. Carbon dioxide and nitrogen combined in the same system also reduces the friction pressure while pumping. These features are important in southeastern New Mexico.

Candidates for Binary Foam Stimulation
Bottom-hole pressure buildup tests are essential for screening candidate wells. Generally, wells with very low bottom hole pressure have little chance for increased production. However, “low” and “high” bottom-hole pressures are relative to the geographic area and the production zone. Additionally, wells with low bottom hole pressure can be stimulated if permeability is high. Conversely, wells with low permeabilities can be stimulated if bottom-hole pressures are high.

Along with bottom hole pressure and skin factors, P/ Z plots give an estimated volume of gas left in the reservoir. Wells with appreciable amounts of remaining gas and reasonable values for bottom-hole pressure and permeability make excellent fracture stimulation candidates. For Morrow, Strawn, and Atoka wells that produce below 150mcf/ day of primary production after break down typically show erratic results when fractures are stimulated. Computer fracture modeling is essential to model almost all fracture treatments. Conventional 3-D fracture models appear to match tagging and temperature profiles better than other models. Once the model has been set up, various job types can be run to maximize the well pay out versus job cost.

CONNECTIONS:

Robert Casavant
Department of Geosciences, University of Arizona Gould-Simpson Building,
1040 E. Fourth St.
Tuscon, AZ 85721-0077
Phone 520-621-6024 E-mail casavant@ geo.arizona.edu

Michael Gerstner, Senior Technical Rep.
BJ Services Company, USA
400 N Pennsylvania, Suite 900 D
Roswell, NM 88201
Phone 505-622-0027, Fax 505-622-7872 E-mail mgerstner@bjservices.com

Kevin Kohles
Geological Data Services
4951 Airport Pkwy. Suite 600
Addison, TX 75001
Phone 800-GDS-MAPS, Fax 214-934-1081 E-mail kevin@gdsdatamaps.com

Ralph Worthington, President
TRW Exploration Inc.
PO Box N
Roswell, NM 88202
Phone 505-623-1771, fax 505-622-1711 e-mail trwexp@dfn.com

Curtis Anderson, Exploration Manager
Chi Energy, Inc.
POBox 1799
Midland, TX 79702
Phone 915-685-5001, Fax 915-687-2662

For information on PTTC’s Southwest Region and its activities contact:
Robert Lee, Director, Petroleum Recovery Research Center,
New Mexico Tech 801 Leroy Pl., Socorro, NM 87801
Phone 505-835-5685, Fax 505-835-5210, E-mail lee@prrc.nmt.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, 2916 West T. C. Jester, Suite 103, Houston, TX 77018
Toll-free 1-888-THE-PTTC; Fax 713-688-0935; E-mail hq@pttc.org; web www.pttc.org