POSTER SESSIONS

PROMENADE AREA

Monday, March 3, 1:30-4:00

PERMIAN BASIN

Reservoir Geology of the Willard Unit in the San Andres Wasson Field, West Texas: Robert G. Loucks

The Willard unit has produced 199 MMBO out of 450 MMBO originally in place. Enhanced oil recovery methods are necessary to acquire sustainable amounts of the remaining 54%. The Willard Unit is located on the northeast limb of a broad domal paleostructure that localized the Wasson field and created arid ramp-setting conditions favorable to carbonate production. Three facies complexes are defined: (1) hypersaline peritidal/sabkha, (2) inner ramp, and (3) outer ramp. Vertical heterogeneity of facies reflects parasequences deposited in a transgressive/regressive cycle related to long-term, relative sea-level rise and fall. Lateral heterogeneity is caused by variations in water depth produced by paleotopography and by relative facies position on the ramp. The highest reservoir quality and most continuous reservoirs are in the dolomitized, inner-ramp restricted lagoon (mean porosity is 8.4%, geometric mean permeability is 1.0 md) and moderate-energy shoal (mean porosity is 8.5%, geometric mean permeability is 1.78 md) facies.

The dolostone pore network consists of vuggy, moldic, and interparticle pores reduced by several forms of anhydrite. Because of strong lateral and vertical variations in facies and diagenesis, there are significant variations in reservoir quality. Several field-scale permeability barriers are in the section. There appears to be no direct method to develop high-quality, porosity/permeability transforms because of the complex history of diagenesis, effects of anhydrite cement on measurements in small core plugs, and the probable poor cleaning of relatively low reservoir-quality rocks. This is a limiting factor in log analysis and modeling of the field for defining an enhanced recovery program.

Simulated Expert Interpretation of Data to Predict Drilling Risk on a Regional Scale, Case Study-Brushy Canyon Formation, Delaware Basin, New Mexico: R.S. Balch

Incomplete or sparse information introduce high levels of risk for oil exploration and development. To more accurately and consistently predict drilling risk, a degree of automation of data analysis is desirable. "Expert" systems developed and used in several disciplines and industries, have demonstrated beneficial results in modeling the decision making process of human experts. A state-of-the-art "expert" exploration tool using computerized multidisciplinary databases, expert developed "rules", and computer maps generated by neural network's, is being developed using fuzzy logic, a relatively new mathematical treatment of imprecise or non-explicit parameters.

The system employs a web interface for users to select prospect(s) of interest and to allow data review or addition, and includes security to maintain proprietary information. Two types of rules are applied to the data. Heuristic rules are generated directly from engineering, geophysical and geological databases. Expert rules are developed through interviews with successful prospectors. Rules are applied in four categories: Regional Indications, Trap Assessment, Formation Assessment, and Oil Price. Some users may elect to not factor in certain aspects, or to use their own values.

Each of the sub systems assigns a numerical score based on the answers to individual "expert" questions. Results are then combined to form an overall risk assessment associated with the selected prospect(s). This Expert System can help companies of all sizes, to more efficiently evaluate prospects, and to more rapidly eliminate poor prospects.

Reducing Dry Hole Risk with Artificial Intelligence: William W. Weiss

A datset set consisting of 520 Lower Brushy Canyon wells located on a 64,000 40-ac-grid map was used to generate a predicted oil rate map for the Delaware Basin. Fuzzy ranking was used to prioritize attributes generated from regional gravity, structure, aeromagnetic and thickness maps for use as inputs to a neural network that was trained to correlate the input attributes with the first years oil production. The neural network training dataset consisted of 520 wells with production varying from less than 500 bbl/mo to 6500 bbl/mo. Thus, a regional map was available to compare to local information available on a well scale.

It is difficult to estimate water saturation in the thin-bedded turbites that make up the Delaware formation. Since 1990 many operators have based their completion decisions on sidewall core porosity and oil saturation measurements. A neural network was developed to correlate open-hole logs with bulk volume oil as measured in samples from 200 ft of whole core taken from the Lower Brushy Canyon interval in a well 30-miles from NE Lea. The trained neural network was used to generate pseudo-BVO logs in the NE Lea wells.

Pseudo-BVO logs were generated for 34 wells producing from the LBC throughout the region. The statistics of the BVO logs were correlated with the respective first years oil producing rate. The correlation was used to forecast the first years oil rate from the NE Lea wells. A 65% agreement was observed between the local and regional estimates.

Interpretation of Depositional Environments of Upper Seven Rivers Formation from Core and Well Logs, Grayburg Jackson Pool, Eddy County, New Mexico: Brian S. Brister

The Seven Rivers Formation is a potential oil and gas reservoir in many fields across the northern shelf of the Delaware Basin. The largest Seven Rivers reservoir, Grayburg Jackson Pool (formerly Fren Pool), has yielded more than 5.4 mmbo and 1.6 bcf of associated gas. Grayburg Jackson and other fields that overlie the Artesia-Vacuum Abo reef trend mark the northernmost significant Seven Rivers production where porous dolomite stringers pinch out landward into bedded anhydrite. Two wells were cored and thin sectioned to study these thin (< 4 feet) dolomite reservoir beds. The cores demonstrate that the upper Seven Rivers is comprised of massive to bedded nodular anhydrite (majority); non-reservoir, algally laminated, fenestral, dolomitized boundstone/mudstone; and dolomitized grainstone/packstone reservoir rocks. Petrography reveals complete dolomitization of carbonate units, abundant anhydrite cements in the laminated facies, and excellent porosity preservation in the higher energy facies. These lithofacies represent depositional environments that range from supratidal sabkha to intertidal mud flat and tidal channel. The grainstone/packstone facies are the primary contributors to production having porosity ranging from 10 to 28.5 % and permeabilities ranging from 0.1 to 35 md. Well log-derived pore volume mapping demonstrates that the higher energy facies are related to shore-perpendicular porosity zones suggestive of tidal channels.

Petrophysical Discrimination of Seven Rivers Formation Reservoir Zones Using Natural (Spectral) Gamma Ray Logs, Grayburg Jackson Pool, Eddy County, New Mexico: Brian Brister

The shallow Seven Rivers Formation has been a volumetrically minor contributor to Permian oil and gas production from southeastern New Mexico. It tends to contain thin reservoir zones that are difficult to evaluate petrophysically. In fact, most discoveries date to the era of cable-tool drilling when subtle shows were more apparent. It is rarely evaluated today in wells drilled for deeper targets. Thus, it has the potential to be an overlooked, behind-pipe pay zone in thousands of existing wells.

At Grayburg Jackson Pool (formerly Fren Pool), the upper part of the formation consists primarily of anhydrite with thin beds (< 4 feet) of dolomitized packstone to grainstone oil reservoir, non-reservoir dolomitized algal boundstone-mudstone, and red mudstone (shale), all deposited in a sabkha environment. Porosity of the grainstone facies ranges up to 28.5% and it is uranium enriched with corresponding high gamma ray activity. Due to common drilling and logging problems in the field related to water flows and poor borehole stability, it is often difficult to successfully acquire open-hole logs. Common cased-hole gamma ray-neutron logs do not allow discrimination between the dolomite reservoir and shale, which have nearly identical log characteristics.

A core-based petrologic study of the upper Seven Rivers Formation was used to calibrate log curves in a modern open-hole log suite that included the natural (spectral) gamma ray log. Simple methods of comparing the relative concentrations of U, K, and Th from the gamma ray log, combined with a porosity log, discriminates reservoir zones. The combination is also effective in the cased-hole environment and is a low-cost tool for finding otherwise overlooked, subtle, behind-pipe pay at Grayburg Jackson, and presumably, other fields in the Seven Rivers play. Such logs should also be useful in evaluating other radioactive reservoirs zones in the region such as in the Grayburg and Yates Formations.

Preliminary Investigation of the Regional Stratigraphy of Siluro-Devonian Carbonates, Tobosa Basin, New Mexico: Destini Baldonado

Over 1,600 wells in Southeastern New Mexico were drilled into Silurian and Devonian age rocks. Known more commonly as the late Paleozoic Permian Basin, during the Siluro-Devonian this area was part of the much larger early Paleozoic Tobosa Basin. The Tobosa Basin covers all of Lea County and parts of Roosevelt, Chaves, and Eddy Counties in New Mexico and extends to the south and southeast into Texas. Within the Siluro-Devonian carbonates, most of the oil reservoirs are found to lie in rocks beneath the pre-Woodford angular unconformity of Middle Devonian age. Internal stratigraphic correlations of the Siluro-Devonian carbonates have resulted in subdivision of the section into eleven sub-units. The most productive of these units correspond with the upper Fusselman Dolomite, the lower Wristen Formation, and the middle Wristen Formation.

Data obtained from 466 wells in this area shows that the eleven units are thickest to the west of the Central Basin Platform. Beds thin to the north, northwest, and over the Central Basin Platform. Depths to the tops of the Siluro-Devonian units range from approximately 5000 feet in the north and west to over 18000 feet in the central and southern parts of the basin. These large-scale changes are structural in origin, related to the uplift of the Central Basin Platform during Late Mississippian-Early Pennsylvanian and accompanying subsidence of the Delaware Basin. Small-scale, local changes in bed thickness are the result of facies changes where small-scale pinchouts and bioherms occur. Production has a correlation between stratigraphic proximity to the pre-Woodford unconformity, lithologic unit, and bed thickness.

Tuesday, March 4, 9:00-11:30

OKLAHOMA BASINS

Structural Geometry of Thrust Faulting in the Hartshorne Area of Frontal Ouachitas, Arkoma Basin, Oklahoma: Steve Hadaway

The Ouachita Mountains and Arkoma basin are two related tectonic provinces formed during the Late Paleozoic Ouachita Orogeny. The Arkoma basin consists of gentle synclines and thrust-cored anticlines. The frontal Ouachitas are characterized by imbricate thrusts and complex fold geometries.

This study is concerned with the structural geometry of thrusting within the Hartshorne SW quadrangle in southeastern Oklahoma. The study area includes the Hartshorne gas field where gas production ranges from five bcf in 17 months (middle Atoka from Agnes #1 well) to numerous dry holes.

Five balanced structural cross-sections are being constructed to determine the geometry of the Late Paleozoic thrust system. Data from the surface geological maps by the Oklahoma Geological Survey, wire-line well logs, scout tickets, and seismic profiles, from BPAmoco and ExxonMobil Corporations are used to construct the cross-sections. Upon their completion, the cross-sections will be restored to determine the amount of shortening induced by thrusting in the area.

The Hartshorne, Red Oak, Panola, Brazil, and Spiro sandstones are identified as marker beds to construct the cross-sections. We considered the Spiro to include the Wapanucka and Cromwell formations. Our preliminary interpretation of the available data suggest that a triangle zone exists between the Carbon Fault to the northwest and the Choctaw Fault to the southeast. A duplex structure and associated horses appear to exist above the Woodford and Springer detachments with the Lower Atokan Detachment as the roof thrust.

Structural Geometry and Evaluation of Thrust Faulting in the Damon and Wilburton Quadrangles in Latimer County, Southeastern Oklahoma: Marline Collins

The Arkoma Basin and the Ouachita Mountains of southeastern Oklahoma and western Arkansas were formed during the late Paleozoic Ouachita orogeny. In Oklahoma, the Choctaw fault forms the structural boundary between the frontal Ouachitas and the Arkoma Basin.

This study is aimed at determining the structural geometry of the Late Paleozoic thrust faults in the Damon and Wilburton Quadrangles in Latimer County, in Southeastern Oklahoma. Six balanced structural cross-sections are under construction to delineate the structural geometry in the study area. Data from the surface geological maps by the Oklahoma Geological Survey, wire-line well logs, scout tickets, and seismic profiles, donated by Exxon and Amoco corporations, were used to construct the cross-sections.

The two main structural features of the study area are the south dipping Choctaw and the north dipping Carbon faults. Our preliminary interpretations of the available data suggest that the two faults form a triangle zone and a duplex structure present in the footwall of the Choctaw fault. The Springer detachment is the floor thrust and the Lower Atokan Detachment is the roof thrust of the duplex. The Carbon fault loses its surface trace north of the Wilburton gas field. Seismic data indicate that the Carbon fault becomes a blind thrust as it continues to define the northern flank of the triangle zone within the eastern part of the study area, probably through a lateral ramp along its fault surface. Our cross-sections should provide a better understanding of subsurface geometry of this lateral ramp along the Carbon fault.

Subsurface Structural Geology of the Potato Hills area of the Ouachita Mountains, Southeastern Oklahoma: Gultekin Kaya

The Late Paleozoic Ouachita Orogeny formed the Ouachita Mountains of southeastern Oklahoma and western Arkansas. The Potato Hills area is located to the south of the Frontal Ouachitas and contains lower and middle Paleozoic strata. The exposed rock units range from Middle Ordovician Womble Shale to the Mississippian Stanley Group. Recently, gas production from Jackfork and Stanley group has been very important in the area.

This study is an attempt to reconcile the structural geometry of Late Paleozoic thrusting in the Potato Hills area with the Frontal Ouachitas. In the Potato Hills area, there are three major thrust faults exposed on the surface and there are several blind thrusts in the subsurface. Five balanced structural cross sections are being constructed to better understand the subsurface geometry of thrusting in the Potato Hills area. At least, two of these cross-sections will be extended northward to the Wilburton gas field area where previous workers have already established the structural geometry.

Well logs, seismic data, topographic maps, geologic maps and several computer programs are being used to construct the cross sections. Our preliminary interpretation suggests that the Windingstair fault is a major discontinuity within the Ouachita Mountains. It separates a zone of imbricate reverse faults to the north (frontal Ouachitas) from a zone of broad syncline structures separated by sharp anticlines or high angle faults (central Ouachitas). Windingstair fault is a high angle fault at the surface. However, it gets almost horizontal at depth. We intend to delineate its structural relationship with the Woodford and Choctaw Detachment surfaces.

Naturally Underpressured Reservoirs: Applying the Compartment Concept to the Safe Disposal of Liquid Waste: Jim Puckette

The Oklahoma Panhandle region contains abnormally low-pressure reservoirs that are isolated from the shallow hydrostatic domain and overpressured reservoirs in the deep Anadarko basin. These underpressured reservoirs, which can be identified and mapped using available petroleum industry data, are potential repositories for liquid waste. They contain naturally low pore-fluid pressures and are completely sealed by thick confining units. Many of these compartments contain oil and gas. Fluid withdrawal during production has further reduced reservoir pressures, facilitating disposal by lowering injection and displacement pressures.

Types and sizes of compartments were strongly influenced by depositional environment. Individual channel-filling sandstones within valley-fill sequences form small-compartments, whereas sandstone reservoirs formed from sediments reworked during marine transgressions became large ones. Within the carbonate domain, thick accumulations of grain-rich sediment, subsequently altered by dissolution and/or dolomitization, form large- to regional-sized compartments. Selected sandstone and carbonate reservoirs have calculated disposal volumes ranging from approximately 0.5 million barrels to 21 million barrels per well.

Compartmentalized reservoirs with abnormally low fluid pressures offer an intriguing alternative for liquid waste disposal. They exist as self-contained vessels whose seals have confined pore-fluid pressures for durations of geologic time. Seal longevity and integrity are evidenced by the very existence of naturally occurring subnormal pressures that did not equalize with the normally pressured hydrostatic environment. These reservoirs, by virtue of their compartmentalized nature, fulfill two critical criteria for safe liquid waste disposal, (1) non-migration and (2) total isolation from the sphere of human activities.

Thermal Regime of the Mid-Continent El Dorado Oil Field (Kansas) Interpreted from High-Resolution Temperature Logs: Jason R. McKenna

The giant, multizone-producing El Dorado oil field (Butler County in south central Kansas) was discovered on the Nemaha Anticline in 1915. Early indications from bottomhole (BHTs) and drillstem (DSTs) temperature measurements indicated a close relationship between the anticlinal structure and higher subsurface temperatures. Recently, a suite of high resolution temperature logs was made from shut-in wells on the East and West Shumway domes in the field to confirm the three dimensional thermal modeling. The temperature logs generally are conductive, equilibrium profiles demonstrating that these types of logs can provide reliable, equilibrium temperature measurements in an active petroleum setting. Lower temperatures measured in several of the wells on the East Shumway Dome seem to be the result of a significant change in thermal gradient from mass transport of hydrocarbons and in situ thermal conductivity changes related to the presence of hydrocarbons and not to interwell lithologic variability. An analysis of the high resolution temperature logs and log header BHTs taken near the top of the Kansas City Group (Upper Pennsylvanian) and Arbuckle Group (Lower Ordovician) productive zones on the West Shumway Dome indicate that the anomalously high BHT data are close to the actual formation temperature substantiating that the higher temperatures encompass a broader region on the dome than previously assumed.

Tuesday, March 4, 1:30-3:45

BARNETT SHALE AND GENERAL

Project STARR-State of Texas Advanced Oil and Gas Resource Recovery Program: Ramón Treviño

Project STARR at the Bureau of Economic Geology has one major goal-increased royalty income to the Permanent School Fund of Texas from State Lands leases. This goal is accomplished by conducting integrated studies, which encourage new wells, recompletions, secondary or tertiary recovery projects, or other economically justified techniques for increasing production. State Lands fields now contain more oil and gas than has been recovered over their production history. This remaining oil and gas is recoverable through the targeted deployment of advanced recovery technologies. Sixteen operators have been, or are, involved in Project STARR. During its 7-year history, Project STARR analyses have been used to recommend 69 infill wells, 56 recompletions, and 4 step-out wells. Of the targeted opportunities, at least 45 infill wells and 32 recompletions have been drilled on State Lands and in State waters.

All operators of State Lands leases are eligible to apply to STARR for assistance. Selection of projects is based on potential economic value of the project to the State and on the operator's commitment to implementing economic opportunities. Operators are required to share data, requested to participate in the study, and invited to report results of implemented recommendations.

STARR has completed more than 10 major studies since its inception. The most recent West Texas study involved Ozona field in Crockett County. More recently STARR studied several fields located in State waters. Among these is a study, in conjunction with IBC Petroleum, of Red Fish Bay field in "middle" Frio reservoirs.

Possible New Petroleum Well-logging Tool Using Positron Doppler Broadening to Detect Total Organic Carbon in Hydrocarbon Source Rocks: Casey Patterson

One of the few remaining geochemical properties yet to be accurately characterized by conventional wireline logging tools is the total organic carbon (TOC) content of hydrocarbon source rocks. The amount of organic carbon in a source rock is important in that it determines the productivity and economic viability of a potential formation. Currently, the most accurate methods for determining TOC involve the manipulation of formation resistivity and formation density logs. However, these methods often produce poor results because of the number of assumptions inherent in the analysis.

Using a Ge-68 source, Ortec Ge-crystal detector, and Triumph Maestro® software, we analyze Doppler broadening spectrum along the length of a recovered source rock in the laboratory. Using a piece of annealed NiCu plate to restrict the location of annihilations to either the core or the plate, we cover the source and place it in the center of a four-inch wide slab of source rock. Located in between the edges of the core, we conduct runs at pre-determined optimum intervals. Distance between the source and detector stays fixed at 6.75" to achieve a satisfactory counting rate. The core under study belongs to Mitchell Energy, from well T.P. Simms #2 and is from the Barnett Shale Formation under Wise County, Texas. We measured twelve feet of the core at 2" increments based on core recoverability, variance in TOC, and the presence of a drastic change in lithology in the form of a turbidity current.

Analysis of the results shows a remarkable correlation between S-parameter calculations and geochemically measured TOC values. Future studies involve an expansion of the project into different core of varying geologic locations, periods and conditions.

Landslides Above the Walnut and Paluxy Formation's Contact: Mahipal Jadeja

Recent landsliding occurs in Lower Cretaceous sedimentary rocks in north Texas. The failure plane lies near the contact between the overlying Walnut Formation of the Lower Fredricksburg Group and the underlying Paluxy Formation of the Trinity Group within the Comanchean Series. The Walnut is predominantly an indurated fossiliferous (oyster rich) limestone with interbedded clay seams, and is an aquitard. The lower 5-6 feet of the Walnut consists of less indurated expansive clay seams. The Paluxy consists of silty and clayey sands and sandstone. The Paluxy has higher permeability, and is an economic aquifer in north Texas. The less indurated expansive clay seams at the base of the Walnut clay could behave like cohesive soils. With a high Plasticity Index, those layers would loose significant strength if the water table in the underlying Paluxy sand rises and saturates them. Another possible failure mechanism is a pore pressure increase in the Paluxy reducing effective stress.

Laboratory investigations to determine the mechanism(s) that induce the landsliding include Direct Shear and Plasticity tests on undisturbed samples from the slide zones. Grain size distribution was determined by sieve analysis, and X-ray diffraction was used to confirm the presence of expansive clays. Data from various lab tests were used to generate computer models of possible natural conditions during the sliding to test the various failure mechanisms.

Avulsion of Terminal Distributary Channels in Modern and Ancient Delta Deposits: Cornel Olariu

Terminal distributary channels are relatively small features within delta front deposits, formed by multiple bifurcation of a trunk channel. In modern deltas (Atchafalaya, Lena, Volga) numerous coeval terminal distributary channels are formed. Two main phases can be distinguished in evolution of terminal distributary channels:
1 initial distributary channel forms a mouth bar;
2 mouth bar growth causes the channel to split and may initiate an avulsion.
Usually high occurrence of avulsion results from the high sedimentation rates in front of the distributaries. Mouth bar growth in front of distributary change the channel hydraulic geometry by extension of terminal distributary channel and by increase of friction. Alternation of mouth bar growth/ avulsion phases occur in a quasi-cyclic manner, resulting in an increase in the number of terminal distributary channels. Such an evolution has been described in the growth of the Atchafalaya delta.

In ancient delta front deposits we propose the name "terminal distributary channels", to describe high-order channels contained within delta front deposits and presumed to be at the terminus of the delta system. A strike cliff face exposes terminal distributary channels of the Cretaceous Panther Tongue delta front deposits in north-central Utah. Terminal distributary channels appear as shallow and narrow channels filled with structureless or trough-cross stratified fine sandstone. A distinguishing characteristic is intimate alternation of terminal distributary channels with mouth bar deposits. Panther Tongue terminal distributary channels die out over a distance of a few hundred meters, on the opposite cliff faces and pass into distal bar deposits.

Oil Geochemistry in the Fort Worth Basin: Dan Jarvie

Ichnology and Sedimentology of Two Reservoir Sands: A Shelf-edge Delta and an Incised Valley Fill Within the Frio Formation, West Mustang Island 470-ARCO 45-47 #4 Well, Corpus Christi Bay, Nueces County, Texas: Bo Henk

Integrating ichnology (biogenically derived structures) and sedimentology (physical sedimentary structures) in a core description of bioturbated shallow-marine sandstones greatly facilitated interpreting the depositional environment of Oligocene age, Frio Formation reservoir sandstones. Within a 1200-foot continuous cored interval, in the West Mustang Island 470 ARCO 45-47 #4 well, two separate fine- to medium-grained, quartz-rich subarkosic, sandstone reservoirs were described in detail for their physical and biogenic structures.

The N30 sandstone is interpreted as an incised valley fill consisting of brackish water deposits of subtidal mixed sand and mud flats with flaser bedding and a low-diversity suite of diminutive Planolites and Arenicolites, overlain by a fully-marine subtidal sand body with a robust ichnoassemblage of Ophiomorpha, Asterosoma, Conichnus, Cylindrichnus, and Palaeophycus. The isopach of this fully marine sand body has a shoreline perpendicular trend and is interpreted as part of an incised valley fill system. The N40 sandstone, characterized by an almost total absence of marine ichnogenera, has an abundance of primary sedimentary structures including planar cross stratification, and low-angle cross bedding and lies directly above a fully marine silty shale section. It is interpreted as a shelf-edge delta-front sand body. The ichnogenera within the shelf sediments include distal suites of Anconichnus, Helminthopsis, Palaeophycus heberti, Zoophycos and Terebellina. Soft-sediment deformation structures are present at the base of the sandstone suggesting rapid loading onto middle to outer shelf deposits as the delta front sand body advanced seaward.