Granite Wash Research Articles

Seismic Exploration in the Dalhart Basin, Western Texas Panhandle

The Dalhart basin, the Texas panhandle's [open quotes]other[close quotes] basin, is accountable for over 17 million bbl of oil production since the 1954 discovery of Rehm field by Standard Oil of Texas in Hartley County, Texas. The primary objective in most of the seismic exploration has been the Pennsylvanian/Missourian granite washes, one of several sequences of wash deposition that occurred in the basin. These granite washes, sourced from the Bravo dome of the extreme western Texas panhandle and eastern New Mexico, have been distributed into the Dalhart basin in both deltaic and long-shore patterns across and along carbonate shelf margins of Pennsylvania Missourian-Virgilian age. In same cases, this carbonate [open quotes]bank[close quotes] has been productive and should be considered prospective in any exploration program. More recently, production from Permian Wolfcampian granite wash has been found to exist in the form of a stratigraphic trap adjacent to the Bravo Dome. Development continues in this encouraging play. In most cases, the application of seismic in the Dalhart basin appears to reflect the concrete data of subsurface geology. Primarily, the use of seismic to delineate structure has prompted the majority of penetrations throughout the basin and has resulted in the acquisition of anmore » estimated 6000+ mi of two-dimensional seismic data to date. Whereas anomalies of same type may be uncovered in most seismic surveys, coupling of subsurface stratigraphic information to determine fairways of clean granite washes combined with detailed, high-quality seismic data is a necessity. With the increasing prominence of three-dimensional seismic data, these goals by be achieved both in terms of cost effectiveness and technical superiority. The density of three-dimensional data collection satisfies nearly all criteria to minimize error in mapping these subtle, critical structural and stratigraphic closures.« less

Thermal Conditions in the Anadarko Basin, Oklahoma

Heat flow, bottom-hole temperature (BHT), and thermal conductivity data are used to evaluate the present thermal conditions in the Anadarko basin. Heat flow values decrease from 54-62 mWm{sup {minus}2} in the northern part of the basin to 39-53 mWm{sup {minus}2} in the southern portion of the basin. The variation in the regional conductive heat flow is controlled by basin geometry and by the distribution of radiogenic elements in the basement. The heat flow, thermal conductivity, and lithologic information were combined to construct a 3-D model of the temperature structure of the Anadarko basin. The highest temperatures sedimentary rocks older than Pennsylvanian are offset 35 km north-northwest of the deepest part of the basin. This offset is related to the regional increase in heat flow to the north and to the presence of high thermal conductivity granite wash adjacent to the Wichita Mountains. A plot of the temperature difference between the equilibrium temperatures estimated from the model and the measured BHTs as a function of depth is remarkably similar to the published correction curve for BHTs for wells in Oklahoma. Vitrinite reflectance and apatite fission-track (FT) data are used to estimate the paleogeothermal conditions in the basin. Published vitrinite reflectance valuesmore » are consistent with a past geographic temperature distribution comparable to the observed distribution with the maximum values offset from the basin axis. FT analysis of sandstones from wells in the southeastern portion of the basin indicates that subsurface temperatures were at least 30C higher than at present, suggest the possibility of substantial erosion in this area.« less

Thermal history of crystalline nappes of the Maria Fold and Thrust Belt, west central Arizona

The thermal history of the crust in west central Arizona, as documented by 40Ar/39Ar step‐heating analysis of mineral suites from crystalline nappes of the Maria fold and thrust belt, is characterized by three distinct stages for Late Cretaceous and Tertiary time. Regional heating of the crust occurred during basement‐involved folding and thrust faulting in middle Late Cretaceous time (∼80–90 Ma) and represents the earliest phase recorded by the 40Ar/39Ar data. The second stage was dominated by uplift and slow cooling (5–10°C/m.y.) of the crust throughout latest Cretaceous and early Tertiary lime. Tectonic denudation in late Oligocene to early Miocene time resulted in rapid uplift and cooling of midcrastal rocks in the footwall of the Whipple‐Buckskin‐Rawhide detachment system, marking the final thermal signature in the region. Evidence for variable argon loss in the hornblende spectra implies exposure of differing structural levels within the thrust belt and/or significant thermal heterogeneity in the crust during Late Cretaceous orogenesis. Partially outgassed hornblende in the northern Granite Wash Mountains reflects temperatures of ∼450°C, whereas complete resetting of hornblende at Mesquite Mountain suggests that this area attained temperatures in excess of 500°C. In contrast, data from the northern Plomosa Mountains indicate that this area did not attain temperatures sufficient to completely degas biotite or K‐feldspar (>350°C) during Late Cretaceous time. The range of early Tertiary muscovite and biotite ages in the region reflects slow cooling, presumably associated with uplift and erosion following crustal thickening. K‐feldspars yield saddle‐shaped age spectra with minimum apparent ages ranging from 22–28 Ma, and reflect quenching due to rapid exhumation of midcruslal to upper crustal rocks in the detachment terrain. Collectively, the data are consistent with either of two models for the thermal evolution of the crust in middle to late Tertiary time. Either (1) lower plate rocks were still sufficiently hot following Late Cretaceous heating that argon clocks were set simply due to rapid cooling or (2) the area experienced a renewed thermal input associated with extension, causing argon loss from previously cool rocks. Based on consideration of diffusion domain behavior in K‐feldspars, we infer that a renewed thermal pulse was associated with the early stages of extension and was related to the cause for crustal weakening.

Fan-Delta and Interdeltaic Shoreline Sediments of Middle Devonian Granite Wash and Keg River Clastics, Red Earth Field, North Alberta Basin, Canada: ABSTRACT

A detailed sedimentological investigation of over 4000 ft of core and 500 well logs of the Middle Devonian granite wash and Keg River clastics in the Red Earth field, North Alberta basin, Canada, has led to the recognition of a granite wash subaerial fan-delta system that is laterally continuous with a Keg River subaqueous delta component along an eastern shoreline of the ancestral Peace River arch. The subaerial fan delta includes alluvial fan facies, sheet wash and mud flows, and playa lakes. The subaqueous delta component includes lower shoreface, upper shoreface, beach-foreshore, eolian sand dunes, lagoon, washover sands, tidal channels and flats, and supratidal carbonates and anhydrites. Within this system, six mappable units are defined. A conceptual depositional model for the sequence depicts four main events. (1) Erosion of Peach River arch uplifted fault blocks, which produced coarse-grained fan-delta sediments in an adjacent fault-bounded margin. Subsequent fluvial reworking resulted in the deposition of thick, lenticular, wedge-shaped alluvial fans of granite wash. (2) Progradation of alluvial fans seaward into the Keg River Sea. (3) Transgression by Middle Devonian seas from the east, which reworked alluvial fans and led to deposition of discontinuous linear sand bodies represented by the Keg River regressivemore » shoreline sediments. (4) Restriction of the sea by the Presqu'ile barrier reef to the north, which deposited evaporites of the Muskeg Formation over the whole sequence. Modern analog to this fan-delta system is the coastal fans of the Gulf of Aqaba, Red Sea. Red Earth field contains over 27 million bbl of recoverable oil, related to a combination structural-stratigraphic trap.« less

Progressive deformation and superposed fabrics related to Cretaceous crustal underthrusting in western Arizona, U.S.A.

In the Maria fold and thrust belt, a newly recognized E-trending Cretaceous orogenic belt in the southwestern United States, ductile thrusts, large folds and superposed cleavages record discordant emplacement of crystalline thrust sheets across previously tilted sections of crust. Style of deformation and direction of thrusting are in sharp contrast to those of the foreland fold-thrust belt in adjacent segments of the Cordillera. The net effect of polyphase deformation in the Maria belt was underthrusting of Paleozoic and Mesozoic metasedimentary rocks under the Proterozoic crystalline basement of North America. The structure of the Maria belt is illustrated by the Granite Wash Mountains in west-central Arizona, where at least four non-coaxial deformation events ( D 1– D 4) occurred during the Cretaceous. SSE-facing D 1 folds are associated with S-directed thrusts and a low-grade slaty cleavage. D 1 structures are truncated by the gently-dipping Hercules thrust zone ( D 2), a regional SW-vergent shear zone that placed Proterozoic and Jurassic crystalline rocks over upturned Paleozoic and Mesozoic supracrustal rocks. Exposures across the footwall margin of the Hercules thrust zone show the progressive development of folds, cleavage and metamorphism related to thrusting. D 3 and D 4 structures include open folds and spaced cleavages that refold or transect D 1 and D 2 folds. The D 2 Hercules thrust zone and a D 3 shear zone are discordantly crosscut by late Cretaceous plutons.

Regional underpressuring in Deep Brine Aquifers, Palo Duro Basin, Texas: 1. Effects of hydrostratigraphy and topography

Deep brine aquifers of the Palo Duro Basin, Texas Panhandle, ranging in depth from about 1000 to 3000 m below land surface, are underpressured compared with the shallow Ogallala aquifer. Two‐dimensional simulations of flow in an east‐west regional cross‐sectional model through the basin reveal the causes of underpressuring as well as mechanisms of groundwater circulation in the basin. The regional groundwater flow regime consists of a shallow flow system governed primarily by topography and a deeper flow system recharging in the New Mexico area and passing deep beneath the Pecos River into the deep brine aquifers of the Palo Duro Basin. The low‐permeability Evaporite aquitard limits flow between the shallow and deep systems, although leakage through the aquitard is important on a regional scale and could contribute a significant portion of water to the deep aquifers: Repeated simulations with the model demonstrate that chief causes of underpressuring are regional topography and geology. The elevated position of the Ogallala aquifer on the High Plains together with its segregation from the deep brine aquifers by the low‐permeability Evaporite aquitard creates an apparent underpressuring that is further accentuated by efficient drainage through the permeable granite wash deposits in the Deep‐Basin Brine aquifer. The Pecos River serves as a discharge area of some of the ground water from the west that would otherwise move downdip into the deep aquifers; thus capture of recharge water enhances underpressuring in the deep section beneath the western half of the High Plains.

Depositional Environment and Reservoir Characteristics of Middle Pennsylvanian Granite Wash, Northern Palo Duro Basin, Oldham County, Texas: ABSTRACT

The Lambert 1, Hryhor, and Sundance fields in Oldham County, Texas, produce oil from the Middle Pennsylvanian Canyon granite wash. Canyon granite wash conglomerates and sandstones have a maximum thickness of approximately 450 ft (140 m) and were derived from granitic rocks of the Bravo dome. The sediment was transported across carbonate platforms by streams and deposited into the Oldham trough as fan deltas. The granite wash deposits consist primarily of imbricated gravels and cross-stratified sands. Debris-flow deposits are also present. The sediment is dominantly feldspar, granitic rock fragments, and quartz. Carbonate cement averages 5% of the bulk composition. The overall geometry of the granite wash deposits is lobate. Parts of the reservoir show high lateral variability with no continuity between wells on 40-ac spacing. These reservoir facies are thus limited in areal extent and drainage area. However, some intervals can be correlated between wells, which suggests that part of the reservoir may be simulated as layered with no crossflow. The reservoir conglomerates and sandstones have an average porosity of 18% and an average permeability of 75 md/ft. Reasonable net-pay cutoff values in these granite wash reservoirs are 9.5% for porosity and 1.5 md for permeability, and were established bymore » crossplots and cumulative volume capacity.« less

Oil and Gas Developments in Oklahoma and Panhandle of Texas in 1986

In 1986, a 46% drop in the price of oil and a 10% drop in the price of gas, coupled with a decrease in demand, forced a 40.4% decrease in drilling, a 67% drop in gas production, and an 11% drop in oil production in Oklahoma and the Panhandle of Texas (Texas Railroad Commission District 10). Exploration focused on development and extension of existing fields, with development wells outnumbering exploratory wells 18 to 1. Operators completed 58.6% fewer exploratory wells and 59.2% fewer development wells in 1986 than in 1985. The 1986 success rate for exploratory wells dropped 0.8%, and the success rate for development wells increased 0.9%. The Cherokee shelf was the most active trend, with 53 exploratory wells completed in 1986. The dominant plays were the Morrow-Springer and granite wash in the Anadarko basin, Misener on the Sedgwick shelf, Viola and Hunton in the Golden Trend along the Pauls Valley uplift, and Wapanucka, Cromwell, and Atoka in the Arkoma basin.

Sand Fracturing The Slave Point Carbonate

Abstract The Slave Point carbonate in the Red Earth – Loon Lake area of Alberta is generally regarded as a secondary prospect to the area's prolific Granite Wash zone. Since late 1980, large sand fracture treatments have been used to stimulate newly completed and producing Slave Point zones with some impressive production results. Post frac analysis of these wells with the use of a hydraulic fracture simulator has confirmed the effectiveness of the sand fracturing techniques, as well as the need to integrate geologic factors, reservoir characteristics and economic payout with fracture treatment design. This paper will discuss reservoir parameters, fracture geometry, economics of the treatments and the evolution to the present choice of fluids, rates and sand concentrations of the hydraulic fracture treatments. Introduction The Slave Point carbonate possesses a complex lithology, with "reer "or "platform " oil production potential: This limestone zone has in-situ permeability and porosity that seldom exceeds 5 md and 10%, respectively. Because the Slave Point is historically the second zone considered during the initial drilling of Red Earth, DST and core data is not available. In addition, well tests are difficult to execute on these law permeability, pumping oil wells to gain further reservoir data. Computer simulation offers a new opportunity to evaluate the Slave Point. Well production histories can be matched by a hydraulic fracture simulator to evaluate the reservoir's range of parameters in the absence of other well information. The hydraulic fracture simulator is a numerical model that combines a reservoir simulator with crack generation, proppant transport and fluid rheology models(1,2). It has the capability of simulating three-dimensional, two-phase flow in the reservoir simultaneously with the propagation of a two-wing vertical hydraulic fracture. Proppant transport and settlement, as well as fluid leak-off from the fracture to the reservoir, are calculated during the pumping and closure sequences of the treatment. Stress in the reservoir and on the fracture proppant is calculated throughout the simulation, enabling the transmissibilities to vary continuously as pressures in the reservoir change during production. With this tool, and the application of the history match technique, it is possible to evaluate the reservoir and any subsequent stimulation treatments. Adjustment to reservoir parameters (within the limits of available data) is made until the simulator calculated production matches the actual production decline. With a history match, the reservoir and fracture are verified as accurate. This reservoir model can then be used to evaluate stimulation treatments. Slave Point sand fracs have evolved from a field trial to a computer-assisted design procedure. The most important considerations of present carbonate sand fracturing techniques will be discussed. Geology The Slave Point Formation is a carbonate zone found in the north-central and northwest area of Alberta. The Slave Point is thickest in northern Alberta and it thins progressively southward to Red Earth. The Peace River arch marks the western extent of the Slave Point(3), shown in Figure 1. The Slave Point is primarily limestone, only slightly dolomitic. Its complexity has been described in the Lubicon area, where four facies developments fringe a granite basement high(4).

Pennsylvanian Fan-Delta Deposition Resulting from Tectonic Uplift Along Southwestern Margin of Anadarko Basin: ABSTRACT

Pennsylvanian sedimentation on the southwestern margin of the Anadarko basin was dominated by a clastic wedge of conglomeratic alluvial fan-delta deposits, referred to locally as washes. Chert, carbonate, and granite (arkosic) washes were shed basinward in response to thrusting and uplift of the Ancestral Wichita Mountains. Chert and carbonate washes were deposited in the Early Pennsylvanian, as lower Paleozoic limestones and dolomites eroded from the Wichitas. Arkosic washes predominated during the Middle and Late Pennsylvanian, as drainage basins composed primarily of Precambrian-Cambrian crystalline rocks eroded. The detailed stratigraphy available from well control in the Anadarko basin permits relatively precise timing of orogenic events along the Ancestral Wichitas. Wash deposition in the basin began in the Morrowan and continued episodically in seven major pulses through the Missourian. These wash sequences range from 200 to 1500 ft thick; each terminates with an unconformity. Wash sequences are further subdivided into as many as nine conformable subsequences, 100-400 ft thick and correlative for 10-20 mi, which appear to record individual drainage-basin erosional cycles. Subsequences generally coarsen upward abruptly, then gradually fine upward to the next subsequence. Basinal marine shales interfinger with the wash sequences and are a possible source of structurally and stratigraphically entrappedmore » gas and condensate. Optimal reservoir quality occurs in braided channels and fan-delta fronts. Reserves average 2-5 bcf and 50,000-200,000 bbl/well, making granite wash an economically attractive target at present Anadarko drilling costs.« less

The geochemistry of Ca, Sr, Ba and Ra sulfates in some deep brines from the Palo Duro Basin, Texas

The geochemistry of Ca, Sr, Ba and Ra sulfates in some deep brines from the Palo Duro Basin of north Texas, was studied to define geochemical controls on radionuclides such as 90Sr and 226Ra. Published solubility data for gypsum, anhydrite, celestite, barite and RaSO 4 were first reevaluated, in most cases using the ion interaction approach of Pitzer, to determine solubility products of the sulfates as a function of temperature and pressure. Ionic strengths of the brines were from 2.9 to 4.8 m, their temperatures and pressures up to 40°C and 130 bars. Saturation indices of the sulfates were computed with the ion-interaction approach in one brine from the arkosic granite wash fades and four from the carbonate Wolfcamp Formation. All five brines are saturated with respect to gypsum, anhydrite and celestite, and three of the five with respect to barite. All are undersaturated by from 5 to 6 orders of magnitude with respect to pure RaSO 4. 226Ra concentrations in the brines, which ranged from 10 −11.3 to 10 −12.7 m, are not controlled by RaSO 4 solubility or adsorption, but possibly by the solubility of trace Ra solid solutions in sulfates including celestite and barite.

Geology of McMordie and Hale Ranch Fields, Roberts County, Texas: ABSTRACT

The McMordie Ranch and Hale Ranch fields produce from multiple stratigraphic traps representing several depositional environments. The fields, located in the southwestern Anadarko basin northeast of the Amarillo uplift, are traversed by the prominent northwest-southeast-trending Lips fault. Major down-to-the-northeast displacement along this fault during the Early Pennsylvanian affected deposition of the lower and middle Morrow. The McMordie Ranch field produces from multiple stratigraphic traps in the lower and upper Morrow, Cherokee granite wash, and Douglas sandstones on the downthrown side of the Lips fault. The producing lower Morrow sandstone, which occurs only on the downthrown side, reaches a maximum net-pay thickness of 34 ft (10.4 m). This sand facies appears to be a beach or offshore bar, 1 mi (1.6 km) wide and 2 mi (3.2 km) long, deposited parallel to a shoreline controlled by the Lips fault. In the upper Morrow, two distinct reservoir facies are recognized--point bars and stream mouth bars, which were deposited on a southeast-sloping delta plain. The lower Cherokee Group contains two productive granite wash sandstones, which were deposited near the distal north edge of a fan-delta complex sourced from the Amarillo Mountain uplift. The productive sections are each 8-14 ft (2.4-4.3 m) thick with variable porosity development. The shallowest reservoir in the field is the lower Douglas sandstone, an east-west-trending channel sandstone, 10-15 ft (3-4.5 m) thick and approximately 0.5 mi (0.8 km) wide. The one-well Hale Ranch field produces from the Lower Mississippian Kinderhook sandstone in a fault block on the upthrown side of the Lips fault. This 16-ft (5-m) thick sandstone averaging 10% porosity is interpreted as a northwest-southeast-trending barrier bar encased in shale. Characteristically, this sand shows an excellent SP deflection, despite a high gamma-ray reading due to the thorium content in the sand. End_of_Article - Last_Page 1316------------

Seismic Exploration for Pennsylvanian Granite Wash Reservoirs, Palo Duro Basin: ABSTRACT

A seismic reflection common-depth-point technique was designed specifically for the Palo Duro basin. The goal was to locate hydrocarbon traps in the Pennsylvanian granite wash. Success ratios using the designed techniques were approximately as follows: (1) to locate hydrocarbon-bearing features, approximately 25%; (2) to locate structures, approximately 50%; (3) to pinpoint development locations, approximately 75%. The specific technique design is presented as it relates to: (a) density and layout of seismic lines; (b) spread lengths and configuration; (c) field parameters, e.g., geophone array and shot-hole depths; (d) data correction techniques, including weathering correction, choice of datum plane, and choice of datum velocity; (e) data processing requirements and quality control; and (f) interpretation of data, including depth conversion and well ties. This paper covers the aforementioned topics with a minimum of advanced mathematics, and it poses questions for the advanced mathematician. End_of_Article - Last_Page 1318------------

The Thermodynamics and Geochemistry of Ca, Sr, Ba, and Ra Sulfates in Some Deep Brines From the Palo Duro Basin, Texas

AbstractThe work reported here involved application of the ion-interaction approach of Pitzer [1] [2] to model the activities of some major and minor cations and major anions in deep brine systems at elevated temperatures and pressures.The solubilities of anhydrite (CaS04), gypsum (CaSO4·2H2O), celestite (SrS04), barite (BaS04), and radium sulfate (RaSO4) in brines from the Wolfcamp Formation and granite wash facies, Palo Duro Basin, Texas, were modeled using ion-interaction equations. Waters with ionic strengths ranging from 2.89 to 4.76 m, and temperatures and pressures up to 40°C and 130 bars were sampled from five horizons in three wells, at depths between 970 and 1,670 meters. Theoretical solubility products as a function of temperature and pressure were obtained for comparison with ion activity products computed using ion-interaction theory. The effect of temperature on model calculations was found to reside almost entirely in the Debye-Hückel AΦ parameter, which accordingly was corrected for brine temperatures [3].Modeling results indicated that all five brines are saturated with respect to anhydrite and celestite, and three of the five with respect to barite. Saturation may result from hydrologic connection with adjacent overlying evaporite units, or increased Ca, Sr and Ba concentrations caused by their desorption from clays. Radium concentrations, which range from 10-11.3 to 10-12.7 m, are not controlled by RaSO4 solubility or adsorption, but probably by solid solution in other sulfate minerals in these low pH (4.4 – 6.3) high calcium (0.18 – 0.52 m) brines [4] [5].

Tectonic History and Influence on Sedimentation of Rhomb Horsts and Grabens Associated with Amarillo Uplift, Texas Panhandle: ABSTRACT

The Amarillo uplift consists of an en echelon series of fault blocks separating the Anadarko basin from the Palo Duro basin. The uplift is part of a northwest-southeast zone of basement weakness that extends from the Wichita Mountains in Oklahoma to southeastern Colorado. Initial faulting, related to the opening of the southern Oklahoma aulacogen, took place from late Precambrian through Middle Cambrian time. Renewed movement in the Late Mississippian or Early Pennsylvanian, probably of a left-lateral transcurrent nature, broke the Amarillo uplift into a series of rhomb grabens and rhomb horsts. The Lefors basin, for example, in Gray County is a small rhomb graben 4 mi (6.4 km) by 8 mi (12.8 km) that contains in excess of 4,000 ft (1,200 m) of Pennsylvanian and Wolfcampian arkose (granite wash). The Amarillo uplift continued to subtly affect depositional patterns following its burial in Wolfcampian time. Salt beds in the Clear Fork Formation (Leonardian) are purer and thicker in grabens where salt deposition proceeded at a faster rate relative to horsts. Recurrent motion on the Potter County fault in northern Potter and northeastern Oldham County produced cumulative displacements of 1,600 ft (488 m) on top of the Pennsylvanian, 800 ft (244 m) on Wolfcampian strata, 600 ft (183 m) on top of the Clear Fork Formation, and 450 ft (137 m) on the Dockum Group (Triassic). Post-Permian displacements are the result of both salt dissolution and minor structural movement. There is no direct evidence for Quaternary faulting, although the uplift is seismically active. End_of_Article - Last_Page 511------------

The Use of Natural Radionuclides to Predict the Behavior of Radwaste Radionuclides In Far-Field Aquifers

ABSTRACTIn appropriate aquifers the natural radionuclides of the U and Th decay series are important sources of information about the behavior of radwaste radionuclides in far-field aquifers. The Wolfcamp Carbonate, Pennsylvanian Carbonate and Granite Wash aquifers in the Palo Duro Basin of the Texas Panhandle are prime examples of such aquifers. Sampling and analysis for key radionuclides in the ground waters of these aquifers are quite feasible and have been accomplished. Key early results are: (1) Ra does not appear to be retarded by sorption, (2) Th appears to be strongly sorbed, (3) kinetics seem to be different on time scales of days to months than on ones of hundreds of thousands of years, and (4) U and Th behave similarily when the time scales (half-lives) are similar, leading to the suggestion that uranium is in the +4 valence state in these aquifers.

Carbon-Oxygen Log Applications in Complex Reservoir Evaluation by Neutron Interactions from (D,t)accelerators

Granite Wash reservoirs in Oklahoma, Texas, Colorado and New Mexico have proven to be effective commercial producers of hydrocarbons. Substantial drilling activity continues to penetrate this formation either as a primary or secondary objective. A new technique to provide additional lithologic data to engineers and geologists will yield significant benefits in the evaluation and treatment of these reservoirs. This information can be obtained by data available from spectrum analysis through the use of tools such as the Carbon/Oxygen Log, Spectralog and NGS.

Palo Duro Basin, An Exploration Frontier in the Texas Panhandle: ABSTRACT

Recent oil discoveries in the northwestern and central Palo Duro basin have renewed interest in this sparsely drilled area. Production in the northwest, in Oldham and Potter Counties, is from Pennsylvanian granite wash and carbonates. These fields are located in a highly faulted area south of the Amarillo uplift, and traps are structural. Discovery wells here produce oil at rates that range from 150 to 650 bbl per day. Oil production in the central basin, in Briscoe County, is from Pennsylvanian carbonate. The reservoir is probably a Strawn shelf-margin buildup or a debris flow into the basin from a younger Pennsylvanian shelf margin. The Palo Duro basin seems to contain potential reservoirs, traps, and source rocks; thermal maturity is probably the limiting factor for hydrocarbon production in the basin. The current geothermal gradient is relatively low, 1.1°F/100 ft (20°C/km), and it apparently has not been significantly different in the past. Vitrinite reflectance (Ro) measured in cores increases linearly with depth (temperature) by the relation: Ro = 0.00003 × depth (ft) + 0.36. Ro values seem to be in equilibrium with current depths and temperatures of the vitrinite. This suggests that (1) rocks in the basin are at or near their maximum burial depth, and (2) the geothermal gradient was not higher in the past. Shales of different ages that are at approximately the same depth have similar vitrinite reflectance values, an indication that increased time did not cause increased maturity in these Paleozoic samples. Deeply buried shales, 7,000 to 9,000 ft (213 to 2,743 m), from Pennsylvanian and Wolfcampian basin facies theoretically should have reached temperatures sufficient to generate hydrocarbons. Recent discoveries provide evidence that oil actually was generated in the Palo Duro basin. End_of_Article - Last_Page 454------------

Natural gamma ray spectral logging aids granite wash reservoir study : Schenewerk, P A; Sethi, D K; Fertl, W H Oil gas J, V79, N32, 10 Aug 1981, P180–190

Natural gamma ray spectral logging aids granite wash reservoir study : Schenewerk, P A; Sethi, D K; Fertl, W H Oil gas J, V79, N32, 10 Aug 1981, P180–190

Geologic Interpretation Based on Dipmeter Data--Field Study: ABSTRACT

The Lambert Granite Wash field was discovered in Oldham County, Texas, in 1979. With the exception of the discovery well, every well in the field was logged with a 4-arm high-resolution dipmeter, and the log data were processed by computer. The data interpretation identified the paleoenvironment of the field and determined the source of the granite wash and how it was transported. Log data indicated that a subsea distributary-channel system transported the detrital granite, and that the deposition was influenced by the remnants of a small Precambrian ridge. The channels were diverted around the ridge until it was eventually buried. The deposition continued, from the west, until the source of granite was depleted. Through analysis of the dipmeter data, the Bravo dome was identified as the source of the granite, and it was determined that the channel system was located on the north side of the dome in Oldham County. During Late Pennsylvanian time, a horst formed in the area as a result of basin subsidence. Log data indicate this horst is a suitable structure for the accumulation of hydrocarbons and has overlying shale which forms a stratigraphic trap. End_of_Article - Last_Page 245------------