Tuscaloosa Sandstone Research Articles

Depositional Environment and Reservoir Properties of the Lower Tuscaloosa B"Sandstone, Baywood Field, St. Helena Parish, Louisiana: ABSTRACT"

Baywood field was discovered in September 1987 with the drilling of the Keck Partners Clemons No. 1, located in Sec. 45, T4S, R4E, St. Helena Parish, Louisiana. The discovery well encountered a 47 ft thick Lower Tuscaloosa sandstone in the B stratigraphic interval at 14,540 ft with a 21 ft gas column on water. The perforated interval 14,544 to 14,554 ft potentialed 2,200 MCFGPD, 290 BCPD, and 12 BWPD with a flowing tubing pressure of 3,200 psi. Subsequent development drilling to date has led to three gas completions, one oil completion, and three dry holes. Detailed sedimentological analysis of a conventional core from the discovery well reveals that the reservoir sandstone was deposited in a deltaic channel to point bar environment and not a shoreline as interpreted by others. In terms of composition and diagenesis, the reservoir sandstone is anomalous to most Lower Tuscaloosa sandstones. Core porosity in the reservoir sandstone ranges from only 2% to 17%, and permeability is from 0.1 md to 402 md. Average porosity is 13%, and average permeability is 88 md. Porosity is comprised of both primary intergranular and leached-grain, secondary pores. Microporosity that usually comprises a significant amount of the total porosity in mostmore » Lower Tuscaloosa sandstones is minimal, resulting in lower immobile water saturations and no low-resistivity pay problems. Determination of critical water saturations derived through special core analysis and used in conjunction with detailed log analysis is imperative to recognizing pay within the sandstone. Reservoir fluid studies indicate that the reservoir exhibits retrograde condensation characteristics. The primary drive mechanism is depletion gas with a partial water drive.« less

Preservation of Primary Porosity in Deeply Buried Sandstones: A New Play Concept from the Cretaceous Tuscaloosa Sandstone of Louisiana: ABSTRACT

Preservation of Primary Porosity in Deeply Buried Sandstones: A New Play Concept from the Cretaceous Tuscaloosa Sandstone of Louisiana: ABSTRACT

Subsurface Study of Lower Tuscaloosa Formation at Olive Field, Pike and Amite Counties, Mississippi: ABSTRACT

ABSTRACT Olive Field is located on the Amite-Pike County line in southwestern Mississippi. The field was discovered by Shell Western Exploration and Production Inc., and produces from a sandstone within the Lower Tuscaloosa Stringer Member; the trap is stratigraphic. The Stringer Member consists of alternating sandstones, siltstones, and shales, which have an average thickness of 230 ft (76 m) at Olive Field. The Stringer Member is a transgressive sequence deposited on eroded Washita-Fredericksburg sediments and is overlain by Middle Tuscaloosa marine shales. The coarse-to fine-grained sandstones are quartz-rich with a high percentage of sedimentary rock fragments. The majority of sandstones are shale arenites. However, a large number of rock fragments were badly altered; these fragments could not be identified with confidence; many may be of volcanic origin. The sandstones are cemented by quartz overgrowths, Fe-rich carbonate cement, and chlorite. Sandstones commonly have a high preserved interparticle porosity that is characteristic of Lower Tuscaloosa sandstones. This interparticle porosity is attributed to chlorite, which occurs as an isopachous cement that coats grains and reduced nucleation sites for quartz overgrowths. The Stringer Member was subdivided into five zones in this study based on lithology and electric log responses. The lower three zones were deposited in a fluvial environment. The sandstones were deposited as point bars and channel sands in a meandering system. Siltstones and shales represent overbank, flood basin, and channel fill deposits. The upper two zones consist of sediments deposited at or near sea level. Finely laminated shales and siltstones represent marsh and bay deposits. The topmost zone is a thin continuous sand body that represents a remnant beach deposited before major marine transgression.

Reservoir Characterization of Tuscaloosa Sand by Mineralogical and Petrophysical Data

Summary A laboratory investigation has been made of the relationship between mineralogical and petrophysical properties of Tuscaloosa sandstone with a combination of petrographic analyses, formation-resistivity-factor measurements, and rock failure analyses. Petrographic analyses revealed that on the basis of the mineralogy of pore-filling and pore-lining cements, Tuscaloosa sandstones can be divided into two distinct types: those with authigenic quartz-overgrowth cement blocking the pore throats and those with authigenic chlorite cement coating the sand grains and preserving the pore system. For each type of sandstone, a well-defined relationship exists between the cementation factor m and other physical properties of the rock, such as porosity, type of cement, compressive strength, cohesive strength, failure angle, angle of internal friction, Young's modulus, Poisson's ratio, and drilling strength. Furthermore, we found that the fracture mechanism is grain fracturing in a fairly brittle mode for silica-cemented sandstone, while the fracture mechanism is grain sliding and pore closure or expansion for chlorite-cemented sandstones.

Fluid-Flow Patterns in Central Tuscaloosa Trend, Louisiana: ABSTRACT

Contoured hydraulic-head cross sections constructed from well logs in the central Tuscaloosa gas trend of Louisiana provide information about fluid flow near the hydropressure-geopressure interface. Extensive head inversions correspond to long, dip-oriented convolutions of the interface. The inversions occur where permeable, hydropressured, massive sandstone facies in the lower Tuscaloosa underlie geopressured Eagle Ford Shale updip of fault zones that preserve geopressures downdip. Thus, regional fluid pressure regimes in the Tuscaloosa and Eagle Ford are predominantly structurally controlled, with some lithofacies control updip. Hydraulic-head trends indicate an overall pattern of regional upward flow from depth, with highest hydraulic gradients corresponding to the top of the Austin Chalk in most places. This pattern is complicated by inversions--which are nearly horizontal and tend to show high hydraulic gradients--and by a sharp, upward-protruding head peak that becomes nearly vertical along a trend above the Lower Cretaceous limestone shelf edge. This peak represents the escape of highly pressurized fluids from depth along a preferred path, which may be fault controlled. Highest hydraulic gradients occur locally and regionally where fluids flow from geopressured shale toward permeable, hydropressured sandstone. Salinities are also reported to show a regional increase toward End_Page 1427------------------------------ hydropressured, sandy, updip facies of the Tuscaloosa. Thus, reverse osmotic effects are probably unimportant. The head peak above the Lower Cretaceous shelf edge, although characterized by relatively low hydraulic gradients, could be a locus of membrane filtration at the top of Tuscaloosa sandstone if bypassing of reverse osmosis by fluid escape along faults has been minimal. The role of permeable Tuscaloosa sandstone as a sink for fluids near the top of geopressure may have localized gas along the producing trend. End_of_Article - Last_Page 1428------------

Lockhart Crossing Field: New Wilcox Trend in Southeastern Louisiana : ABSTRACT

A 1982 Wilcox oil discovery in southeastern Louisiana constituted one of the more significant onshore United States discoveries for the year and illuminated a new oil trend. Prior to this discovery, Lockhart Crossing field was known for its gas and condensate production from Cretaceous lower Tuscaloosa sandstones at depths of 17,000-18,000 ft (5,200-5,500 m). Oil production from sandstones of the lower Eocene of the uppermost Wilcox Group was recently established at 10,000 ft (3,000 m) with successful completion (630 BOPD), of the Callon 1 Reed Erickson. To date, 30 producers and 5 dry holes have been drilled in the field, with production peaking at 10,000 BOPD and recoverable reserves of 15-20 million bbl of oil after secondary recovery. The main field reservoir is a 40-80 ft (12-24 m) marine sandstone with two distinct facies present. The most dominant of these two facies is a coarsening-upward sequence of very fine to fine-grained glauconitic sand deposited as a nearshore bar. The second is a tidal channel facies with a fining-upward sequence of medium to very fine grained sand. The spatial relationship of these two facies defines a progradational sequence of tidal channels overstepping and eroding into existing nearshore bars. The primary trapping mechanism, however, is structural in the form of a rollover anticline. In April 1983, Callon and Amoco extended the trend southeast with the discovery of Livingston field. Chances are good that this new trend will yield additional discoveries with continued exploration. End_of_Article - Last_Page 306------------

Decade of Exploration in Deep Lower Tuscaloosa Gas Trend in Southern Louisiana: ABSTRACT

The deep lower Tuscaloosa gas trend, now in a mature stage of exploration, was discovered in 1975. Production is from lower Tuscaloosa sandstones of Late Cretaceous age. During the past decade, the petroleum industry has drilled approximately 217 new-field wildcats and 232 development wells in the trend. This exploration effort has discovered 24 fields. Most of these fields produce from depths between 15,000 and 20,000 ft. In February 1984, the average daily production was 426.6 mmcf of gas and 18,350 bbl of liquid hydrocarbons from approximately 115 wells. Five fields, False River, Irene, Judge Digby, Moore-Sams, and Port Hudson, all discovered prior to 1980 and concentrated northwest of Baton Rouge, Louisiana, have produced about 72% of the cumulative gas and 80% of the cumulative liquids. Reservoirs in deep lower Tuscaloosa occur in a terrigenous clastic sequence, which thickens rapidly downdip from a carbonate shelf of Early Cretaceous age. Occurrences of commercial hydrocarbons in the trend are primarily dependent on depositional environment, syndepositional tectonics, source rock, original sand mineralogy, and burial diagenesis. Salt diapirism is locally important. End_of_Article - Last_Page 308------------

Effects of Diagenesis on Porosity Development, Tuscaloosa Sandstone, Louisiana: ABSTRACT

The Lower Cretaceous Tuscaloosa sandstone is of interest because of high porosity (up to 29%) at depths as great as 21,000 ft (6,400 m). We believe that the porosity is 70% primary and 30% secondary. Diagenetic events are major controls for the high porosity but overpressure also contributes. Primary porosity exists because quartz diagenesis was retarded by chlorite grain coats. Where grains coats are absent or thin, prismatic quartz overgrowths occur. Chlorite coats constitute up to 29% of the rock. Chlorite originates from alteration of lithic material (i.e., volcanic and basic igneous intrusives) in the sandstone. An excellent direct correlation exists between the amounts of lithic fragments and chlorite coats. Sandstones with extensive chlorite and lithic fragments are not good reservoirs because of reduced permeability resulting from rearrangement and mechanical breakage of weak grains during compaction. Commonly, authigenic titanium minerals (e.g., anatase) are associated with the altered lithic material. Secondary porosity has formed from the dissolution of lithic fragments and feldspars, and to a lesser degree carbonates. Secondary porosity related to highly chemically susceptible lithic fragments developed early (prechlorite) and was subject to later collapse; whereas pores related to later dissolution of less soluble lithic material and feldspar were less affected by compaction because of a more stable framework. Diagenetic evidence indicates that the dissolution occurred prior to, during, and after the formation of chlorite coats. Calcite cement occludes porosity in some intervals. However, textural evidence from leaching experiments suggests that dissolution of this calcite is not a major source of secondary porosity. End_of_Article - Last_Page 498------------

Hydropressure Tongues Within Regionally Geopressured Lower Tuscaloosa Sandstone, Tuscaloosa Trend, Louisiana: ABSTRACT

ABSTRACT A regional study of the Tuscaloosa Formation in Louisiana, undertaken to assess geopressured-geothermal potential, revealed lobate, downdip extensions of the hydropressured zone in lower Tuscaloosa massive sandstone facies below the regional top of geopressure. Normal pressure zones within geopressured section were identified by drilling mud weights less than 13 pounds per gallon on electric logs of massive lower Tuscaloosa sandstone, and cross sections demonstrated updip continuity of these zones with the regional hydropressured zone. These hydropressure are permitted by the anomalously high permeabilities reported from the deep Tuscaloosa trend which have been attributed to both primary and secondary porosity. The hydropressure tongues correspond with lobes of thick net sandstone, principally in Pointe Coupee, East Feliciana, East Baton Rouge, and Livingston parishes in the central Tuscaloosa trend. Limited control suggests at least one hydropressure tonge in the Chandeleur Sound area to the east. Dimensions of hydropressure tongues range up to 17 miles (27 kilometers) parallel to strike and 11 miles (17 kilometers) oblique to strike. In many places, tongues are terminated downdip by faults, which, by acting as pressure seals, prevent the tongues from extending to the downdip edge of the massive sandstone in the expanded sections of the downthrown blocks. The areal extent of geopressured Tuscaloosa sandstone is controlled updip by these fault zones, and downdip by pinch-out of the sandstone units basinward. Local hydropressure tongues diminish the geopressured-geothermal potential of the Tuscaloosa trend, but show no discernible relation to gas-productive areas.

Sedimentology of Tuscaloosa Sandstones from False River and Judge Digby Fields, Pointe Coupee and West Baton Rouge Parishes, Louisiana: ABSTRACT

Significant gas reserves at depths ranging from 19,800 to 20,400 ft (6,035 to 6,218 m) have been established in Tuscaloosa sandstones at False River and Judge Digby fields (Chevron U.S.A. Inc. discoveries) located within the deep Tuscaloosa gas trend. The sandstones are within an Upper Cretaceous clastic wedge that thickens in front of, and to the south of, a Lower Cretaceous carbonate shelf. Reservoirs at Judge Digby field are part of a thick clastic section comprised of gray shales and medium to coarse-grained sandstones, in part conglomeratic. Paleontology, textural grading, bed contacts, and sequential arrangement of sedimentary structures suggest fluvial and deltaic environments. Reservoirs at False River field are stratigraphically younger and are interpreted as part of a barrier bar sequence. These sandstones are fine to medium-grained and occur at the top of upward-coarsening gradational sequences. In both fields, the reservoirs commonly have maximum porosities above 25% and permeabilities in excess of 100 md. Although these reservoirs are presently geopressured, petrographic evidence and density of the associated shales indicate that the sandstones are not underco pacted. A study of the sandstone framework suggests that burial diagenesis dramatically reduced the primary pore system, eliminating significant permeability. Leaching of the grain framework created an important contribution to effective secondary porosity and reestablished lost permeability. The secondary pores are easily identified by relic rims of authigenic, grain-coating chlorite cement which persisted after selective grain removal by dissolution. Commercial End_Page 993------------------------------ Figure production from these deeply buried Tuscaloosa sandstones is dependent upon secondary enhancement of a reduced primary pore system and its subsequent maintenance by geopressure. End_of_Article - Last_Page 994------------

Future Petroleum Provinces of Gulf Coast--Upper Cretaceous: ABSTRACT

According to the findings of a geologically oriented study of the National Petroleum Council's Region 6, the prospects for significant additions to reserves in the Gulf Series are in southeast Louisiana, Mississippi, Alabama, and Florida, and to in the rest of the area. In order to assign more finite terms to the potential of the unexplored area of the Gulf Series of Region 6, the following parameters have been derived: an area classed as good has a yield of 150,000 bbl/cu mi; fair has a yield of 80,000 bbl/cu mi, and poor has a yield of 50,000 bbl/cu mi. The presence or absence of reservoir-type rocks, source beds (which usually can be assumed to be present in the Gulf basin), and trap-forming structural deformation is used as criteria for rating the various geographic areas. In the explored area of southeast Louisiana-Mississippi-Alabama-Florida, which contains 30,000 cu mi of sedimentary rock, limited additional reserves may be expected in new discoveries and extensions. In the unexplored area containing 17,000 cu mi of sedimentary rocks, lenticular Tuscaloosa sandstones should provide excellent possibilities for both structurally and stratigraphically trapped oil. Fair possibilities exist in similar sandstones of the Eutaw Formation. Carbonate buildups of reeflike limestones are possible in beds of the Navarro Group on the carbonate banks off the Florida Gulf Coast. Louisiana-Arkansas' explored area (10,000 cu mi) may have minor additions. The unexplored part (4,700 cu mi) of south Louisiana has potential with one possible exception; where Woodbine sandstones may occur as turbidites or as deep-water sands swept out past the Comanchean shelf, prospects are fair. The explored part of East Texas (11,200 cu mi) will have minor additions to reserves through further exploitation. The potential of the unexplored area (3,600 cu mi) is rated to fair. In the Woodbine, possible turbidites and marine sandstones on the south and southwest flanks of the Sabine uplift offer prospects. In the Austin-Eagle Ford section, possibilities are to on the south and southeast flanks of the Sabine uplift. South Texas potential in the explored area (8,800 cu mi) is except for minor additions. The potential of the unexplored area (10,200 cu mi) is also rated poor, because of the expected absence of reservoir beds. End_of_Article - Last_Page 1785------------

Petrography and Origin of Lower Tuscaloosa Sandstones, Mallalieu Field, Lincoln County, Mississippi: ABSTRACT

Upper Cretaceous sandstone of the lower Tuscaloosa Formation in southwestern Mississippi is part of a fluvial-deltaic depositional system. At the Mallalieu field, lower Tuscaloosa sandstone is of two types: (1) channel-fill sandstone--thin, lenticular bodies which have irregular distribution across the field; and (2) point-bar sandstone--thick, more continuous bodies which have a ridge-and-swale pattern of sandstone distribution and which laterally are terminated End_Page 1828------------------------------ abruptly by narrow, broadly arcuate, shale-filled channels. These two fluvial interpretations are supported by mineralogy, textural gradation, internal structures, and sand-body geometry. The average composition of lower Tuscaloosa sandstone is quartz, 60 percent; matrix, 32 percent; calcite cement, 4 percent; feldspar, 1 percent; muscovite, 1.5 percent; and other minerals, 1.5 percent. Average mean grain size of quartz is 0.24 mm (fine grained); mean grain size decreases upward within individual sandstone beds. Four distinct sandstone zones produce oil at Mallalieu. The lower two zones are characterized by more extensive, point-bar sandstone whereas the upper two zones are narrow, channel-fill sandstone. This vertical sequence suggests an upward gradation from fluvial meander-belt deposition, through deltaic distributary deposition, to inner neritic deposition of the overlying marine shale--an overall transgressive sequence. The change from meandering below to braided above probably resulted from a change in stream gradient by basin subsidence. End_of_Article - Last_Page 1829------------