Amounts Of Anhydrite Research Articles

Petrophysical Analysis of Well Logs for Asmari Reservoir in Abu Ghirab Oil Field, South Eastern Iraq

The present study includes the evaluation of petrophysical properties and lithological examination in two wells of Asmari Formation in Abu Ghirab oil field (AG-32 and AG-36), Missan governorate, southeastern Iraq. The petrophysical assessment was performed utilizing well logs information to characterize Asmari Formation. The well logs available, such as sonic, density, neutron, gamma ray, SP, and resistivity logs, were converted into computerized data using Neuralog programming. Using Interactive petrophysics software, the environmental corrections and reservoir parameters such as porosity, water saturation, hydrocarbon saturation, volume of bulk water, etc. were analyzed and interpreted. Lithological, mineralogical, and matrix recognition studies were performed using porosity combination cross plots. Petrophysical characteristics were determined and plotted as computer processing interpretation (CPI) using Interactive Petrophysics program. Based on petrophysical properties, Asmari Reservoir in Abu Ghirab oil field is classified into three sub formations: Jeribe/ Euphrates and Kirkuk group which is divided into two zones: upper Kirkuk zone, and Middle-Lower Kirkuk zone. Interpretation of well logs of Asmari Formation indicated a commercial Asmari Formation production with medium oil evidence in some ranges of the formation, especially in the upper Kirkuk zone at well X-1. However, well X-2, especially in the lower part of Jeribe/ Euphrates and Middle-Lower Kirkuk zone indicated low to medium oil evidence. Lithology of Asmari Formation demonstrated a range from massive dolomite in Jeribe/ Euphrates zone to limestone in upper Kirkuk zone and limestone and sandstone in middle-lower Kirkuk zone, whereas mineralogy of the reservoir showed calcite and dolomite with few amounts of anhydrite.

Origin of the Neoproterozoic rim dolomite as lateral carbonate caprock, Patawarta salt sheet, Flinders Ranges, South Australia

The ‘rim dolomite’ of South Australia’s Central Flinders Ranges is a prominent ridge-forming, layered dolomitic and siliceous unit. The rim dolomite is interpreted to be a lateral caprock found exclusively at the salt–sediment interface between the Patawarta diapir and the Ediacaran-aged Bunyeroo Formation. Lateral dolomite caprock is defined by the following field relationships: (1) the rugose dolomicrite base that parallels the contact of the diapiric matrix and the bedding in the overlying stratigraphy, (2) the exclusive presence of dolomite at the salt–sediment interface, (3) the lack of sedimentary structures or fossils (cyanobacterial laminites and stromatolites), (4) the lack of interbedded Bunyeroo lithofacies, and (5) the inability to trace the rim dolomite capstone away from the diapir margin into the outboard stratigraphy. In addition to the field relationships, the rim dolomite displays the following capstone fabrics: (1) massive—microcrystalline dolomite, (2) porphyritic—two distinct crystal sizes, one forming microcrystalline dolomite groundmass and the other forming rosettes of silica, (3) banded—microcrystalline dolomite forming pressure-dissolution layers of silica and authigenic hematite, and (4) brecciated—mosaic to disorganised, forming a microcrystalline dolomite groundmass, which locally contains remnant clasts of Callanna non-evaporite lithologies, such as quartz arenite to arkosic sandstones and basalts, surrounded by an anastomosing cement-filled vein network. All capstone fabrics contain various amounts of anhydrite, quartz, feldspar and non-evaporite grains that represent the insoluble residue during halite dissolution and caprock accretion. Three different genetic models for the lateral caprock are described and tested, and that of these, only the halokinetically rotated caprock model fits the data. The field relationships and capstone fabrics of the rim dolomite match other lateral caprocks in salt basins such as the Paradox Basin and Gulf Coast, USA.

The origins of the Mengye potash deposit in the Lanping–Simao Basin, Yunnan Province, Western China

The Lanping–Simao Basin (LSB) is a Mesozoic–Cenozoic continental margin rift basin in Western China. It formed during the opening and closing of the Tethys Ocean. This basin is also known as a “metal belt” as it hosts several metal deposits, besides, the Mengye potash deposit. However, the exact dates of the formation either in the Paleocene or the Cretaceous, and thus the origins of the marine, continental or mixed origins of the Mengye deposits, remain disputed. Based on the basin's evolution, materials of marine origin and/or remnant seawater should be present, but instead the salt layers of the Mengye potash deposit present typically continental lithological features. This study examines and reviews evaporative minerals, Br/Cl and I/Cl molar ratios, and isotopes of S, B, and Sr·I and I/Cl data for this area has not been previously reported. The basin's evaporative minerals are dominated by halite and sylvite. The amounts of anhydrite, chlorocalcite, langbeinite, glaserite, tachyhydrite and glauberite are small. All of these form in both marine and continental environments. The values of I and the I/Cl molar ratios of halite and sylvite are from 0.07 to 0.27ppm, and from 0.03 to 0.11×10−6, respectively, dependent on organic substances. Br and molar Br/Cl values are from 89.08 to 555.45ppm and from 0.06×10−3 to 0.38×10−3, respectively. All of the Br/Cl molar ratios are lower than those of seawater, and most of them are <0.1, suggesting continental or mixed origin. Previously published δ34S, δ11B and 87Sr/86Sr values for evaporative minerals indicate a continental origin for the Mengye potash deposit. However, materials of hydrothermal origin are widely distributed in the basin and may have played an active role for the formation of the potash deposit. Thus the Mengye potash deposit could be of continental origin, with a remnant seawater trace.

The effects of leaching and floatation on the ash fusion temperatures of three selected lignites

Experiments have been conducted with Huolinhe (HLH), Xiaolongtan (XLT), and Ethiopian (ET) lignites to investigate the effects of washing with water, acid-leaching, and floatation on their ash fusion temperatures (AFTs). The results show that the AFTs of XLT and ET are elevated by washing with water and floatation, but the AFT of HLH is decreased. The AFTs of all three lignites are increased markedly by acid leaching. A decrease in the total basic composition in ash increases its AFT, and vice versa. Changes in the mineral contents of the coals after treatment contribute to the variations in their AFTs. After washing with water, the lower AFT of HLH is brought about by the increases in the amounts of cordierite and anhydrite, whereas the higher AFT of XLT is caused by the decreases in the amounts of anhydrite and calcite. For the floatation treatment, the decrease of AFT for HLH is due to the reduction in the amount of kaolinite, but the elevation of AFT for XLT or ET is caused by the decrease in the amount of pyrite and the reductions in the amounts of gypsum and xanthoxenite, respectively. For the acid-leaching treatment, a decrease in the amount of pyrite and an increase in the amount of kaolinite result in increases in AFTs for HLH and XLT. Increases in the amounts of kaolinite and cristobalite in FET (ET after floatation), WET (ET after washing with water), and AET (ET after acid-leaching) lead to corresponding increases in the AFTs.

The Effect of Anhydrite on Oil Production in Dolomite Reservoirs -- Some Early Observations

Results from wireline log analysis of recently drilled wells in the San Andres dolomite of the Slaughter and Levelland fields, west Texas, suggested a correlation between the presence of anhydrite and poor oil production. Log data from wells in the North-Central Levelland, Wright and Boyd Mallet units show that a high percentage of wells that perform poorly all have significant amounts of anhydrite in their reservoirs. Preliminary indications suggest that more than 20% anhydrite in the reservoir will severely reduce porosity and permeability and cause higher than average water saturations. In addition, the spacing of new wells indicates that reservoir degradation by anhydrite may be sporadic and areally restricted, allowing a poorly performing well to be located no more than 1500 ft from better performing wells that have low amounts of anhydrite. These observations imply that uneconomic infill well locations could be minimized by mapping the percent of anhydrite within the reservoir section. On a practical basis, the only way to acquire a sufficiently large enough database for good anhydrite prediction in west Texas is to refine log analysis to yield accurate mineralogy from cased hole logs.

Diagenesis of Keg River Bioherms, Rainbow Lake, Alberta: ABSTRACT

The Keg River bioherms consist mainly of mechanically deposited carbonate sediments and of stromatolites. True skeletal boundstone is rare. The salinity of the contemporaneous sea fluctuated repeatedly between normal marine and highly supersaline. Accordingly, fossiliferous marine carbonates are intercalated with essentially nonfossiliferous evaporitic carbonates. Parts of these sediments were intermittently at or above sea level. Intensive penecontemporaneous cementation by high magnesium calcite and, possibly, aragonite occurred on the bioherms at times of near-normal salinity. Unconsolidated fossiliferous carbonate sediments and soft algal mats became solidly lithified, wave-resistant rocks. The bioherms grew as cementation welded most loose carbonate particles firmly to the reef body. Abundant early fractures opened after cementation. These fractures commonly were filled with internal sediment of evaporitic facies. Early diagenetic anhydrite is present in evaporitic carbonates mainly as replacement, displacement nodules, and pore cement. Dolomitization of bioherms occurred mainly during evaporitic episodes at subtidal to supratidal sites. Unconsolidated evaporitic carbonate sediments selectively were dolomi ized completely and lithified. The dolomitization produced finely crystalline dolomite in evaporitic carbonates and medium to coarsely crystalline dolomite in previously lithified fossiliferous carbonates. Temporary subaerial exposure caused little or no cementation by meteoric low-magnesium calcite. Late diagenetic processes after effective burial include: (1) conversion of all metastable calcium carbonate to low-magnesium calcite; (2) cementation and replacement by minor amounts of anhydrite, calcite, and dolomite; (3) moderate fracturing; (4) weak stylolitization; and (5) deposition of large amounts of carbonaceous material in pores. End_of_Article - Last_Page 868------------

Depositional History and Paleotectonic Framework of Comanchean Cretaceous Trinity Stage, Gulf Coast Area

The Trinity Stage is subdivided into four operational units, referred to herein as formats, each based on the type section of a recognized formation. The formats, in ascending order, are Pearsall, Rodessa, Ferry Lake, and Rusk. Correlations are extended from the type localities by an electrical log network. Isopach-lithofacies maps show the variation in thickness and composition of the Trinity Stage from Mexico to Florida and of each of the formats from central Texas to Alabama. During Comanchean time the Gulf Coast basin was intracratonic with only part of its perimeter flanked by a shelf. Southward the basin graded into the oceanic depths of the Gulf of Mexico. Trinity rocks were deposited under tectonic conditions which varied from stable shelf near the basin margin through various degrees of stability to intracratonic basinal conditions. From west to east, the major tectonic elements during Trinity deposition were the San Marcos platform, the East Texas basin and Henderson embayment, the Panola platform, the Louisiana-Mississippi basin and northwest Louisiana embayment, the Appalachian highlands, the Ocala uplift, and the Florida basin. The transgression of the Lower Cretaceous seas onto the craton in the Gulf Coast area occurred during Coahuilan time. Transgression continued during early Comanchean time throughout most of Trinity deposition. The seas regressed during late Trinity deposition because the balance between the supply of clastic detritus and subsidence altered, allowing the basin to fill and marginal and non-marine environments to advance basinward. Rocks of the Trinity Stage were deposited as a wedge of sediments thickening downdip from the zero edge to more than 4,000 feet. Although the zero edge is erosional, it approximates the original extent of Trinity rocks except in the areas of the Llano and Monroe uplifts. The section grades from a predominantly limestone facies in South Texas, through a limestone and shale association in East Texas and North Louisiana, into a sandstone and shale association in Arkansas, Mississippi, and Alabama. The clastics become coarser toward the margin of deposition and the major source area, the Appalachian highlands. Southeastward from this source the per cent of clastics in the section decreases abruptly. In the Florida basin the Trinity Stage is predominantly carbonate with significant amounts of anhydrite. The depositional environments were relatively constant in areas of clastic deposition near shore and the areas of predominantly limestone deposition along the tectonic hinge. The greatest lithological variation resulting from environmental control occurs in East Texas and North Louisiana. In this area of intermediate clastic-ratio values early Trinity environments alternated from lagoonal conditions, with varying degrees of restriction in which shales were deposited, to epineritic biostromal conditions. Rocks deposited, in these various environments are present in the Pearsall Formation. Extensive biohermal development began along the tectonic hinge during deposition of the Rodessa. Shoreward from the biohermal development the Ferry Lake was deposited in a back-reef lagoonal environme t which allowed sufficient concentration of calcium sulphate for the deposition of gypsum. Subsequently the gypsum was altered to anhydrite by pressure of the overlying sediments. The factors restricting the lagoonal environment gradually diminished and normal marine circulation returned to the shelf during Rusk deposition. The alternating beds of dense limestone and shale of the Rusk were deposited in a quiet, offshore, neritic environment with uniform variation of depositional conditions over a wide area. Clastic material was deposited farther basinward, and biohermal development along the hinge ended as the seas became shallower during late Rusk deposition. The two most important zones for the production of hydrocarbons from the Trinity Group are the sands in the upper part of the Rusk and the sands and the porous, oolitic, or fossiliferous-fragmental limestones in the Rodessa. The trend of hydrocarbon production from each of these zones and from others less important, appears to be related to the facies patterns of the respective units. No important production has been found in rocks of the Trinity time-stratigraphic unit beyond the limits of anhydrite in the Ferry Lake format.