Dissolution Loss Research Articles

Diagenetic Control of Reservoir Quality of Araba and Naqua Diagenetic Quartzarenites (Cambrian), Gebel Araba-Qabeliat, Southwest Sinai, Egypt

Sandstones of the marine Lower Cambrian Araba Formation and the overlying fluvial Upper Cambrian( ) Naqus Formation in Gebel Araba-Qabeliat, southwest Sinai (the eastern side of the Gulf of Suez) were studied to evaluate the major factors controlling potential hydrocarbon reservoir quality. The formations have a composite thickness of 873 m and overlie Precambrian granite and metamorphic rocks and underlie Cretaceous marine strata. The framework composition of both sandstones is almost entirely quartz with trace amounts of muscovite, K-feldspar, and heavy minerals. Up to 21.5% oversize pores, some filled with younger cements, attest to extensive dissolution loss of detrital grains, chiefly feldspar. Because the final mineralogical maturation of these quartzarenites was through diagenesis, they are diagenetic quartzarenites. Following deposition, the introduction of thin coatings of infiltered clay was followed by the precipitation of 6.3% unhomogeneously distributed quartz cement. Some outcrop samples contain pore-occluding gypsum cement or mixtures of gypsum and halite cement. Sr{sup 87}/Sr{sup 86} ratios of seven samples of gypsum cement have values (0.7077 to 0.7083) that are equal to Miocene and slightly younger seawater. These Cambrian sandstones have excellent reservoir potential (mean thin section porosity = 25.7%) because they contained few ductile grains to enhance compaction, and theymore » developed significant amounts of secondary pores by both dissolution of calcite cement and unstable detrital grains. Kaolinite and dickite are potential problems for hydrocarbon production in some beds.« less

Syndepositional dissolution of calcareous foraminifera in modern shallow-water sediments

Dissolution of calcareous tests in waters undersaturated with respect to calcium carbonate causes postmortem changes to assemblages of modern benthic foraminifera. Comparison of the percentage of agglutinated tests in the living and dead assemblages from the same sample enables the amount of dissolution to be quantified. Re-examination of data from the continental shelf off New York and the estuarine Chezzetcook Inlet, Canada, reveals major dissolution losses which lead to dead assemblages rich in agglutinated tests. It is probable that partial dissolution of the calcareous component of modern assemblages is more widespread than has been recognised.

Chromatographie Transport of Alkaline Buffers Through Reservoir Rock

Summary Use of relatively low-pH alkaline buffers, such as sodium carbonate or sodium silicate, is explored as a means for overcoming sodium/hydrogen ion-exchange delay in alkaline waterflooding. A local-equilibrium chromatographic model is outlined to describe the concentration velocities for injection of alkaline buffers into a linear porous medium that exhibits reversible sodium/hydrogen exchange. The theory predicts a buffer ion-exchange wave that is substantially faster than that for equivalent-pH sodium hydroxide solutions. New experimental displacement data are presented for NaOH over a pH range from 11 to 13 and for 0.1, 0.5, and 1.0 wt% Na2CO3 flowing through a 1 wt% NaCl brine saturated Berea sandstone core at 50°C [122°F]. To permit a complete description of the system, column effluent concentrations are measured for sodium ions, hydroxide ions, H3-tagged water, and 14C-tagged carbonate. The experiments confirm that Na2C03 propagates through the Berea sand at a higher rate than NaOH. For example, at pH=11.4, Na2CO3 migrates with a velocity that is 3.5 times faster than NaOH. Comparison of experiment with the ion-exchange chromatography theory shows good agreement. We successfully model the concentration histories of tritium-labeled water, total carbon, sodium, and hydroxide, all with no adjustable parameters. This work establishes with both theory and experiment that buffered alkali significantly increases the propagation speed of hydroxide in reservoir sands in comparison with unbuffered alkali at equivalent sodium and hydroxide concentrations. Because lower-pH buffered alkali can also protect against rock dissolution loss, the validated reduction of buffer ion-exchange lag considerably improves the promise of the alkaline flooding process for field application.

THE INFLUENCE OF THE META-STABLE TRIPLE POINT SOLUTION OF MONOCALCIUM PHOSPHATE MONOHYDRATE UPON THE CLAY SEPARATES OF TWO ONTARIO SOILS

Samples of material less than 2 μ in diameter were obtained from the surface horizon of a Guelph loam and of a Haldimand clay loam. These samples were subjected to six successive treatments with the meta-stable triple point solution of monocalcium phosphate monohydrate (MTPS) to simulate the environment near a dissolving superphosphate granule. Samples of montmorillonite and illite standard clays were also included. The dissolution losses in per cent were: Guelph clay 59.5, Haldimand clay 40.4, montmorillonite 3.4, and illite 8.1. Total chemical analyses, X-ray diffraction techniques, differential thermal analyses and electron microscope observations were used to determine the nature of these losses. In the soil clay separates, vermiculite and interstratified montmorillonite were more susceptible to the action of MTPS than were the illite or halloysite clay minerals.