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The discovery of significant reserves in the Middle Bakken of the Elm Coulee Field in 2000 changed the development of Bakken Formation in the Williston Basin. In 2006 the Elm Coulee success led to the exploration of other fields in the Williston Basin, such as Parshall and Sanish fields in North Dakota. Thousands of Middle Bakken wells have been drilled and produced in the primary production mode, yet there is likely significant potential for enhanced oil recovery, which prompted this multi-facetted research study. First, the physical properties of the reservoir brine, oil, and gas of fluid samples from different Middle Bakken geographic locations are presented to emphasize significant physical property differences across North Dakota. This information is essential to understand the impact of fluid properties on primary production and potential for oil recovery at different locations. Second, we identified reservoir connectivity by combining petrographic analysis, scanning electron microscopy, and permeability measurements. The permeability measurements included core-based steady-state permeability and unsteady-state water-oil relative permeability. The selected cores were characterized using X-ray diffraction mineralogy, thin section petrology, and scanning electron microscopy (SEM) to correlate flow capacity to the petrophysical properties. The conclusion is that interconnected microfractures make current production possible in successful wells. Finally, the high salinity formation water compared to the low salinity of fracturing and IOR fluids was investigated by performing spontaneous imbibition using both low and high salinity brines. It was concluded that in the oil-wet environment of the Bakken, the low salinity injection fluids can enter part of the reservoir because of osmotic pressure while high salinity makes the clay surface extremely hydrophobic and causes local oil-wetness.

Novel apparatuses have been developed to measure permeability using steady-and unsteady-state methods on nano-Darcy (nD) shale (source rock) using intact cylindrical samples returned to isostatic effective reservoir stress. The steady-state method uses a high pressure dual pump system using supercritical fluids. High pressure supercritical fluids have low viscosity and low compressibility. The effect of low viscosity fluid results in measureable flow rates and the effect of low compressibility fluid minimize unsteady-state transients thereby reducing the amount of time required to achieve steady-state equilibrium. Specially designed and configured pump systems, seals and sleeves reduce leak rates to allow Darcy flow and permeability determination below 1 nD. The unsteady-state method is based upon standard designs but is optimized for small pore volume. In this report we present a summary of over 200 such permeability measurements. Permeability is observed to be dependent on geologic parameters, such as, texture and composition. Stress dependence, with hysteresis, is observed for samples with and without fractures as is rate dependent skin (Forchheimer). An interpretation model where matrix storage feeds a progressively larger fracture network provides a logical basis for a dual-porosity reservoir simulation model. This dual-porosity model is used to understand the influence of reservoir production parameters, such as choke management.An additional observed effect is possibly related to pore collapse and disconnection. Pores associated with organic matter are softer than the surrounding mineral matrix. If these pores have a sufficiently small throat diameter, it is not hard to envision that they easily compact and close under increased effective stress as the result of reservoir depletion. Therefore, organic pore systems can become isolated unlike those of a sponge where fluids remain in pressure communication at all times. The implication of such pore isolation phenomena is that fluid material balance is not preserved during production and can contribute to large production decline rates. Development of an Unsteady-State Apparatus and Methodology for Low Permeability and Porosity Shales. SummaryA device and methodology has been developed for subject purpose under axial, radial and restricted three dimensional flow geometries. The intended use for this is as input to petroleum engineering models to evaluate producing potential of gas shales and other similar geologic formations. The application of this method to radial and three dimensional is new and without, to the authors knowledge, known published literature.Motivation for this work was to develop a method which would preserve geologic rock texture at reservoir stress utilizing cylindrical plug samples as opposed to standard commercial methods which uses crushed samples without stress.An outline of the mathematical model is presented in the second appendix and examples of the history match result at high, medium, and low permeability are shown in the below ex...

Based on studies of petrographic thin sections from core and cutting samples, the pre-Permian siliciclastics in four deep wells in southern Kuwait were found to be tight. Three of these wells are located on the crestal region of the Burgan Arch, and one on the Umm Gudair anticline. These clastics were encountered beneath a thin brick-red shale of unknown thickness, immediately below the pre-Khuff unconformity at the base of the Permian-Triassic Khuff Formation. The pre-Khuff clastics range in thickness from a few tens of feet to more than 4,000 ft, and overlie a Proterozoic argillite (Economic Basement). Based on Illite Age Analysis (IAA) of samples from cores, the depositional K-Ar age of the pre-Khuff clastics is estimated to be younger than 509 Ma (90 percent confidence interval: 544–481 Ma, i.e. Cambrian-Early Ordovician). The argillite was uplifted through the 300°C isotherm at about 611 Ma (90% confidence interval: 635-588 Ma, i.e Late Proterozoic); its deposition and metamorphism preceded this date. During the Paleozoic, the pre-Khuff clastics were buried to depths of 10,000–15,000 ft, but were subsequently uplifted in the Late Paleozoic. IAA diagenetic K-Ar ages of the Economic Basement (421 Ma; 90 percent confidence interval: 442-397 Ma; Late Ordovician-Early Devonian) and pre-Khuff clastics (369 Ma; 90 percent confidence interval: 404–337 Ma, i.e. Devonian-Early Carboniferous) indicate that by these times the pre-Khuff section was already deposited and undergoing burial diagenesis. The interpretation of gravity data indicates that in Paleozoic basinal regions (e.g. between the Burgan Arch and Umm Gudair Anticline), the Paleozoic sedimentary section is likely to be more complete and may exceed 10,000 ft in thickness.