James R. Wood

Vertical and Lateral Fluid Flow Related to a Large Growth Fault, South Eugene Island Block 330 Field, Offshore Louisiana

Data from sediments in and near a large growth fault adjacent to the giant South Eugene Island Block 330 field, offshore Louisiana, indicate that the fault has acted as a conduit for fluids whose flux has varied in space and time. Core and cuttings samples from two wells that penetrated the same fault about 300 m apart show markedly different thermal histories and evidence for mass flux. Sediments within and adjacent to the fault zone in the U.S. Department of Energy-Pennzoil Pathfinder well at about 2200 m SSTVD (subsea true vertical depth) showed little paleothermal or geochemical evidence for throughgoing fluid flow. The sediments were characterized by low vitrinite reflectances (Ro), averaging 0.3% Ro, moderate to high d18O and d13C values, and little difference in major or trace element composition between deformed and undeformed sediments. In contrast, faulted sediments from the A6ST well, which intersects the A fault at 1993 m SSTVD, show evidence for a paleothermal anomaly (0.55% Ro) and depleted d18O and d13C values. Sodium is depleted and calcium is enriched in a mudstone gouge zone at the top of the fault cut in the well; this effect diminishes with distance from this gouge zone. Cuttings from other wells in South Eugene Island Block 330 show slightly elevated vitrinite reflectance in fault intercepts relative to sediments outside the fault zone. Overall, indicators of mass and heat flux indicate the main growth fault zone in South Eugene Island Block 330 has acted as a conduit for ascending fluids, although the cumulative fluxes vary along strike. This conclusion is corroborated by oil and gas distribution in downthrown sands in Blocks 330 and 331, which identify the fault system in northwestern Block 330 as a major feeder. Simple modeling of coupled heat and mass flux indicates the paleothermal anomaly in the fault zone intersected by A6ST well was short-lived, having a duration less than 150 yr. The anomaly could have been produced by a 2 ´ 106 m3 pulse of fluid ascending the fault at an actual velocity of over 1 km/yr (Darcy flux of 330 m/yr) from 3 km deeper in the basin. Simple Darcy law computation indicates a transient fault permeability on the order of 110 md during this flow. Pulsing of fluid up the fault was probably the norm, although most flow did not produce such strong thermal anomalies as the one detected in the A6ST well. Analysis of fluid pressures shows that the main fault is a profound lateral permeability barrier having up to 1800 psi of water pressure differential across it. The hydrocarbon sealing capacity of the fault depends on the pressure difference across the fault. Fault permeability is best understood in terms of effective stress. Under ambient conditions, the fault is at high pressure relative to downthrown reservoirs. A pulse of high-pressure fluid ascending End page 244---------------- the fault lowers effective stress in the fault zone sufficiently to produce a significant transient increase in permeability. If the fluid is in an area of the fault adjacent to downthrown, relatively low pressure reservoir sands, the fluid will discharge into them. Permeability in and adjacent to the fault then decreases, such that fluid cannot reenter the fault zone and escape from the reservoir.

Prediction of thermal conductivity in reservoir rocks using fabric theory

An accurate prediction of the thermal conductivity of reservoir rocks in the subsurface is extremely important for a quantitative analysis of basin thermal history and hydrocarbon maturation. A model for calculating the thermal conductivity of reservoir rocks as a function of mineral composition, porosity, fluid type, and temperature has been developed based on fabric theory and experimental data. The study indicates that thermal conductivities of reservoir rocks are dependent on the volume fraction of components (minerals, porosity, and fluids), the temperature, and the fraction of series elements (FSE) which represents the way that the mineral components aggregate. The sensitivity test of the fabric model shows that quartz is the most sensitive mineral for the thermal conductivity of clastic rocks. The study results indicate that the FSE value is very critical. Different lithologies have different optimum FSE values because of different textures and sedimentary structures. The optimum FSE values are defined as those which result in the least error in the model computation of the thermal conductivity of the rocks. These values are 0.444 for water-saturated clay rocks, 0.498 for water-saturated sandstones, and 0.337 for water-saturated carbonates. Compared with the geometric mean model, the fabric model yields better results for the thermal conductivity, largely because the model parameters can be adjusted to satisfy different lithologies and to minimize the mean errors. The fabric model provides a good approach for estimating paleothermal conductivity in complex rock systems based on the mineral composition and pore fluid saturation of the rocks.

Well-log tomography and 3-D imaging of core and log-curve amplitudes in a Niagaran reef, Belle River Mills field, St. Clair County, Michigan, United States

Well-log tomography, a recently developed technique that generates subhorizontal slices through log curves, was used to create a series of amplitude slices from the core permeability, core porosity, and gamma-ray log curves for the wells penetrating the Silurian Brown Niagara reservoir in the Belle River Mills field. Log-curve amplitude slicing and three-dimensional (3-D) imaging of the core permeability and core porosity amplitudes show the detailed anatomy of the pinnacle reef in terms of these important reservoir properties. Although the reef has been dolomitized, the spatial distribution of permeability and porosity amplitudes in the reservoir appears to be controlled by the original pore and depositional fabrics of the wackestone, boundstone, stromatolite, and reef conglomerate rock types.Trends and patterns observed in the normalized gamma-ray log tomography approximate the trends and patterns observed in the core permeability and core porosity tomography in the Belle River Mills field. The similarities in the tomography trends and patterns establishes a potentially significant relationship that can be used to interpret log-curve amplitude patterns in other Niagaran pinnacle reef fields with log-curve data only and perhaps lead to improved sequence-stratigraphic models for these reservoirs.Well-log tomography and 3-D imaging provide complementary visualization tools that use existing data to image reservoirs and geologic formations. These imaging tools can be used to improve the design and placement of vertical, deviated, and horizontal wellbores for primary, secondary, tertiary, and gas storage operations in these reefs and other reservoirs.

Devonian Dundee Formation, Crystal Field, Michigan Basin: Recovery of Bypassed Oil Through Horizontal Drilling

Carbonate reservoirs of the Devonian Dundee Formation represent the most productive interval in the Michigan basin, yet have suffered widespread abandonment due to improper early reservoir management and completion practices. Dundee carbonate reservoirs, deposited in marginal-marine and shallow-marine environments, have produced over 351 MMbbl oil from 137 fields, most of which were discovered in the 1930s and 1940s. Initial potentials for many Dundee wells ranged from 2000 to 9000 bbl/day, presumably due to high- permeability fractures and solution-enhanced porosity in some areas and excellent primary interparticle porosity in other areas. Crystal field, discovered in 1935 at a depth of less than 3500 ft (1060 m), was aggressively developed and produced at high rates, causing widespread water coning, such that 95% of the field was drilled and abandoned in less than 5 yr, leaving considerable interwell reserves in the ground. No cores or wireline logs existed for the field prior to 1995, when the field became the subject of a multiyear study aimed at determining the feasibility of employing horizontal drilling to recover bypassed reserves. A vertical test portion of the TOW 1-3 horizontal well, located in a structurally elevated portion of the field, cored and logged the entire reservoir interval, yielding crucial new information. On the basis of relevant data, a horizontal leg was drilled, resulting in an excellent producer with estimated recoverable reserves of 200,000 bbl. Two subsequent horizontal tests with poor results were drilled in downdip locations and oriented perpendicular to the TOW well, suggesting the importance of both structural position and azimuth. Selective use of horizontal drilling is considered an appropriate, cost-effective means for recovering bypassed reserves in Dundee fields where sufficient geologic data exist to adequately characterize the reservoir and oil occurrence. For some fields, this may require new coring and logging operations.

Using Recent Advances in 2D Seismic Technology and Surface Geochemistry to Economically Redevelop a Shallow Shelf Carbonate Reservoir: Vernon Field, Isabella County, Class Revisit

Continued the fault study to find more faults and develop new techniques to visualize them. Data from the Dundee Formation was used to document 11 major faults in the Michigan Basin which have now been verified using data from other horizons. These faults control the locations of many of the large anticlinal structures in the Michigan Basin and likely controlled fluid movements as well.

Using Recent Advances in 2D Seismic Technology and Surface Geochemistry to Economically Redevelop a Shallow Shelf Carbonate Reservoir: Vernon Field, Isabella County, M, Class III

In this project a consortium consisting of Cronus Exploration (Traverse City, MI), Michigan Technological University (Houghton, MI) and Western Michigan University (Kalamazoo, MI) proposed to develop and execute an economical and environmentally sensitive plan for recovery of hydrocarbons from an abandoned shallow-shelf carbonate field that is typical of many fields in the U.S. Midwest. This is a 5-year project that will use surface geochemistry as a tool to reduce risk in locating and producing hydrocarbons in Class II fields. The project will develop new techniques for measuring hydrocarbon gases in the soil horizon to locate new and bypassed oil in the shallow-shelf carbonate environments typified by the Dundee and Trenton Formations of the Michigan Basin (Fisher et. al., 1988). In Phase I of the project, the consortium proposes to re-develop the Vernon Oil field located in Vernon Twp, Isabella County, Michigan and produce both bypassed hydrocarbons from the original field and to locate and produce extensions of the original field.

Facilitating interaction between universities and industry: Mechanisms for personnel and technology transfer

While a variety of technology transfer mechanisms are generally available to any scientists or engineer, creative solutions to the problem of {open_quotes}getting information out{close_quotes} are constantly appearing. The authors of this poster are active in the technology transfer process, because of their participation in DOE-funded cooperative projects involving universities and industry.