Henry P. Heasler

Organic-Inorganic Interactions and Sandstone Diagenesis

The maturation of organic material in hydrocarbon source rocks and inorganic diagenetic reactions in reservoir sandstones are a natural consequence when a prism of sedimentary rocks is buried. We can predict the distribution of porosity and permeability enhancement in potential hydrocarbon reservoirs by integrating the reaction processes characterizing the progressive diagenesis of a reservoir/source rock system. A variety of observations suggests that the organic solvents needed to increase aluminosilicate and carbonate solubilities in sandstones can be generated either by thermal or oxidative cracking of carbonylic or phenolic groups from kerogen in adjacent source rocks. For example, nuclear magnetic resonance (NMR) spectra of kerogen show that peripheral carbonylic and phenolic groups are released from the kerogen molecule before liquid hydrocarbons are generated. Experimental data indicate these water-soluble organic species can significantly affect the stability of both carbonates and aluminosilicates. Water-soluble organic acid anions (carboxylic) have been observed in oil-field waters in concentrations up to 10,000 ppm, and they commonly dominate the alkalinity in the fluid phase from 80° to 120°C. We can model the integration of organic and inorganic diagenetic reactions by constructing a series of potential reaction pathways with increasing temperature for a system that includes aluminosilicates, carbonates, organic chelate species (carboxylic and phenolic), and CO2. The important chemical divides in these diagenetic flow diagrams are dependent on temperature, the nature of the pH buffer (carbonate species or organic acid anion species), and the relationship between organic acid anions and PCO2 (P = partial pressure). Forward predictive capabilities result when this general diagenetic model is placed in a time-temperature framework. The detailed organic and inorganic geochemistry and the general thermal scenario used in the time-temperature ana ysis must be basin specific. Casting the diagenetic history of a sandstone into this type of process-oriented model helps us move from a descriptive mode to a predictive mode of analysis. Two types of information result: (1) general optimum conditions for porosity and permeability enhancement in sandstones are delineated and (2) specifically, the degree and potential for porosity and permeability enhancement are determined. Predictive models have been developed for several tectonic settings, including rift or pull-apart basins and intermontane or Laramide basins. From these reconstructions, we can forward-predict the porosity-enhancing potential of a diagenetic system based on an understanding of the reaction process in a time-temperature framework.

Analysis of Sonic Well Logs Applied to Erosion Estimates in the Bighorn Basin, Wyoming

An improved exponential model of sonic transit time data as a function of depth takes into account the physical range of rock sonic velocities. In this way, the model is more geologically realistic for predicting compaction trends when compared to linear or simple exponential functions that fail at large depth intervals. The improved model is applied to the Bighorn basin of northwestern Wyoming for calculation of erosion amounts. This basin was chosen because of extensive geomorphic research that constrains erosion models and because of the importance of quantifying erosion amounts for basin analysis and hydrocarbon maturation prediction. Thirty-six wells were analyzed using the improved exponential model. Seven of these wells, due to limited data from the Tertiary section, were excluded from the basin erosion analysis. Erosion amounts from the remaining 29 wells ranged from 0 to 5600 ft (1700 m), with an average of 2500 ft (800 m).

Thermal Evolution of Coastal California with Application to Hydrocarbon Maturation

Coastal California has evolved through a series of plate tectonic interactions that significantly affected the geologic, thermal, and hydrocarbon maturation histories of the area. Numerical solutions for steady-state heat transfer are used to estimate temperature suppression resulting from plate subduction along coastal California, and to model thermal refraction within the Pismo basin. Numerical solutions for time-dependent heat transfer estimate the thermal effect of the passage of the Mendocino triple junction with consequent upwelling of asthenosphere. Thermal solutions vary for different areas along coastal California depending on the magnitude of the temperature suppression due to subduction, the geometry of the space into which the asthenosphere upwells, the time s nce passage of the triple junction, and the specific depositional history of each basin. Paleo-temperatures are calculated for the Pismo basin, predicting that the basal 300 m of source rocks have generated hydrocarbons.

Thermal and Hydrocarbon Maturation Modeling of the Pismo and Santa Maria Basins, Coastal California

Thermal and hydrocarbon maturation models have been developed for the Pismo and Santa Maria basins of coastal California. The thermal models derived for the temperature history of Miocene Monterey Formation source rocks include the effects of subduction, triple junction migration with consequent asthenospheric upwelling, thermal refraction, and temporal changes in thermal conductivities due to diagenesis and compaction. Hydrocarbon maturation models use the technique described by Tissot and Espitalie in 1975 and the derived temperature history to predict the timing of hydrocarbon maturation.

Geothermal Resources of Wyoming Sedimentary Basins: ABSTRACT

Geothermal resources of Wyoming sedimentary basins have been defined through analysis of over 14,000 oil well bottom-hole temperatures, thermal logging of 380 wells, measurement of rock thermal conductivities, calculation of 60 heat-flow values, drilling of 9 geothermal exploratory wells, conductive thermal modeling, and the study of existing geologic, hydrologic, and thermal spring data. All data have been integrated into interpretations of the thermal structure of the Big Horn, Wind River, Washakie, Great Divide, Green River, Laramie, Hanna, and Shirley basins of Wyoming. Controlling factors for the formation of geothermal resources in these basins are regional heat flow, rock thermal conductivity values, depths to regional aquifers, and hydrologic flow directions. Regional basin heatflow values range from about 40 to 80 milliwatts/m2; measured thermal conductivities are in the general range of 1.5 to 4.0 watts/m°K; and depths to aquifers are up to 11,000 m (36,000 ft). This results in regional geothermal gradients for Wyoming basins in the range of 15° to 40°C/km (44° to 116°F/mi) with predicted maximum aquifer temperatures near 300°C (570°F). Anomalous geothermal areas within the basins contain measured thermal gradients as high as 400°C/km (1,160°F/mi) over shallow depth intervals. These anomalous areas are the combined result of local geologic structures and hydrologic flow. A simplified model for such areas requires water movement through a syncline with subsequent heating due to regional heat flow and thermal conductivities of overlying rock units. Consequent flow of the heated water up over an anticline produces a localized area of anomalous geothermal gradients. Access to Wyoming basin geothermal resources is primarily through producing oil wells. Fifty two oil fields which account for over 90% of Wyomings oil field water production, produce 575 million L (152 million gal) of thermal water per day. The temperature of this water ranges from 30° to 110°C (86° to 230°F) with 88% warmer than 38°C (100°F) and 60% warmer than 50°C (122°F). Over 50% of this water is disposed of, generally by discharge to the surface. End_of_Article - Last_Page 1342------------