Eve S. Sprunt

Streaming potential from multiphase flow

In trying to understand the affect of electrokinetics on the spontaneous potential (SP) log, the focus has generally been on the solid‐brine streaming potential. Within the accuracy of the measurements, the streaming‐potential coupling coefficient is shown to be independent of the permeability of the rock. The solid‐brine streaming potential is of much smaller magnitude than the electrostatic potentials from gas‐liquid and liquid‐liquid flow. Air bubbles were found to increase the streaming potential coupling coefficient by more than two orders of magnitude over the value for single‐phase brine flow. Thus, two‐phase gas‐liquid flow is more likely to have a significant impact on the SP log than is single phase liquid flow. Two‐phase oil‐brine flow may also produce a larger electrokinetic potential than single‐phase flow. The magnitude of the electrokinetic potential caused by oil‐brine flow will depend on the composition of the oil and the brine. Trace materials can have a major impact on the electrokineti...

Improved Data-Analysis Method Determines Archie Parameters From Core Data (includes associated paper 24964 )

This paper presents a data-analysis approach to determine Archie parameters m and n from standard resistivity measurements on core samples. The analysis method, core Archie-parameters estimation (CAPE), results in computer water saturations that agree well with core-measured saturations. CAPE determines m and n by minimizing the error between computed and measured water saturations. The conventional method minimizes the error in nonphysical quantities. Also, CAPE provides a natural, physically meaningful method of averaging: Archie parameters, and with an error statistic, aids in zonation of a well or reservoir into different sets of Archie parameters. Finally, we show that the Archie constant a is a weak-fitting parameter, with no physical significance, that can generally be set to unity.

Obtaining Reliable Laboratory Measurements

Laboratory measurements on reservoir rock and fluid samples are required for many applications, including reserves determination, reservoir simulation, stimulation design, formation damage assessment, and recovery monitoring.

Predicting the Permeability of Unconsolidated Sediments From Grain Size Measurements

ABSTRACT Laser diffraction particle size measurements are shown to be superior to porosity-permeability correlations in predicting the permeability of unconsolidated samples. For slightly laminated, deep water, Plio-Pleistocene, medium silt to very fine-grained sand samples from an offshore Louisiana well, there are good correlations between the grain size parameters and measured permeability. Although the permeabilities calculated from the Krumbein and Berg equations are well correlated with permeability, the Carman-Kozeny equation is preferred because it comes the closest to a one-to-one fit. For samples with significant laminations, a good fit between measured and calculated permeability was obtained by modifying the Carman-Kozeny equation for the proportional amount of the coarser layers. For samples with median grain diameters of 90 microns or less (very fine-grained sand) sieve analysis does not adequately resolve the grain size for prediction of permeability.

Origin and Distribution of Fractures in Tertiary and Cretaceous Rocks, Piceance Basin, Colorado, and Their Relation to Hydrocarbon Occurrence: ABSTRACT

Gas production in the lower Tertiary Wasatch Formation and Upper Cretaceous Mesaverde Group, Piceance basin, Colorado, is controlled by a network of open and partly mineralized natural fractures. These fractures formed in response to high pore-fluid pressures that developed during hydrocarbon generation, and to widespread tectonic stress associated with periods of uplift and erosion that occurred during the late Tertiary. Sandstone beds commonly contain vertical extension fractures that are cemented with fine to coarsely crystalline calcite and locally with quartz, barite, and dickite. These minerals cut detrital grains, authigenic cements, and secondary pores, indicating that fracture mineralization occurred during later stages of diagenesis. Isotopic compositions for fr cture-fill calcite in the Wasatch vary from -5.0 ^pmil to -11.6 ^pmil for ^dgr13C and from -9.5 ^pmil to -14.9 ^pmil for ^dgr180. In the Mesaverde, calcite ranges from -0.7 ^pmil to -10.4 ^pmil for ^dgr13C and from -13.3 ^pmil to -17.7 ^pmil for ^dgr180. These isotopic data indicate that fractures were mineralized during burial by fluids of meteoric origin, with temperatures that remained fairly constant, or by fluids that circulated at a rate that End_Page 860------------------------------ prohibited significant cooling. The wide range in ^dgr13C compositions reflects mixtures of organically derived carbon and dissolved marine carbonate. In reservoir rocks that are extensively fractured, gas generated in situ from carbonaceous and coaly shales and tongues of lacustrine rock may have migrated locally along open faults and fractures. End_of_Article - Last_Page 861------------

A New Coring Fluid for Vuggy Carbonates

This paper reports a salt-weighted coring fluid that contains a biodegradable cotton-fiber product, normally used to control lost circulation, used to obtain 1,048 ft (319.4 m) of carbonate core from a well in the Arun field in northern Sumatra, Indonesia. The vuggy core was free of mud solids and required special cleaning only to remove salt deposits. This fluid should be beneficial in coring other vuggy carbonates, and modifications should make the fluid usable for both high-permeability and unconsolidated sandstones, in which mud-solids invasion is a problem.