Abstract

The correlations among the physical properties of core samples taken from the Hartselle Sandstone formation were examined. porosity, permeability, formation factor, cementation factor, porosity, permeability, formation factor, cementation factor, saturation exponent, clay mineralogy and cation exchange capacity were determined. Constants such as, a, a*, m, m*, n, n* and no were found to be unique and significantly different from those for normal shaly sands. The cation exchange capacities (CEC) were determined by the strontium exchange technique. The curvelinear equation correlating CEC vs. Gamma Ray has been proven to be useful for the prediction of CEC for the Hartselle Sandstone. It has been found that water saturation calculation using Dual-Water and Waxman-Smits models are very sensitive to the values of m*, n* and the clay content, particularly when water saturation excess 50 percent and Vsh exceeds 15 percent. Therefore accurate determination of these constants is necessary. It was also found that Fertl-Hamm ck equation can be used as a suitable alternative for the tight gas sands, with an accuracy similar to Waximan-Smits model, when the core data is not available.

Introduction

Significant quantities of natural gas exist in low permeability (tight) sandstone reservoirs in Alabama and across permeability (tight) sandstone reservoirs in Alabama and across the United States. The recoverable potential of these tight sands is very large; current estimation of recoverable reserves range from 192 to 574 tcf in the lower 48 states.

In Alabama, the Hartselle Sandstone qualifies as a tight sand formation. The areas included in this study are Walker County and the Southern half of Winston County in the northwestern part of the state (Figures 1 through 3). In this area, the Jasper Field is a proven producing field. It was found that productivity within the proven producing field. It was found that productivity within the Jasper Field is initially enhanced by a natural fracture system, which increases the permeability within that localized area. In contrast, all other parts of the areas showed an initial production below measurable quantities. In the past, conventional log interpretation using existing log data failed to bring about a logical evaluation of the possible reserves in these areas. The limitation of conventional log interpretation in the Hartselle Sandstone formation make the search for a new approach necessary. The purpose of this study is to present a procedure using the data obtained from core analyses of the Hartselle Sandstone to enhance the reliability of the log Interpretation for the Hartselle Sandstone Formation.

CORE ANALYSES

The core samples were obtained from the Brooks Core Hole #1 well which is located in Township 15 South, Range 9 West, Section 26 in Walker County. Measurements, such as porosity, permeability, clay content, sand grain density, formation resistivity factor, and saturation exponent, were made based on more than 180 chips and plug samples. Others, such as mineral content and cation exchange plug samples. Others, such as mineral content and cation exchange capacity (CEC) of the clay minerals were also dealt with in this study.

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