Computer-aided statistical analysis of the correlation between shaly sand analysis using old logs (pre-porosity): and modern logs : Pennsylvanian Hoover sand, Harper and Beaver counties, Oklahoma

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Title: Computer-aided statistical analysis of the correlation between shaly sand analysis using old logs (pre-porosity): and modern logs : Pennsylvanian Hoover sand, Harper and Beaver counties, Oklahoma
Author: Grim, Gerald Kenneth
Abstract: Inaccurate calculation of water saturation and porosity can mean the difference in billions of cubic feet in recoverable gas hydrocarbons . In a "clean" formation of sand matrix , water , and gas , an accurate water saturation and porosity can be calculated from the petrophysical log response using the Archie equation . When shale is present , the Archie equation must be modified to compensate for the effect of clay minerals on log response . The more log suites available for a particular well , the more accurate and more complex the correction for shale becomes . Many possibly productive shaly sand zones discovered prior to the 1960's were logged with only electrical logging tools . The lack of additional log devices severely limits the number of shaly sand corrections that can be made to the Archie equation . Therefore , several old electric log shaly sand methods are compared here to the dual water shaly sand model as determined from a nearby modern log (electrical , gamma -ray , density and neutron logs ) . Four old electric log analytical methods were attempted : uncorrected Archie equation (automatic compensation ) , Archie equation with a volume of clay correction , no -porosity log dual water model , and ratio water saturation . Each of these methods generated effective water saturations which were compared to the effective water saturation determined by the dual water model performed on a neighboring well with modern logs . The total porosity and effective porosity determined from old logs and modern logs , were also compared . The formation chosen for this study was the Pennsylvanian (Virgilian ) Hoover Sand located in the panhandle of Oklahoma . The Hoover Sand was chosen based on its lithology , structure , well spacing , and the availabílity of a mixture of modern logs and old logs . The Hoover Sand in the Mocane -Laverne field was discovered in 1955 and has been a productive gas sand for almost 40 years . The formatíon consísts of laminated silt and sand deposited via density flows or turbidity currents onto a shallow , broad shelf area that covers approximately 98 ,560 acres . Because the Hoover Sand is bounded above and below by shale and pinches out horízontally into a shale , the trapping mechanism is a structural /stratigraphic combination . Thirty -two pairs of wells were evaluated in 4 foot intervals . Based on the comparisons between old log shaly sand methods and a "comprehensive" modern log shaly sand model (dual water ) , the uncorrected Archie equation (automatic compensation method ) resulted in water saturations that closely approximated the results obtained from modern logs . These values can then be used to determine a more accurate value for recoverable hydrocarbons . The use of the volume of clay corrected Archie method determined effective water saturations which were consistently more optlmistic than the other methods . The ratio water saturation returned the poorest correlation to the effective water saturation as determined from the dual water method used on a modern log .
URI: http : / /hdl .handle .net /2346 /12380
Date: 1995-05

Citation

Grim, Gerald Kenneth Computer-aided statistical analysis of the correlation between shaly sand analysis using old logs (pre-porosity): and modern logs : Pennsylvanian Hoover sand, Harper and Beaver counties, Oklahoma. Master's thesis, Texas Tech University. Available electronically from http : / /hdl .handle .net /2346 /12380 .

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