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Integrating Core Data and Wireline Data for Formation Evaluation and Characterization of Shale Gas Reservoirs

Quirein, John¹; Buller, Dan²; Witkowsky, Jim¹; Truax, Jerome¹
¹Halliburton, Houston, TX.
²Halliburton, Shreveport, LA.

The development and production of shale gas reservoirs involves the drilling, interpretation, and stimulation of many vertical and horizontal wells, all with varying amounts of core and wireline data. This paper presents several Haynesville shale interpretation workflows for scenarios with varying combinations of core and wireline/LWD data, and emphasizes answers obtained from wireline/LWD data. It demonstrates how wireline and core data can be combined to provide total organic carbon (TOC), total porosity, gas filled porosity, mineralogy, grain density, and mechanical properties, including anisotropy and an indicator of where to fracture.

Generally, TOC is measured in weight percent, and is associated with the organic compound, kerogen. The TOC of 10 wt% is associated with an approximate kerogen volume of 20 vol%. Unfortunately, the neutron and density logs sense kerogen as an additional porosity. Consequently, with an actual kerogen volume of 20 vol%, and without accounting for kerogen in the interpretation, the traditional neutron-density cross plot porosity will be high by 20 vol%. Any quantitative log interpretation predicting porosity and gas saturation must properly predict the amount of kerogen. This paper presents an approach for predicting kerogen volume through calibration to core data to enable an initial porosity prediction. A Haynesville example is used to show that, when geochemical logs and core XRD are available, mineralogy and grain density can be predicted from wireline logs, enabling a more accurate prediction of porosity gas saturation, and a mineralogy based shale brittleness index.

Economic recovery of gas from shale reservoirs requires optimal multistage hydraulic stimulation in horizontal wells. This type of formation evaluation requires careful correlation and calibration to petrophysical measurements and interpretations obtained in either vertical pilot holes or direct offset wells. An example of a horizontal well using LWD sonic and pulsed neutron cased hole data is presented. Fracture stages for the logged horizontal well were evaluated vs. the log data. Generally, lower normalized treating pressures per fracture stage are noted where lower clay volumes exhibit less transverse anisotropy and a higher calculated shale brittleness index. Radioactive tracer and production log data also confirm lower amounts of gas production from zones that are apparently fractured, but are more ductile and clay-rich.

 

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012