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Enhanced Production Profiling of Gas Wells Using a New Method To Model the Geothermal Temperature Gradient

M.D. Johnson, SPE, ProTechnics Division of Core Laboratories; M.G. Briceño, Oxy USA Inc.; A.C. Hutchings, SPE, and D.R. George, SPE, ProTechnics Division of Core Laboratories

Quantitative gas and water production profiling is very useful in completion and production performance evaluation. Production profile analysis that incorporates mass rate modeling of the flowing temperature has dramatically increased confidence in profiling results. Accurate mass rate modeling requires an accurate estimate of the geothermal temperature gradient. The conventional technique of estimating a linear geothermal gradient is not reasonable in producing regions with long completion intervals and complex lithologies. This paper will detail a new method of simulating the geothermal temperature gradient and advances in quantitative production profiling.

A multi-well study was conducted in the Piceance Basin in Northwestern Colorado because of the unique effect of lithology on the geothermal gradient. Coal, sand and shale sequences which impact the geothermal gradient must be taken into consideration. The study includes open and cased hole log data to define lithology and shut-in temperature data to characterize the geothermal gradient. An analytical simulator was developed to model the geothermal gradient. Research in rock, mineral and fluid thermal conductivities is utilized to qualify the field data and analytical model.

Results demonstrate that higher shale volume and coal beds increase the geothermal gradient above clean sand layer gradients. Measured geothermal gradients across coal bearing intervals are an order of magnitude higher than clean sand intervals. Geothermal gradients from the simulator were used as constraints in production profile analyses. The analyses will illustrate the identification and quantification of zonal gas and water production, even when some of the wells were flowing under adverse conditions of low gas rate, severe slug flow and high water production.

Enhanced production profiling has enabled the operator to enhance their reservoir characterization, completion strategies and production performance of future offset wells. Other applications for the technology include: 1) production profiling in similar regions with complex lithology and non-linear geothermal gradient, and 2) distributed temperature sensing used for continuous temperature and production profile monitoring.