Comparison Between Well Production Performance Tests and Reservoir Simulation Predictions Based on Log Data Including Multicomponent Induction Measurements in a Low-Resistivity, Electrically Anisotropic, Laminated Shaly Sand Gas Reservoir
Authors: Damodaran Raj M. , Fanini Otto , Colley Nick , Mezzatesta Alberto 
Published: December 2007

Well production performance tests were performed for a low resistivity, electrically anisotropic, laminated shaly sand gas reservoir. This paper compares such production test results with reservoir well simulation predictions based on log data, which include multicomponent induction measurements of formation resistivity anisotropy. Previously accurate gas well production performance evaluation of low contrast, low resistivity laminated shaly gas sand zones often required the performance of a production well test. A reliable prediction of well production performance through reservoir simulation based on log data has been a challenge. Such a predictive ability is required for optimum completion and field development decisions. The reliability of these simulation predictions has been compromised by the petrophysical limitations of gas-in-place evaluations for thinly bedded, laminated reservoirs. This situation arises whenever traditional scalar saturation equations are applied to conventional resistivity instrumentation data. Traditional laminar shaly sand saturation equations are based on a horizontal parallel conductivity model dominated by the high shale conductivities in vertical wells. These equations typically result in significant underestimates and uncertainties in gas-in-place evaluation in laminated zones. Such equations must be fine-tuned from one well to the next. Formations containing laminated sand-shale sequences and laminated sands of different porosity and/or grain size exhibit macroscopic electrical anisotropy. This formation property provides us with additional information about laminated hydrocarbon-bearing sands. New multicomponent induction logging hardware makes it possible to directly measure the vertical, Rv, and horizontal, Rh, resistivities and the resulting resistivity anisotropy (in the so-called transversely anisotropic media) for vertical, deviated, and horizontal wells. The use of both vertical and horizontal resistivities in petrophysical evaluation provides improved reservoir characterization, leading to better prediction of well production performance using reservoir simulation techniques.

A standard suite of logs, including multicomponent induction data, was recorded in a well interval with thick and laminated sands within a gas reservoir. Petrophysical analysis of these laminated zones utilizing resistivity anisotropy has resulted in an approximately 20% increase of estimated gas-in-place over estimation methodologies previously applied to similar gas reservoirs1. Production test flow rates were compared with reservoir simulation predictions. Two interpretation results were considered in generating the simulation model, one incorporating the resistivity anisotropy tensor estimated from multicomponent induction tool measurements, and the other where a conventional, single resistivity interpretation was used. The 3DEX resistivity anisotropy data interpretation has lead to a more accurate shaly sand reservoir characterization of hydrocarbon volume-in-place which, when used with standard reservoir simulation techniques, resulted in better production flow rate prediction results in comparison with actual production well test results.