Abstract

Up to now, an indirect generalized method to predict pore pressure under subpressured conditions has not been reported in the literature. In this work, an innovative procedure is presented for estimation of pore pressure and optimization of wells drilled in the abnormally subpressured Deep Basin of the Western Canada Sedimentary Basin (WCSB). The procedure starts with detailed evaluation of 5 wells drilled in a township that covers the study area. Pore Pressure was calculated from Sonic Logs and the Modified D Exponent using Eaton’s Method (Eaton, 1975), which proved to be the most effective approach for abnormal subpressured conditions over a variety of methods tested (Contreras et al., 2011). The optimization procedure was carried out using the Apparent Rock Strength Log (ARSL), which is an effective indicator of formation-drillability and very sensitive to the pore pressure. Next, optimization of individual sections in each well was carried out to determine the optimum types of bits and operational parameters for the lowest cost of drilling.

An artificial intelligence function was implemented to set up the optimum combination of parameters in such a way that the rate of penetration (ROP) (m/h) was increased after a number of simulation runs while controlling the bit wear. Especial attention was focused on tight gas reservoirs for selection of the most suitable parameters that increase the quality of drill cuttings. It was concluded that the rollercone bit IADC 547 with at least 0.73 horsepower in the bit per square inch provides the best quality of cuttings for the Nikanassin Group. This is of paramount importance for increasing accuracy in the quantitative determination of permeability and porosity from cuttings particularly in those tight gas reservoirs where the amount of cores is very limited.

It is concluded that wells in the Deep Basin of the WCSB can be drilled efficiently with 7 bit runs while keeping the cuttings quality, bit wear and well stability at a significantly high average ROP of 13 m/h. Another conclusion is that the normal trend methods from sonic logs are the most effective approach when dealing with an abnormally subpressured basin.

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