Pacific Section AAPG Convention

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The Merits Of Mud Logging: Using Gas Ratio Analysis To Salvage A Well With Poor Quality Open Hole Logs


Formation evaluation has evolved to rely on technologically advanced well logging tools and techniques. This focus on new technology, however, has caused some analysts to underutilize data available from more basic tools such as mud logs. The mud log provides a variety of data including lithology, oil/gas shows, interval thickness, relative permeability and porosity, reservoir fluid types, and gas ratios. These data are the product of direct measurement and observation of the cuttings and entrained hydrocarbons from the formation as the well is drilled, providing a near real-time record of the well's progress. This case study presents a recent example of the mud log's utility from a well drilled in the Ventura Avenue Field. High salinity drilling mud and high borehole angle relative to the formation created difficult logging conditions for open-hole logs. The mud log was the basis for a successful well completion with initial production rates of 225 BOPD and 140 MCFPD of gas. If the mud log had not been included in the drilling package for this well, which is located down dip and on the flank of the previously known productive area, abandonment might have been the end result.