Producibility of Deepwater Reservoirs in the North Sea and Gulf of Mexico
Published:December 01, 2000
A goal of field development is to place high rate, productive wells in sweet spots or areas where pay is thickest. However, thick pay does not necessarily mean high flow rates. Producibility (normalized flow rate) of a reservoir should be used in conjunction with pay thickness to locate sweet spots. This study uses data from over 159 completions in deep-water clastic reservoirs from 11 Gulf of Mexico and North Sea fields. The data have been analyzed to determine which geological and engineering factors might contribute to a higher normalized flow rate or Specific Productivity Index (SPI), here defined as BOPD/psi of drawdown/per foot perforated. SPI has been compared to tubing size, permeability, viscosity, architectural element, net-to-gross, and log shape. The highest SPI s in the North Sea are from reservoirs having net/gross >90%, although 60% is a critical cut-off in the Gulf of Mexico. There is a good correlation between average reservoir permeability and maximum SPI in unconsolidated Gulf of Mexico reservoirs. In addition, good correlation is observed between average permeability and minimum SPI in more consolidated North Sea reservoirs. The highest SPI s also are found in completions with 4.5 tubing. A simple classification of log shape has been used in the study to determine the range of uncertainty of SPI for each reservoir type. Reservoirs having blocky log shapes have the highest SPI s, and reservoirs having funnel or bell log shapes have lower but similar ranges of uncertainty in SPI s. Hilterman (1998) has shown that acoustic impedance varies with log shape in the Gulf of Mexico, indicating that some aspects of producibility may be mappable from seismic data.