Applied Research Work from Density Log Responses in Thinly Laminated Sediments Is Leading to a Better Understanding of Reservoir and Well Performance in West Africa

Edward J. Stockhausen
Drilling and Completion, ChevronEnergy Technology Company, The Woodlands, TX

The application of joint industry and university research focused on quantifying density log responses from high angle and horizontal wells drilled in thinly laminated sediments is providing the basis for improved understanding of Cretaceous shallow marine reservoirs in the Congo Basin, West Africa. These reservoirs are dominated by a series of transgressive-regressive cycles, recognizable and correlateable on a field-wide scale of several kilometers. Temporal variations in silt and carbonate deposition during these cycles cause vertical segregation of the reservoirs to a fine scale.

Research has shown that in vertical wells it is the source to detector spacing that drives the vertical resolution of the density log response. In horizontal wells, it is the depth of investigation that drives the log response. There is approximately a 3 to 1 ratio difference in vertical resolution between the density log response in horizontal and vertical wells. The density log data from horizontal wells is able to fully define beds on the order of 6 inches (15.2 Cm). Vertical wells drilled through these reservoirs show lazy log responses that tended to smooth out and average adjacent non permeable low porosity beds with higher permeable high porosity beds. The horizontal wells, on the other hand show very dynamic log responses. Deviated wells show improved bed resolution with increased hole angle.

Additional parts of the research effort look at using enhanced vertical resolution processing of density logs, using data derived primarily from the short-spaced detector, and on quantifying the effects of relative dip angles and bed thickness on LWD density images acquired in high-angle and horizontal wells.

Both of these studies have lead to an improved understanding of our producer/injector wells’ performance and are leading to more effective field development strategies.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery