Abstract: Practical Application of NMR Logging in Carbonate Reservoirs

LOGAN, DALE, JACK HORKOWITZ, ROB LARONGA and DAVE CROMWELL

Nuclear Magnetic Resonance (NMR) data acquisition and interpretation in carbonate reservoirs is much more challenging than in sandstones, where it is a well established technology. Heterogeneous porosity distribution, wide ranges of pore sizes, low surface relaxivity, varying T1/T2 ratios and a wide variety of complex textures combine to complicate the picture in carbonates considerably. The successful practical application of NMR in these reservoirs requires the development of acquisition and interpretation methods specifically suited to the task.

In carbonate reservoirs dominated by intercrystalline or intergranular porosity, NMR can deliver accurate estimates of porosity, permeability, bound fluid volume and residual oil saturation. However, in vuggy, heterogeneous carbonates more complex interpretation models, based on the integration of whole core and log data, are required for reliable answers. The new models handle both homogeneous reservoirs dominated by primary porosity and heterogeneous reservoirs dominated by vuggy porosity. NMR answer products, based on these new models, are validated through production results and by comparison to other logging measurements. Six applications of NMR interpretation are demonstrated using logs from six different formations (San Andres, Grayburg, Clearfork, Glorietta, Tubb and Drinkard).

AAPG Search and Discovery Article #90936©1998 AAPG Southwest Section Meeting, Wichita Falls, Texas