--> Evaluation of Low-Resistivity pay with Oil Base Mud Imager and NMP techniques, Example from Deep Water Nigeria, by Kamal Osman, Parvez Butt, and Souvick Saha; #90037 (2005)

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Evaluation of Low-Resistivity pay with Oil Base Mud Imager and NMP techniques, Example from Deep Water Nigeria

Kamal Osman, Parvez Butt, and Souvick Saha
Chevron Texaco
Schlumberger

Exploration wells in deep water Niger Delta have encountered series of oil bearing sand in lower & middle Miocene reservoirs. Sands appear to be deposited in channels and over bank fills and fans.

Hydrocarbons bearing over bank deposits are thinly laminated turbidite sequences yielding the largest reserves and are the highest contributors to deepwater production in the world. These sands are practically invisible to all conventional logging tools except high resolution tools such as HMI and OBMI due to the very thin vertical nature of the individual sand layers. However, the Sand quality of over bank deposits are practically of similar quality to that of the massive turbidite channel fills. What makes the over bank deposits or thinly laminated turbidite sequences so attractive and productive is that they frequently have huge aerial extent.

A recent well drilled in deepwater Nigeria has encountered such finely bedded sediments. Standard resolution logs did not allow accurate quantification of the petrophysical parameters. High gamma ray, low resistivity and separation on density-neutron suggested a fine grained and poorly sorted rock. However, high resolution NMR log displayed that formation had significant free fluid volume and permeability. Thin bed identification with oil base mud image (OBMI) showed that formation is a fining upward turbidite sequence with bed thickness going down to few inches.

Standard resolution logs response was sharpened using high resolution image log and this thinly bedded reservoir was fully characterized and refined net-pay count indicated a reservoir thickness of more then sixty feet.