--> ABSTRACT: Use of Core and Cross-Plot Analysis for Rock-Type Definition over a Mature Nigeria Fields Delivers Substantial Increase in STOIIP and Reserves

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Use of Core and Cross-Plot Analysis for Rock-Type Definition over a Mature Nigeria Fields Delivers Substantial Increase in STOIIP and Reserves

Huerlimann, Alex 1; Ernster, Greg A.2
(1) Nigeria Business Unit, OML-126, Addax Petroleum, Geneva, Switzerland. (2) MHA Petroleum Consultants LLC, Denver, CO.

The Niger Delta reservoirs are characterised by the common presence of thin bedded deposits and the abundance of potassic feldspars, zircon, micas and other radioactive minerals. Whilst this combination makes petrophysical evaluations challenging when using a standard logs suite (GR, DENS-NEUT, RES), it also provides opportunities for improved rock-typing and facies/property population in 3D reservoir models.

Better than expected and sustained production from multiple wells in the Okwori and Nda fields (OML-126 Nigeria) led to the review of well-established assumptions. Using old core data, a new simple rock-type scheme was designed. This scheme had to be;

a) Sufficiently refined to split the different poro-perm relationships (FZI) that are observed from plug analysis, and,

b) Applicable to non-cored intervals or wells using a standard logs suite.

Using cross-plots of various combinations of logs derived from the standard logs suite and applying the Thomas Stieber thin beds evaluation technique, alternative facies and continuous rock property logs were generated for input into the 3D reservoir models. In the 3D reservoir modelling phase, the zonation, layering, facies and property modelling were performed deterministically using methodologies that preserve the geological and physical trends observed in the data.

The resulting reservoir model was successfully history-matched and accurately forecasted the reservoir and producers behaviour for over three years. This work was a key component to the booking of an additional 40MMstb of 2P reserves for the asset.

 

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.