Well Log Analysis of the Kupe South Field, Taranaki Basin, New Zealand
Authors: Pang J. , Collen John 
Published: December 2007

This study was intended to produce a synthetic index derived from statistical analyses of well data to indicate the reservoir qualities of various drilled intervals, and ultimately to link log response information to seismic traces for 2D/3D reservoir modelling and reserve estimations. Statistics and multivariate statistics were applied to wireline logs from four wells in the Kupe South Field, Taranaki Basin, New Zealand combined with traditional well log interpretation. The results indicates:synthetic wireline indices show good correlation with core and sidewall core data;four sand zones (A-D) of the Paleocene Farewell Formation identified in some previous studies cannot be statistically recognised;closely similar index features were shown in Kupe South-2 and Kupe South-3, while the other wells had different index values; andthere exits a possibility of using synthetic wirelog index correlated with seismic traces for further 2D and 3D reservoir modelling and reserve estimation.

This paper was presented by J. Pang at the 1996 SPE Asia Pacific Oil and Gas Conference held in Adelaide, Australia, 28–31 October 1996.

Introduction

Kupe South Field is a gas condensate/oil field located in the South Taranaki Graben Zone of offshore Taranaki Basin, New Zealand. It was discovered in 1986 with the drilling of Kupe South-1 and four additional wells have since been drilled. The field is one of the most prospective fields for production within the country.

The reservoir for the Kupe South Field is the Paleocene Farewell Formation and the sediments are of fluvial origin that were deposited on an alluvial plain in meandering to braided stream environments with minor tidal component. The sandstones of the reservoir are dominantly medium to coarse grained with subordinate mudstones and clay, and unconformably overlain by Oligocene marine shale. Reservoir quality and distribution are key factors for reserve estimation and field development plans.

Alluvial deposits characteristics show rapid changes of lithologies laterally and vertically. This makes direct comparison and correlation of units from the limited available data extremely difficult and sometimes even impossible. Use of statistical techniques may provide an effective method for predicting reservoir quality and distribution.

This study was intended to examine the use of wireline logs to determine the reservoir qualities of logged intervals by means of statistic and multivariate statistic techniques, and if possible, to examine the possibility of linking wireline log information to seismic data for 2D/3D reservoir modelling. Log responses (gamma ray, sonic, density and resistivity) of four wells (Table. 1) in the Kupe South Field were chosen in this study to examine statistical feature of different Paleocene intervals.

Method of Study

Data Preparation

Based on the core, sidewall core and well completion reports, four reservoir groups were defined. Group one is good quality sandstone and group four is non-reservoir shale and clay. The reservoir quality of group two is similar to group one but contains more shaly sands or shale/clay thin layers. Group three includes shaly sandstone or siltstone with poor reservoir quality. Sixty-six drilling intervals were selected as samples after the exclusion of some intervals with extreme log responses, and each sample was designated to a different reservoir group (Table. 2).

Five attributes of wireline records (GR, DT, RHOB, LLD and LLS) were collected for each interval. Statistical parameters, such as the mean, were used as sample values. This is because that individual wireline record does not represent the interval log response and variation of the log record is common within an interval for the same lithology section; P. 535