Abstract

The Murta Member within the Murteree Horst area consists of a very thin, high permeability sand (HPS) within predominantly low permeability, thinly laminated, carbonaceous siltstones collectively referred to as the low permeability region (LPR). This HPS has a thickness of about 1 foot and a large lateral extent of about 10,000 acres.

The HPS and LPR together have been postulated to contain an OOIP of up to 74 million bbls in the Murteree Horst area, however the LPR also acts as a capillary seal to the underlying Mckinlay reservoir. The production behaviour of the Murta reservoirs has remained enigmatic since their discovery.

Under production the HPS initially shows a rapid pressure drop indicative of oil expansion drive in a closed or almost closed system. However eventually a water drive develops which behaves as though there is a very large or possibly infinite aquifer.

Although most of the postulated 74 MMB of oil was thought to be in the LPR it appeared none of the LPR oil was being produced. It was not clear whether this oil could be mobilised. This investigation suggests that oil contained within the LPR is largely immobile and may even be representative of oil migration conduits only.

1. (a) Introduction

The Murta Member oil pools occur in four fields Alwyn, Jena, Ulandi and Limestone Creek/Biala on the Murteree Horst in the Nappacoongee-Murteree Block about 50km south of Moomba (Figure 1) in central Australia.

The Murteree Horst is part of the Nappacoongee Murteree Trend, a northeast-southwest aligned high which separates the Cooper Basin Nappamerri and Tennaperra Troughs to the northwest and southeast respectively. Cooper Basin sediments are absent on the horst with the Eromanga Basin sequence occurring directly on pre-Permian basement.

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