Georgina Basin Overview
Baraka's primary focus is the Georgina Basin
The Georgina Basin is a region of proven oil potential. Previous test wells drilled in the Georgina Basin have demonstrated oil shows and good quality source rocks, seals and reservoirs with target horizons ranging from 300 metres to 1000 metres.
It is a sparsely explored green field area which makes up part of the Centralian Superbasin, comprising the Amadeus, Georgina and Wiso sub-basins. During the Cambrian era, the Central Australian plate was on the subtropical waters on the fringes of the Rodinia supercontinent.
In this period, the organic-rich Arthur Creek black marine shales were deposited, particularly in the Dulcie and Toko troughs. Similar Cambrian marine shales are the source rocks in the extremely productive fields of East Siberia, Oman and the Tarim Basin in China. Above the Arthur Creek shales are the Thorntonia and Hagen Formations, both of which have been shown by previous drilling to show good reservoir properties and anhydrite seals.
The Georgina Basin therefore has all the attributes of a productive hydrocarbon province. This prospectivity has been enhanced by oil shows in a number of wells, and gas flows to surface in the Ethabuka-1 and the Discovery Creek water bore.
EXPLORATION HISTORY
Early exploration in the Georgina Basin consisted of stratigraphic holes or wells whose location was based on surface geological mapping. This included a number of wells drilled in the 1950s and 1960s, culminating in the Ethabuka-1 well in Queensland which recovered gas at 6,000 m3 per day (240,000 cfd) on test.
Subsequent drilling in the early 1980s was restricted to the stratigraphic drilling program undertaken by the Northern territory Geological Survey (“NTGS”). In the late 1980’s to early 1990s, Pacific Oil and Gas explored areas in the Dulcie and Toko Synclines with the first serious attempt to acquire a regional seismic grid and drill wells based on its results. Some 750 kilometres seismic data were collected and 10 wells were drilled. The seismic lines were 5 to 30 kilometres apart, however most wells, recorded poor to moderate oil shows.
SOURCE AND MATURATION
The main source rock interval in the Georgina Basin is the hot shale at the base of the Arthur Creek Formation of Middle Cambrian age. This interval can be mapped throughout the southern Georgina Basin (Ambrose et al 2001). The richest section of this shale is up to 25 metres thick, and has been described as “finely laminated to massive anoxic, carbonaceous, partly dolomitic shale” (Ambrose, 2006). Total organic carbon levels measured in the shale commonly range from 0.5% to 10% and up to 16% (Ambrose et al 2001).
The Hagan Member of the Arrinthrunga Formation recorded good oil shows in a number of wells which are believed to have been sourced from intraformational shales (Randall-1, Phillip-2, Elkedra-7 and Todd-1) (Ambrose 2001). TOC's have been measured at up to 4% in Macintyre-1 and Baldwin-1 and up to 7.9% in Elkedra-1.
There are a number of seals in the sequence, some regional in nature and others semi-regional or local.
The best regional seal is the basal portion of the Arthur Creek Formation described in the previous section. Much of the lower part of the same formation also has good sealing qualities.
There are a number of semi-regional seals within the upper section of the Arthur Creek Formation as demonstrated on the log of the MacIntyre-1 well. They appear to represent a number of upward shoaling sequences with the seal at the base, followed by gradually coarser grained sequences, culminating in fair to good reservoir facies at the top of the sequence. There are also a number of anhydrite sequences both within the Arthur Creek Formation and the overlying Hagen Member of the Arrinthrunga Formation. These would represent excellent seals, although their lateral extent is not well known.
RESERVOIR
The main reservoir target recognised to date is the Thorntonia Limestone of Middle Cambrian age. This unit flowed 500 barrels of water per day (BWPD) from a test in Ross-1 and a drill stem test (DST) in MacIntyre-1 produced 338 metres of water in the pipe. There is not enough information from wells to enable reservoir trends to be established, however it appears that improved permeabilities occur in areas where the Thorntonia limestone is fractured and vuggy and this probably relates at least in part to effects of karstification (Ambrose et al, 2001).
The upper portion of the Arthur Creek Formation is dominated by a number of shoaling sequences with reservoir quality rock at the top. In MacIntyre-1, the top of one of these sequences had measured permeabilities of 1.2 Darcies. Dolomitic sandstone seen in Owen-2 exhibited core porosities of 10-15% and permeabilities of 15-95 mD.
The Hagen Member of the Arrinthrunga Formation contains dolostones which exhibit vuggy dissolution porosity in some wells. A flow of 300 BWPD was achieved from Randall-1 at this level.
There are also reservoirs in the Kelly Creek Formation of Early Ordovician age. This formation flowed gas at about 240,000 cfd from Ethabuka-1. Much further work on this aspect is required before reservoir trends could be confidently predicted.
FARMIN AND ASSIGNMENT AGREEMENT TERMS
Baraka has signed farm-in agreements covering both EP 127 and EP 128 with NT Oil. Under the agreements, Baraka can earn a 75% interest in each block by funding all costs of exploration on the permits in accordance with the terms of grant up to completion of a well. Funding thereafter will be in accordance with each party’s respective interests in each permit.
Baraka is the operator of the joint venture over each of EP 127 and EP 128, subject to the consent of the Minister. Baraka may withdraw from the joint venture at any time by notice in writing.
PLANNED EXPLORATION PROGRAM
The existing seismic over EP 127 and EP 128 shot by a previous operator has now been digitally reprocessed.
Baraka is now in the process of arranging an initial acquisition of geochemical and gravity data for each of EP 127 and EP 128. This data will then be used to better locate new seismic acquisition within the blocks.