Abstract

Hydraulic Fracturing of the Rewan and Showgrounds formations in the Namarah-Parknook fields of the Red Cap Block was performed in an attempt to establish volume rates of gas production from a large volume of potential gas reserves in the Surat Basin. These formations had not been previously fractured in Australia.

A geological and engineering study was made of the subject area before proceeding with the fracture treatments. This quantified the available gas-in-place and allowed selection of the best candidate wells for stimulation. Several cores were available from veils in the area and selected lengths were sent to the service company stimulation laboratory in the U.S.A. for detailed analysis to determine the best parametric values to employ in the computer-assisted design of the proposed fracturing treatments.

Four stimulation treatments were carried out on three wells in the area, with varying results. Similar sized fracture treatments were performed, but many changes were wade to the pre-frac completions as well as the treatments themselves as they progressed. The changes were made to optimize designs, based on experience gained, and reduce costs while still achieving well-contained deep fractures in the pay zones. The first treated well, Narmrah No. 2 was extensively production tested before stimulation, to allow an accurate comparison with post-frac production rates.

Selection of the proppant was based on the crushing forces on the proppant as well as on the ultimate reservoir pressure at depletion of the formations proposed for fracturing. Pumping rates were determined by the thickness of the pay zone to be fractured and the estimated degree of containment which could be expected from the natural barriers to fracture propagation contained in surrounding formations. Size of the treatment was based on the natural permeability-thickness of the reservoir rock and drainage area, as well as the need to achieve commercial gas flow rates from successful wells. Extensive use of computerized on-site monitoring technology and equipment was employed.

Introduction

Geological and engineering studies were performed to determine the gas development potential of the Showgrounds and Rewan Formations in the Red Cap Block of the Surat Basin in Queensland, Australia. The purpose of the studies was to determined if the geological and reservoir characteristics of the subject formations would support a well stimulation program aimed at developing enough gas deliverability to supply anticipated pipeline delivery contracts.

GEOLOGICAL BACKGROUND

The geographical area that is discussed in this paper is in the Surat Basin of Queensland, paper is in the Surat Basin of Queensland, Australia, Figure 1.

The wells which are the subject of this paper are located approximately 60 in southeast of the Kincora gas field and 35 km northeast of the Silver Springs gas field in the Red Cap block of ATP 145P, Figure 2.

Prior to the commencement of this program, eight Prior to the commencement of this program, eight wells were drilled in the subject area between 1963 and 1987. The presence of gas and gas liquids was demonstrated within both the Early Triassic Rewan Formation and the Mid Triassic Showgrounds Sandstone.

The Showgrounds comprises a gross sandstone interval up to 60 feet (18.3 m) thick and is sealed by the overlying Snake Creek Mudstone.

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