Appraisal and Development of the Murta Reservoir Using Hydraulic Fracture Stimulation

Carnell, S.J. (Santos Ltd.)

OnePetro 

Abstract

This paper describes the evolution and field application of fracture stimulation techniques applied to the Murta reservoir in South Australia, where unique conditions govern fracture stimulation design. The use of a minimum viscosity pad fluid has been shown to provide effective fracture pad fluid has been shown to provide effective fracture height growth constraint and provide for efficient fracture length propagation, resulting in increased productivity index improvement.

Fracture stimulation has proved to be a viable technique to allow economic exploitation of this resource, while allowing its continual appraisal.

Introduction

The Murta member is an oil bearing sandstone, widespread throughout the Eromanga basin in South Australia and Queensland. The Murta member cannot be adequately described by conventional petrophysical analysis due to its thinly laminated nature. The evaluation of the poorer quality wells requires production performance. Completing the well risks capital which may yield an inadequate return. Fracture stimulation techniques have been applied to the reservoir and are shown to result in up to a 6 fold increase in productivity index.

Fracture stimulation is the only viable method of improving productivity as the Murta member is a low permeability productivity as the Murta member is a low permeability formation with a reasonably large gross oil column of 100-125 ft [30-38 m], even though the net pay to gross height ratio is relatively low. This paper shows the evolution of fracture stimulation techniques applied to Murta wells. The optimisation of fracture treatment design is complicated by the inability to accurately quantity key reservoir parameters such as reservoir permeability. Optimisation of parameters such as reservoir permeability. Optimisation of fracture stimulation treatment design has relied mainly on field experience. Obstacles to the optimisation of the design, such as unconstrained height growth, have been identified and the techniques applied to control these potential problems have resulted in increased productivity potential problems have resulted in increased productivity index gains. Treatments use a small volume of thin pad fluid and place about 50 000 lbm [22 600 kg] of proppant in the formation. This technique ensures that the proppant is transported to the limits of fracture extension to efficiently prop the created fracture length while minimising height growth.

The paper is organised in the following way. Firstly there is a statement of the problem. The reservoir characteristics and the difficulties of petrophysical evaluation are described. A historical overview is given. followed by presentation of the data collected and the methods used. presentation of the data collected and the methods used. Interpretation of the data and application of new ideas including case studies follows.

STATEMENT OF THE PROBLEM

Conventional evaluation of the Murta reservoir indicates that many wells may not yield adequate return on investment if completed. Uncertainty exists as to the volume of original oil in place and the potential recovery factor due to the difficulties of log evaluation and ambiguities of open hole DST results. The Murta member is known to be oil bearing with reasonably large gross oil column. Therefore the key problem is to achieve adequate oil productivity from the well. Successful stimulation would encourage the development of the extensive Murta resource.

Fracture stimulation appears to be a promising technique to achieve significant productivity improvement. To maximise the economic benefits of fracture stimulation, the reservoir deliverability, fracture mechanics, fracturing fluid nature and proppant transport mechanism must be considered.

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