FRACTURE NETWORK ANALYSIS OF META-SEDIMENTARY ROCK IN EAST COAST TERENGGANU; AN ANALOGUE TO FRACTURED BASEMENT IN MALAY BASIN

Oil and gas exploration have now moved to the basement rocks. Basement are rocks
with low matrix porosity and permeability, therefore fractures provide a path for
hydrocarbon flow and storage. The research aims to establish an outcrop that could
possibly be an analogue to the fractured basement of the Malay Basin and to apply
seismic attributes to enhance the image of seismic data obtained from a chosen field
in the Malay Basin, thereby reducing the uncertainty of interpretation. Kuala Abang
outcrop in Terengganu has been chosen to be an example of exposed basement in the
Malay Basin. The metasediments in Kuala Abang are 21m wide and 8m tall, with
beds dipping at 340°/60°. Fracture measurements were recorded and analyzed using
the rose diagram. Results shows the Shear1Left is positioned at 340° whereas the
Shear1Right is orientated at 270°. Therefore the mazimum stress σ
1
is located at
NNW-SSE while the minimum stress σ
3
at ENE-WSW. 3D seismic data of Puteri
Field in the Malay Basin was utilized for fracture characterization of the reservoir
basement. Seismic interpretation was first done, followed by the interpretation of
fractures using seismic attributes as image enhancer. The attributes used are
structural smoothing, variance and curvature attributes. Seismic interpretation shows
one major fault and four seismic units whereby the lithology is generally sandstone
and siltstone in a fluvial environment. The basement are not metasediment due to a
presence of feldspar. Fractures are beyond the resolution of seismic data, therefore
the approach to this problem is by analyzing the azimuth of the major fault. The
stress orientation of the fault is relatable to the stress direction of fractures, as both
are within the same stress field. The fault analysis results in a NNW-SSE maximum
stress direction. Although it is correlatable to the stress measurements of Kuala
Abang, the difficulties faced are the difference in lithology, age and scale of the
outcrop and Puteri Field. Nonetheless, the seismic attributes are excellent methods to
assist in the study of fractured basement.