The Cakerawala, Bulan, Bumi and Suriya gas fields in the MTJDA, northern Malay Basin form a major new development hub for the region, with an estimated total GIIP of 9 Tcf. These large assets are very early in their field life with only 300 Bcf of production from Cakerawala field so far. There has however already been significant (USD 1-2 billion) development investment. There is significant subsurface uncertainty due to geological complexities and a detailed, integrated data gathering and interpretation effort was necessary to better understand the asset. The impact of the study is a deeper understanding of the fields' potential and an insight into how to optimally develop these complex resources. This study covers many aspects of the reservoir characterisation process with examples from the North Malay Basin and has application in other complex fields.The subsurface geology comprises a thick interval (more than 7,000 ft) of stacked, clastic, fine grained, often clay-rich reservoirs, deposited in an upper delta plain to shallow marine environment. Significant challenges exist in developing these fields due to the large development area, thick zones of interest, large number of reservoirs and challenging depositional setting. There are also petrophysical issues to overcome, including fine scale reservoir heterogeneity, complex mineralogy and the presence of low-resistivity low-contrast (LRLC) pay.An improved understanding of the factors controlling reservoir quality was achieved by adopting a holistic and multidisciplinary approach. This included the integration of stratigraphic, depositional and lithofacies information along with mineralogical and pore system data.Key lessons learnt include the importance of acquiring good subsurface rock data and the construction of robust databases. The novel application of Lorenz plots and Winland R35 analysis calibrated to test data provided key rock quality and heterogeneity information for inclusion in geo-engineering models. The definition of LRLC reservoirs proved to be an important milestone which led to the development of a water saturation cut-off for gas-productive reservoirs. These findings are now being incorporated into our forward development strategies in Block A-18 and other assets. Success was achieved on a highly complex problem due to the application of an integrated, multi-disciplinary work flow.

SPE Members ABSTRACT: To exploit a reservoir, the geological model must accurately define the depositional environment and the effects of diagenesis on the pore network. Current methods for establishing the geological model of a field usually require subjective, qualitative interpretation of geological and petrophysical data. A method - Numerical Geology - has been developed that greatly reduces the subjectivity in geological modelling efforts. This method also allows geological attributes to be quantified and predicted. Numerical Geology involves the integration of petrophysical, petrological and geological data with wireline log responses. The geology of "Hydraulic or Flow Units" intervals with similar hydraulic characteristics is described using conventional sedimentology, petrography and core analysis data. These data are translated into a matrix of geological indices classified according to hydraulic unit profile of the section. Hydraulic units are then predicted for uncored sections based on their unique log signatures that are obtained from cored sections. By combining predicted hydraulic units profile with the matrix of geological indices for each flow unit, profiles of geological attribute~ are derived. The prediction reliability of hydraulic units is calculated based on the uniqueness of log signatures for each flow unit. Therefore, the confidence level for geological predictions can be assigned to estimated profiles of geological attributes. This eliminates much of the subjectivity from future geological interpretations and predictions. INTRODUCTION: Hydrocarbon reservoirs are heterogeneous and nonuniform. However, these nonuniform and heterogeneous systems are made of multiple homogeneous groups - Hydraulic Units. The basis for this grouping is similarity in flow characteristics which are affected by–grain size–sorting–texture (packing, angularity, grain shape, homogeneity) P. 507^

A recent geological study, integrating sedimentological core-derived descriptions with ichnofacies, high resolution biostratigraphy and wireline log data, establishes the lateral continuity of reservoir sandstones in the Laminaria Formation. By defining a hierarchy of bedding surfaces and correlating this hierarchy with major correlation surfaces, and lateral and vertical facies patterns, it was possible to identify genetically related sediment packages between 12 wells in the study area.The Laminaria Formation is interpreted to have been deposited on a tide and storm-influenced marine shelf, and was strongly influenced by fluctuations in sea level. The formation consists of a series of progradational parasequences, each dominated by good quality, fine- to medium-grained sandstone. These sandstones are believed to have formed as subaqueous dunes or sand banks, exhibiting blanket-like geometry over much of the area. Several sandstones are capped by thin, intraclast-rich layers that mark transgressive surfaces of erosion. These surfaces can be traced across the study area and, therefore, act as important correlative markers.Evidence of gradual transgression, which ultimately led to the drowning of the system, is seen near the top of the formation. Clay content increases upward, while grain size and bedding thickness generally decrease. However, several thin, laterally extensive, medium- to coarse-grained sandstones exist, improving reservoir potential in this part of the formation.The results of this study are being used to estimate reserves and assess reservoir performance, and will serve as a basis for future geological and petrophysical modelling work.

Woodside Energy Ltd. and their Joint Venture Partners recently contracted Core Laboratories to carry out a sedimentological study on the Middle to Late Jurassic succession in the AC / P8 permit, Timor Sea. The aim of the study was to provide insight into the areal distribution of reservoir facies through examination of the reservoir's vertical stacking patterns, expressed in core from key wells in the region. Particular emphasis was placed on thinly bedded sands at the top of the Laminaria Formation, which appeared to exhibit poor reservoir potential based on wireline log analysis. The study included data from a total of twelve wells, nine with core, all with complete suites of wireline log data. Conventional description of sedimentary bedforms from core was integrated with ichno fabrics, routine core analysis, wireline log data and high-resolution biostratigraphy to provide a detailed understanding of major correlation surfaces and vertical stacking patterns. This hierarchy of bedding surfaces and associated genetic packages of sediment were then utilised to assess the continuity of sands across the reservoir. subsequent dynamic simulation modeling based on this work has resulted in a significant increase in estimates of ultimate recovery factor from existing completions. The study will serve as a platform for future geological and petrophysical modeling of the Laminaria Formation. Introduction This paper reviews the methodology and results of a recently performed multi-disciplinary geological study of the Laminaria Formation. The principal aim of the study was to determine both the vertical and areal distribution of facies within the formation, and thus gain a better understanding of reservoir architecture and sandstone continuity, and thus improve estimates of recovery factor. In order to achieve this aim, the study required in-depth integration of hydraulic unitisation, sedimentology, trace fossil analysis, core analysis, core goniometry, log evaluation, and biostratigraphy. In addition, particular emphasis was placed on the occurrence and continuity of thin, high permeability sandstones in the uppermost ten to fifteen metres of the formation. Data Base Data from twelve wells was used in the study (see Figure 1). Analytical work was based on detailed sedimentological core descriptions, integrated with trace fossil interpretations, wireline log profiles, routine core analysis data and biostratigraphy. Of the twelve wells used for the study, nine were cored (Table 1). The top of the Laminaria Formation was cored in only three wells. Geological and Sequence Stratigraphic Background The Laminaria Formation is located in permit AC / P8 of the Australian Timor Sea. The formation consists of a succession of Mid to Late Jurassic sandstones intercalated with minor silty claystones and heterolithics. The sandstones are generally of good quality, and are mostly moderately to well indurated. The base of the Laminaria Formation exhibits a series of facies dislocations indicative of a regressive sequence boundary. Above this boundary, the formation can be subdivided vertically into a series of eight intervals or cycles similar to fourth-order parasequences1. These cycles, labeled A to H in order of deposition, are mostly regressive in nature, with sandstones gradually coarsening and thickening upwards, before being capped by flooding surfaces overlain by either heterolithic beds, or argillaceous, bioturbated sandstones. Most of the best quality reservoir sandstones therefore occupy the upper portions of each cycle. Geological and Sequence Stratigraphic Background The Laminaria Formation is located in permit AC / P8 of the Australian Timor Sea. The formation consists of a succession of Mid to Late Jurassic sandstones intercalated with minor silty claystones and heterolithics. The sandstones are generally of good quality, and are mostly moderately to well indurated. The base of the Laminaria Formation exhibits a series of facies dislocations indicative of a regressive sequence boundary. Above this boundary, the formation can be subdivided vertically into a series of eight intervals or cycles similar to fourth-order parasequences1. These cycles, labeled A to H in order of deposition, are mostly regressive in nature, with sandstones gradually coarsening and thickening upwards, before being capped by flooding surfaces overlain by either heterolithic beds, or argillaceous, bioturbated sandstones. Most of the best quality reservoir sandstones therefore occupy the upper portions of each cycle.

All rocks are sensitive to changes in stress. In the Dulang Field sandstones, stress sensitivity is affected by differences in texture, mineralogy and clay type. In this study, we present the results of stress-induced damage. The findings of this study can be used to make more realistic prediction of future production rates via numerical simulators, thus providing a tool for improving field management and company profits. This is important not only for the Dulang Field, but also for any field where changes in stress are likely to affect production due to heterogeneous compaction ofthe reservoir.