INVESTIGATORS

  •  

Geotrack International Pty Ltd (Melbourne, Vic),

Keiraville Konsultants Pty Ltd (Keiraville, Nsw), and

PetroConsult Pty Ltd (Melbourne, Vic)

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January 1999

Table of Contents

Constraining the timing, distribution and origin of hydrocarbons in the Papuan Basin

Introduction and objectives of this study

Historical perspective on the oil prospectivity of PNG

Source rock maturity, reservoir and the petroleum system

More about the importance and objectives of Basin Modelling

Work program and deliverables

Time frame for this study

Selected references

Background

Geotrack International Pty Ltd

Keiraville Konsultants Pty Ltd

PetroConsult Pty Ltd (www.petroconsult.com.au)

More questions?

 

Constraining the timing, distribution and origin
of hydrocarbons in the Papuan Basin

Introduction and objectives of this study

This proposed study program is designed to answer specific exploration questions that have long confronted explorationists working the Papuan Basin, PNG. Fundamental exploration issues in the Fold Belt and Foreland of PNG remain unresolved. These include:

Agreement on a unified tectono-stratigraphic framework for the Papuan Basin encompassing both Foreland and Fold Belt regions.

The relative effects (structural and thermal) of major tectonic events in the region.

Establishment of accurate thermal histories across the basin.

Evaluation of generation and charge history including local variances.

Determination of the type (oil versus gas) and relative volumes of hydrocarbons generated.

Effect of uplift, erosion and fresh water influx on hydrocarbon accumulations.

Recent drilling results and the extension of seismic data in both the Foreland and Fold Belt make this an appropriate time to re-evaluate the Papuan Basin in terms of the these issues. The timing is also very opportune given that in the near future, companies will have to make major decisions with respect to the future direction of oil and gas exploration in PNG.

Answers to these questions necessarily require a multi-disciplinary approach involving a strong, integrated group of people who have a long working history in the region. Such is the motivation by which Geotrack International, Keiraville Konsultants and PetroConsult have united to target the following key issues in the Papuan Basin.

1. MATURATION, GENERATION AND FLUID MOVEMENT: THE NEED FOR 2-D BASIN MODELLING: The use of multi-dimensional basin modelling software such as PetroMod, is increasingly regarded as an important component of exploration programs. While one-dimensional (1-D) models have been used significantly in the past in PNG, they suffer from severe inherent limitations, particularly in their failure to account for lateral effects of temperature and pressure. They are also unable to account for fluid movement important in both hydrocarbon maturation and migration. 1-D results can therefore be sometimes very misleading.

While many workers assume that the hydrocarbons in the PNG Fold Belt were generated and emplaced prior to Late Tertiary thrusting and formation of the Fold Belt, other evidence suggests synchronous or even later generation and emplacement. Constrained answers to such questions concerning the timing of source rock maturation, hydrocarbon generation, oil versus gas and fluid migration questions are best answered by detailed structural modeling involving sophisticated 2-D (or even 3-D) models tied into and constrained by existing well control.

2. IMPROVED RESOLUTION OF MULTIPLE EVENTS: Two major, late phases (Late Cretaceous/ Tertiary and latest Tertiary) of structuring affected the Papuan Basin. Although both events are considered important to the origin of hydrocarbons in the Papuan Basin, the significance of each is open to debate. While the Foreland and Fold Belt regions were both affected, the relative and absolute magnitude of each event varied across the regions. Understanding and measuring this variation is vital to modelling of hydrocarbon generation and entrapment. Using the latest AFTA technology, we will measure the timing and determine the magnitude of these events across the Fold Belt and Foreland. This will help constrain their effect on hydrocarbon generation and migration allowing better basin models to be built and tested.

3. RIGOROUS ASSESSMENT OF MATURITY: As detailed in the discussion presented in the following Section, there are numerous apparent anomalies in the variation in maturity across the region. These perceived problems are a consequence of multiple factors such as:

the poor quality of some maturity data,

unrecognised suppression and

complexities in the thermal history of the region.

A strategy to distinguish these factors and identify the way for future exploration strategies in the region is an important aim of this study.

The study objectives rely on the combined expertise and experience of Keiraville Konsultants (experts in source rock characteristics and maturity), Geotrack International (experts in measured thermal history), and PetroConsult (experts in 2-D basin modelling). The project is designed to provide constraints on the problems outlined above, and only when taken together, will they allow a better understanding of petroleum systems in the Papuan Basin. Such a project, bringing together world experts in their own field to answer fundamental unresolved questions in PNG, has not been attempted previously.

In the following Section, we provide some background on the exploration history in the Fold Belt and Foreland of PNG. More than an introduction, this background provides an important basis in understanding why fundamental exploration questions remain unresolved and uncertainty continues. The summary includes a discussion of the elements of timing, structuring, source rock maturity, and migration, thus demonstrating the need for an integrated approach in constraining the problems outlined above. In addition, reference is made to some of the more recent developments that make a reappraisal of these factors timely.

Historical perspective on the oil prospectivity of PNG

The oil and natural gas industries in Papua New Guinea have been characterised by a long period of exploration without any commercial discoveries followed by the discovery of some small gas fields in the ‘50s and then some gas and gas/condensate fields in the ‘60s. The first discovery of a significant oil accumulation at Kutubu occurred in 1986.

Subsequent development saw Kutubu oil coming on-stream on 28 October 1991 with the first export shipment taking place on 27 June 1992. Commercial production from Kutubu had been preceded by minor gas and condensate production from Hides. Hides gas is used to generate power for the nearby Porgera gold mine and the condensate is partially refined giving a diesel fraction that is sold within the Papua New Guinea Highlands area.

The Kutubu discoveries were followed by the Gobe discoveries. At this stage, oil was only known from the Fold Belt confined to a row of structures running SW from Mananda to Gobe through the Agogo and Hedinia/Iagifu fields. Until the Paua structure was drilled in 1995/96, the structures lying to the NE of this belt were known only to contain gas with some condensate. It appears that some companies had effectively written off the terrain to the NE of the Mananda - Hedinia - Gobe trend in terms of the existence of oil.

At Paua, a discovery of oil was made in the footwall of the structure. This discovery was followed up by the drilling of the Moran structure where the thrust sheet is present in a hanging wall setting. Within Moran, a thick oil column is present, and unlike the Kutubu fields, no gas cap is known. However, as at the Gobe field, cross -faults have resulted in significant compartmentalisation. The Moran-4x well showed the presence of oil within a different compartment at a different pressure to those found in the initial discoveries. The oil in Moran-4x also has a different API gravity to the oils in Moran-1x and Moran-2x. More detailed information on oil chemistry differences is not available at this stage. The pressure regime within Moran is very different from that in the nearby Kutubu fields. Remarkably, pressures are close to twice those in the Kutubu fields and formation pressures are about 1000 psi higher than the pressure of the solution gas.

Two of the Moran wells have been placed on extended well test through a connection to the Agogo Production Facility with a short pipeline having a capacity of about 25,000 barrels per day. These tests are likely to continue until the field is fully developed. This may take some time due both to the complexity of the structure and to the presence of oil within different permits: PDL2 (Moran-1X and 2X) and PPL 138, and is also likely to be present within parts of PPL 161. Extensive appraisal and unitization of the fields will be required.

Since 1986, exploration has largely focussed on the Fold Belt, but some wells have been drilled within the Foreland Basin to the SW and minor amounts of exploration has taken place within other basins such as the North New Guinea Basin.

The oil discoveries have been restricted to the Fold Belt and most of the gas discovered is also located within structures in the Fold Belt. Smaller amounts of gas have been discovered within the Foreland, including some discoveries in the offshore area within the Gulf of Papua.

Early drilling within the Fold Belt was performed without the availability of useable seismic. Targets were delineated largely from field mapping followed by construction of structural sections. Because of this difficult and imperfect method, a large number of wells did not penetrate their intended targets. Two of the better known are Gobe-1X which drilled too far off-structure intersecting the reservoir below the oil/water contact, and Karius-1X which did not intersect reservoir section in the hanging wall target. Lucky accidents have also occurred as with the Paua discovery.

Recently however, resulting from developments in seismic recording techniques in PNG, swath seismic lines have been recorded down the valleys and dip lines directly across structures have become available, dramatically improving the targeting of drilling.

Source rock maturity, reservoir and the petroleum system

About rank

Within humic coals, vitrinite reflectance has proved a reliable indicator of rank. Coal scientists had generally used a number of measures to assess rank, and therefore within the coal industry vitrinite reflectance was used to assess rank - as opposed to being considered a measure of rank. This lead to its use by the petroleum industry but it has commonly been used as a measure of maturation rather than as a property requiring interpretation.

Cook (in Hutton and Cook, 1980) of Keiraville Konsultants drew attention to the probability that the vitrinite scales constructed for marine sequences differ significantly from those based on humic coals.

This has lead to a major emphasis on the importance of what is termed vitrinite suppression. Such an approach is also over simplistic.

A number of factors can complicate the use of vitrinite reflectance, and these include:

Vitrinite type.

Incorrect identification of other tissue types.

Vitrinite dominated by unusual tissue types.

Sedimentary, and more specifically, organic facies.

Interference effects of other macerals, especially alginite.

Impregnation with bitumen or oil.

Reworking of vitrinite so that the vitrinite reflectance is determined by a previous thermal history.

Oxidation of vitrinite fragments, probably partial conversion to low-reflecting inertinite.

Sediments deposited under marine conditions dominate the sequence in the Papuan Basin, but the majority of the organic matter is derived from higher plants. Sedimentary facies is generally an important qualifier that should be applied to vitrinite reflectance data from well sections in the Papuan Basin. Many of the plant fragments that are preserved as vitrinite or vitrinite-like tissue include suberinite or similar cortical tissues. Suberinite has much lower reflectances compared with vitrinite. These two factors mean that much of the published data understates the real level of maturation.

Careful attention to measurement can largely eliminate the low-reflecting cortical tissues. An approximate correction can be applied to allow for organic facies.

FAMM (fluorescence alteration of multiple macerals) techniques have been applied to some samples from PNG. From the data available to the investigators, the FAMM data are almost always higher than conventional vitrinite reflectance data, in some cases markedly so. The FAMM estimates of vitrinite reflectance effectively form an upper boundary to maturation levels, and uncorrected vitrinite reflectance data a lower boundary.

It is proposed that a small number of FAMM analyses will be undertaken on samples assessed from conventional vitrinite reflectance studies to be of critical importance in evaluating thermal histories.

Other properties that are sensitive to maturation levels will also be used where appropriate.

It is considered that the proposed study will yield high quality and consistent maturation data that can be fully integrated with the AFTA results.

More about source rocks and reservoirs

The main hydrocarbon reserves found within the Fold Belt have been within the Toro Sandstone. The Toro lies below the shale dominated Ieru Formation and above the Imburu Formation. The Imburu Formation is also dominated by shales but also contains a number of important reservoir sandstones, such as the Digimu, Hedinia and Iagifu. The Toro Sandstone is the main reservoir in the Kutubu fields but is water wet at Gobe and there the Iagifu is the main reservoir unit.

The Alene Sandstone is present in some areas above the Toro Sandstone and the Koi-Iange Sandstone is present below the Imburu Formation.

In the Fold belt, vitrinite reflectance values near the reservoir sections have commonly been reported as being in the range 0.45% to 0.55%, however, proprietary data suggests that values in the range 0.55% to 0.65% are more representative. The organic matter within the Ieru and Imburu Formations contains a marine element but is generally dominated by organic matter of higher plant origin. Taking the facies into account, maturation levels within the reservoir sections are most accurately assessed as about 0.6% to 0.7%.

Lateral and vertical variations in maturation levels within the reservoir section are not well understood. The general level of maturation at Gobe appears to be similar to that in the Kutubu fields even though the section at Iagifu is close to one km deeper than that at Gobe. However, the intersections at Gobe tend to be slightly deeper stratigraphically compared with the Kutubu data. Vertical vitrinite reflectance gradients appear to be low with typical data sets showing increases of less than 0.1% over intervals of about 600 m within the Imburu.

Northeast of the Kutubu - Gobe trend within the higher pressure regimes found in some of the thrust sheets lying further from the front of the Fold Belt, maturation levels appear to be similar to those in the Kutubu fields at similar depths.

In the northwest of the PNG Fold-Belt lower levels of maturation at similar depths to those found in the Mananda - Kutubu - Gobe trend occur, although a great distance away. Thus, on the basis of limited data, it is difficult to know if the lower levels of maturation there are due to lower cover or may also represent an element of lateral variation. Even so, the data indicate that the section at the western end of the Fold Belt has a similar assemblage of organic matter and probably a similar thermal history to the sections in the main producing areas to the SE.

Many of the samples examined contain small amounts of reworked coals. Some of these have high rank and appear to be derived from earlier sequences, but a high proportion shows vitrinite reflectances close to those of the host rocks. The shales adjacent to the Toro and Iagifu Sandstones appear to be marine in origin but were deposited close to the shoreline. Additionally, proximity to a shoreline appears to be persistent through a relatively thick sequence.

Within some overpressured zones, high levels of oil saturation also occur. In these cases, the liptinite appears to have been solubilised rather than to have enhanced fluorescence. There may be a case for making a part of the study an integration of known pressure data with the organic petrological characteristics. Although the early oil discoveries within the Fold Belt were largely within the lower pressure zones, most of the potential for additional discoveries appears to be within the highly pressured parts of the system. A better understanding of the effects of pressure on measures for maturation would be an important potential spin-off from any study.

More about migration and physical processes in fluid transport

Conventional vitrinite reflectance data generally can be used to support a local origin for the oil in the Fold Belt with gas generated either much deeper within the section or to the NE where higher levels of maturation are known. Further evidence for the possible local sourcing of oil may be determined from the organic matter assemblages within selected formations.

If it can be established that locally sampled horizons are suitable sources for oil currently in place, then models involving long-distance migration may require significant modification.

Within the Fold Belt, early assumptions appear to have been that the GOR was at its lowest in the Mananda - Kutubu - Gobe trend and that the amount of oil decreased in the thrust sheets NE of this trend. It is clear that the terrain NE of the Fold Belt is of much higher rank. Here units such as the Chime Shale are commonly anthracitic or meta-anthracitic in rank. In contrast, studies on the thrust sheets NE of Hides show no presence of high rank Mesozoic sections in outcrop.

One view on the origin of the hydrocarbons is that they have been generated within sections of similar age to the reservoir units, but of higher maturity lying to the NE of their present location. This view has the GOR increasing to the NE and assumed that, with the exception of the more distal belt containing the early oil discoveries, that oil had been flushed by gas. The discovery of oil at the Moran field would seem to discount this view. In addition, relatively long distance migration implies the presence of carrier beds. The presumed loss of the Toro reservoir to the NE of the producing fields suggests the absence of effective carriers for hydrocarbon migration.

Most authors appear to assume that the oils were emplaced prior to the development of the thrust sheets, possibly as early as the late Cretaceous. Kreiger et al (1996, p. 407) suggest that oil emplacement came before the establishment of the present hydrodynamic flows and it is reasonable to suppose that these post-date the thrusting.

In the Foreland, a high proportion of wells have been drilled within shallower parts of the section with many not well controlled by seismic. The North Paibuna well, a deep test of the Foreland Basin appears to have intersected some liquid hydrocarbons but the reservoir was poorly developed. This well indicates that oil may be present within some parts of the section in the Foreland.

The geological history in the Foreland is much less complex than within the Fold Belt. However, a high proportion of Foreland tests may have been too isolated from effective source areas to receive charge.

Another important physical process possibly affecting the distribution of hydrocarbons in the Papuan Basin is gas expansion. The effects of gas expansion and gas/oil ratios due to uplift (or removal of overburden) on an incipient oil trap cannot be ignored in modelling the possible retention of oil legs in structures. Uplift and removal of overburden leads to phase changes of the reservoired hydrocarbons. Changes in the gas expansion factor results in an expansion of the gas cap, a decrease in the gas/oil ratio, associated 'degassing' of the oil leg leading to expansion of the gas cap and possible loss of the oil leg.

Other features of the basin provide some insight to the hydrodynamics of the Papuan Basin. The Toro Formation is a major regional aquifer.

An analysis of the formation water systems in the Papuan Basin was made by measuring hydraulic potential and formation water salinity from wells (Kotaka, 1996). Regional water flow was interpreted as fresh meteoric water entering the Toro Sandstone outcrops around the Muller Anticline and the Lavani Valley northwest of the Fold Belt. In the mountainous area of the northwestern part of the Fold Belt, the hydraulic potential of formation water is 2,200-2,300 m. In the central area of the Fold Belt, the hydraulic potentials are much lower at ~200-400 m while in Foreland areas they are below 100 m.

This active hydrodynamic regime has almost certainly had, and still has an important effect on oil and gas distribution and thermal modelling. This is particularly so across Highland areas of the Fold Belt where potentiometric gradients and flow rates are significantly higher than in the Foreland. High flow rates together with relative differences in oil density and water salinity have the potential to tilt oil/water contacts (gas/water contacts are little affected) leading to spill of an oil column or complete flushing. This leads to questions about the possible presence of tilted oil columns down-flank of structures and the potential risk posed by hydrodynamic flushing of oil.

Little isotopic data supporting higher maturity of gaseous hydrocarbons has been published. Waples and Wulff (Proc 3rd PNG Petroleum Convention 1996, p417) have published data classifying the oils from reservoirs and seeps on the basis of their chemistry. They distinguished five main families and a number of sub-families within this overall grouping. Families 1 and 2 are stated to indicate a Tertiary origin but the occurrences of these generally lie well to the east of the main producing areas. In the area where Family 1 is indicated, mature Tertiary is known from the base of the Pale Scarp. In the Southern Highlands, some of the Tertiary samples examined at Keiraville Konsultants from the Highland have proved to be highly immature and are not considered likely sources. Most of the commercial oils appear to have been derived from Lower Cretaceous and Upper Jurassic sources on the basis of their chemistry. This would be consistent with an origin from the shales close to the reservoir horizons, but would also fit long distance migration.

The discovery of oil first at Paua and then at Moran has shown that the early models with GOR increasing to the NE are not correct. The presence of these oils and different pressure regimes at the Moran, Makas and Beaver wells may have implications for the timing of emplacement of the hydrocarbons.

Some of the recent unsuccessful wells within the Fold Belt appear to have lacked viable reservoir as the Toro appears to lens out to the E and NE of Kutubu. Within the Kutubu belt, meteoric waters represent an additional complication. The absence of oil from the frontal belt of structures could be due to flushing by meteoric waters.

The source potential of the sequences drilled within the Foreland and Fold Belt provinces will be assessed largely on the basis of organic petrology data, but other data types such as Rock-Eval and pyrolysis will be used where appropriate. It is generally not possible to study the source characteristics of sequences in possible source areas under the long distance migration scenario. However, we do have data on the characteristics of some of the possible source sequences that could be invoked for long distance migration, except at much higher current levels of maturation.

The general issue of source rock potential and oil to source correlation falls outside the present studies but we are aware of the significance of these issues as providing valuable input to the studies that we are proposing and some of the data generated by the study should add to information about source rock potential.

 

 


More about the importance and objectives of Basin Modelling

More recently, improved seismic acquisition has led to significant improvements in structural definition across both the Fold Belt and Foreland regions. In addition, side-track drilling of structures in the Fold Belt provides a much better understanding of the structural geology and better control on structural modelling. Two-dimensional modelling is also a vital aspect in evaluating petroleum systems.

Two general models have been proposed to explain the generation and migration of hydrocarbons in the Papuan Fold Belt:

Model 1 (after Hill, 1991; Earnshaw et al., 1993; Buchanan and Warburton, 1996) invokes an early, main phase of hydrocarbon generation in the Late Cretaceous and Early Tertiary. Maturation of Late Jurassic and Early Cretaceous source rocks is thought to occur through depositional loading of Late Cretaceous - Early Tertiary sediments and a possible increase in heat flow generally associated with opening of the Coral Sea (the Coral Sea 'rift' event). Migrating hydrocarbons were retained in pre-existing traps (e.g. tilted fault blocks) associated with rifting and half-graben development. Generation was curtailed in many areas with the onset of thermally driven regional uplift and erosion also associated with Coral Sea 'rifting'. Oil was retained in these traps until subsequent Plio-Pleistocene compressional structuring in the Fold Belt caused the early traps to be re-mobilized and in some cases spill with remigration into more recently formed traps. In the Papuan Foreland Basin (which did not experience substantial structuring), the hydrocarbons remained largely in the existing trapping situation with gas an increasing generative product accompanying further subsidence and sedimentation.

Model 2 (after Buck and Stone, 1991) calls for much later maturation of source rocks with the predominance of generation taking place in the Pliocene to Pleistocene. In the Foreland Basin, maturation was caused by depositional loading of a thick Plio-Pleistocene section. In the Fold Belt, maturation and consequent hydrocarbon generation was confined to source rocks in synclinal areas and footwall locations of thrust sheets. In these areas, source rocks are buried to varying degrees by the combined overburden of pre-existing sediments and thrust imbricates giving oil and gas products of variable maturities. Generation and migration were largely synchronous with trap formation and many kitchen areas are possibly generative present day. The model implies multiple kitchen areas, each with its own, unique maturation, generation and expulsion properties. In those areas of the Fold Belt that have been uplifted and severely eroded, maturities are relict and reflect the previous maximum burial depth. Even areas that have not been significantly unroofed may not be presently generative due to overall cooling associated with structuring over at least the last 4 Ma.

Model 1 has significant problems in trying to explain the deposition and subsequent stripping of up to 2,000 m of Late Cretaceous to Early Tertiary section across the Papuan Basin. The occurrence of a major regional tectonic event involving significant structuring at this time is not supported by seismic data across the Foreland Basin. The wrench-related tectonism that characterizes the Coral Sea 'rift' event, likely influenced structural development across the entire the Papuan Basin (both present day Foreland and Fold Belt regions). Rather than regionally near-uniform uplift across the basin, the combination of transpression and transtension imposed by the wrenching was responsible for significant but much more localised uplift and subsidence. The consequent structuring is often very similar to rift-related tectonics on dip seismic sections (and has been interpreted as such in the past).

Supporting, although not unequivocal evidence for Model 2 is provided by fluid inclusion and sandstone cementation studies. These suggest that petroleum emplacement occurred during the latest Tertiary and possibly through to Recent in some areas, synchronous or post-dating thrusting and trap formation on the Fold Belt.

The main issue for basin modelling in the Papuan Basin, is to ascertain the timing, magnitude and effect (local and regional) of the two late phases of structuring and hence the validity or otherwise of the two generative models. Solutions to these problems and a consequent enhanced understanding of the petroleum systems that operated in the Papuan Basin are best tackled through the construction of 2-D (or 3-D) basin models. As discussed previously, multi-dimensional models have significant advantages over 1-D models.

Petroleum generation, expulsion and migration are continuously calculated along identified flow paths in 2-D models allowing much better understanding of lateral variability. In addition, the simulation of fluid flow (petroleum and water - not possible in 1-D models), enables the effects of convective heat transport through the sequence to be determined as well as providing a model of petroleum migration and accumulation history through geologic time. Assessment of the additional affects of hydrodynamics and local heating from igneous intrusions is also possible. Simulation results can also be directly compared to fluid inclusion and cementation studies. Other important physical processes must also be included for any basin model to be useful in exploration.

An integrated basin model also needs to accurately describe the pressure regime of sedimentary basins because pressure gradients control the direction and intensity of fluid flow according to Darcy's Law. The difference of the pore pressures of the fluid is called the capillary pressure. It is used to derive the petroleum driving forces of oil to water or gas to water. The petroleum moves from high pore pressure regions to low pore pressure regions. Only modelling of pore pressure in 2-D or 3-D can accurately account for the effects of overpressuring, kerogen conversion on pore pressure, and fluid flow due to lateral compaction.

Intrusions can have dramatic effects on palaeo- temperatures and all thermally controlled values [e.g. calibration parameters]. Although the duration of such events is relatively short, the extremely high temperatures can trigger rapid chemical reactions in the near environment. Such intrusions will be modelled and are known to be significant in the Fold Belt area of Papua New Guinea. Both model output and experimental data from samples will be evaluated to establish the nature and extent of these effects. Contact alteration results in highly distinctive optical properties and existing samples can be examined for evidence of contact alteration. We will also try to target some sections where maturation levels are high and attempt to determine if these result from regional or contact coalification / maturation.

The decay of radioactive elements leads to significant heat generation within the rock body. Such elements may be concentrated in intrusive bodies.

Deterministic basin modelling necessarily offers a definite value for a particular parameter in time and space as a result, and not a range of values or value with error margins. However, sensitivity analyses can define margins of error and are an integral part of the basin modelling procedure, for example during the calibration.

A sensitivity analysis with the simulation program is an efficient and quick method of defining error margins for any particular parameter and range of input values.

Work program and deliverables

In addition to the collection of a range of selected data sets (AFTA, VR, FAMM, fluid inclusions, Rock-Eval), the study will require a number of seismic transects across the Foreland and Fold Belt. Lines adequate for this purpose may be available in the published literature. However, based on early indications, it is hoped that contributions will be made by the participating companies. Collaboration between the principal investigators and company personnel is an important aspect of this study. There are mutual benefits to such interaction. Maximising information exchange will ensure that:

The constructed models are based on a full account of all available information (with proper quality control criteria).

Companies will have an opportunity to better familiarise themselves with the methods used in this study (2D basin modelling, AFTA, source rock analysis) and the quality of the data.

The extent of the success of this project will somewhat depend on the active collaboration and participation from interested companies.

Quantitative models will initially focus on the Foreland where the relatively less complicated structures together with the availability of a more extensive seismic grid, will allow development of meaningful 2-D models. The structural complexity and poor seismic resolution through the upper portion of the Fold Belt sequences introduce much uncertainty and hence, construction of realistic physical models for the charge history here are more difficult but not impossible. Modelling in the Foreland relies on fewer assumptions and in this study, will be heavily "data-driven" with strong emphasis on high data quality (AFTA, fluid inclusion, VR, source rock, FAMM, structure, stratigraphy). All data will be rigorously inspected before the data constraints are allowed to be introduced to the basin models. In contrast, while modelling of the Fold Belt will build from information gained from the Foreland, it will necessarily be less rigorous. Objectives here will be targeted more generally at understanding concepts (effects of pressure, long-distance migration, source rock, diagenetic effects).

Identification of the seismic lines for this study is currently underway; however, final selection of the precise lines for this study will await further discussion with interested companies.

In addition to the wells included in Geotrack’s previous work in the area (Geotrack Report #232), other key wells under consideration for this study are:

Nomad, Cecelia, N. Paibuna, Moran, Beaver, Menga, Gobe, Makas, Ketu Kiunga, Elevala, Koko, and Kimu (of course, sample availability and well information may be subject to appropriate authority).

It is proposed that the study will proceed in four phases with interim reports produced at the end of the first three phases and made available to companies for discussion, with a final report produced at the end of the fourth phase.

Phase 1

Compile and re-evaluate existing AFTA, VR, FAMM, fluid inclusion and Rock-Eval data sets.

Acquire new AFTA and VR data at an additional 2-3 key Foreland wells.

Determine the structural and stratigraphic history at wells using existing geological, basin modelling and seismic data sets.

Phase 2

Perform comprehensive basin modelling at key wells using well and seismic data, incorporating new and re-evaluated maturity data.

Acquire additional maturity data if required and model.

Determine whether new maturity data and basin modelling is consistent with ideas on structural and stratigraphic history at wells.

Modify structural and stratigraphic history if required.

Phase 3

Perform 2-D basin modelling in Foreland on 4-8 regional transects incorporating knowledge on wells gained from Phase 3.

Phase 4

Extend 2-D basin modelling to Fold Belt using knowledge gained from Phases 1 through 3 (additional AFTA and VR analyses may be required).

The final results will be provided to subscribing companies in a detailed report. Issues highlighted in the margins of this report will be addressed directly in the study using our integrated approach. In addition, the following discussion sections will be provided in the final report:

(1) Re-evaluation of previous AFTA data using compositional control (i.e., chlorine measurements and advanced algorithms) and interpretation of new data by Geotrack International,

(2) Basin modelling – results of 2-D modelling by Petroconsult,

Source rock maturation, analysis and discussion by Keiraville Konsultants,

Oral presentations to participating companies to report the main modelling results and exploration implications, if desirable.

Time frame for this study

Commitments are sought immediately and work is anticipated to begin on March 1st 1999. With sufficient pre-commitments, the project will commence in two parallel stages: 1) selection of appropriate regional seismic lines with industry participation, and 2) selection of samples for source rock and maturity analysis (including, VR, FAMM, AFTA, Rock-Eval and fluid inclusions). A final report will be delivered by the end of November 1999, if pre-commitments are met by March 1st 1999, as anticipated.

Selected references

Geotrack International references

Geotrack International Report #232, 1991, The Papuan Basin: Regional thermal and maturation analysis incorporating AFTA of 27 wells, A non-exclusive report, 319 pp.

Green P.F., Duddy I.R., Bray R.J. Green P.F., 1997, Variation in thermal history styles around the Irish Sea and adjacent areas: Implications for hydrocarbon occurrence and tectonic evolution. In: Hardman M. Trueblood, S and Meadows, N. (eds) The Irish Sea and Adjacent Basins. Geological Society of London Special Publication.

Green P.F., Duddy I.R. and Bray R.J. 1995. Applications of thermal history reconstruction in inverted basins. In: Buchanan J.G. and Buchanan, P.G (eds) Basin Inversion. Geological Society of London Special Publication No. 83.

Duddy I.R., Green P.F., Bray R.J. and Hegarty, K.A. 1994, Recognition of the thermal effects of fluid flow in sedimentarty basins. In Geofluids: Origin, Migration and Evolution of Fluids in Sedimentary Basins, Geol Soc Special Publication No 78.

Green P.F., Duddy I.R., Bray R.J. 1993. Early Tertiary heating in Northwest England: fluids or burial (or both?). In Geofluids '93: Contributions to an International Conference on fluid evolution, migration and interaction in rocks. Parnell J., Ruffell A.H. and Moles N.R. (eds) pp 119-123.

Duddy, I.R., Green, P.F., Hegarty, K.A. and Bray, R., 1991, Reconstruction of thermal history in basin modelling using Apatite Fission Track Analysis: what is really possible. Proceedings of the First Offshore Australia Conference (Melbourne). III-49-III-61.

Arne, D.C., Green, P.F., and Duddy, I.R., 1990, Thermochronologic constraints on the timing of Mississippi Valley-type ore formation from apatite fission track analysis. Nucl. Tracks Radiat. Meas. 17, 319-323.

Kamp, P.J.J.and Green, P.F., 1990, Thermal and tectonic history of selected Taranaki Basin (New Zealand) wells assessed by apatite fission track analysis. AAPG Bulletin. 74, 1404-1419.

Green, P.F., Duddy, I.R., Laslett, G.M., Hegarty, K.A., Gleadow, A.J.W. and Lovering, J.F., 1989b, Thermal annealing of fission tracks in apatite 4. Quantitative modelling techniques and extension to geological timescales. Chemical Geology (Isotope Geoscience Section), 79, 155-182

Kamp, P.J.J., Green, P.F. and White, S.J., 1989, Fission track analysis reveals character of collisional tectonics in New Zealand. Tectonics, 8, 169-185.

Green P.F. and Duddy, I.R., 1988. Some comments on paleotemperature determination from apatite fission track analysis. J. Petrol. Geol., 12, 111-114.

Duddy, I.R., Green, P.F. and Laslett G.M., 1988, Thermal annealing of fission tracks in apatite 3. Variable temperature behaviour. Chemical Geology (Isotope Geoscience Section), 73, 25-38.

Green P.F., 1985b, A comparison of zeta calibration baselines in zircon, sphene and apatate. Chem. Geol. (Isot. Geosci. Sect) 58, 1-22.

Keiraville Konsultant references

Cook, A.C.; 1987: Source potential and maturation of hydrocarbon source rocks in Indonesian sedimentary basins. Sixth Regional Congress on Geology, Mineral and Hydrocarbon Resources of Southeast Asia - Geosea VI, paper 16, pp. 1-42.

Cook, A.C.; 1991: Oil and gas prospects. Appendix B IN PAPUA NEW GUINEA Economic Situation and Outlook International Development Issues No. 16, Australian International Development Assistance Bureau, 83-109.

Cook, A.C.; 1992: Environmental aspects of the mining and petroleum industries in Papua New Guinea. Appendix B IN PAPUA NEW GUINEA Economic Situation and Outlook. International Development Issues No. 27, Australian International Development Assistance Bureau, 84-103.

Cook, A.C.; 1992: Oil and gas prospects. Appendix C IN PAPUA NEW GUINEA Economic Situation and Outlook. International Development Issues No. 27, Australian International Development Assistance Bureau, 104-133.

Cook, A. C., 1994. Oil and gas in Papua New Guinea. Appendix D IN, Papua New Guinea - The Role of Government in Economic Development, Australian Development Assistance Bureau, International Development Issues No 33, 211-244.

Cook, A. C., 1996. Oil and gas in Papua New Guinea. Appendix D IN, The Economy of Papua New Guinea 1996 Report, AusAID, Australian Agency for International Development, International Development Issues No 46, 173-202.

Cook, A.C., Davis, A., David, P., Depers, A.M., 1997. ICCP Accreditation system for petrographic analyses. Proceedings of the New Zealand Coal Conference, Wellington, October 1997.

Powell, T.G., Boreham, C.J., Smyth, M., Russel, N. and Cook, A.C.; 1991: Petroleum source rock assessment in non-marine sequences: pyrolysis and petrographic analysis of Australian coals and carbonaceous shales. Organic Geochemistry, 17, 3, 375-94.

Project references

Allen, P.A. and Allen, J.R., 1990: Basin analysis: principals and applications. Blackwell Scientific Publications, Oxford, 451 pp.

Bracken, B.R. and Popek, J.P., 1995: Depositional interpretation and reservoir quality assessment, Juha-2X, Juha-3X and P’nyang-2X cores, Papua New Guinea.Reservoir Management Report for Chevron Overseas Petroleum Inc, March 1995.

Buchanan, P.G. and Warburton, J., 1996: The influence of pre-existing basin architecture in the development of the Papuan Fold and Thrust Belt: implications for petroleum prospectivity. In: Buchanan, P.G. (Ed.), Petroleum Exploration, Development and Production in Papua New Guinea: Proceedings of the Third PNG Petroleum Convention, Port Moresby, 9th-11th September, 1996.

Buck, S.P. and Stone, J.F., 1991: Source rock and basin modelling study of PPL 93 plus addendum. Unpublished report for Mobil. GSPNG Open File Rept. No. F1/R/92-249.

Cawley, S.J., 1991: Thermal modelling and phase prediction in the Papuan Basin. Unpublished report for BP Petroleum, Technical File Note: TFN 463, May 1991.

Cooper, G.T., Hill, K.C. and Baxter, K., 1996: Rifting in the Timor Sea and New Guinea: a template for compressional forward modelling. In: Buchanan, P.G. (Ed.), Petroleum Exploration, Development and Production in Papua New Guinea: Proceedings of the Third PNG Petroleum Convention, Port Moresby, 9th-11th September, 1996.

Earnshaw, J.P., Hogg, A.J.C., Oxtoby, N.H. and Crawley, S.J., 1993: Petrographic and fluid inclusion evidence for the timing of diagenesis and petroleum entrapment in the Papuan Basin. In: Carman,G.C. and Carmen, Z. (Eds.), Petroleum Exploration, Development and Production in Papua New Guinea: Proceedings of the Second PNG Petroleum Convention, Port Moresby, 31st May – 2nd June 1993.

Hill, K.C., 1991: The structure of the Papuan Fold Belt, Papua New Guinea. AAPG, V 75, No.5, p 857-872.

Hill, K.C. and Gleadow, A.J.W., 1990: Apatite fission track analysis of the Papuan Basin. In: Carman, G.J. and Carman, Z. (Eds.): Proceedings of the First PNG Petroleum Convention, Port Moresby, p 119-136.

Kotaka, T., 1996: Formation Water Systems in the Papuan Basin, Papua New Guinea. Petroleum Exploration, Development and Production in Papua New Guinea: Proceedings of the Third PNG Petroleum Convention, Port Moresby, 9th - 11th September, 1996. Buchanan, P.G. (Ed).

Krieger, F.W., 1996: Hydrocarbon and pore water migration in the Papuan Basin – PPL 101. Australian Petroleum Co-operative Research Center confidential report No. 224, November, 1996

Krieger, F.W., Eadington, P.J. and Eisenberg, L.I., 1996: Rw, reserves and timing of oil charge in the Papuan Fold Belt. In: Buchanan, P.G. (Ed.), Petroleum Exploration, Development and Production in Papua New Guinea: Proceedings of the Third PNG Petroleum Convention, Port Moresby, 9th-11th September, 1996.

Lisk, M., Hamilton, J., Eadington, P. and Kotaka, T. 1993: Hydrocarbon and pore water migration history in relation to diagenesis in the Toro and Iagifu sandstones, S.E. Gobe-2. In: Carman, G.J. and Carman, Z. (Eds.):Proceedings of the Second PNG Petroleum Convention, Port Moresby, 31st May-2nd June, 1993.

Waples, D.W. and Wulff, K.J., 1996: Genetic classification and exploration significance of oils and seeps of the Papuan Basin. In: Buchanan, P.G. (Ed.), Petroleum Exploration, Development and Production in Papua New Guinea: Proceedings of the Third PNG Petroleum Convention, Port Moresby, 9th-11th September, 1996.

Background

Geotrack International Pty Ltd

Geotrack is probably best known as the pioneer of the AFTA technique (Apatite Fission Track Analysis) and while they continue to be recognised as the world leader in this field, Geotrack has extended its expertise to the broader field of basin modelling focussing on constrained thermal histories. Using an appropriate mix of analyses, Geotrack routinely provides reports that quantitatively constrain the timing and magnitude of thermal episodes in an effort to resolve problems related to the hydrocarbon generation and maturation history of a basin. AFTA offers the potential for directly determining the timing of maximum paleotemperatures and maximum maturity development in the section. Clearly the timing of hydrocarbon generation with respect to trap formation is a key element in exploration and not normally derived directly by conventional techniques. Thus, Geotrack’s thermal history methods have proved to play a key role in constraining the number of viable basin models for a basin.

Recognising the powerful and unique contribution of AFTA, most of the world's major oil companies now use Geotrack's thermal history techniques on a routine basis. Nevertheless, Geotrack continues an exhaustive research program to further refine and improve the AFTA technique. Since incorporation in 1987, Geotrack has completed more than 700 proprietary studies and more than 35 regional basin studies using AFTA as a cornerstone of the thermal history solution. Geotrack's head office and laboratory are in Melbourne, Australia, while representative technical and marketing offices are also located in London, Egypt and Houston. The owners of Geotrack International Pty Ltd are Drs. Ian R. Duddy and Paul F. Green.

Keiraville Konsultants Pty Ltd

Keiraville Konsultants Pty Ltd undertakes work in source rock potential and maturity, organic geochemistry appraisals, coal and coke petrology and economic assessments of mining and petroleum. The majority of work relates to the petroleum industry and studies have been undertaken in almost all petroleum provinces in the world for most of the major international companies in the industry. The company is a recognised authority on the measurement and use or vitrinite reflectance. Dr Alan Cook, as Chair of Commission I within the International Committee for Coal and Organic Petrology, has been a key figure in the establishment of an International Accreditation system for vitrinite reflectance and maceral composition measurements.

PetroConsult Pty Ltd

PetroConsult is an independent geoscience consultancy that has gathered a substantial experience base, technical ability and geographical coverage. This allows a full range of quality consultancy services to be offered to clients including: prospect identification, sequence and seismic stratigraphy, regional tectono-stratigraphic analysis, petroleum charge evaluation and basin modelling. Based in Melbourne, the company is well positioned to meet the needs of petroleum exploration and production companies in New Zealand, Australia and South East Asia.

Company activity has included evaluation of exploration areas covering the North West Shelf including the Dampier Sub-basin, Browse Basin and Bonaparte Basin; Papua New Guinea; Otway Basin; onshore Tasmania; and the Nam Con Son Basin offshore Vietnam. Further information on the company can be found in PetroConsult’s internet web site (www.petroconsult.com.au). The site also provides an extensive list of other industry related web sites in Australia.

More questions?

Please contact us with any technical or administrative enquiries. We would be happy to answer any outstanding questions:

Dr Ian Duddy
Geotrack International Pty Ltd
37 Melville Rd.
Brunswick West, VIC 3055
Australia
ph: +61-3-9380-1077
fax: +61-3-9380-1477
email
Dr. Alan Cook
Keiraville Konsultants
7 Dallas St.
Keiraville, NSW 2500
Australia
ph:  +61-2-4229-9843
fax:  +61-2-4229-9624
email: acc@ozemail.com.au
Mr. Geoff Geary or Ian Reid
PetroConsult Pty Ltd
21 Loraine Ave.
Box Hill North, VIC 3129
Australia
ph: +61-3-9849-0221
fax: +61-3-9849-0220
geoff@petroconsult.com.au
ian@petroconsult.com.au
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