Deepwater Exploration Research Articles

ABSTRACT: Fluid and lithology prediction using seismic amplitude analysis: A deepwater exploration program case study, Northwest Shelf Australia

ABSTRACT: Fluid and lithology prediction using seismic amplitude analysis: A deepwater exploration program case study, Northwest Shelf Australia

Deepwater reservoir prediction using seismic and geomechanical methods

In deepwater exploration, due to a lack of well information, seismic data become the main means of predicting reservoirs and hydrocarbons. AVO is the most popular method to detect hydrocarbons. However, factors such as pressure, lithology, and thin‐bed effects can cause false AVO effects. The deepwater Gulf of Mexico, in addition to these complex factors, has simple‐to‐complex salt sheet morphologies. The evolution of these salt sheets through time significantly influences the accumulation and migration pathways of deepwater sediments. In this article, we propose that the hydrocarbon migration pathway and seal integrity can be better understood by combining information about pore‐fluid pressure, effective stress, lithology, and seismic energy attenuation.

Turbidite systems, Part 1: Sequence and seismic stratigraphy

With the increased emphasis on deepwater exploration and development globally, considerable work has been done to understand turbidite systems. These are defined as sediments initially deposited in deep water, and which may now occur in the deeper parts of sedimentary basins (sometimes in great water depths). These deposits have been studied in terms of the lithofacies distribution, reservoir architecture, 2-D and 3-D seismic appearance, and their production capabilities. There are considerable stratigraphic variabilities in turbidite systems that affect reservoir performance and development plans. The petroleum industry’s increased understanding of these variabilities and their effects has occurred through the integration of a number of disciplines: 2-D and 3-D seismic, wireline logs, biostratigraphy, cores, petrophysics and rock properties, reservoir simulation, and outcrop studies for building semiquantitative reservoir models.

Hydrocarbon potential in Indian deep waters

Deep-water exploration is a natural step forward to assess and accrete hydrocarbon reserves after having accomplished this task to a certain extent along the continental shelf areas of India. In recent years Oil and Natural Gas Corporation Limited of India (ONGC) has made a gradual but steady progress in the deep-waters beyond the 200 m isobath exploring for hydrocarbons, acquiring multichannel seismic data and other geoscientific data. Hydrocarbon potential in the deep-water areas of five offshore basins viz. Kutch, Bombay, Kerala-Konkan, Cauvery and Krishna-Godavari is analysed in this paper.The evolution of these polycyclic basins was initiated as intracratonic rifts in divergent margins set up at different geological times. Later these basins acquired a pericratonic character evolving through typical syn-rift and post-rift phases. The recently acquired seismic data corroborate the extension of identified lineaments of onshore and shelf into deep-water areas, differentiating the deep-sea basinal region into segmented linear ridge-depression complexes. The sedimentary thickness in these deep-sea basins varies from 2 to 8 km, with thicker areas being near the shelf break and in areas over 2500 m water depth near the various river mouths in the basins.The hydrocarbon potential of deep-waters of India covering about 1.4 million km2 of the Indian offshore is estimated to be between 5.0-9.0 billion tons of oil and oil equivalent gas. Analysis of about 90,000 line km seismic data has helped in identifying and mapping the geological features such as submarine fans, turbidites, build-ups, wedge-outs, growth fault-related rollover anticlines and other structural features relevant to hydrocarbon prospectivity in these basins. These prospects range in area from 10 to 600 km2, in water depths from 300 to 2000 m. The average prospect size is about 200 km2 in the western offshore and about 20 km2 in the eastern offshore. Exploration of these will help in establishing a reserve base for India’s future energy supply.

Abstract: Volume Interpretation Technology: Impact on Cycle-Time Reduction in Deep Water Exploration and Production

Abstract: Volume Interpretation Technology: Impact on Cycle-Time Reduction in Deep Water Exploration and Production

The prospectivity of the Vøring and Møre basins on the Norwegian Sea continental margin

The focus of exploration activity on the Norwegian Sea Continental Shelf has shifted westwards from the shallow water areas over the Trøndelag Platform and Halten Terrace to the deep water areas over the Cretaceous Vøring and Møre basins. The basins, especially the Vøring Basin, have been involved in a complex tectonic development since the main extensional phase in the late Middle Jurassic to Early Cretaceous, including Cenomanian–Campanian and Maastrichtian–Eocene extension and thermal uplift and intermittent phases of compression/transpression. While the Jurassic is the prospective interval in the Trøndelag Platform and Halten Terrace, the potential in the Vøring and Møre basins is seen mainly in the Cretaceous and Paleocene – the Jurassic is too deeply buried. The two first deep water exploration wells in these basins, 6707/10-1 and 6305/5-1, have already proven two effective plays, with excellent reservoir sands in the Upper Cretaceous and lower Paleocene charged with thermogenic gas in structural traps in rotated fault blocks and compressional domes. Palaeogeographical reconstructions indicate that these reservoir rocks may be widespread within the basin areas. No good oil-prone source rock at a suitable depth of burial is so far proven, but the palaeogeographical reconstructions linked to surrounding well data and regional analyses indicate a chance for the existence of Upper Cretaceous oil source intervals. The thermal history of the basins is as complex as their tectonic history, and is further complicated by the possible effects of the Paleocene–Eocene magmatic activity, making any basin modelling results at the present stage unreliable.

大水深海域の開発動向と国内におけるチャレンジ

The world offshore operation is moving to the deeper and deeper water recently. Japan also has its first deepwater program of drilling two MITI wells offshore Japan in 1999. One well is targeting the natural hydrate, which is very new even in the world. This lecture outlines the world trend of deepwater exploration first, then introduces the forthcoming domesticdeepwater program with discussion of technology and safety consideration for this challenging project.

Abstract: Managing Risk and Uncertainty in Frontier Deep-Water Exploration Ventures

Abstract: Managing Risk and Uncertainty in Frontier Deep-Water Exploration Ventures

Abstract: Environmental Management of Deep-Water Exploration, Rockall Trough 

Abstract: Environmental Management of Deep-Water Exploration, Rockall Trough 

Abstract: Lower Congo Basin, Deepwater Exploration Province, Offshore West Africa

Abstract: Lower Congo Basin, Deepwater Exploration Province, Offshore West Africa

COMMONWEALTH PERSPECTIVE ON PETROLEUM TAXATION

In 1997 the petroleum industry sought modifications to the petroleum resource rent tax (PRRT) regime which applies to all Commonwealth offshore areas except the North West Shelf Project area. Industry argued that the PRRT impeded deepwater exploration and development activity and the exploitation of large stranded gas deposits suitable for conversion to liquids such as LNG. Industry suggested that a more appropriate risk/reward balance in the tax structure could be achieved by providing a volume based PRRT exemption for projects located in water depth greater than 400 m and by increasing the uplift rates for unrealised losses. It was proposed that the risk premium for the general (development) expenditure carry forward rate be increased by five percentage points to the long term bond rate (LTRR) plus 10 percentage points. Another industry recommendation was that exploration expenditures incurred more than five years before the issue of a production license (PL), which currently attract the lower GDP factor rate (the five year rule), be uplifted at the long-term bond rate for the period prior to the five year mark and then rolled forward at LTBR plus 15 percentage points. In addition, industry asked that the reference date for the five year rule should be based on the application date for a PL and not the issue date. For integrated gas to liquid projects, industry requested clarification of the basis for valuing feedstock gas for determining gas liability.In response, the Commonwealth decided to adopt a gas transfer price (GTP) methodology based on a combination of established cost plus and net back formulas to be applied to the up and downstream stages of the project respectively. The difference in the price outcome of the two methods, the residual price, is split 50:50 to obtain the GTP. Details of how the residual price method will be applied are currently being finalised with a view to enacting legislation in 1999-2000. The Commonwealth also responded positively to the industry suggestion that the reference date of the five year rule be applied from the date of application for the PL on the proviso that the appropriate authority receives all information pertaining to a successful application. Recommended changes to the PRRT for deepwater areas and proposed increases to the carry forward rates of undeducted losses were rejected mainly on economic efficiency grounds.

20 000 barrels (per day) under the sea

In 1968, Brazil's state-owned oil company, Petrobras unearthed the first offshore oil deposits in the Guaricema field, off the north-east coast of Brazil. At that time however, no-one knew how to remove it. Thirty years later, the company has introduced a brand of subsea multiphase pumping technology that has helped it become a world record breaker in deep water exploration. It is now achieving depths of well over a mile. Here we look at Westinghouse's contribution to Petrobras' deep water achievements — a deep water multiphase pumping system.

Wind and wave induced behaviour of offshore guyed tower platforms

Offshore guyed tower platforms belong to the group of compliant offshore platforms which are most suited for deep water exploration. The basic feature of compliant offshore platforms is that they are designed to move with the waves, in at least some degrees-of-freedom. As far as excitation of wave frequencies is concerned, the system opposes wave forces by inertial effects. The offshore guyed tower derives its stability against lateral movement from its mooring system. In this study, the response of offshore guyed towers to random forces generated by wind and wave is investigated. The exposed portion of the tower is subjected to the action of turbulent wind, while the submerged portion is acted upon by random wave forces. The analysis includes the nonlinearities due to the Morison equation of drag force, the variable submergence effect due to waves, the instantaneous position of the tower and force excursion relation of the mooring lines. A parametric study is conducted to investigate the behaviour of the tower under waves, and the combined effect of wind and wave forces.

Abstract: Future Subsurface Technologies and Their Role in Deepwater Exploration, Appraisal and Development 

Abstract: Future Subsurface Technologies and Their Role in Deepwater Exploration, Appraisal and Development 

Salt-Sediment Interaction, Northern Green Canyon and Ewing Bank (Offshore Louisiana), Northern Gulf of Mexico

Structural and sequence stratigraphic interpretations of two-dimensional seismic and well data from northern Green Canyon and Ewing Bank were integrated to evaluate how salt deformation influenced the distribution of Pliocene-Pleistocene facies in time and space. Two techniques were employed. First, twelve palinspastic maps of near-surface structure were constructed. These were combined with maps of interpreted depositional environments to show how shallow salt diapirism created bathymetric relief that influenced the configuration of sediment transport systems and depocenters through time. Second, tectonostratigraphic packages comprising multiple sequences were defined based on external geometry. Different stacking patterns of these packages characterize four types of minibasins, each with a distinct history of salt evacuation from underlying salt stocks and sheets. Interpreted seismic facies were analyzed within this minibasin framework to evaluate how deep-salt withdrawal influenced the distribution of depositional systems. The results show that both structural and sedimentological variables influenced lithofacies development. External factors dictated the volume and type of systemwide clastic input. Regional factors, such as nearby salt structures and the position of deltas, controlled the dispersal of clastics. Local factors, such as the thickness of underlying salt, influenced minibasin-specific evolution. These factors interacted at three scales: (1) a broad transition from sand-rich ponded settings to shale-dominated bypass settings during the Pliocene-Pleistocene, (2) fluctuations over periods of several sequences that created highly variable stratigraphic stacking patterns, and (3) a progression from ponded to bypass facies within individual sea level cycles. Analysis of these various factors can improve the prediction of reservoir distribution within slope minibasins, and thereby reduce the risk in subsalt and deep-water exploration.

Abstract: Reducing Reservoir and Source Rock Risk in Deepwater Plays: Examples from Southeast Asia

Abstract The Kutei (Indonesia) and Sarawak (Malaysia) basins are two important petroleum producing provinces in Borneo where deepwater exploration efforts require an integrated technical approach to reducing pre-drill reservoir risk. In Southeast Asia, additional risk pertains to increased distance from Type III coaly source rocks formed in updip coastal-plain paleoenvironments. In Sarawak (northern Borneo), successful pre-drill prediction of reservoir type and content in deepwater blocks was based on regional sequence stratigraphic correlation and seismic facies calibration. Sequence stratigraphic analysis resulted in interpretation of a NE-SW trending fluvial-dominated delta in the deepwater prospect area. As predicted, abundant, thick marine sandstone reservoirs were penetrated in wells drilled in the deepwater. Less success was experienced with predicting hydrocarbon charge which post-drill studies indicate are related to maturity and the distance (>20 km) from coeval coastal-plain coals. In the Mahakam delta (southeast Borneo), regional mapping of Miocene and Pliocene shelf sequences proved critical to identifying sand-prone fairways for deepwater lowstand reservoirs. Maps constructed from seismic, cores, and logs pointed to key canyon system entryways and adjacent sand-prone highstand deltas. Defining the location of lowstand depocenters also reduced risk regarding source rock, as these provide the major kitchens for hydrocarbon migration. Recent discoveries of oil, gas, and condensate in thick Upper Miocene and Pliocene deepwater sandstone reservoirs have validated the pre-drill predictions in reservoir and source rocks.

Sequence Stratigraphy of Pliocene and Pleistocene Turbidite Systems, Northern Green Canyon and Ewing Bank (Offshore Louisiana), Northern Gulf of Mexico

Neogene turbidite systems are major reservoirs in the northern deep Gulf of Mexico. Few publications have described the stratigraphic variations or the three-dimensional geometries of these turbidite systems in detail; hence, an understanding of the stratigraphic characteristics of the producing sands is important for deep-water exploration in the Gulf of Mexico and similar basins worldwide. This study focuses on the northern Green Canyon and central Ewing Bank protraction (lease) areas, where the Pliocene-Pleistocene turbidite systems were mapped using an integrated exploration database. Interpretation of 10,000 km of two-dimensional seismic, 185 well logs, and biostratigraphy from 180 wells allowed us to define the regional sequence stratigraphic framework for this area and potential areas for future exploration. A complex Pliocene-Pleistocene geologic evolution of the area is indicated by the seismic and geologic facies, depositional rates, nature of turbidite systems, and sand content. Significant sand deposits (basin-floor fans) were deposited in most sequences and directly overlie sequence boundaries. Salt tectonics and faulting greatly influenced the loci of these fans’ deposition. Large, thick fans fill entire salt-withdrawal minibasins at the base of the Pliocene sequences. In the Pleistocene sequences, where the rate of salt withdrawal was less, smaller and thinner fans were deposited downdip of faults and adjacent to shallow salt bodies. Channel systems, interbedded with overbank shales, constitute most of the sediments in the sequences. The older sequences contain more channels and sandier channel fills than the younger sequences. Analysis of all sequences indicates a complex depositional history where significant sands were deposited where abrupt decreases in bathymetric gradient are associated with salt tectonics or faulting.

Detection of paraffin deposition inside a draining tubulation by the Compton Scattering Technique

This work shows an application of the Compton Scattering Technique (CS) in the detection of the problem produced by the formation of paraffin (condensed petrol) inside the petrol draining pipeline in deep-water exploration (off-shore). This study was made using an inspection system by CS. The measurements were made with two types of beam, punctual and fan-beam, by analysing a pipeline cross-section or small elements of volume through a transversal line. The punctual system can detect a minimum of 10% paraffin. This value is about 20% with a fan-beam system.

Tectonic, magmatic and depositional processes at passive continental margins

The papers presented in this thematic collection all derive from a meeting on geological processes at passive margins, held at Burlington House in February 1996. The meeting was co-hosted by the Geological Society, The Norwegian Geological Society and The Norwegian Petroleum Society. We would like to thank our colleagues Bjørn Larsen and Olav Eldholmfor ensuring the strong Norwegian participation at the meeting and Mike Daly for organizing contributions from the UK hydrocarbon industry. The formation of passive continental margins during continental rifting to form new oceans is a fundamental component of the plate tectonic process yet many aspects of the formation of passive margins are still poorly understood. Passive margins are amongst the more difficult areas of the earth's surface to study, because of their great water depths and the difficulty of acquiring data. Much of the current upsurge of attention to passive continental margins, which is particularly strong for the Irish, UK and Norwegian Atlantic margins, arises from the increased interest in their hydrocarbon potential resulting from advances in deep water exploration and production technology. This renewed interest has led to the collection of new data and the increased exchange of ideas between industry and academia, some of the results of which are presented here. The successful geological analysis of passive margins calls for the integration of many different disciplines. The papers presented here show how we need to understand the link between tectonics, depositional systems and magmatic processes in order to understand margin evolution. In addition much of

News US and UK offer attractive terms to lure high risk investment in deep water exploration Ocean bottom cable survey navigation system on trial New twist to data management and IT Flexible vessel for seismic surveys Winners of EAGE draw announced BGS to remain public Russian minerals on CD-ROM News in brief People in the News Refinements to inherited modelling

news US and UK offer attractive terms to lure high risk investment in deep water exploration Ocean bottom cable survey navigation system on trial New twist to data management and IT Flexible vessel for seismic surveys Winners of EAGE draw announced BGS to remain public Russian minerals on CD-ROM News in brief People in the News Refinements to inherited modelling