Reduce Exploration Risk Research Articles

Application of AEM for cover thickness mapping in the southern Thomson Orogen

Regional airborne electromagnetic (AEM) surveying in the southern Thomson Orogen of southwest Queensland and northwest New South Wales highlights the efficacy of AEM for mapping near-surface Paleozoic basement rocks, the basement-cover interface, and the hydrostratigraphy of cover rocks of the Eromanga and Lake Eyre basins. Interpretations of AEM data are applied to model the basement-cover interface and answer the important question “how thick is cover” in this underexplored region, and encourage the mineral exploration industry to explore more widely. This paper shows some of the interpretation highlights from regional AEM surveys conducted in 2014 and 2016. The interpretations, when considered with regional borehole basement intersections, reduce exploration risk by demonstrating that large portions of the basement are within reach of exploration drilling.

Hydrocarbon migration and accumulation in the northwestern Bozhong subbasin, Bohai Bay Basin, China

An important exploration breakthrough has been achieved in the western subsag of the Bozhong subbasin, but the hydrocarbon accumulation mechanism was not clear. The hydrocarbon migration and accumulation mechanism of the western subsag of the Bozhong subbasin is discussed based on the modeling of hydrocarbon migration pathways and the study of late-stage reactivation of neotectonic faults. Three processes for lateral petroleum migration and accumulation can be recognized in the studied area: 1) migration and accumulation along the T8 unconformity; 2) migration and accumulation within the Guantao Formaiton (N1g); and 3) interaction of migration and accumulation along the T8 unconformity and Guantao Formation (N1g). The reactivation of faults in the studied area began 5.1 Ma. Following hydrocarbon lateral migration, late-stage reactivated neotectonic faults serve as effective vertical conduits for hydrocarbon migration and accumulation into the shallow Minghuazhen Formation (N1m) reservoirs.The modeling results of preferential petroleum migration pathways (PPMPs) and favorable accumulation areas are consistent with the actual exploration results. Two kinds of potential exploration targets can be predicted in the northwestern Bozhong subbasin: the first kind is hydrocarbon accumulation areas near or within generative kitchens (e.g. Target 1); the other kind is hydrocarbon accumulation areas removed from the generative kitchens, but with hydrocarbon sourcing from multiple generative kitchen and numerous PPMPs (e.g. Target 2). Studying preferential petroleum migration pathways will help reduce exploration risk.

Workflow for improvement of 3D anisotropic CSEM resistivity inversion and integration with seismic using cross-gradient constraint to reduce exploration risk in a complex fold-thrust belt in offshore northwest Borneo

The focus of hydrocarbon exploration has now moved into frontier regions where structural complexity, heterogeneous overburden, and hydrocarbon system fundamentals are significant challenges requiring an integrated exploration approach. Three-dimensional controlled-source electromagnetic (CSEM) anisotropic resistivity imaging is emerging as a technique to combine with seismic imaging in such regions. However, the typically reconstructed horizontal resistivity [Formula: see text] and vertical resistivity [Formula: see text] models often have conflicting depth structures that are difficult to explain in terms of subsurface geology. It is highly desirable to reduce ambiguity or subjectivity in depth interpretation of [Formula: see text] and [Formula: see text] models and also achieve comparability with other coincidentally located subsurface models. We have developed a workflow for integrating information from seismic well-based inversion, interpreted seismic horizons, and resistivity well logs in a cross-gradient-guided simultaneous 3D CSEM inversion for geologically realistic [Formula: see text] and [Formula: see text] models whose parameter estimates for a selected reservoir interval can then be better optimized to aid reservoir characterization. We developed our workflow using exploration data from a complex fold-thrust belt. We found that the integrated cross-gradient approach led to [Formula: see text] and [Formula: see text] models that have a common depth structure, are consistent with seismic and resistivity logs, and are hence less ambiguous for geologic interpretation and reservoir parameter estimation.

Past, present, and future of basin and petroleum system modeling

Basin and petroleum system modeling (BPSM) has had increasing impact on industry decisions related to exploration and new venture opportunities over the last decade. Basin and petroleum system modeling technology, usability, and user group size have grown as a result of its capacity to reduce exploration risk. Based on current statistics, improvements in BPSM have significant potential to reduce future well failures, particularly when caused by lack of petroleum charge. To bring BPSM practitioners from academia and industry together, an AAPG Hedberg Research Conference was organized to discuss the latest developments and issues in this field. A survey was conducted during the conference in Santa Barbara, California (April 2016), and this paper summarizes the results. A key takeaway was an overarching consensus throughout the BPSM community that improved understanding of hydrocarbon migration and more flexible workflows are necessary to better assess charge and migration risk in exploration and new ventures. In addition, BPSM is increasingly used to predict pore pressure and porosity at field scales, which opens new opportunities to integrate BPSM workflows with other technologies, such as seismic rock property analysis and reservoir quality modeling. In this paper, we discuss these and other issues that arose from in-depth discussion and an online survey.

How to predict thermal stress in hyperextended margins: Application of a new lithospheric model on the Iberia margin

Although passive margins have been explored for decades, they remain frontier zones with commonly little or no data available for calibration of basin models. The thermal history modeling of these margins, critical for maturity assessment, thus strongly relies on the rifting models available in basin-modeling tools. Coupling lithospheric evolution with sedimentation and integrated petroleum system modeling has proven to add value compared with user-defined heat flows applied at the base of sediments. However, classic approaches based on uniform stretching factors are limited in hyperextended margins where more complex models are required. The different basement domains and their structural complexity as well as rock-property evolution through time must be considered. An improved lithospheric model has been developed with this objective. Still coupled with sedimentation, it allows a precise description of the lithosphere’s shape and properties through time. This new model is applied to a two-dimensional cross section located on the Iberia margin. A basin model is built from published data, and focus is on the basement using a conceptual model as input only and using available surface-heat-flow measurements for calibration. Thermal stress and maturity resulting from the margin evolution are analyzed and discussed. Results demonstrate the strength of the approach to build reliable geological reconstruction of the heat flow through time in areas where classic rifting models cannot be applied, from a minimum of data and in a limited time, leaving room for sensitivity analysis to reduce exploration risk.

Pre-drilling geothermal assessment of porosity and permeability of the Bunter Sandstone Formation, onshore Denmark

Denmark constitutes a low-enthalpy geothermal area. Current geothermal production takes place from two sandstone-rich formations: the Bunter Sandstone and Gassum Formations. These formations form major potential geothermal reservoirs, but information about the permeability of the potential sandstone reservoirs is difficult to obtain. This may be explained by deposition in a variety of environments under different climatic conditions, and by variable diagenetic overprint (Olivarius et al. 2015). Thus, the sandstone characteristics and properties are diverse, and in areas where wells are scarce, the assessment of the extent and reservoir properties of sandstone layers is associated with much uncertainty. In order to reduce exploration risk it is therefore essential to develop a robust method for prediction of porosity and permeability prior to drilling.

Integrative 1D-2D Basin Modeling of the Cretaceous Beni Suef basin, Western Desert, Egypt

An integrated seismic, borehole petrophysical and geochemical data constrained 1D and 2D basin model study is conducted for the Beni Suef basin (Western Desert, Egypt) to enhance the understanding of the Cretaceous plays while demonstrating how basin modeling can be used to reduce exploration risk and improve exploration success. The Cretaceous petroleum systems consist of two major source rocks (the Upper Cretaceous limestone of Abu Roash “F’’ member, and Lower Cretaceous shales of Kharita and Alam El-Bueib formations), five reservoirs (Cretaceous sandstones of Abu Roash “A, E & G’’, Baharyia and Kharita formations), three seals (Lower Cretaceous and Upper Cretaceous shales of Kharita and Bahariya formations and fine grained limestones of the Abu Roash Formation), and vertical source mixing migration pathways owing to vertical faults resulting from four episodes of elastic crustal extension and above trap lateral migration. The entrapment style of the generated hydrocarbons and its roles on the charge and migration process in the Cretaceous reservoir rocks were determined from the seismic interpretation. Three episodes of uplift erosion (Early Cretaceous, Late Cretaceous-Paleocene, and Paleogene-Neogene) have occurred in the basin and have increased exploration risk in some areas by breaching the integrity of the seal. Migration from the source rock into the trap is mainly vertical migration. However, in areas where the hydrocarbons have escaped through the faults at the boundaries of the basin, migration in the layers above the trap is mainly lateral. The hydrocarbons generated are predominantly oil. The Lower Cretaceous shales of the Kharita and Alam El-Bueib formations exhibit good thickness, total organic content (TOC), kerogen type (mixed type II and III), and maturation.

The Research and Application of Bright Spot Quantitative Interpretation in Deepwater Exploration

Prospectors usually recognize the event with strong amplitude in seismic sections as bright spots. However, such a simple and rough method can’t distinguish whether these bright spots are related to favorable gas layer or water layer directly. In this paper, for the high correlation between reservoir gascontent and amplitude anomaly in research area, based on rock physical analysis of the wells drilled, using forward modeling technique respectively simulates and analyzes the seismic amplitude of gas layer and water layer. Then, combining the simulation result with corresponding statistics amplitude obtains the numerical relationship between each layer amplitude. At last, using the display technique directly recognizes the bright spots of gas layer in seismic profile and gets rid of those false bright spots caused by water layer, which improved the robustness in the bright spots interpretation and provided reliable basis for reducing exploration risks. Moreover, applying the method to the target zone, we obtain huge success.

Comparing P-P, P-SV, and SV-P mode waves in the Midland Basin, West Texas

We acquired 3D multicomponent data in Andrews County, Midland Basin, West Texas with a seismic survey. We extracted direct-SV modes generated by a vertical-force source (an array of three inline vertical vibrators) from the vertical component of multicomponent geophones. This seismic mode, SV-P, was created by reprocessing legacy 2D/3D P-wave seismic data to create converted-wave data and consequently forgoing the need for a multicomponent seismic acquisition program to obtain important S-wave information from the subsurface. We have compared P-P, P-SV, and SV-P traveltime and amplitude characteristics to determine which seismic mode provided better characterization of the targeted reservoirs and reduced exploration risk.

Hidrogeologia do sistema aquífero serra geral no Estado do Paraná

Este trabalho tem como objetivo caracterizar aspectos hidrogeológicos regionais do Sistema Aquífero Serra Geral (SASG) no estado do Paraná. São descritas as características hidrodinâmicas e hidroquímicas, mediante a compartimentação hidroestrutural do aquífero. Foram analisados condicionantes exploratórios como: distância do poço ao arcabouço estrutural, análise direcional e tectônica, densidade de lineamentos e geomorfologia regional. As principais características hidroquímicas dos compartimentos estruturais são apresentadas, indicando contribuições da interação água-rocha e possíveis aportes de efluentes antrópicos no aquífero. O modelo indica que, poços situados na área de influência de lineamentos geológicos, com direção norte-sul e leste oeste, apresentam índices de produção (vazão e capacidade específica) acima da mediana. Predominam águas bicabornatadas cálcicas, com destaque para as águas dos compartimentos Maringá e Campo Mourão. Nos compartimentos Foz do Iguaçu e Foz do Areia são descritas ocorrências de águas com maiores valores de sódio, pH, sulfato, quando comparados aos outros compartimentos. O conhecimento das características regionais do SASG, contribui na determinação de áreas potenciais à captação, reduz o risco exploratório e subsidia a gestão deste estratégico manancial subterrâneo.

Methane adsorption measurements and modeling for organic-rich marine shale samples

Understanding methane sorption behavior in the gas-shale system is of great importance for evaluating reservoir production potential and reducing exploration risk. In this study, methane sorption capacities of total 12 organic-rich marine shale samples from the southwest of China were measured by volumetric method. The absolute sorption results were modeled using Langmuir, Brunauer–Emmett–Teller (BET), Dubinin–Radushkevich (D–R) and Dubinin–Astakhov (D–A) models. The accuracy of each model for quantifying shale gas sorption capacity was analyzed and compared by using a residual error analysis technique. The impacts of organic and inorganic constituents on the methane sorption capacity were also analyzed. The experimental results indicate that the maximum absolute methane sorption capacity of the collected marine shale samples is between 0.50cm3/g and 3.41cm3/g, which positively correlates with the total organic carbon (TOC) content. The TOC-normalized methane sorption capacity shows a positive correlation with the total clay mineral content and exhibits a significant increase with increasing illite–montmorillonite mixed layers content when it is greater than 9%. For the results of gas sorption modeling, the D–A model is superior to the Langmuir, D–R and BET models, because of the additional parameter describing the micro-heterogeneity of shale rocks. The most commonly used Langmuir model gives a reasonable fit for most of the shale samples, which is comparable to D–A modeling results when TOC content is greater than 5%. The BET model performs poorly and thus it is not recommended for methane–shale sorption modeling exercise. Therefore, both D–A and Langmuir models are recommended for describing methane adsorption on organic-rich shale samples.

Type and evolution of carbonate platforms in Jixian Period Mesoproterozoic: southwestern margin of Ordos Basin

The Ordos block experienced extension in the Mesoproterozoic, during which the Longshan–Kuanping and Haiyuan rifts developed on its southwest margin. The Jixian Group (1.6–1.4 Ga) is mainly exposed on the rimmed and ramp-type platforms at the Qishan County, southwest of the Ordos block. The deposition associated with the rimmed platform margin consists of platform facies, platform edge facies, and slope facies, which are characterized by small tidal creeks, mud cracks and scour troughs, rockfalls, respectively. The ramp-type platform is dominated by platform edge facies, shelf facies and slope facies and featured by intraclastic dolostones, tempestites and debris flow sediments respectively. The syndepositional normal faults were well developed at the early stage of the rifting. Fault-related cracks and folds present in the adjacent strata. The uplift of the footwall rimmed the platform. The drag structures determine the local sedimentary environment. In the final stage of the rifting, the fault movement stopped. The surrounding rocks were undeformed. The slope became less steep, resulting in the formation of ramp-type platform. The study area in the Jixian period, Mesoproterozoic is located at a palaeo-continental margin, which has already shown good petroleum prospectivity. A clear study on the type of carbonate platforms and the evolution of the platforms can help reduce exploration risks by improve the understanding of the presence of the source rocks.

On a method for reducing interpretation uncertainty of poorly imaged seismic horizons and faults using geomechanically based restoration technique

To reduce exploration risk and optimize production in structurally complex areas, the geologic interpretation must be based on sound geomechanical principles. Despite advances in 3D seismic acquisition and processing techniques as well as in the availability of computationally robust interpretation software, the challenge associated with interpreting complex structures from seismic reflection data is that highly deformed areas surrounding faults, folds, and salt surfaces are often poorly imaged and therefore their interpretation is highly uncertain. We have developed a methodology that should help geophysicists quickly check the strengths and weaknesses of their interpretation and to automatically reduce the uncertainty in a faulted horizon geometry. Our workflow consisted of restoring interpreted seismic horizons and relating the concentrations of computed deformation attributes to areas of interpretation uncertainty. We used the technique based on an iterative finite-element formulation that allowed unfolding and unfaulting of 3D horizons using physical elastic behavior. A fast algorithm has been developed to automatically correct the interpreted structures in zones that exhibited anomalous deformation concentrations after restoration. This approach is able to mechanically check and reduce uncertainty in a faulted seismic horizon interpretation. Its application to synthetic and reservoir data has a high degree of reliability in the characterization of structurally complex reservoirs. This technique is also applicable to 2D models (geologic cross sections) and 3D models (volume).

Research on Identification of Petroliferous Unit Based on Seismic Data Structure Characteristics

The identification and classification of petroliferous unit is the key to the success in the exploration for oil-gas fields with geophysical knowledge that are the main means and ways to reduce exploration risk and improve exploration efficiency. In this paper, it analyzes geophysical response characteristics under conditions of gas, oil and water through the establishment of horizontal layered medium model. Then it extracts and analyzes seismic abnormal characteristics of the data structure combining the method of grey system theory based on the experiment, which are considered as an important reference for further objectively identifying petroliferous unit and the exploration of oil-gas fields in the practical application with comparison and analysis.

Cooperative joint inversion of 3D seismic and magnetotelluric data: With application in a mineral province

The integration of different geophysical data has the potential to provide more accurate estimate of subsurface rock properties. Several methodologies and attempts have been developed over the years with the objective of reducing exploration risk. We have developed a cooperative joint-inversion approach intended to facilitate recovery of acoustic impedance (AI) using seismic and magnetotelluric (MT) data. In this approach, the MT data provided a pathway for iteratively building large-scale low-frequency information content not directly recoverable from the seismic data themselves. The MT data provided complementary information to seismic, especially in seismically complex terrains such as overthrust belts, subbasalt and subsalt, carbonate reefs or for targets below deep cover containing limestone, concretionary layers, or basalt. On the other hand, the seismic data provided structural information necessary to derive accurate resistivity models from MT inversion and small-scale features during seismic impedance inversion. The connections between resistivity and the elastic property of rocks are obtained from petrophysical relationships derived from available borehole data, or if not available, from empirical relationships. We tested our technique on synthetic and field data. The application of cooperative joint inversion to 3D seismic and MT data sets acquired in a mineral province made it possible to recover AI distribution across a wide range of geologic environments. The resulting rock property images provided a direct link to geology that is exceedingly difficult, if not impossible, to extract from the individual data sets.

HYDROCARBON POTENTIAL OF TOLO BAY MOROWALI REGENCY: QUALITATIVE ANALYSIS

Tolo Bay is located between East Arm and Southeast Arm Sulawesi, reaching a water depth of up to 3500 meters below sea level. Regionally, this block is situated within Banggai Basin where some gas and oil fi elds are already in production. The closest fi eld is Tiaka Oil Field located about 125 kilometers northwest of the study area. A geo-science review has been conducted to clarify the potential existence of hydrocarbon in this block. Based on previous reports, papers, and subsurface data from the Directorate General of Oil and Gas, the study area is located within the collision area between Banggai-Sula Microcontinent and Sulawesi. This collision occurred during Late Creataceous and Middle Miocene periods. During drifting phase a sedimentation process occurred at the front of the Banggai-Sula Microcontinent. This sediment is potentially source rock and reservoir rock. Meanwhile, during the drifting phase the study area is interpreted as located at the southern part of Banggai-Sula Microcontinent. This different tectonic setting will impact on the type of sedimentary rock, hence source rock and reservoir rock occurrence in the study area is still unclear. As source rock and reservoir rock within the study area are unclear, hydrocarbon explorations will be very risky. In order to reduce exploration risk, it is proposed to conduct geological and geophysical studies using the latest seismic data that was surveyed by PT. TGS – NOPEC and PT. ECI – PGS.

Complex structural imaging of transition zones in Bohai Bay, China, by OBC technology

A series of ocean-bottom cable (OBC) surveys has been conducted in the Bohai Sea in China in recent years to overcome difficulties experienced with streamer surveys in shallow water, such as strong currents, missing near offsets, and obstacles. The main challenges in OBC data imaging include steeply dipping structures, serious multiples in the shallow-water environment, large lateral velocity variations, fault shadow effects, and low signal-to-noise ratio (S/N). To obtain optimal images, advanced processing technologies have been developed and applied to OBC data which involve effective PZ summation and shallow-water demultiple, a high-fidelity beam migration in the wide-azimuth domain, and accurate velocity-model building in 3D tilted-transverse-isotropy (TTI) media. The PZ summation and shallow-water demultiple methods aim to effectively eliminate shallow-water ghosts to achieve broadband seismic data. Furthermore, high-fidelity controlled-beam migration (CBM) and TTI velocity-model updates greatly enhance steep dip imaging, improve S/N, and reduce turnaround time. Through the combination of these technologies, OBC data processing provides high-quality images with well-defined steeply dipping structures to reduce exploration risk in the Bohai area.

Shallow-marine reservoir development in extensional diaper-collapse minibasins: An integrated subsurface case study from the Upper Jurassic of the Cod terrace, Norwegian North Sea

Understanding the factors controlling the development of accommodation above collapsing salt diapirs and their influence on reservoir distribution is critical in reducing exploration risk in salt-influenced sedimentary basins. In this study, we use an integrated subsurface data set (three-dimensional and two-dimensional seismic reflection, wire-line-log, core, and biostratigraphic data) from the Upper Jurassic of the Cod terrace, Norwegian North Sea, to understand the influence of rifting on accommodation creation and shallow-marine deposition during the initial-stage collapse of salt diapirs. We demonstrate that rifting resulted in the rise and fall of salt diapirs, and the formation of supra-diapir minibasin-style depocenters that became sites for deposition and preservation of up to 500 m (1640 ft) thick net-transgressive shallow-marine sandstone reservoirs. Maximum thickness is recorded in the axis of minibasins with a reduction in thickness of up to 65% noted on their flanks. The stratigraphic architecture of individual minibasins is variable. Proximal-to-distal facies variations from shoreface to offshore shelf and commensurate changes in reservoir quality occur over scales larger than individual minibasins. These deposits contain large sand volumes, and are not confined to areas of localized sandstone subcrop. In combination, these features suggest that the minibasins formed a linked network supplied by regional sediment-routing systems. The results of this study provide a new tectono-stratigraphic model for prediction of reservoir presence, thickness, and continuity in diapir-collapse minibasins along salt walls in the Central North Sea, and in other less mature, data-poor basins where reservoirs have been identified in depocenters above salt walls.

Tracing migration pathways by integrated geological, geophysical, and geochemical data: A case study from the JX1-1 oil field, Bohai Bay Basin, China

Tracing petroleum migration pathways is essential for predicting petroleum occurrence and reducing exploration risks associated with hydrocarbon charge, but a difficult task because of rapid lateral and vertical facies changes in lacustrine basins. An integration of geological, geophysical, and geochemical analysis is employed to investigate the origin of crude oil, the carrier-bed architecture, and migration pathways from source to trap in the JX1-1 oil field, Liaodong Bay subbasin, Bohai Bay Basin. Detailed geochemical studies suggest that three potential source-rock intervals (, , and ) exist in the Liaodong Bay subbasin, and crude oil in the JX1-1 field was derived from the and source rocks. The carrier beds from and source rocks to the trap were characterized using geophysical data. The fan-delta sandstone in the Member has an immediate contact with source rock and served as dominant conduit for the expulsion and migration of oil generated from source rock. The braided-delta sandstones overlying the source rock served as dominant conduit for -sourced oil. The focusing of petroleum migration pathways and the merge of migration pathways in and sandstones account for the accumulation of the JX1-1 field and the mixing of - and -sourced oil in the field. This study suggests that the distribution of permeable sandstones and their stratigraphic contact with the source rocks are key for petroleum migration and occurrence, and integration of geophysical, geological, and geochemical studies provide an effective way to trace petroleum migration pathways.

Experiencing the full bandwidth of energy from exploration to production with the art of BroadSeis

Jo Firth, Idar Horstad and Menne Schakel present the latest developments in BroadSeis broadband technology. The exceptionally broad bandwidth of more than 6 octaves delivered by BroadSeis variable-depth streamers, in combination with a BroadSource multi-level broadband source and advanced imaging algorithms, not only provides unprecedented information about the subsurface, it also produces stunning images. In particular, the additional high signal-to-noise ratios at low frequencies, down to 2.5 Hz, provide extra ‘texture’ as these provide an envelope to the seismic signal which shapes the larger-scale impedance variations, to deliver clear distinction between stratigraphic packages (see Figure 1). This full bandwidth has been exploited in many areas of the world to reduce exploration risk, improve development plans and maximize return on investment.