Subsea Level Research Articles

Estimation of Initial Hydrocarbon Saturation Applying Machine Learning Under Petrophysical Uncertainty

SummaryThe initial hydrocarbon saturation has a major effect on field-development planning and resource estimation. However, the bases of the initial hydrocarbon saturation are indirect measurements from spatially distributed wells applying saturation-height modeling using uncertain parameters. Because of the multitude of parameters, applying assisted-matching methods requires trade-offs regarding the quality of objective functions used for the various observed data. Applying machine learning (ML) in a Bayesian framework helps overcome these challenges. In the present study, the methodology is used to derive posterior parameter distributions for saturation-height modeling honoring the petrophysical uncertainty in a field. The results are used for dynamic model initialization and will be applied for forecasting under uncertainty. To determine the dynamic numerical model initial hydrocarbon saturation, the saturation-height model (SHM) needs to be conditioned to the petrophysically interpreted logs. There were 2,500 geological realizations generated to cover the interpreted ranges of porosity, permeability, and saturations for 15 wells. For the SHM, 12 parameters and their ranges were introduced. Latin hypercube sampling was used to generate a training set for ML models using the random forest algorithm. The trained ML models were conditioned to the petrophysical log-derived saturation data. To ensure a fieldwide consistency of the dynamic numerical models, only parameter combinations honoring the interpreted saturation range for all wells were selected. The presented method allows for consistent initialization and for rejection of parameters that do not fit the observed data. In our case study, the most-significant observation concerns the posterior parameter-distribution ranges, which are narrowed down dramatically, such as the free-water-level (FWL) range, which is reduced from 645–670 m subsea level (mSS) to 656–668 mSS. Furthermore, the SHM parameters are proved independent; thus, the resulting posterior parameter ranges for the SHM can be used for conditioning production data to models and subsequent hydrocarbon-production forecasting. Additional observations can be made from the ML results, such as the correlation between wells; this allows for interpreting groups of wells that have a similar behavior, favor the same combinations, and potentially belong to the same compartment.

The aetiology of the neotectonic evolution of Turkey

The neotectonics of Turkey comprises a time slice since about the end of the Oligocene and has been dominated by the shortening of Eastern Turkey, which created the Turkish–Iranian high plateau, extension in western Turkey, which created the Aegean Sea and the basin-and-range system of western Anatolia and the escape westward from the converging jaws of Arabia and Eurasia along the North and East Anatolian transform faults onto the Hellenic/Cypriot subduction zone. The escape of Turkey along the North and East Anatolian Faults began when eastern Turkey was still at subsea level, while western Turkey was a high plateau of some 3 km elevation. These inferences make it unlikely that the gravitational potential of the Turkish–Iranian Plateau initiated the escape. The pull of the Hellenic/Cypriot subduction system seems influential in western Turkey, but not necessarily in creating the escape regime. The high topography in eastern Turkey developed gradually between the Serravallian and the present coevally as western Turkey lost elevation, which probably aided in accelerating the rate of the escape.

Cathodic protection criteria of low alloy steel in simulated deep water environment

PurposeThe purpose of this work is to provide theoretical guidance and experimental analysis for optimized cathodic protection (CP) design of low alloy steel in deep water environments.Design/methodology/approachIn the present study, the CP criteria of 10Ni5CrMoV low alloy steel were investigated in a simulated deep water environment (350 m) regarding the theoretical protection potential and measured protection potential. The influences of hydrostatic pressure (HP) and temperature were also discussed in detail. The theoretical protection potential was analyzed with the Nernst equation, and the measured minimum protection potential was derived by extrapolating the Tafel portion of anodic polarization curves.FindingsThe results indicate that the minimum protection potential of low alloy steel shifts to a positive value in a deep-ocean environment. This can be attributed to the combined effects of HP and the temperature. Moreover, the temperature has a stronger influence compared with HP. The results suggest that the CP potential criteria used in shallow water are still applicable in the deep ocean, which is further confirmed through the SEM and x-ray diffraction analysis of the corrosion products resulted from the potentiostatic cathodic polarization experiments at −0.85 VCSE.Originality/valueIn recent decades, successful applications of CP for long-term corrosion protection of the steel components applied at a subsea level have enabled the offshore industry to develop reliable and optimized CP systems for shallow water. However, differences in the seawater environment at greater depths have raised concerns regarding the applicability of the existing CP design for deeper water environments. Hence, this research focuses on the CP criteria of low alloy steel in simulated deep water environment concerning the theoretical protection potential and measured protection potential. The influences of HP and temperature were also discussed.

Downslope Winds and Dust Storms in the Salton Basin

Abstract The Salton basin is a closed, subsea level basin located in extreme southeastern California. At the center of the basin lies the Salton Sea, the state’s largest inland lake, which is surrounded by a desert landscape characterized by paleo lakebed surfaces, dry washes, alluvial fans, and interdunes. Dust storms are common occurrence in this region. However, despite the regularity of dust outbreaks here, little is known about the meteorological processes responsible for these storms. Here I use observations and output from reanalysis to elucidate the meteorological controls on dust emission events in the Salton basin during 2015–18. Analysis of surface and upper-air observations, satellite data, and reanalysis, suggest that the largest dust storms in the region are associated with an upper-level low centered near the coastline of western Canada, which directs a zonal low-level jet over the region. Flow blocking by a coastal mountain range results in isentropic drawdown of air in the lee of these mountains. Once surface warming at the floor of the Salton basin is sufficient such that the density of the descending air is greater than that of the ambient air at the surface, the downslope windstorm reaches the desert floor and initiates dust emission. This process may also be accompanied by a downwind propagating hydraulic jump. These processes appear to be similar to those responsible for the strongest dust events in the Owens Valley, and may represent the main mechanisms for emission from other closed basins.

On the Structural Integrity of S-Lay Method of Pipeline Installation

This study presents a design template to analyse and check the structural integrity of subsea pipelines installed by S-Lay method. A typical static configuration of the pipeline in equilibrium with wave, current, drag, etc forces was considered in the structural analyses of the installation method. In the template, two scenarios namely: the laying of a single-pipe and the laying of a pipe-in-pipe, were considered. The template developed which was based on a Microsoft Office Platform also considered the lay barge/vessel specifications, met Ocean data, the pipe parameters, critical parameter, and the pipe-lay equipment specifications. The output results from the template include; catenary parameters, tension in pipe, stresses at subsea level and maximum deflection during installation. Typically, with applied top tensions TT of 1177.2kN and 1842.4kN on a pipeline of length 36 m, maximum deflections of (0.26m) and (0.17m), respectively were obtained. The results obtained by the user-friendly template developed corroborate those obtained by manual calculation for the relevant deflections, stress and catenary models for the structural integrity of the pipeline for an S-Lay installation.

ベネズエラにおけるスキンバイパスフラクチャリング

In Venezuela, Teikoku has been operating oil fields in two blocks since 1992. In the Copa Macoya gas field located East Guarico Block, Teikoku has conducted skin by-pass fracturing (hydraulic fracturing to bypass near-wellbore damage) in 2004 through 2005. Copa Macoya fields consist of lower Oligocene coastal sandstone (5-10ft) at a depth of approximately 7,000ft subsea level. According to well tests, permeability range in this reservoir from 100 to 1,000md, however skin factors show around 50 in several wells. It was considered that the reasons of high skin factors resulted from severe damages during drilling operations and/or workover operations. In order to remove these, the skin by-pass fracturing was done in two wells. These fracturing operations were successfully completed and resulted in a decrease of the skin factors to almost zero after main treatments. The design points and the results of skin by-pass fracturing operations in the high permeability reservoir are presented in this paper.

Paleogeographic Evolution of Early Deep-Water Gulf of Mexico and Margins, Jurassic to Middle Cretaceous (Comanchean)

The paleobathymetric configuration of the early Gulf of Mexico is inferred from (1) Cretaceous carbonate shelf margins interpreted from seismic profiles and other stratigraphic data; (2) distribution of Jurassic and Cretaceous platform and basinal facies; and (3) hindcasting of subsidence history in the central basin. Substantial paleogeographic ambiguity results from uncertainty about (1) kinematics and timing of Late Triassic to Jurassic extensional opening of the Gulf basin, which probably involved major strike-slip faulting, (2) the magnitude of subsequent compressive deformation on the western and southern basin margins, and (3) possible accretion of allochthonous terranes. The initial sub-sea level topographic depression created by crustal extension is manifested by the distribution of Callovian (?) pre-marine salt and Oxfordian basinal marine facies. Late Jurassic sea-floor spreading split the main salt body and created a central deep-water (> 1 km) trough. From the Oxfordian to early Neocomian, ramp-like platform margins generally underwent net retreat, except in the northern Gulf, where major clastic progradation took place. Carbonate platform margins with sufficient paleorelief for geometric expression on seismic profiles developed early in the Cretaceous. These Cretaceous carbonate margins exhibit a variety of architectural styles, including (1) in the northwestern Gulf, two cycles of progradation (Coahuilan and Comanchean) terminated by drowning events; (2) in the southwestern Gulf, a single cycle of progradation; (3) continuous aggradation along the Florida and Campeche Escarpments. Paleobathymetric relief across Cretaceous carbonate margins ranges from high and steep, to low-relief, to ramplike. The close-of-Comanchean drowning event greatly and permanently reduced the extent of circum-Gulf carbonate platforms and especially rimmed margins. Locations of Cretaceous carbonate margins were influenced by basement hinge zones and paleohighs developed on attenuated continental crust, by the distribution of salt, and by clastic progradation. Eustacy is commonly invoked to explain behavior and architecture of carbonate margins in the Gulf, but other paleoenvironmental variables such as nutrient abundance are probably important as well.

Stratigraphy and Radiocarbon Chronology of a Subaerially Exposed Holocene Coral Reef, Dominican Republic

A subaerially exposed coral reef records a period of marine conditions following earliest Holocene transgression into the technically active, subsea level Enriquillo Valley, Dominican Republic. Field mapping, detailed leveling of reef elevations, and I4C dating of fossil corals and mollusks reveal the following chronology of reef development in an unusual geologic and tectonic environment: (1) earliest Holocene ($$9760 \pm 100$$ yr B.P.) marine transgression and growth of oysters on an alluvial fan surface approximately 33 m below sea level (BSL); (2) colonization of reef corals at approximately 34 m BSL on the oyster shell deposits ($$8990 \pm 60$$ yr B.P.); (3) middle Holocene development of a typical Caribbean fringing reef in a protected environment ($$6200 \pm 80$$ to $$4760 \pm 90$$ yr B.P.); (4) late Holocene sedimentation over the reef with fossil bivalves ($$5710 \pm 90$$ to $$2820 \pm 40$$ yr B.P.) that record a gradual change from marine to brackish water that accompanied growth of shoreline th...

Ross Ice Shelf temperatures support a history of ice-shelf thickening

The ice sheet in West Antarctica is grounded on a sub-sea level basin in the Antarctic continental shelf. At the seaward margins, where ice thicknesses are reduced sufficiently to attain neutral bouyancy, floating ice shelves form. The two largest are the Ross and Ronne ice shelves (Fig. 1). Because the depth of the continental shelf increases towards the centre of the West Antarctic ice sheet, ice discharge could accelerate irreversibly until the grounded portion of the ice sheet had completely disappeared1–3. The resistance to ice discharge provided by the ice shelves is the major factor preventing such a collapse4,5. Geological evidence indicates that the extent of grounded ice in the West Antarctic has fluctuated widely during the Pleistocene6,7, and complete removal of the ice sheet may have occurred during the Sangamon interglacial following a climatic warming which was probably associated with a retreat of the ice-shelf seaward margins8. One of the most active ice streams draining West Antarctica flows into the south-east corner of the Ross Ice Shelf. Surface observations in this area indicate that, either the ice shelf is thickening9, or that there is appreciable melting from beneath ice shelf that is >500 km from the open sea10. Such melting would strongly influence temperatures within the ice shelf, and here we use a temperature–depth profile from the ice shelf to estimate the basal regime. We conclude that, for much of the south-east corner, basal freezing/melting rates have been near zero for the past few hundred years. This implies that, within this region, the ice shelf is thickening at ∼0.3 m yr−1.

The Prediction of Oil Recovery by Gravity Drainage

An approximate theory of free-fall gravity-drainage recovery is expanded to account for residual oil saturation. The recovery equation is derived and seven comparisons are made of observed gravity-drainage recovery with calculated recovery. Examples show how the theory can be applied. Introduction The gravity-drainage mechanism is one of the most efficient ways of producing an oil field. Unfortunately, most oil fields cannot be produced economically under free-fall gravity alone because the effective oil permeability is too low, the oil viscosity is too high, or the dip of the formation is too small. Nevertheless, many reservoirs take advantage of the gravity component, especially under pressure maintenance in areas where gas is available, such as overseas, or where inert gas can be used. The most ideal system would be one where oil is produced only under free-fall gravity drainage, giving the highest possible recovery at the most efficient rate. However, because a producing mechanism must be justified economically as opposed to another producing mechanism must be justified economically as opposed to another producing mechanism, an engineer must calculate gravity-drainage recovery producing mechanism, an engineer must calculate gravity-drainage recovery as a function of time.An approximate theory of strict gravity drainage has been presented by Cardwell and Parsons. They ignored capillary pressure terms and show how gravity-drainage equations can be solved. They give only one comparison of recovery calculated from theory with recovery obtained experimentally from a draining column.In addition to that study, many other papers have been published describing how to calculate reservoir performance where gravity effects influence the production mechanism. An early investigation describing the potentially high recovery with gravity drainage is Katz's discussion of potentially high recovery with gravity drainage is Katz's discussion of Oklahoma City Wilcox sand. Katz also presented data on the low (6 to 8 percent) residual oil saturations that could be obtained from a completely percent) residual oil saturations that could be obtained from a completely drained portion of the Wilcox sand. Lewis enlarged upon the gravity- drainage mechanism for oil recovery and gave four examples of gravity- drainage fields. Beginning in 1949, more studies discussed methods of calculating the effect of gravity component on oil recovery during depletion or pressure maintenance, and case histories of fields where gravity was an important factor in production. All the papers describing a calculating procedure used the Buckley-Leverett method. These studies also used historical rates of production or a pre-selected rate of production to get the advance of gas-oil front and to calculate recovery. More recently, high-speed computers were used to solve mathematical equations of various reservoir simulators. These reservoir simulators still required that rates or drawdown be pre-selected as a boundary condition to the solutions of mathematical equations. Thus, these simulators could not be used to determine the free-fall, gravity-drainage rate of production.One study attempted to determine production rate based on the location of the gas-oil front below a stated level. Essley et al. determined an approximate producing rate by arbitrarily assuming a maximum capacity for each well remaining on production below a given subsea level and determining the total production rate from that. They did not state how the arbitrary assumption was made, nor how this rate was related to a true gravity-drainage rate. JPT p. 818