Giant Gas Field Research Articles

Four-dimensional analog and geometrical modeling of the Hides anticline, Papua New Guinea: Structure of a giant gas field

The Hides anticline in the Papua New Guinea fold belt is the core part of the Papua New Guinea liquified natural gas project that commenced production in 2014, yet little is known about its internal structure, particularly at depth. The structure of the upper 3 km (9843 ft) is relatively well constrained from surface data, recent development wells, and poor-quality two-dimensional seismic data, but the deep structure has been obscure. Seismic data and gravity modeling suggest an underlying large normal fault in basement. Forward geometrical modeling using MoveTM and four-dimensional analog sandbox modeling under an x-ray tomography scanner have greatly constrained the structural interpretation. The modeling confirms the presence of the underlying basement normal fault and suggests that it was mildly inverted prior to the onset of pure compression deformation in the sedimentary section. The main detachment level was just above basement approximately 8–10 km (∼5–6 mi) beneath the surface, but this ramped up at the basement fault creating an array of triangle-zone faults through the overlying sedimentary section, building the Hides anticline. The early inversion was instrumental in initiating a back thrust and hinterland-verging tight fold in the Mesozoic section, including the source, reservoir, and seal. Deformation in the thick Miocene carbonates at the surface was detached from that in the underlying reservoir along an Upper Cretaceous mudstone horizon that varies strongly in thickness such that the 2–4-km (6562–13,123-ft)-high Mesozoic structure verges northeast and the overlying Miocene structure verges southwest. Analog modeling shows that a ductile stratigraphy is required with slow strain rates of approximately 1–3 km/m.y. (∼3281–9843 ft/m.y.).

New giant gas fields in Saudi and UAE add to growing Mideast Gulf supply

New giant gas fields in Saudi and UAE add to growing Mideast Gulf supply

Distribution rules, main controlling factors and exploration directions of giant gas fields in the Sichuan Basin

Over the past decade, great progresses have been made in natural gas exploration in the Sichuan Basin, where several large gas fields (such as Anyue) have been discovered. With the increase of data and the deepening of exploration, new knowledges have been gained in geological theory, thus it is necessary to further analyze the distribution characteristics and main controlling factors of large gas fields, thus to put forward new exploration directions for large gas fields. Therefore, based on the statistics on the geological parameters of 20 large gas fields discovered in this basin, the distribution rules, formation conditions and main controlling factors of large gas fields were analyzed, and the follow-up exploration directions were proposed. The following results were achieved. (1) Large gas fields are developed in different tectonic regions in the Sichuan Basin, mostly in the low and gentle tectonic belts in the central Sichuan Basin. Large gas fields are developed in seven series of strata in longitudinal stratigraphic sequences, which are dominated by the reef-shoal large gas fields formed in the Upper Permian Changxing–Lower Triassic Feixianguan Fms. (2) There are four sets of source rocks contributing to the formation of large gas fields, mostly from the assemblage of Xujiahe Fm source rocks. (3) Reservoirs in the large gas fields are dominated by porous carbonates and tight sandstones; large gas fields are mostly structural–lithological ones and normal pressure ones. (4) The development of marine large gas fields are mainly controlled by intracratonic rifts and paleo-uplifts. The controlling effect of intracratonic rifts is mainly from three aspects, namely the hydrocarbon generation center of source rocks, high-energy facies belts on the platform edges, and lateral sealing for hydrocarbon accumulation. The controlling effect of the paleo-uplifts mainly acts from another three aspects: intra-platform high-energy facies belts, karstic dolomite reservoirs and long-term hydrocarbon accumulation. The structures of foreland basins controlled the development of the continental large gas fields from four aspects: tectonic setting, source and reservoir assemblage, trap type and fracture distribution. In conclusion, a total of 5 domains with 14 favorable zones are the follow-up exploration directions of large gas fields in the Sichuan Basin.

Discovery of Intracratonic Rift in the Upper Yangtze and Its Control Effect on the Formation of the Anyue Giant Gas Field

Abstract —According to drilling and seismic data, the Late Sinian–Early Cambrian intracratonic rift was found in the Deyang–Anyue area of the Upper Yangtze craton. This rift is controlled by a tensional fault and extends in the N–NW direction with a N–S length of 320 km and an E–W width of 50–300 km. After three stages of the rift evolution, i.e., the formation stage, development stage, and dying stage, a favorable near-source accumulation assemblage formed. The research results indicate that: (1) the sedimentation stage of the Late Sinian Dengying Formation is the rift formation stage, during which trough-basin facies sedimentation is developed in the rift, while platform marginal-facies mounds and shoals are developed on both sides, controlling the formation and distribution of high-quality reservoirs in the Dengying Formation; (2) the sedimentation stage of the Early Cambrian Meishucun–Qiongzhusi Formation is the rift development stage, during which deep-water continental-shelf facies argillaceous rocks accumulated in the rift with a thickness of 500–1000 m, indicating the sedimentation of high-quality source rocks; (3) the sedimentation stage of the Canglangpu Formation is the rift dying stage, terminating the evolution history of the intracratonic rift by gap filling. The intracratonic rift is a key factor for the formation of the Anyue giant gas field, where the high-quality source rocks provide abundant gases for the giant gas field. A regional lateral sealing occurred during the rapid rise of the western paleouplift in Central Sichuan during the Late Yanshan–Himalayan period, favorable for the preservation of the Gaoshiti–Moxi giant gas field on the eastern wing of the rift. The intracratonic rift and its role in giant gas accumulation provide a significant reference for deep oil and gas exploration in paleocratonic basins.

МОДЕЛЮВАННЯ ІСТОРІЇ ЗАНУРЕННЯ ТА МІГРАЦІЇ ВУГЛЕВОДНІВ У ПІВДЕННО-КАСПІЙСЬКІЙ ЗАПАДИНІ

We study the mechanisms of migration and spacial distribution of hydrocarbon deposits along a regional 1000 km long SW - NE seismic cross section of the South Caspian Basin. A retrospective 2D geological simulation of basin subsidence and sediment filling history is performed taking into account accompanying processes of thermal and catagenetic transformations of organic matter, and subsequent migration and accumulation of hydrocarbons. The start of the basin opening with accumulation of considerable sedimentary mass can be dated as middle Mesozoic (Triassic or Jurassic), and hydrocarbon prone horizons can now be located at depths of 12 km. The hydrocarbon saturation of the Pliocene Productive Series is of epigenetic (allochtonous) nature, which is also confirmed in literature by geochemical data from mud volcanoes and by other facts. Geochemical age, depth of provenance and reworking degree of hydrocarbons point at generation sources in Mesozoic (gas) and Paleogene-Miocene formations (oil) with only subordinate participation of the lower "Productive Series" Pliocene suites. The dominant migration pattern of fluids is interformational (interstratal) intermittent injective subvertical flow along disjunctive planes, zones of increased fracturing and loose rocks, diapir intrusion contacts, eruptives of mud volcanoes, lithofacial unconformities and other structures, breaking the rocks continuity. This implies the possibility of commercial-scale accumulations of hydrocarbons at ultra high depths, if trap structures of sufficiently large sizes are available, comparable with already discovered giant oil and gas fields (Shah-Deniz, Azeri-Chirag-Gyuneshli etc).

Oil Discoveries and Protectionism: Role of News Effects

Can oil discovery shocks affect the demand for protectionism? An intertemporal model of Dutch disease indicates that if the tradable sector is politically dominant then an oil discovery can induce protectionism. If the economy is also credit constrained, this effect is intensified upon discovery, but partially reversed when oil revenues start to flow. We test these predictions using 16.2 million, HS-6 level, bilateral tariff rates that cover 5,718 products in 155 countries over the period 1988-2012, and data on worldwide discoveries of giant oil and gas fields. Our identification strategy rests on the exogeneity of the timing of discoveries. Our empirical results indicate that an oil discovery increases tariffs during pre-production years and decreases tariffs in the years to follow yet to a lesser extent, most notably in capital scarce economies with a relatively dominant tradable sector. Our baseline estimates indicate that a giant oil field discovery induces a rise of approximately 13% in the average tariff over the course of 10 years; this increase is approximately 2.5 times larger during the pre-production period when the oil discovery represents a pure news shock.

Fracture analysis and in situ stress estimation of a gas condensate field in Persian Gulf using FMI and DSI image logs

A giant gas field (called Field X in this study) in the Persian Gulf is located in the northern part of Qatar’s North field was considered in this study. Since the reservoir subjected to a strong tectonic compression, an accurate estimation of in situ stresses is important for reservoir-related issues and stress-related geo-hazards, such as wellbore stability, well completion, drilling a horizontal well, and fracture conductivity in Kangan and Upper Dalan formations. The formation microimager (FMI) and dipole sonic imager (DSI), as effective borehole image techniques, were used for stress determination and borehole breakouts (BOs) and drilling-induced fractures (DIFs) detection in field X. Based on 10 DIFs and 65 BOs derived from FMI logs and measured velocities of P-wave and S-wave from DSI logs in 3 gas wells, in situ stresses were determined in different tectonic units. The orientations of the maximum and minimum horizontal stresses in well B and well C were identified to be NE–SW and NW–SE, respectively. Additionally, the value of minimum horizontal stress was varied from 6210 to 9664 psi, the maximum horizontal stress was ranged between 7124 and 9968 psi, and the vertical stress was gradually increased with the depth from 10,000 to 12,000 psi. Hence, according to the relationships between the in situ stresses ( $$\sigma_{v} > \sigma_{Hmax} > \sigma_{hmin}$$ ), the tectonic stress regime of the studied area is normal.

Distribution and characteristics of paleo-oil reservoirs in Cambrian Longwangmiao Formation in Anyue area of Sichuan Basin, China

The Anyue gas field is a giant marine gas field with the largest reserves of a single reservoir and the oldest strata in China. In this area, the proved gas reserves in the Cambrian Longwangmiao Formation are 4, 404×108 m3, which are believed to originate from crude oil cracking according to substantial evidences. The paleo-oil reservoirs in the area have been destroyed, and their fluid properties, scale and other characteristics are unclear, despite of the distribution preliminarily determined. In this paper, the paleo-oil reservoirs in the Cambrian Longwangmiao Formation in the Moxi–Gaoshiti area were analyzed thoroughly through conventional microscopic observation, together with quantitative grain fluorescence (QGF), total scanning fluorescence (TSF), and micro-laser Raman analysis. The study results indicate that the Longwangmiao Formation contains bitumen, which is mainly distributed in four types of pore space, i.e. vein-like fractures, dissolution pores, intergranular pores, and intercrystalline pores. The bitumen in vein-like fractures was formed mostly in relation to hydrocarbon migration, while the bitumen in dissolution pores, intergranular pores and intercrystalline pores was formed by in-situ cracking of petroleum, mostly as a result of thermal alteration. The QGF index suggests the existence of paleo-oil reservoirs in certain scale in the study area, and the high QGF-E intensity indicates the property of residual bitumen. The laser Raman spectroscopy reveals the maturity of the extensive solid bitumen in reservoir rocks. The well-cross section illustrates that the paleo-oil reservoirs are mainly layered, have experienced mostly in-situ cracking, and match with the present gas reservoirs.

Effect of tectonic evolution on hydrocarbon charging time: A case study from Lower Shihezi Formation (Guadalupian), the Hangjinqi area, northern Ordos, China

A giant gas field has been discovered in the Lower Shihezi Formation in the Hangjinqi area, northern Ordos Basin, China. Coal seams and mudstone in the Taiyuan and Shanxi Formation are considered as source rocks and sandstone in the Lower Shihezi Formation is treated as reservoirs for gas. The charging time in the sandstone reservoirs was studied based on the homogenization temperature of aqueous inclusions, thermal and burial history simulation and K-Ar dating of authigenic illite. Two episodes of gas charging in the northern part and one episode in the southern part were delineated in the reservoirs of the Hangjinqi area, evidenced by microscopic observation of the occurrence of fluid inclusions and the analysis of salinity in aqueous inclusions. In the southern part of the study area gas charging occurred between circa 171-162 Ma, whereas in the northern part gas charging was between 158-144 Ma and 120-109 Ma, respectively. The gas charging events appeared to be influenced by the tectonic evolution of northern Ordos Basin. Paleo topography caused reduction in thickness of source rocks northwards, and contributed to differences in hydrocarbon generation potential and thermal evolution between the northern and the southern part of the study area. Therefore, gas charging occurred in the southern part prior to that in the northern part. Furthermore, tilting occurred in Middle Jurassic and provided the driver and pathways for gas, leading to a first charging event in the northern part of the study area.

The Lower Yangtze area: A next shale gas block for China? Preliminary potential assessment from some geology and organic geochemistry information

In the last several years, the massive success of the Fuling shale gas field in south‐western China has shown great potential in finding giant shale gas fields in the Upper Yangtze area, and it has also attracted the increasing attention from geologists to find more shale gas reservoirs around the world. However, there is still a great dispute as to whether the neighbouring Lower Yangtze area is a next potential shale gas block in China. In this study, we evaluate preliminarily the shale gas potentials of five important sets of marine shales based on systematic analyses for the sedimentary environment, thickness, total organic carbon (TOC), thermal maturity, and other organic geochemistry parameters of both geological records from outcrops and wells in the Lower Yangtze area. The first two sets of marine shales occur in the Lower Cambrian and the Ordovician, and they all are of over–high organic maturity due to strong effects from regional tectonic movements and thus have poor potential. Although the Lower Silurian shales are widely distributed in the Lower Yangtze region, a terrigenous delta, a low amount of organic matter (TOC < 1.2%), and late tectonic activity together created unfavourable conditions for the generation and accumulation of the Lower Silurian shale gas. The Permian black shales occur in the Middle and Upper Permian. Several proxies, such as the appropriate maturity (vitrinite reflectance Ro of approximately 2.0%), abundant organic matter (TOC of approximately 4 wt%), good total hydrocarbon potential (S1 + S2), and high level of hydrocarbon conversion have resulted in good conditions for shale gas generation. However, the relative thinness (only 30 m), severe tectonic modification, and regional cap rock are not favourable for shale gas preservation. The Lower Yangtze area therefore is not an excellent block for shale gas exploration compared to its neighbouring Upper Yangtze area. However, in some areas with less structural deformation, the possibility of finding shale gas reservoirs cannot be ruled out, especially for the Permian shales, which had a greater opportunity to generate and accumulate shale gas than the other marine shales. In addition, for new shale gas exploration breakthroughs in the future, structural studies are essential in offering better understanding of the preservation conditions in the Lower Yangtze area.

Main factors controlling the organic matter enrichment in the Lower Cambrian sediments of the Sichuan Basin, SW China

The Lower Cambrian Qiongzhusi Formation contains more than 200 m of marine sediments mainly consisting of mudstone and black shales, which are widely accepted as the most important hydrocarbon source rocks of the Ediacaran–Cambrian giant gas field in the Sichuan Basin. The geochemical compositions of biomarkers and trace elements obtained from black shales at the bottom of the Qiongzhusi Formation were used to reconstruct the palaeoproductivity and palaeoenvironment and to determine the main factors controlling the deposition and preservation of this organic‐rich shales. Based on varieties of steroids and hopanoids compositions, multifarious palaeobios such as pelagophyceae, dinoflagellate, diatom (or its ancestor), sponges, and aerobic/anaerobic bacteria have been proved to evolve in the Early Cambrian in the Sichuan Basin. In addition, a relative high concentration of Cubio compared with modern oceanic palaeoproductivity proxies indicate a moderate to relatively high palaeoproductivity, which is favourable for the organic matter accumulation of this source rocks. Moreover, the evidence from biomarkers and trace element ratios suggest that the Lower Cambrian sediments were deposited under a non‐sulphurized anoxic condition, which provided a favourable preservation condition. The covariation among Porg, Cubio, and TOC shows that the palaeoproductivity is the main controlling factor for the high organic content of the black shales of the Qiongzhusi Formation.

The significance of coal-derived gas in major gas producing countries

Abstract The core of coal-derived gas theory is that coal measure is the gas source, and the hydrocarbon generation of coal measure is dominated by gas and supplemented by oil, so discoveries in related basins are dominated by gas fields. Discovering and developing giant gas fields, especially those super giant gas fields with recoverable reserves more than 1×1012 m3, plays a key role in determining whether a country can be a major gas producing country with annual output over 500×108 m3. The coal resource and coal-derived gas reserves are abundant and widespread in the world, and coal-derived gas makes a major contribution to the gas reserves and gas production in the world. By the end of 2017, 13 super giant coal-derived gas fields have been discovered in the world. The total initial recoverable reserves were 49.995 28×1012 m3, accounting for 25.8% of the total remaining recoverable reserves (193.5×1012 m3) in that year in the world. In 2017, there were 15 giant gas producing countries in the world, with a total gas yield of 28 567×108 m3. Among them, six major coal-derived gas producing countries had a total gas yield of 11 369×108 m3, accounting for 39.8% of total gas yield of major gas producing countries. The Urengoi gas field is a super giant coal-derived gas field with the most cumulative gas production in the world. By the end of 2015, the Urengoi gas field had cumulative gas production of 63 043.96×108 m3, with the highest annual gas yield in the world. Its gas output was 3 300×108 m3 in 1989, accounting for 41.4% and 15.7% of the gas output of Russia and the world, respectively. This study introduces the gas source rocks of the basins with super giant coal-derived gas fields in Russia, Turkmenistan, Netherlands, Mozambique and China, and their significances for these countries becoming giant gas producing countries in the world.

Oil Discoveries and Protectionism

Can oil discovery shocks affect the demand for protectionism? An intertemporal model of Dutch disease indicates that if the tradable sector is politically dominant then an oil discovery can induce protectionism. If the economy is also credit constrained, this effect is intensified upon discovery, but partially reversed when oil revenues start to flow. We test these predictions using 16.2 million, HS-6 level, bilateral tariff rates that cover 5,718 products in 155 countries over the period 1988-2012, and data on worldwide discoveries of giant oil and gas fields. Our identification strategy rests on the exogeneity of the timing of discoveries. Our empirical results indicate that an oil discovery increases tariffs during pre-production years and decreases tariffs in the years to follow yet to a lesser extent, most notably in capital scarce economies with a relatively dominant tradable sector. Our baseline estimates indicate that a giant oil field discovery induces a rise of approximately 13% in the average tariff over the course of 10 years; this increase is approximately 2.5 times larger during the pre-production period when the oil discovery represents a pure news shock.

Partitioned transtensional Cenozoic stratigraphic development of North Sumatra

Abstract The Cenozoic sedimentary history of North Sumatra is reviewed and a new account of basin development is proposed that accommodates contrasting stratigraphic histories across the region, especially times of sudden facies change. Micropalaeontology and geohistory techniques have been used to estimate the magnitude of stratigraphic change and, together with the timing of events, this indicates that North Sumatra developed in a dynamic transtensional tectonic setting, as has been proposed in regional structural models, and not the back-arc setting usually assumed by oil industry workers. This style of basin development has direct control on the nature and areal distribution of the petroleum systems elements. New definitions of common formation terms are suggested, based on a well-constrained sequence stratigraphic model, which has been assigned a new nomenclature of NS10 to NS50 Megasequences. It is noted that the stratigraphic and geographic position and extent of the source rock for the Arun, NSO A, NSO J and South Lho Sukon giant gas and condensate fields is still not known.

Controls on hydrocarbon accumulation in clastic reservoirs of the Tarim Craton, NW China

The Tarim Craton of NW China hosts abundant hydrocarbon resources within clastic reservoirs characterized by a complex entrapment and fill history. In this paper, we review the processes of hydrocarbon accumulation in typical clastic reservoirs from the literature, and combine this with new research from six hydrocarbon-bearing regions (the Yakela Faulted-Uplift, the southern slope of the Tabei Uplift, the Tazhong Uplift, the northern slope of the Tazhong Uplift, the southern margin of the Bachu Uplift, and volcanic reservoirs) to identify the key controls on hydrocarbon accumulation and distribution in reservoirs of the Tarim Craton. Favorable reservoir–trap configurations exist on structural highs created during the evolution of paleo-uplifts and paleo-slopes in the region, with hydrocarbons accumulating in both structural (fault, salt dome, and thrust-fault anticline) and combined structural-primary stratigraphic traps. Vertical hydrocarbon migration occurred via deep–shallow superposed faults, and (rarely interpreted) fault textures in volcanic conduits. Unconformity surfaces and sand bodies provided pathways for both limited lateral redistribution and significant long-distance (>100 km) migration of hydrocarbons. The prospectivity of upper Paleozoic sandstone facies and paleogeography was controlled by denudation of the paleo-uplifts, and these reservoirs are most likely to host giant oil and gas fields in the region.

Quantitative prediction of oil and gas prospects of the Sinian-Lower Paleozoic in the Sichuan Basin in central China

Abstract Reliably and conveniently predicting oil and gas prospects and avoiding costly drilling mistakes are the goals pursued by oil explorers and companies. In 2013, the Anyue gas field was discovered in Sichuan Basin, and it was the first discovery of a giant natural gas field in Precambrian strata attracting extensive attention since then. However, the complexity of geology in the Sinian-Lower Paleozoic makes prediction of oil and gas prospects very challenging. Based on the comprehensive review of the Anyue gas field, we identify four functional elements, i.e., a source kitchen (S), paleo-uplift (U), reservoir depositional facies (D), and regional cap rock (C). The combination of these four functional elements in time and space (T- CDUS) controls the Sinian-Lower Paleozoic hydrocarbon accumulation. The probability for hydrocarbon accumulation is determined by a proposed index, Tcdus. As a tectonic movement can damage oil and gas reservoirs formed prior to the movement, a model for calculating the hydrocarbon reservoir preservation probability is also established. The oil and gas prospects in Sinian-Lower Paleozoic are predicted with the combination of the hydrocarbon accumulation and preservation model. 137 wells drilled in the Sichuan Basin show that 88.9% of the successful wells are distributed in the predicted zones.

The Identity of Petrophysical Properties of Oceanic Serpentinites and Continental Granitoids: Implications for the Recognition of Buried Hydrocarbon-bearing Serpentinite Geobodies

The Earth’s lithosphere is commonly investigated by both direct and indirect methods, corresponding to rock sampling and geophysical surveys, respectively. The interpretation of geophysical data is generally based on the combination of values measured in the lithosphere with those obtained in laboratories from rock samples. However, petrophysical properties of numerous lithotypes overlap, yielding the misleading interpretation of geophysical surveys in many areas of the world. A heated debate particularly concerns non-volcanic rifted margins, fuelled by the possible presence of giant oil and gas fields: thinned continental crust or serpentinized oceanic basement. One of the possible causes of ambiguity is related to the intimate similarity of oceanic serpentinites and various crustal rocks (e.g. basalts, gabbros, limestones, sandstones, shales, etc.), in terms of petrophysical properties. Can variably serpentinized peridotites mimic typical continental crustal rocks, such as granites and granodiorites? To answer this question, we compared literature data of worldwide samples of such lithologies. The results show the complete overlap of the considered petrophysical properties (density, magnetic susceptibility, VP, VS, VP/VS, and Poisson’s ratio) of these lithotypes (P = 10–1000 MPa, depth = 0.33–33.33 km), further confirming the difficulty in discriminating variably serpentinized mantle rocks from crustal lithologies. Therefore, the recognition of buried serpentinite geobodies, being potential sites of exploitable gas and oil reservoirs, like those probably ensconced in non-volcanic rifted margins, necessitates a robust lithological model inferred from direct methods, namely the study of core drillings, deep-seated xenoliths and tectonic exposures of deep-crustal sections to substantiate the interpretation of geophysical data.

Full-waveform event location and moment tensor inversion for induced seismicity

Locating microearthquake events below complex heterogeneous overburden requires robust location methodologies that can honor multipathing in the seismic wavefield. We have developed two full-waveform event location methods that form a complementary solution for locating earthquakes and simultaneously deriving focal mechanisms via moment tensor inversion. The methods are based on the application of 3D elastic wavefield modeling, which is used to generate waveforms and extract wavefield attributes, for comparison to the observed field data. Events are located and focal mechanisms are derived via a multiparameter inversion, which minimizes the differences between synthetic and observed data. The results have been applied to the induced seismicity observed within the giant Groningen gas field, onshore Netherlands, where recorded earthquakes are triggered by stress changes, induced in the reservoir through pressure depletion. Locating events below the field is compounded by the presence of strong guided waves, which are trapped in the lower velocity reservoir interval. This complex multivalued wavefield is problematic for traditional event location methods, which assume a single traveltime arrival. We overcome this limitation by using all event arrivals in a wave-based solution to improve the accuracy of locating earthquakes and overcome the ambiguity of solving for location and the focal mechanism simultaneously. The event location methods have been applied to shallow and deep monitoring networks, and 150 events have been located with high accuracy. The interpretation of the earthquake activity indicates that the events studied originate from the movement of larger graben bounding faults, which are oriented in a north-northwest–south-southeast direction.

Numerical investigation for determination of aquifer properties in newly developed reservoirs: A case study in a carbonate reservoir

Aquifer strength is one of the main parameters in surface water separation facilities design. The material balance method is a common approach to calculate the aquifer strength and water influx in mature reservoirs which are in the second half of their lives. However, this method could not be used for green and newly developed reservoirs. In this type of reservoirs, the suitable vertically and laterally distance between aquifer and perforation intervals in the development wells is a main question which depends on future aquifer behavior. In this study, a methodology has been presented to estimate aquifer properties using water pressure data and also well testing data in a newly developed giant gas field in Middle East. The numerical sector model is used to match simulated water pressure data with actual MDT (Modular Dynamic Tester) data. The water relative permeability for each rock type and vertical-horizontal permeability relationship have been determined in history matching process. The tuned model can be used for the prediction of the aquifer performance and also the water production in future development wells.

Reservoir forming conditions and key exploration technologies of Lingshui 17-2 giant gas field in deepwater area of Qiongdongnan Basin

On September 15, 2014, China National Offshore Oil Co., Ltd announced that a high production of oil and gas flow of 1.6 × 106 m3/d was obtained in Well LS17-2-1 in deepwater area in northern South China Sea, which is the first great oil and gas discovery for self-run deepwater exploration in China sea areas, and a strategic breakthrough was made in natural gas exploration in deepwater area of Lingshui sag in Qiongdongnan Basin. Under the combined action of climax of international deepwater exploration, high oil prices, national demands of China, practical needs of exploration, breakthroughs in seismic exploration and testing technologies, innovations in geological cognition and breakthroughs in deepwater operation equipment, Lingshui 17-2 gas field is discovered. Among these factors, the innovation in reservoir forming geological cognition directly promotes the discovery. The quality of seismic data in the early time is poor, so key reservoir forming conditions such as effective source rocks, high quality reservoirs and oil-gas migration pathways are unable to be ascertained; with support of new seismic acquisition and processing technology, some researches show that Lingshui sag is a successive large and deep sag with an area of 5000 km2 and the maximum thickness of Cenozoic stratum of 13 km. In the Early Oligocene, the Lingshui sag was a semi-closed delta-estuarine environment, where the coal-measure and marine mudstones in Lower Oligocene Yacheng Formation were developed. The Lingshui sag is a sag with high temperature, and the bottom temperature of source rocks in Yacheng Formation can exceed 250 °C, but the simulation experiment of hydrocarbon generation at high temperature indicates that the main part of this set of source rock is still in the gas-generation window, with resources of nearly 1 trillion cubic meters, so the Lingshui sag is a hydrocarbon-rich generation sag. In the Neogene, the axial canyon channel from the Thu Bon River in Vietnam passed through the Lingshui sag, and five stages of secondary channels were developed in the axial canyon channel, where four types of reservoirs with excellent physical properties including the axial sand, lateral accretion sand, natural levee sand as well as erosion residual sand were developed, and lithologic traps or structural-lithologic traps were formed. The diapiric zone in the southern Lingshui sag connects deep source rocks in Yacheng Formation and shallow sandstones in the channels, and the migration pattern of natural gas is a T-type migration pattern, in other words, the natural gas generated from Yacheng Formation migrates vertically to the interior of the channel sandbody, and then migrates laterally in the channel reservoirs and forms the reservoirs. Innovations of geophysical exploration technologies for complicated geological conditions of deepwater areas are made, such as the detuning comprehensive quantitative amplitude hydrocarbon detection technology, which greatly improves the success rate of deepwater exploration; key technologies of deepwater safety exploratory well testing represented by the platform-dragged riser displacement technology are developed, which greatly reduces the drilling test cost. The above key exploration technologies provide a strong guarantee for the efficient exploration and development of Lingshui gas field.