Oil Zone Research Articles

Application of artificial neural network for predicting the performance of CO2 enhanced oil recovery and storage in residual oil zones

Residual Oil Zones (ROZs) become potential formations for Carbon Capture, Utilization, and Storage (CCUS). Although the growing attention in ROZs, there is a lack of studies to propose the fast tool for evaluating the performance of a CO2 injection process. In this paper, we introduce the application of artificial neural network (ANN) for predicting the oil recovery and CO2 storage capacity in ROZs. The uncertainties parameters, including the geological factors and well operations, were used for generating the training database. Then, a total of 351 numerical samples were simulated and created the Cumulative oil production, Cumulative CO2 storage, and Cumulative CO2 retained. The results indicated that the developed ANN model had an excellent prediction performance with a high correlation coefficient (R2) was over 0.98 on comparing with objective values, and the total root mean square error of less than 2%. Also, the accuracy and stability of ANN models were validated for five real ROZs in the Permian Basin. The predictive results were an excellent agreement between ANN predictions and field report data. These results indicated that the ANN model could predict the CO2 storage and oil recovery with high accuracy, and it can be applied as a robust tool to determine the feasibility in the early stage of CCUS in ROZs. Finally, the prospective application of the developed ANN model was assessed by optimization CO2-EOR and storage projects. The developed ANN models reduced the computational time for the optimization process in ROZs.

Hydrocarbon source-rock potential of the Jurassic succession in eastern part of the North Western Desert, Egypt

The hydrocarbon potential is determined by the quantity and quality of organic matter encountered in the Jurassic sediments in two wells at the Northern Western Desert. It utilizes to define the zones of oil and gas using the well logging data for calculates the total organic carbon (TOC). The evaluation of source rock has been based on two steps; the first one depended on the geochemical parameters including TOC, S1, S2, Tmax, and Vitrinite reflectance (Ro %) of two wells JG-1 and JD-4. The second step was to calculate (TOC) from wireline logs. The well log types utilized in such kind of analysis are the density log, sonic log, resistivity log and gamma-ray log. The stratigraphic sequence, in the studied wells ranges in age from Paleozoic to Recent. The present work focuses on the Jurassic rocks represented by Khatatba Formation as they include the main source horizon. Based on the obtained results, Jurassic sediments called as fair to excellent source rock potential. The genetic type of organic matter can be identified through the study of pyrolysis data, which indicate that is rich in mixed oil and gas-prone kerogen except few samples reflect type I organic facies.

Patterns of water 87Sr/86Sr variations in oil-, gas- and water-saturated rocks: Implications for fluid communication processes, distances and timescales

This study reviews 87Sr/86Sr depth profiles of formation waters sampled by Sr residual salt analysis (Sr RSA) from >100 oil/gas wells and research sites, including reservoirs with clastic and carbonate host rocks and with gas, oil and water as the continuous fluid phase. Globally, the water data form a smooth trend between low seawater-like 87Sr/86Sr ratios (~0.706) at shallow depths and high (~0.724) ratios in deeply buried rocks, where water-rock interaction dominates.We test the hypothesis that 87Sr/86Sr depth profiles in individual wells could be influenced by diffusional mixing processes by developing 1D diffusion mixing equations to simulate compositional patterns through time and comparing them with observed profiles. Different combinations of boundary and initial conditions generate various patterns characteristic of diffusion, including non-steady-state curves relating to incomplete mixing and steady-state patterns (such as vertical or inclined straight lines) where initial heterogeneities have fully mixed. The dataset yielded 193 occurrences of these patterns. Steady-state patterns are more common and longer in water zones, while non-steady-state patterns are more common and longer in oil and gas zones. The detection of diffusional mixing patterns in hydrocarbon-saturated rocks suggests that diffusion is active, although on average a factor of ~13–18 slower, than in comparable water-saturated rocks.Pattern generation and equilibration times were modelled for each non-steady-state pattern and compared with the time since reservoir filling with oil/gas, revealing that 90% of them could have been generated since filling, but 60% of them would already have mixed to steady state had the initial compositional heterogeneities arisen during or before reservoir filling. This is critical evidence that at least some of the initial heterogeneities must have arisen, and subsequently partially mixed, after filling; these patterns tend to be short (<40 m, usually <20 m). We conclude that it is essential to consider post-filling processes when interpreting 87Sr/86Sr depth profiles. This may enable the effects of post-filling processes to be stripped back to reveal larger-scale patterns inherited from oil/gas filling. This approach provides a new framework for identifying and quantifying barriers to fluid communication in petroleum reservoirs, which could be applied to help optimize oil/gas production and water or gas injection, including CO2 injection for enhanced oil recovery and/or subsurface storage.The evidence for post-fill water-rock interaction and diffusive transport has important implications for porosity/permeability prediction, indicating that key diagenetic processes like quartz cementation may be inhibited by hydrocarbon filling but not stopped altogether. Compositional differences of water within oil/gas zones reveal the folly of using one aquifer water sample as the basis for interpreting water saturations from well resistivity logs for in-place resource estimation. Sr RSA studies may thus be useful in designing water sampling strategies.

Bangladesh-Myanmar Border Relations: A Study of Some Geopolitical and Economic Issues

Myanmar is a neighboring country of Bangladesh with long border. It has huge natural resources such as oil, gas, forestry, fisheries, agricultural land and other mineral resources. Myanmar is a country with an easy access to South Asia, South East Asia, and North East Asia. It is also linked with the Bay of Bengal and Indian Ocean which have strategic importance for navigation, trade, and investment purposes. Two-neighboring countries, China and India, are both beneficiaries through maintaining friendly relations with Myanmar. Both China and India are using Myanmar’s ports, Bay of Bengal and Indian Ocean, for exports and imports. They have also invested a huge amount of money in the different development projects including oil, gas, electricity, regional connectivity, and special economic zones in Rakhine state. The result of the study shows that the relationship between Bangladesh and Myanmar is not very good diplomatically. Bangladesh, being a close neighbor, has not been able to be benefit from Myanmar’s natural resources, strategic location, and trade and investments. It is high time for Bangladesh to look at the potentials that are important in terms of its geo-strategic, geopolitical, and economic interests. The crisis of Rohingya ethnic minority occurs as a result of the lack of intimate relationship between Bangladesh and Myanmar. This paper focuses on pointing out the bilateral problems between these two countries. It also aims to provide some policy recommendations for both countries, particularly Bangladesh, which is suffering tremendously due to Rohingya influx. This study recommends that Bangladesh government should take necessary steps to maintain the relationship with Myanmar’s government to resolve the bilateral border issues amicably. To carry out this study, both secondary and primary data were used qualitatively.

A study on correlations between antimicrobial effects and diffusion coefficient, zeta potential and droplet size of essential oils

Abstract It was hypothesized that inhibition zone of an essential oil (EO) in a Petri dish might be relevant to its diffusion coefficient (DC) into agar medium, which may be calculated from the Fick’s diffusion. Antibacterial activities of cumin, dill weed, fennel, ginger and oregano EOs were evaluated against Campylobacter jejuni and Campylobacter coli. DCs, zeta potential and droplet sizes of EOs were measured. The inhibition zones of EOs had in accordance with DCs whereas they had a reverse relation with droplet size. The measured DCs were in the range of 0.82–1.50 × 10−12 m2 s−1. The effective DC of EOs calculated from the total flux exhibited good correlations with measured DCs. Outcomes of this study may provide a pre-assessment for the antimicrobial activity of any EOs from its DC. Furthermore, it may help to understand the studies on how EOs pass through a bacterium cell and show antimicrobial effects.

ПЕРСПЕКТИВЫ НЕФТЕГАЗОНОСНОСТИ АНТИКЛИНАЛЬНОЙ ЗОНЫ ХАЛИ-НЕФТ ДАШЛАРЫ В СВЯЗИ С ЕЁ ПАЛЕОТЕКТОНИЧЕСКИМИ УСЛОВИЯМИ

Актуальность. Абшеронский нефтегазоносный район, где были проведены исследования, является одним из продуктивных в Азербайджане. Цель поисково-разведочных работ в основном заключается в увеличении добычи углеводородов, а это достигается выявлением новых нефтегазоносных объектов. С этой точки зрения в антиклинальном поясе Хали‒Нефт Дашлары в разрезе палеоген-миоценовых отложений выявление залежей, связанных с антиклинальными и неантиклинальными типами ловушками, имеет важную практическую особенность и это однозначно сыграет немаловажную роль в повышении добычи нефти и газа в республике. Наши исследования были проведены по определяющим нефтегазоносность критериям: геотермическим, литофациальным, тектоническим, палеотектоническим и т. д., по стратиграфическому разрезу палеоген-миоцен и плиоцена для определения новых объектов. Цель: определить с геотермической точки зрения в какой зоне нефтегазообразования в настоящее время находятся отложения продуктивной толщи и, в соответствии с этим, уточнить перспективность зоны, а также исследовать распространенность неантиклинальных ловушек в связи с палеотктоническими особенностями и конседиментационным развитием зоны. Объекты: отдельные структуры, представляющие антиклинальную зону Хали‒Нефт Дашлары, свиты нижнего отдела продуктивной толщи. Методы. Изменения общей мощности и песчанистости отложений продуктивной толщи в исследуемых структурах были проанализированы в локальном и региональном направлениях, были построены соответствующие диаграммы, отражающие закономерности изменения мощности и песчанистости по свитам. Наряду с этим были построены палеопрофили, отражающие палеотектоническое развитие структур антиклинальной зоны Хали‒Нефт Дашлары. Результаты. Построение графика скорости осадконакопления и, в связи с этим, анализ данных, изучение палеотемпературных условий Пираллахи-Келькорской впадины и проведенный анализ позволяют определить время нахождения отложений как продуктивной толщи, так и нижележащих отложений миоцена, палеогена и мезозоя в главной зоне нефтегазообразования, а также сопоставить главные этапы миграции со временем образования структур в пределах данной территории. Результаты всех исследований, проведенных в этом направлении, позволяют утверждать, что область исследований и ее окрестности также являются перспективными с точки зрения нефтегазоносности.

ОЦЕНКА ТЕХНОЛОГИЧЕСКОЙ И ЭКОНОМИЧЕСКОЙ ЭФФЕКТИВНОСТИ ГИДРАВЛИЧЕСКОГО РАЗРЫВА ПЛАСТА С ИСПОЛЬЗОВАНИЕМ ГЕОЛОГО-ГИДРОДИНАМИЧЕСКОЙ МОДЕЛИ, УЧИТЫВАЮЩАЯ ОСОБЕННОСТИ СТРОЕНИЯ КАРБОНАТНЫХ КОЛЛЕКТОРОВ

Актуальность работы.В настоящее время одним из эффективных методов интенсификации добычи нефти на территории Пермского края и во всем мире является гидравлический разрыв пласта. Проведенные мероприятия гидравлического разрыва пластачасто сопровождаются увеличением обводненности добываемой продукции в виду того, что в процессе проведения мероприятия трещина гидравлического разрыва пластараспространилась в вертикальном направлении и тем самым увеличила каналы, соединяющие водонасыщенную и нефтяную зоны. Данного негативного последствия вполне можно было избежать, если бы перед проведением работ на скважине данное мероприятие было смоделировано на геолого-гидродинамической модели, которая учитывает особенности геологического строения данной залежи. Знание особенностей строения карбонатных залежей позволяет значительно уточнить и улучшить действующие геолого-гидродинамические модели. Соответственно использование геолого-гидродинамической модели, которые учитывают особенности строения карбонатных объектов, позволит подобрать рациональную систему разработки и обеспечить оптимальные геолого-технологические мероприятия и как следствие приведет к снижению экономических рисков. Цель: оценка технологической и экономической эффективности гидравлического разрыва пласта с использованием гидродинамической модели, которая учитывает геологические особенности строения карбонатной залежи. Объект: фаменская карбонатная залежь Гагаринского месторождения. Методы: использование гидродинамического симулятораTempest версии 8.3.1 компании Roxar. Результаты. Полученные в ходе моделирования технологии гидравлического разрыва пластана шести скважинах-кандидатах результаты показали, что использование стандартной модели (применяется на сегодняшний момент) по сравнению с модифицированной геолого-гидродинамической моделью (учитывает анизотропию проницаемости и трещиноватость) приводит к завышению одних технологических показателей (прирост дебита нефти и накопленная добыча нефти) и к занижению других (обводненность добываемой продукции), что соответственно в последующем может привести к искажению картины экономической составляющей мероприятий.Проведенный экономический анализ позволил установить, что чистый дисконтированный доход, рассчитанный на модифицированной геолого-гидродинамической модели,оказались в 3,7 раз меньше по сравнению со стандартной, что является несомненно важными показателями при подборе скважин-кандидатов для планирования геолого-технологических мероприятий.

Oil Reservoir on a Chip: Pore-Scale Study of Multiphase Flow During Near-Miscible CO2 EOR and Storage

CO2 injection into oil reservoirs is widely accepted as an effective enhanced oil recovery and CO2 storage technique. While oil recovery and CO2 storage potential of this technique have been studied extensively at the core-scale, complex multiphase flow and fluid–fluid interactions at the pore scale during near-miscible CO2 injection have not, and this area needs more study. To address this, a unique high-pressure microfluidic system was implemented which allows for the optical visualisation of the flow using optical microscopy. The results show that during tertiary near-miscible CO2 injection, when CO2 phase contacts the oil, the oil spreads as a layer between the CO2 phase and water preventing CO2 phase from contacting the water phase. This is attributed to the positive value of the spreading coefficient. Furthermore, due to the presence of pore-scale heterogeneity in the chip, an early breakthrough of CO2 was observed causing a large amount of oil to be bypassed. However, after CO2 breakthrough, CO2 gradually started to diffuse and flow inside the bypassed oil zones in the transverse directions which is a characteristic of capillary crossflow. The driving force for this capillary crossflow was the interfacial tension gradient formed by the diffusion of CO2 into the oil phase and the extraction of light to medium hydrocarbon components from the oil into the CO2 phase. The same mechanism led to the recovery of the bypassed oil trapped in dead-end pores. This unique mechanism produced the majority of the bypassed oil after CO2 breakthrough and significantly increased the oil recovery. In our three-phase flow water-wet system, CO2 flow displaced the water through a multiple displacement mechanism which is unique to three-phase flow. CO2 displaced the oil in oil-filled pores thorough bulk flow, and the spreading oil layers were gradually produced by layer flow.

Squeeze Cementing Using Braden Head Squeeze Method On ‘Dsr-29’ Well Tarakan Field PT. Medco E&amp;P Indonesia

Squeeze cementing is an operation in which a cement slurry is pressed to a certain pressure on an oil or gas well. The purpose of doing squeeze cementing is to block water or gas flow and oil zones, close certain zones to produce other productive zones, repair damaged casing, and as a continuation of primary cementing work. Squeeze Cementing is done when workover a well. Workover and well service operations in a well, is a type of activity in the oil industry aimed to maintain wells so that they can continue to produce optimally and increase productivity back wells due to production problems. Squeeze Cementing Project on Tarakan field, DSR-29 well serves to block perforation that is no longer needed or open hole section at a depth of 630 - 635 m (670 MZ) so that a reservoir can be isolated and the casing can be firm or strong against pressure. Squeeze cementing method used in the well is the Braden Head Squeeze method. In the middle of workover process, there are problems such as existence of remaining perforating gun, and gas traps. Certain procedure is applied so that the cementing process has been carried out successfully.

FEATURES OF THE DEVELOPMENT OF WATER OIL ZONES OF DEPOSITS WITH HIGH VISCOSITY OIL

He process of developing platform-type oil fields is significantly affected by water oil zones (WOZ), which contain significant oil reserves. In most cases, there is a lag and insufficient production of WOZ in comparison with the initial pure oil parts of the reservoir. This lag is associated with many factors: technological (operating conditions, grid density) and geological (layer and zonal heterogeneity, the ratio of oil-saturated and water-saturated capacities, the configuration and dimensions of the upper water storage zone, their occurrence relative to the anhydrous parts of the deposits, etc.). This article discusses the features of the development of oil fields in the north-west of Bashkiria, establishes the relationship between the main development indicators, such as the maximum production rate, oil recovery coefficient, water cut, and density of the well network, both among themselves and from various external factors. Besides, additional difficulties are identified associated with increased viscosity, density and low gas saturation of reservoir oil in water oil zones. For analysis, we will consider 5 of the most characteristic sections of the Arlan area: Ashitskaya I, Saklovskaya IV, Arlanskaya V, Arlanskaya VI and Urtaulskaya VIII, where water oil and fully oil zones of the CVI layer are developed. These areas have significant oil reserves in the oil and water zones, while the selected areas are hydrodynamically quite isolated either by deflections or by the absence of reservoirs or low permeability formations, which determines the independence of the relationships established between the considered technological indicators from any external geological factors.

Polarity and phase in reflection seismic data: Stratton field

Seismic interpretation is often based on the analysis of amplitude anomalies, which depend strongly on the seismic wavelet presented in the data. However, if the wavelet polarity or phase is unknown or fine-scale impedance variations are complex, interpretation of the anomaly can be ambiguous. The Stratton data volume contains a dome-like feature that may be interpreted as the top of a potential gas target, the top of a buried tight reef, or as a thin layer of either higher or lower impedance, depending on the interpreter’s assumption of polarity and phase. This observation provoked our interest in modeling the seismic response of domes using wavelets of differing polarity and phase on stacked data. Because there appears to be only a single event, perhaps the top of an anomalous feature, and not its base, a “gradational” decrease in impedance contrast with depth is included among our models. We have determined that the seismic response from a layer with an impedance contrast decreasing with depth is quite different from that of a layer with constant impedance contrast when the bed thickness exceeds one quarter of the wavelength; that is, a reflection from the base of a “thick” gradational layer is not visible, as expected. We independently determine the polarity and phase of the Stratton data, finding that the surface-based seismic and VSP data are of opposite polarity (European and American, respectively), and concluding that the dome structure represents the top of a gradational thick bed. A model based on a nearby reservoir containing thin gas, oil, and water zones supports this conclusion. This anomaly in the Stratton data appears to represent a hydrocarbon reservoir with thin layers of gas and oil, each with lower impedance than the surrounding beds but with stepwise decreasing contrast over a sufficient thickness to avoid a basal reflection at these wavelengths.

Main Controlling Factors for the High Production of Tectono-Stratigraphic Reservoirs in Continental Down-Faulted Basin

Huoduomoer structural zone is one of the most favorable oil and gas accumulation zones in Beier depression of Hailaer basin. However, the exploration in this zone has experienced a long and tortuous process, and the exploration is almost stagnant until the natural production capacity of well x1 has obtained daily output of 472m3, which has achieved a major breakthrough in the exploration of tectono-stratigraphic and stratigraphic unconformity reservoirs in this structural zone. Based on the comprehensive study of the subdivided layers of the structural belt, this paper holds that the Nantun Formation suffered from long-term denudation after deposition, the Nantun Formation at the high part of the uplift belt was denuded completely, and the remaining Nantun Formation at the periclinal area was the main target layer for exploration. Based on the analysis of the main controlling factors of hydrocarbon accumulation, it is considered that feldspar lithic sandstone and lithic sandstone mainly developed in the subaqueous distributary channel deposition of braided river delta front are easy to be leached and eroded, forming high-quality reservoir with secondary porosity near the unconformity surface, and the multi-direction oil and gas migration system is the key to the oil and gas accumulation; the stable and thick mudstone deposition in the large section provides a good sealing condition for traps.

Preservation of lateral pressure disequilibrium during the uplift of shale reservoirs

A pressure gradient increase from normal pressure in oil zones to overpressure in dry gas zones indicates a lateral disequilibrium of pore pressure in many shale reservoirs. In this work, conditions for the preservation of the lateral pressure disequilibrium during uplift and erosion are investigated. Numerical simulations were conducted by coupling pressure–volume–temperature (PVT) and fluid dynamic calculations. Results show that temperature decrease and pore volume expansion during erosion tends to increase the pressure gradient in the gas or condensate zone and tends to decrease the pressure gradient in the black oil zone; therefore, the PVT effect tends to enhance lateral pressure disequilibrium during erosion. Low permeability is crucial for the preservation of the lateral pressure disequilibrium. The persistence of disequilibrium over geological time (tens of millions of years) requires extremely small vertical permeability (sub-picodarcy range) and horizontal permeability (10 nd or even lower). The horizontal permeability is 10–100 times smaller than laboratory measurements on shale plugs, indicating a discontinuity of laminations and fractures within a shale formation.

Mineral Oil Slicks Identification Using Dual Co-polarized Radarsat-2 and TerraSAR-X SAR Imagery

This study is devoted to a generalization of C-band Radarsat-2 and X-band TerraSAR-X synthetic aperture radar (SAR) data in the form of a diagram serving to easily identify mineral oil slicks (crude oil and emulsions) and separate them from the other oil slicks. The diagram is based on the multi-polarization parameter called Resonant to Non-resonant signal Damping (RND) introduced by Ivonin et al. in 2016, which is related to the ratio between damping within the slick of the short waves and wave breakings. SAR images acquired in the North Sea during oil-on-water exercises in 2011–2012 containing three types of oil spills (crude oil, emulsion, and plant oil) were used. The analysis was performed under moderate sea conditions (wind speeds of 2–6 m/s and sea wave heights of less than 2 m), the incidence angles of 27°–49°, and the signal-to-noise ratio (SNR) of −3 to 11 dB within slicks. On the diagram plane, created by the RND parameter and the Bragg wave number, the mineral oil samples form a well-outlined zone, called a mineral oil zone. For C-band data, the plant oil samples were clearly distinguished from the mineral oils in the diagram. Determination of the confidence level for the detection of mineral oils versus plant oil was proposed using the mineral oil zone boundaries. The mineral oil data with SNR within slicks better than 2 dB lay within this zone with a confidence level better than 65%. The plant oil data with the same SNR lay outside this zone with a confidence level of better than 80%. For mineral oil with SNR of −3 dB, the confidence level is 55%.

RESEARCH OF THE MECHANISM OF OIL RECOVERY FROM HYDROCARBON DEPOSITS WITH LOW PERMEABILITY RESERVOIRS

The main part of Russia's hard-to-recover reserves is 73% for low-grade and carbonate reservoirs, 12% for high-viscosity oil, about 15% of extensive sub-gas zones of oil and gas deposits and 7% of reservoirs lying at great depths. The development of such stocks with the usage of traditional technologies is economically inefficient. It requires the application of new technologies for their development and fundamentally new approaches to design, taking into account the features of extraction of hard-to-extract reserves (HtER). The purpose of this research is to find ways to improve the performance of low-permeability reservoirs. To accomplish this task, the Novobogatinsk South-Eastern Oil Field has been taken as an example and described. The necessary properties of production facilities in the field are highlighted, along with economic feasibility and technological efficiency. The reserves involved in the development are determined and, thanks to the knowledge of the geological oil reserves of the deposits, the potential oil recovery factor is calculated with the existing development technology. As a result of the research, development options were worked out with the results of the calculation of design indicators for the field as a whole. The comparison of oil recovery schedules and ORI, as well as the layout of wells, have been presented. As a result of the study, a description of 3 options for the development of design indicators for the field as a whole is given. The figures show oil production graphs, as well as location patterns. The authors of the study conclude which of the recommended development options can help extract maximum oil reserves.

Conditions of oil and gas formation in the territory of the Eastern and Central Ciscaucasia

The results of studies of hydrocarbon systems of the Eastern and Central Ciscaucasia are shown. The research area covers part of the Scythian platform, namely, the northern side of the Terek-Caspian foredeep, the north-eastern part of the East Kuban depression, the Tersko-Kum depression and the Stavropol arch. Based on the results of the work and basin modelling of hydrocarbons generation, emigration and accumulation processes, the reconstruction of the history of oil and gas formation and oil and gas accumulation in the sedimentary cover of the region was completed. The basin modelling of hydrocarbon formation processes in Central and Eastern Ciscaucasia was carried out using the PetroMod (Schlumberger) program complex. The obtained results made it possible to determine the dynamics of organic substance transformation processes, evolution of oil and gas formation zones, time and expected paths of hydrocarbon migration and phase composition and degree of hydrocarbon saturation of the section. The model reliability was corrected by comparing the values of benchmarks (modern reservoir temperatures measured in wells, with their calculated values obtained as a result of modelling). The location of possible foci of hydrocarbon generation in the sedimentary cover, the migration paths, the phase composition of hydrocarbons, the intensity of hydrocarbon saturation within individual tectonic zones and structures were determined. It has been established that the main foci of hydrocarbon generation in the southern part of the studied region are located in the Chechen depression (Tersko-Caspian deep), on the platform part–in the zone of the Manych deep and Nogai stage.

Methodology for estimating the prospective CO2 storage resource of residual oil zones at the national and regional scale

Residual oil zones (ROZs) are increasingly gaining interest as potential reservoirs for carbon dioxide (CO2) storage. Here, we present a national- and regional-scale methodology for estimating prospective CO2 storage resources in residual oil zones. This methodology uses a volumetric equation that accounts for CO2 storage as a free phase in pore space and as a dissolved phase in oil and does not assume any oil production associated with CO2 storage. Reservoir modeling and the CO2-SCREEN tool are used to demonstrate that CO2 storage in residual oil zones will predominantly take place in the free phase (approximately 92–97%) with some storage as dissolution in oil (approximately 3–8 %). Based on this preliminary demonstration, the CO2 storage efficiency for ROZs using this national- and regional-scale method ranges from 0.61 to 7.1 %. This range indicates ROZs have a similar efficiency potential for storing CO2 as deep saline formations (0.51–5.4 %).

ИЗОТОПНЫЙ СОСТАВ НЕФТЕЙ АРЫСКУМСКОГО ПРОГИБА (ЮЖНЫЙ КАЗАХСТАН)

Одним из обсуждаемых направлений в современной геологии является нефтегазоносный потенциал более глубоких горизонтов, в том числе фундамента осадочных бассейнов. Генезис залежей нефти является предметом острых дискуссий. Современные геохимические методы исследования вещества в совокупности с приборными возможностями, к которым можно отнести изотопный масс-спектрометр, позволяют различать нефти, генерированные разными нефтематеринскими отложениями. Важнейшим показателем, идентифицирующим генезис углеводородов по отношению к зонам нефтегазообразования в конкретном разрезе, является изотопный состав углерода. Каждая зона, в свою очередь, характеризуется индивидуальными геохимическими и термодинамическим параметрами, включающими тип и степень преобразованности рассеянного органического вещества, современные геотемпературы и палеотемпературные условия, фазовый состав углеводородов. Месторождения Арыскумского прогиба Южно-Торгайского нефтегазоносного бассейна (Южный Казахстан) связаны с различными литолого-стратиграфическими комплексами юрско-меловых отложений, девонско-нижнекаменноугольными образованиями квазиплатформенного комплекса и дезинтегрированными выступами фундамента. В последние годы перспективы Южно-Торгайского прогиба расширяются и связываются с доюрскими отложениями. В этой связи возникает вопрос о природе углеводородных масс и формировании их скоплений в мезозойских и домезозойских образованиях Арыскумского прогиба. Цель исследования: проведение сравнительного анализа изотопного состава углерода нефтей Арыскумского прогиба из мезозойских, палеозойские отложений, а также из зоны контакта палеозоя с мезозойским осадочным чехлом для решения генетических задач и выяснения особенностей формирования нефтяных месторождений Арыскумского прогиба. Результаты позволили установить закономерность изменения величины d13С в зависимости от возраста, глубины, территориальной приуроченности месторождений в пределах Арыскумского прогиба и на основании изотопных данных высказать предположение о генезисе мезозойских и домезозойских нефтей.

Pushing the Limits of Damage Identification Through the Combined Use of Coiled Tubing, Distributed Sensing, and Advanced Simulations: A Success Story from Japan

Summary The success of water-conformance operations often depends on clear identification of the water-production mechanism. Such an assessment can be complicated significantly when formation damage is also occurring. Coiled tubing (CT) and distributed-temperature sensing (DTS) were combined to overcome challenging conditions (high temperature, low injectivity, high deviation, long perforated intervals, and wellbore damage) to identify damaged oil zones and suspected water-bearing zones in an onshore well in Japan. The subject well experienced unexpected contamination of oil-based mud (OBM) and completion brine, which generated tight emulsions in the wellbore during the completion phase. Despite a thorough cleanout and perforations, severe damage was observed and mostly water was produced. With the presence of persistent damage in the wellbore preventing any logging-tool use, DTS was selected as main diagnostic method, with the fiber optics being deployed with CT to ensure full coverage of the interval. Acquired temperature surveys were processed and matched with simulated profiles, which tested various scenarios of damage. Ultimately, results were used to drive the design of remedial actions. The following operational sequence was implemented: temperature-baseline measurements (6 hours), brine bullheading through the CT/tubing annulus at 0.2 bbl/min (22 hours), and shut-in (6 hours) for warmback. The long injection stage was required to ensure that enough fluid was being injected across the entire interval while keeping the downhole pressure at less than the fracturing pressure. Real-time DTS data during pumping and warmback indicated the presence of a main intake zone in the middle of the interval. Below that section, only marginal temperature changes were observed, which might be a direct consequence of the low-injection-rate limitation. Post-job processing using numerical temperature simulation was performed to complement that analysis and quantify intake along the well. Temperature inversion against the DTS response was conducted independently using two different simulators, both of which yielded similar profiles, confirming the soundness of this approach. The results supported the presence of a larger intake in the middle interval and also showed that the bottom zone most likely took some fluid. Complementary information eventually pointed to the larger-intake interval being the primary water-bearing zone. This analysis led to the selection of the remedial actions to be performed in damaged oil zones. This study demonstrates how integrated use of data from design to job execution to interpretation can change the perception of a well and how DTS can be a viable alternative to damage and water-production diagnostics in some extreme conditions when production-logging tools (PLTs) cannot be used. Results of the DTS quantitative analysis provided local damage profiles along the well, which were critical to the subsequent planning of remedial activities.

New technologies for site selection and evaluation of salt-cavern underground gas storages

In order to meet the demand of constructing salt-cavern underground gas storages (UGSs) in favorable salt mines for the regions that are neither major oil and gas production zones nor major natural gas consumer markets in South China, and solve the problems of unclear conditions for selecting salt-cavern gas storage sites and of inconsistent content and depth in evaluating gas storage conditions, based on investigation and analysis of salt-cavern UGS data in China and other countries, we proposed the principles of selecting gas storage sites in combination with geology and ground surface conditions, and developed a set of technologies in evaluating construction conditions for salt-cavern gas storages. By applying the selection principles of salt-cavern UGSs, we selected and sorted some salt mines in the three major natural gas consumer markets (the Yangtze River Delta, Central–South China, and Southeast Coast of China), and evaluated the conditions of constructing a gas storage in the Huai'an salt mine with better conditions. The following findings were obtained. First, the principles of selecting gas storage sites can be applied to quickly optimize and sort the selected targets, including 6 items of geological factors such as structure, burial depth, salt-bearing layer thickness, NaCl content, top rock, and reserves, and 3 other items such as ground surface conditions, water source and brine, distance from pipeline networks. Second, the evaluation system of UGS construction conditions integrates features of structure and salt-bearing strata, tightness, firmness, dissolubility evaluation, prediction of gas storage scale, and analysis of cavity making condition. In conclusion, the new evaluation technologies can not only effectively guide the site selection and evaluation of salt-cavern UGSs but provide foundation and power support for their scheme designs, and the presented pilot proposal for utilizing thick interlayers has achieved a perfect on-site application effect. This study is of great significance for constructing UGSs in China.