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Wei, Chenji (PetroChina) | Wang, Yuhe (Texas A&M University at Qatar) | Li, Baozhu (PetroChina) | Zhang, Jingjian (PetroChina International Company Ltd.) | Zhang, Wan (China National Oil and Gas Exploration and Development Company Ltd.) | Wu, Jin (PetroChina)
Miscible gas displacement is a promising enhanced oil recovery method in carbonate reservoirs technologically and economically. Though miscibility can be well understood using core-scale experimental and numerical models, the miscible displacement process in complex heterogeneous and multi-dimensional carbonate reservoirs is more complicated and needs further analysis. In this paper, we present our effort in probing the miscible gas displacement characteristics in a carbonate reservoir with baffles based on data from a real field.
Using compositional modeling, we evaluate miscible gas injection process in heterogeneous carbonate reservoir with baffles. Together with the detailed miscible front development in specific parts of the reservoir, the analysis also takes advantage of gravity stabilization realized by implementing the corresponding injector-producer pattern.
This paper presents an analysis of miscible gas displacement process, which can be considered as an extension from a simple one-dimensional model to more complex heterogeneous and multi-dimensional system. Using data from a real carbonate reservoir with baffles, we analyze the CO2 injection for the drive processes. The analysis is combined with the consideration of the effects of baffles and wettability. Mainly due to the multi-dimensional flow, our results show that the minimum miscibility pressure is higher than one-dimensional system. Besides, our results indicate gravity stabilization could be well maintained by proper injector-producer pattern. We also report the sensitivity analysis for wettability changes in carbonates.
This paper offers a study to analyze and evaluate miscible gas flooding process in heterogeneous carbonate reservoirs. Using a real case data, the study can help reservoir engineers to better design miscible gas flooding for other similar situations.
Wei, Chenji (Research Institute of Petroleum Exploration and Development, CNPC) | Zheng, Jie (Research Institute of Petroleum Exploration and Development, CNPC) | Ouyang, Xiaohu (China Petroleum Pipeline Engineering Co., Ltd, CNPC) | Ding, Yutao (China National Oil and Gas Exploration and Development Company Ltd. CNPC) | Ding, Mingming (China National Oil and Gas Exploration and Development Company Ltd. CNPC) | Lin, Shiyao (China National Oil and Gas Exploration and Development Company Ltd. CNPC) | Song, Hongqing (University of Science and Technology Beijing)
Understanding the heterogeneity is critical for a successful water injection in a carbonate reservoir. Thief zone is one of the most obvious forms of heterogeneity, which indicates the thin layer with higher permeability compared to the average reservoir permeability. The existence of thief zone results in earlier water breakthrough and faster water cut increase, which then lead to lower sweep efficiency and smaller recovery factor. Therefore, determining the distribution of thief zone and its impact towards production, and proposing a corresponding development plan are very important.
In this paper, a novel method is established to determine the thief zone distribution based on dynamic surveillance data. A new index is proposed as the relative contribution index to characterize the relative contribution of a certain layer, which is fundamental for thief zone determination. In addition, effect on water flooding development of thief zone's location is studied by experimental and theoretical analysis. The changes of water cut and production rate are analyzed under different conditions such as location of the thief zone, injection rate, and variogram. Finally, optimized development strategy is proposed to deal with the existence of thief zone.
Distribution of thief zone is characterized based on the proposed method, which indicates that thief zone development has intimate relationship with depositional facies and diagenesis. Experimental and theoretical analysis results show that the present model considering stratified water-flood is consistent with the experimental results. The water displacement effect is the best when the thief zone is located in the upper reservoir. This paper also points out the optimal adjustment period for water shutoff and profile control of the reservoir with thief zones. In addition, the greater the injection rate, the faster the water cut increase. Furthermore, the smaller the variogram, the slower the water cut increase, and the later the water breakthrough time.
This study provides a method to characterize thief zone, which can be used as a reference for similar oilfield development. In addition, it provides a quick and reasonable guide in the later adjustment of water flooding development of carbonate reservoirs with thief zones.
Liu, Shuangshuang (PetroChina) | Wei, Chenji (PetroChina) | Gao, Yan (PetroChina) | Li, Yong (PetroChina) | Luo, Hong (PetroChina) | Liu, Zhuo (PetroChina) | Xiong, Lihui (PetroChina) | Zheng, Jie (PetroChina) | Lou, Yuankeli (PetroChina)
The Middle East carbonate reservoirs are mostly reef flat sedimentary complexes, which are high heterogeneous and have extensive baffles. It brings great challenges to the efficient development of such reservoirs. Focus on the problem, a method of describing baffle distribution conjunctively using static and dynamic data is put forward in this paper. The distribution of baffles in the target formation is characterized based on core observation, well loggings, image logs, etc. Then, their impact towards reservoir performance is evaluated based on production data and dynamic surveillance data. Based on the study, it is acquired that cementation mainly controlled the upper baffles and compaction controlled the lower. Generally speaking, permeability of baffle is higher in the crest area and lower in the flank area. Baffles are stably distributed throughout the reservoir, although their ability to block fluid flow varies from region to region. The existence of baffles and their ability to block fluid flow had impact to the development effect, so development optimization and scheme comparison carried out. The corresponding development strategies are proposed for reservoirs with extensive baffles. Injectors and producers with highly-deviated well-type will help establish effective displacement system and achieve better reservoir production, it can improve the development effect and enhance oil recovery. This study offers a comprehensive case study for engineers and geologists to better understand this reservoir, it also provides a methodology that can be referred when developing similar fields.
Carbonate reservoirs accounted for about 40% of the world's total oil and gas reserves, and oil and gas production accounted for about 60% of the total output [Roehl P O et al. 1985]. About 80% of the oilbearing formations in the Middle East are carbonate rocks, and the oil and gas production accounts for nearly 2/3 of the world output [Alsharhan A S et al. 1997]. Carbonate reservoirs contain more than 50% of the world's conventional oil and gas reserves, and generally have relatively low recovery rates [S.K.Masalmeh et al. 2012].
Carbonate reservoir types are diverse, and different types of reservoirs have great difference in permeability characteristics [Zhang Ningning et al. 2014]. The carbonate reservoirs in China mainly include fractures and fractured-cavity carbonates, the displacement mechanism of which is mainly carried out on the fractured-cavity media [Jin Zhijun et al. 2010, Liu Xiao-lei et al. 2017]. The large-scale carbonate reservoir in the Middle East is mailly reef-flat sedimentary complex, and the distribution of reservoir properties in the plane and in the vertical direction is very complicated [Bai Guoping 2007]. The heterogeneity is serious in lithology, physical property and reservoir scale [Jia Ailin et al. 2013]. The baffles are non-permeable or low-permeability layer sandwiched between the smallest cells in which the regional contrast can be performed [Cui Jian et al. 2013]. The existence of baffles strengthens the heterogeneity of the reservoir and makes the relationship between oil and water movement complex and changeable, which is one of the main factors affecting the reservoir development effect [Han Rubing et al. 2014].
Carbonate reservoirs are of strong heterogeneity. Their geological features and dynamic behaviors vary significantly for different types of carbonates. Characterizing the distribution of different types of carbonates and proposing different development strategies are critical for a successful development of carbonate reservoirs. This paper focuses on a super-giant carbonate reservoir with OOIP (Original Oil in Place) of more than 20 billion barrels. However, it has been naturally depleted over the past 40 years. Its reservoir pressure is approaching the bubble point pressure. Therefore, it is critical and urgent to propose optimized water flooding plan for this reservoir.
In this paper, the dataset includes seismic data, well logs, production history, dynamic surveillance data, et al. Firstly, three reservoir types are characterized as good, medium and poor reservoirs based on static and dynamic data. Then, the stacking patterns of different reservoir types are concluded and their distributions are determined, which provide us the foundation to propose customized water flooding plan. Finally, the water flooding performances of different stacking patterns are analyzed and full-field development strategies are proposed based on fine-scale geological modeling and numerical simulation.
Results indicate that stacking pattern has intimate relationship with facies map. For example, the distribution of stacking pattern A, in which good reservoir accounts for the majority, is consistent with the distribution of favorable grainstone shore facies, indicating very good reservoir quality that resulted in higher production rate, longer stable production period, and slow decline. In addition, different offtakes, well patterns, pressure maintenance, well types of different reservoir stacking pattern are determined based on the simulation results and distribution of different stacking patterns. The EUR is increased by more than 20% compared with natural depletion.
This paper offers a reference case of grouping different types of reservoirs and proposing customized water flooding plan, which help engineers and geologists to better develop other similar fields.
Liu, He (Research Institute of Petroleum Exploration and Development, PetroChina) | Yang, Siyu (Research Institute of Petroleum Exploration and Development, PetroChina) | Wei, Chenji (Research Institute of Petroleum Exploration and Development, PetroChina) | Yao, Zixiu (Research Institute of Petroleum Exploration and Development, PetroChina) | Ye, Peng (Daqing Oilfield Limited Company, PetroChina)
Daqing oilfield is the largest chemical flooding oilfield in the world. The polymer flooding can enhance oil recovery by 10-15%, while the ASP flooding can enhance oil recovery by over 20%, which is 1.5 times more efficient than the polymer flooding. By the end of 2016, there are 31529 chemical flooding wells, which cover the already proved reserves of more than 1 billion tons. These wells have had cumulative oil production of 0.2 billion tons, and have production more than 10 million tons each year since 2001, thus playing an important role in the production of Daqing Oilfield. Dynamic monitoring, as an important part for oilfield development, aims to acquire the dynamic and static information in oilfield development, and to provide data for oilfield development dynamic analysis and adjustment by means of testing, logging, coring and analyzing. Since chemical flooding is different from water flooding in oil displacement mechanism, oil-water migration and development process, some indexes in chemical flooding process are especially significant, which are directly related to the development effects, and require timely and dynamic monitoring. Because of the high viscosity of chemical flooding fluids, the monitoring techniques based on the radioactive isotope carrier method of water flooding is not suitable due to problems such as serious contamination and no even dispersion. Therefore, on the basis of tracer monitoring technique for water flooding wells, chemical injection profile logging technique based on electromagnetic flowmeter, oxygen activation and tracer correlation is formed for high viscosity fluids, and has been applied in Daqing Oilfield in more than 4000 wells. This technology could guide dynamic analysis and tracking adjustment, and could have further development of continuous fluid monitoring chemical flooding, and then expand the electromagnetic exploration techniques into the chemical flooding fluid description.
Wang, Min (Texas A&M University) | Wei, Chenji (Research Institute of Petroleum Exploration & Development, PetroChina) | Song, Hongqing (University of Science and Technology Beijing) | Efendiev, Yalchin (Texas A&M University) | Wang, Yuhe (Texas A&M University)
In this paper, we couple Discrete Fracture Network (DFM) and multi-continuum model with Generalized Multiscale Finite Element Method (GMsFEM) for simulating flow in fractured and vuggy reservoir. Various scales of fractures are treated hierarchically. Fractures that have global effect are modeled by continua while the local ones are embedded as discrete fracture network based on the geologic observation. For independent vugs, a continuum is used to represent their effects with specific configuration that there's no intra-flow of this continua. GMsFEM enables us to systematically develop an approximation space that contains prominent sub-grid scale heterogeneous background information based on the multi-continuum and DFM model. Conforming unstructured mesh is used to surrender the application of random discrete fracture networks. This paper targets on the improvement of the flow simulation performance in complex high-contrast domain by extending the ability of multiscale method to modeling arbitrary discrete fracture network. This advancement by GMsFEM is motivated by the limited capability of Multiscale Finite Element Method (MsFEM) on modeling discrete fractures when multiple fracture networks present in same coarse block. Multiple numerical results are shown to validate the efficiency of our coupled method.
Wei, Chenji (PetroChina) | Wang, Yuhe (Texas A&M University at Qatar) | Ding, Yutao (PetroChina) | Li, Yong (PetroChina) | Shi, Jing (PetroChina) | Liu, Shuangshuang (PetroChina) | Tian, Changbing (PetroChina) | Li, Baozhu (PetroChina) | Xiong, Lihui (PetroChina) | Zhang, Qi (PetroChina)
This paper presents an uncertainty assessment project using Artificial Neural Network (ANN) for a giant multi-layered sandstone reservoir in Middle East, which contains several uncertainties and associated risks. Uncertainty quantification in history matching, production forecasting and optimization approaches often requires hundreds of thousands of forward flow simulations to explore the uncertain parameter space, causing forbidden computational time requirement, especially for large-scale reservoir models. In order to bypass this limitation, one can use a proxy to replace the time-consuming flow simulator. In this work, an optimized ANN is used as the proxy and an uncertainty assessment workflow is implemented for the giant Cretaceous multi-layered sandstone reservoir using a global optimizer. Using the ANN based uncertainty assessment framework, the impacts of the main uncertain parameters on production forecasting are assessed for this multi-layered sandstone reservoir. Then, field development optimization is also performed to optimize wells injection and production rates to maximize the economic measures considering uncertainties. Using a real field as a case study, the capability of our uncertainty assessment workflow is demonstrated. The optimized ANN successfully captures the complex nonlinear dynamics as a proxy and significantly reduced the computation time.
Wei, Chenji (Research Institute of Petroleum Exploration & Development, PetroChina) | Li, Yong (Research Institute of Petroleum Exploration & Development, PetroChina) | Song, Benbiao (Research Institute of Petroleum Exploration & Development, PetroChina) | Tian, Changbing (Research Institute of Petroleum Exploration & Development, PetroChina) | Li, Baozhu (Research Institute of Petroleum Exploration & Development, PetroChina) | Zhou, Jiasheng (Research Institute of Petroleum Exploration & Development, PetroChina) | Zheng, Jie (Research Institute of Petroleum Exploration & Development, PetroChina) | Luo, Hong (Research Institute of Petroleum Exploration & Development, PetroChina) | Lan, Jun (Research Institute of Petroleum Exploration & Development, PetroChina)
Accurately understanding the geological and dynamic characteristics determines the recovery and life cycle of a reservoir. Several uncertainties and risks exist during the development especially for giant multilayered sandstone reservoirs. Pilot is one of the most effective steps to manage risks and reduce uncertainty, which help better understand the reservoir, expose the conflict during development, propose corresponding surveillance plan, determine development plan, and eventually improve the reservoir performance. This study focuses on a giant Cretaceous multi-layered sandstone reservoir in the Middle East, which started to produce since 1960s without any energy supply, and the current reservoir pressure is approaching the bubble point pressure. Therefore, water flooding is urgently needed. In order to reduce uncertainty and risks, criteria and workflow of selecting waterflood pilot is proposed by integrating the geology, dynamic data, well status, and existing facilities etc.. 4 pilots are selected and each pilot represents a typical reservoir type to better understand the performance and adaptability of different development plan. Each pilot has its own specific objectives and detailed operation plan. Finally, surveillance plans are proposed based on geological understanding, dynamic behavior, and simulation results. According to the proposed criteria and workflow, pilots are selected to represent good, medium, and poor reservoir quality respectively.
Alfaleh, Abdulhamed (Saudi Aramco) | Wang, Yuhe (Texas A&M University at Qatar) | Yan, Bicheng (Texas A&M University) | Killough, John (Texas A&M University) | Song, Hongqing (University of Science & Technology Beijing) | Wei, Chenji (PetroChina)
Data analysis is one of the most important topics in any industry. In petroleum engineering, the large, complex, and multi-dimensional reservoir data sets (big data) presents a challenge for engineers to study the masses of unstructured information and make decisions. A new approach to analyze complex data is called Topological Data Analysis (TDA) which aims to extract meaningful information from such data. TDA relies on the concept that complex data has shapes where shape has meanings. It analyzes the shape of complex data, identifying clusters and their statistical significance. The objective of this paper is to introduce TDA to reservoir engineering using an example of inverted 4D seismic data for studying reservoir connectivity and compartmentalization.
In this paper, we introduce the principles of TDA and discuss its potential in reservoir engineering, which could allow identification of reservoir engineering data behavior, recognition of new opportunities, detection of anomalies and events, and minimizing uncertainties. The TDA procedures are introduced using inverted 4D seismic data set to study reservoir connectivity and compartmentalization. The process to generate and process the data set is explained. Similarity distance function and lenses are defined and used to create TDA graphs for feature identification and analysis.
It is shown that TDA is able to predict the compartmentaliztion of the reservoir models with various process configurations. Variance normalized Euclidean and topological neighborhood function are used successfully to compartmentalize the reservoir model. Using normalized input dataset, correlation and principle component analysis also create similar compartments. The success of TDA in discovering meaningful patterns is attributed to the similarity distance function representing the objective of study, one or more lenses exposing the data, and the right combination of input data, similarity distance function and lenses.
A promising big data analysis method, TDA, is introduced to reservoir engineering application with principles, procedures and examples. It has been shown that TDA can automatically discover critical intelligence within the 4D seismic data set for studying reservoir connectivity and compartmentalization, which are essential to the accuracy of forecasts and development plans, the validity of reservoir simulation, and the success of performance diagnostics and optimization.
Zhu, Yixiang (Research Institute of Petroleum Exploration and Development, PetroChina) | Zhao, Wenzhi (Research Institute of Petroleum Exploration and Development, PetroChina) | Song, Benbiao (Research Institute of Petroleum Exploration and Development, PetroChina) | Deng, Xingliang (Tarim Oilfield Company, PetroChina) | Wei, Chenji (Research Institute of Petroleum Exploration and Development, PetroChina) | Yang, Haijun (Tarim Oilfield Company, PetroChina) | Gao, Yan (Research Institute of Petroleum Exploration and Development, PetroChina) | Cai, Zhenzhong (Tarim Oilfield Company, PetroChina)
The reservoir characterization and prediction of carbonate reef-flat complexes often have great difficulties because of the complexity of rock-fabrics and the rapid changes of carbonate depositional facies. This paper focuses on a carbonate reservoir in Tarim Basin, China. The dynamic behaviors between adjacent wells vary considerably although they belong to the same depositional facies, which indicates that the reservoir has strong heterogeneity.
This paper proposes a new set of carbonate reservoir characterization in genetic units by integrating the geological, petrophysical and geophysical data. According to core-log interpretations, rock fabrics, pore types, reservoir properties, secondary porosity indexes have been acquired. The depositional cycles and key interfaces in stratigraphy sequence framework are determined. The relationships between the rock-fabrics, depositional cycles, reservoir properties, palaeo-weathering surfaces, responses of logs and seismic attributes have been studied, and reservoir genetic-unit models are constructed, which reveals that carbonate genetic units in different phases have specific rock-fabric associations and reservoir properties. The genetic units in different phases are delineated comprehensively in log and seismic data, and different reef-flat distributions are constructed. Finally, the seismic attribute relating to the secondary porosity indexes have been extracted in genetic-unit framework and it reveals the distribution of favorable reservoirs of carbonate reef-flat complexes.
This paper reveals that different phases of genetic units of carbonate reef-flat complexes, as containing specific rock-fabric associations, crucial interfaces and fracture-vug development, thus key factors, control the distribution of favorable reservoirs. Phase I genetic unit, formed in relative sea-level rise, mostly with fine rock-fabric association of micrite calcarenite and micrite algae-bound limestones, are filling on the depressions, grooves or the flat area of carbonate platform, and its reservoir properties are very poor. Phase II genetic unit, with the tendency of upward- coarsening fabric association and top exposure surface, is overlaid on highlands along platform margin. Phase III genetic unit, composed of fracture-vug developed sparry gravel-bearing reef-skeletal limestones and sparry gravel- bearing calcarenites of reef-flat complexes, is almost distributed in the platform margin and overlaid on tops and nearby of previous genetic units, which means that, shallow water is suitable to reef-building organism mass-production, but frequent exposures and weathering have made favorable reservoirs developed. Drillings have proved that almost all high-production wells are within the area of phase II and III genetic units. Furthermore, the distribution and complicated internal structure of favorable reservoirs have been revealed by log-calibrated seismic attribute extraction in the framework of phase II and III genetic units.
This paper illustrates an integrated case study, which helps geologists and reservoir engineers to support the development of Central Tarim Basin. In addition, it offers a methodology for the research of other similar oilfields.