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Chen, Bo (PetroChina Changqing Oilfield Company) | Ma, Fujian (Schlumberger) | Li, Yanlu (PetroChina Changqing Oilfield Company) | Yuan, Hailong (PetroChina Changqing Oilfield Company) | Li, Zhijun (PetroChina Changqing Oilfield Company) | Zheng, Wei (Schlumberger) | Li, Dengsheng (PetroChina Changqing Oilfield Company) | Wang, Yong (PetroChina Changqing Oilfield Company) | Ding, Li (PetroChina Changqing Oilfield Company) | Wang, YongKang (PetroChina Changqing Oilfield Company) | Li, Peng (PetroChina Changqing Oilfield Company)
In order to increase oil production and minimize footprint within the surrounding natural habitats within the Ordos Basin, China, operators are drilling multi-well pads. This paper will discuss a project where twenty stacked horizontal wells, some having extended reach, were drilled from a single pad measuring 86 43 m(282 141 ft).
The drilling targets include three different gravity flow deposits within the stratigraphic section and have a high degree of vertical and lateral heterogeneity. Each layer is about 40m in gross thickness, with 6–10m of good quality reservoir. Porosity ranges from 4 to 10% and permeability from 0.01 to 0.1 mD within these high-quality intervals.
Due to a multitude of both surface and subsurface risks, a geo-engineered and integrated solution is required for mitigation in these high-profile projects and has been proven as an effective approach for targeting unconventional resources around the world.
The results of the project have been encouraging. The laterals were successfully placed within the best quality rock which historically results in optimal drilling efficiency and well performance.
The Ordos Basin is an intracratonic basin located in north central China that can be divided into six tectonic units: Yimeng Uplift, Western Thrust Belt, Tianhuan Depression, Yishan Slope, Jinxi Flexure Belt and Weibei Uplift (Fig. 1). The study area is in the southwestern Yishan Slope and the reservoir layers are upper Triassic predeltaic and lacustrine deposits.
The Chang7 is one of the major unconventional plays in Ordos Basin, at around 2000 m true vertical depth. The succession is thought to have been deposited in a semi-deep and deep lacustrine environment. The sand- and siltstone is laminated with mudstones in what has been interpreted as gravity deposits and represents the hydrocarbon bearing zone (Fig. 2). The laminations and lateral discontinuity in the gravity deposits result in significant variability in the reservoir quality.
Over the last decade of drilling and production, a positive correlation between well placement within the best quality rocks in drilling efficiency and well performance has been clear. Because of the surface risks, and motivation to minimize operational footprint, and subsurface risks associated with reservoir heterogeneity, a geo-engineered integrated solution is critical to project success and economics.
Imaging technologies from azimuthal logging-while-drilling (LWD) tools provide valuable insight into borehole conditions and address multiple drilling and formation evaluation applications, such as wellbore stability assessment and fracture and bedding plane analysis. Although high-resolution images are widely available for water-based mud (WBM) applications, such as from azimuthally focused resistivity tools, their availability in oil-based mud (OBM) applications is limited.
This paper presents a 4.75-in. LWD ultrasonic imaging tool that provides high-resolution borehole caliper and reflection amplitude images, independent of the mud type used. Analysis of datasets collected by the tool, in OBM with varying mud weights and under multiple drilling conditions, demonstrate the suitability of the imaging technology in boreholes ranging from 5.75- to 6.75-in. diameter. We present log data and analysis from the field tests that illustrate the quality of both the caliper and the reflection amplitude measurement provided by the tool.
The comparison of these datasets with wireline measurements demonstrates the potential for these LWD ultrasonic logs to be the primary imaging solution in applications where the deployment of wireline technologies is either too risky or costly to be considered.
Li, Peng (School of Civil and Resource Engineering / University of Science and Technology Beijing) | Cai, Mei-feng (School of Civil and Resource Engineering / University of Science and Technology Beijing) | Guo, Qi-feng (School of Civil and Resource Engineering / University of Science and Technology Beijing) | Huang, Zheng-jun (School of Civil and Resource Engineering / University of Science and Technology Beijing) | Ren, Fen-hua (School of Civil and Resource Engineering / University of Science and Technology Beijing)
The 21st century is a century of underground space development and utilization. The stability of the underground rock engineering openings has always been a critical issue in rock mechanics. In recent decades, many researchers worldwide have carried out a large number of important and insightful physical simulation experiments on the stability of underground openings and achieved fruitful results. They have reached a certain consensus in some aspects of the failure behavior. However, due to the different research emphases and simplified assumptions for the problems studied, the research results obtained are scattered. In view of this, the research progress and representative achievements of physical simulation tests of surrounding rocks failure of underground openings are systematically analyzed and summarized by combing existing literature. Specifically, the deformation and instability behavior and mechanism of the underground opening are emphatically discussed from three aspects of mechanical characteristics, failure mode, and fracture evolution process. Meanwhile, some constructive views are put forward on the specific experimental conclusions. In addition, some deficiencies in the current research of physical simulation experiments in the underground opening stability are pointed out, and the development tendencies of future research are prospected from many aspects. The above work has important practical significance for an in-depth study of the failure mechanism of underground openings and for guiding the design and construction of underground rock engineering.
The 21st century is a century of underground space development and utilization. The development and utilization of underground space is an inevitable choice for human social development, economic construction and national security strategy. The stability of the underground rock engineering openings has always been a critical issue in rock mechanics. Many disasters, such as inward extrusion deformation, spalling, collapse, and rockburst, occur frequently in underground openings, seriously threatening the safe construction and service of the underground engineering.
Physical simulation test plays an irreplaceable role in studying the stability of surrounding rock of underground opening, and its main idea is to regard the hole in a rock/rock-like sample containing prefabricated hole as underground cavity itself, and to study the deformation and failure mechanical behavior of the surrounding rock from the perspective of excavation damage. For a long time, scholars at home and abroad have done a lot of work on the physical simulation test research of surrounding rock stability in the underground cavity and reached a certain consensus in some aspects. However, due to different research emphases, the results obtained are scattered and lack of representativeness. This paper systematically summarizes and analyzes the representative research results in terms of mechanical behavior, failure mode and fracture evolution process of opening surrounding rock. In addition, the shortcomings of the current research in this field are pointed out and the development tendencies of future research are prospected in many aspects.
Obtaining high-resolution borehole images in oil-based mud (OBM) from logging-while-drilling (LWD) tools has been made possible through the recent development of ultrasonic imaging technologies. High-resolution acoustic impedance images enable reservoir evaluation through the identification of faults and fractures, bedding and laminations, and assessment of rock fabric. This paper presents examples of high-resolution images from a 4¾-in. ultrasonic imaging tool in OBM applications and discusses their value in assessing reservoir quality.
This paper provides details of field trials of an LWD ultrasonic imaging tool for use in boreholes ranging from 5¾ to 6¾ in. High-resolution images detailing both borehole caliper and acoustic impedance in both vertical and horizontal wellbores are shown, illustrating the high level of formation evaluation now available when OBM is used. The methodology used to address the impact of tool motion on the impedance images will also be covered. The value of real-time data on borehole stability assessment will be discussed, along with additional applications made possible from the real-time data, such as wellbore placement enhancement.
Both real-time and recorded data from field trials show the potential applications for the ultrasonic imaging tool. High-resolution impedance images covering different formations and lithologies show bedding planes and laminations and enable the calculation of stratigraphic dip, while the identification and assessment of fractures show the potential to aid operators during the development of their hydraulic fracturing program. Borehole caliper and shape assessment in real time can be used to modify the drilling parameters and to adjust mud weight, while providing an input into geomechanics assessment.
The LWD logs presented illustrate the factors that influence data quality and the methodology used to ensure high-resolution images are available in both vertical and high-angle wellbores using OBM. A direct comparison between data acquired while drilling and while re-logging sections is shown, highlighting the repeatability of the measurement while also illustrating the impact of time-since-drilled on the borehole. A comparison with wireline measurements highlights the potential for using the high-resolution LWD images as an alternative to wireline, where cost and risk of deploying the wireline may be high.
The ability to collect high-resolution images in OBM in wellbores ranging from 5¾ to 6¾ in. ensures that increased reservoir characterization is possible, leading to significant improvements in determining the viability of unconventional and other challenging reservoirs. The high-resolution amplitude images are comparable with those available on wireline technologies, and the real-time application of borehole size and shape for input into wellbore stability and geomechanics analysis ensures that common drilling hazards can be avoided.
The definition of unconventional reservoirs continues to evolve over time as advances in technology make it more viable to extract hydrocarbons. The need for reservoir characterization in such reservoirs, however, will continue to increase to optimize wellbore placement and enhance production. For high-angle or horizontal wellbores common in unconventional drilling, obtaining information from wireline technologies may be either too expensive or risky, although obtaining a wellbore stability assessment while drilling provides a key input into the real-time geomechanical model. This paper presents field test results of a new 4¾-in. ultrasonic imaging logging-while-drilling (LWD) tool that provides a real-time assessment of borehole shape and high-resolution caliper and acoustic impedance images in both water-based mud (WBM) and oil-based mud (OBM) applications.
Images from measurements, such as gamma ray, resistivity, or density, are common in LWD applications. However, high-resolution images have historically been limited to WBM applications. This paper describes the sensor physics and tool configuration that enable the acquisition of borehole caliper and acoustic impedance images in all mud types, with examples of logs obtained while drilling in boreholes using OBM. Details of the comparison with wireline data sets are also given.
Vertical and horizontal wellbores covering different lithologies are described, showing that high-resolution images are now available in slimhole OBM applications. Caliper images illustrate small changes in borehole shape, and impedance images can be used to evaluate geological features and determine stratigraphic dip. The evaluation of caliper data with a wireline multifinger caliper illustrates the potential to eliminate a separate wireline run before completing the well. Comparison of while-drilling data with tripping out of hole data provides crucial insight into wellbore deterioration with time.
The technology described addresses key challenges encountered while drilling and evaluating unconventional reservoirs. Real-time wellbore stability assessment enables optimization of drilling parameters and mud weight in all unconventional reservoirs. Identification of faults and fractures provides valuable information to optimize the hydraulic fracturing program in shale gas applications. Inputs into the geomechanical model are valuable in the assessment of tight sand reservoirs with extremely low porosity and permeability. Limestone reservoirs with minor shale content may require OBM to minimize wellbore deterioration with time. Monitoring such deterioration is critical in optimizing the placement of packers and the hydraulic fracturing program design.
Providing the industry's highest-resolution images in all mud types, even under high logging speeds represents a unique method of assessing real-time wellbore stability and enhancing formation evaluation in slim wellbores in unconventional reservoirs.
Imaging technologies from azimuthal logging-whiledrilling (LWD) tools provide valuable insight into borehole conditions and address multiple drilling and formation evaluation applications, such as wellbore stability assessment and fracture and bedding plane analysis. Although high-resolution images are widely available for water-based mud applications, such as from azimuthally focused resistivity tools, their availability in oil-based mud applications is limited.
This paper presents field test results from a 4%-in. ultrasonic imaging tool that provides high-resolution borehole caliper and acoustic impedance images, independent of the mud type used. Analysis of data sets collected in oil-based mud with varying mud weights under multiple drilling conditions are provided, highlighting the suitability of the imaging technology for multiple while-drilling applications. Log data and analysis from the field test wells illustrate the deliverables from both the caliper measurement and the acoustic impedance measurement. Caliper deliverables detailed include: average hole size calculation for input into cement volume calculation, as a borehole quality indicator, and for environmental corrections for other LWD sensors; borehole ellipse and azimuthal sector image plot outputs for real-time geomechanics analysis; and high-resolution borehole images for the identification of faults and fractures. Acoustic impedance deliverables detailed include: real-time images for potential porosity steering applications; and high-resolution memory images for detailed analysis of faults and fractures, and geological and lithological analyses of bedding planes, laminations, and determination of stratigraphic dips. The caliper and acoustic impedance data sets are compared directly with corresponding wireline measurements, including a multifinger caliper and ultrasonic imaging tool.
An overview of the tool geometry and associated sensor physics is given, along with details of the laboratory setup and testing performed to evaluate the sensors and the associated measurements and images. Details of the field tests, which illustrate the steps taken to ensure the sensors were evaluated across different lithologies from vertical to horizontal, using different mud weights, logging speeds, and drillstring rotation parameters are described. The logging program was optimized to obtain direct correlation with wireline data sets and maximize image quality.
Analyses of the deliverables from the field trials illustrate the value that the ultrasonic caliper and acoustic impedance measurements provide to a variety of LWD applications in boreholes ranging from 5¾ to 6¾ in., adding high-resolution imaging capability to oil-based mud systems. The excellent comparison with wireline measurements demonstrates the potential for the LWD logs to be used as the primary imaging solution in applications where deployment of wireline technologies is either risky or costly, such as in high-angle or horizontal wells, while enabling the same high level of formation evaluation.
He, Youwei (China University of Petroleum, Beijing and Texas A&M University) | Chai, Zhi (Texas A&M University) | Huang, Jingwei (Texas A&M University) | Li, Peng (China University of Petroleum) | Cheng, Shiqing (China University of Petroleum) | Killough, John (Texas A&M University)
Although hydraulic fracturing enables economic production from tight formations, production rates usually decline quickly and result in low hydrocarbon recovery. Moreover, it is difficult for conventional flooding methods to provide enough energy supplement in the tight formations. This paper develops an innovative approach to enhance oil recovery from tight oil reservoirs through inter-fracture injection and production, including synchronous inter-fracture injection-production (SiFIP) and asynchronous inter-fracture injection-production (AiFIP). This improves flooding performance by transforming fluid injection between different wells to between adjacent fracture stages from the same horizontal well.
The multi-stage fractured horizontal well (MFHW) comprises of recovery fractures (RFs), injection fractures (IFs) and natural fractures. In all the cases demonstrated in this work, the odd fractures and even fractures are defined as RFs and IFs respectively. Fluid is injected into IFs from injection tubing, and hydrocarbon is recovered synchronously or asynchronously through oil tubing connecting to the RFs. To quantitatively evaluate the performance of SiFIP and AiFIP in tight oil reservoirs, reservoirs are simulated based on the compartmental embedded discrete fracture model (cEDFM). The production performance of different recovery methods is compared, including primary depletion, water flooding, CO2 flooding, water Huff-n-Puff, CO2 Huff-n-Puff, SiFIP (water), SiFIP (CO2), AiFIP (water), AiFIP (CO2). The AiFIP and SiFIP achieve higher cumulative oil production than other methods. AiFIP obtained the highest cumulative oil production, which is more than two times that of primary depletion. The AiFIP (CO2) obtained almost the same cumulative oil production with SiFIP (CO2) with only 50% of CO2 injection rates, and AiFIP (water) obtained 19.3% higher cumulative oil production than SiFIP (water) with only 50% of water injection rates. Therefore, AiFIP is also a better choice when CO2 or water resource is not abundant. Sensitivity analysis is carried out to discuss the impacts of fracture and injection parameters on cumulative oil production. The fracture spacing, fracture networks, and injection rates influence the production significantly, followed by injection-production schedule and fracture length. The recommended well completion schemes of AiFIP and SiFIP methods are also provided, which is significant for the potential application of the proposed methods. This work illustrates the feasibility of SiFIP and AiFIP to enhance hydrocarbon recovery in tight reservoirs.
Ding, Shuaiwei (National & Local Joint Engineering Research Center for Carbon Capture and Sequestration Technology, State Key Laboratory for Continental Dynamics, Northwest University) | Liu, Guangwei (CNOOC Research Institute) | Li, Peng (National Engineering Laboratory for Exploration and Development of Low-Permeability Oil & Gas Fields) | Xi, Yi (Exploration and Development Research Institute, Petro-China Changqing Oil Field Company Ltd) | Ma, Jinfeng (National Engineering Laboratory for Exploration and Development of Low-Permeability Oil & Gas Fields)
Oil reservoirs are considered good storage structures for CO2 geological storage. With the right selection of candidate reservoir, injection of CO2 into tertiary and depleted oil reservoirs can result in enhanced oil recovery (EOR) and permanent sequestration of CO2 underground. The selection of candidate reservoirs for future CO2-EOR and storage projects mainly depends on storage potential evaluation. The aim of this work is to estimate the storage potential of CO2 stored in tertiary (CO2-EOR) and depleted oil reservoirs. In tertiary oil reservoirs, a method to estimate the geological CO2 storage capacity (CO2SC) in the reservoir during well open operations (EOR operations), which is a function of reservoir parameters, original geological reserves and oil volume factor is first built. In depleted oil reservoirs, a method to calculate the CO2SC in the reservoir during well shut down operations, which is based on the material balance method is proposed. In both cases, the methodology of storage capacity of CO2 dissolved in remaining oil, formation water and by mineral trapping is presented based on the model established by
The high-speed railway between Beijing and Zhangjiakou in China that is a very famous project all around the world is now under construction. Badaling station is at the middle of this railway line and is designed as an underground station. The transition zone between the running tunnel to Zhangjiakou direction and Badaling station has a large span cross section with a dimension of up to 30 meters. Meanwhile, this large cross section also goes through the fault fracture zone. As a result, the supporting scheme and stability of the surrounding rock as well as seismic safety are the main concern about this major project. In this paper a 3-D rock-tunnel dynamic interaction finite element modeling is carried out to analyze the construction stage and seismic performance of the large span tunnel cross section. Numerical results have demonstrated the rationality of support system and revealed the seismic performance of the large span cross section.
The new Badaling Tunnel is located between Changping Nankou Town and Badaling Town in Yanqing County. The world’s deepest and largest high-speed train station (Badaling underground station) which will be an important part of the 12km long tunnel between Beijing and Zhangjiakou will be 102m deep with a floor area of about 36000 m2. Starting section of the transition section of the station in Beijing directions is DK67+653 and that in Zhangjiakou direction is DK68+285. This tunnel station comprises of three different sized cross sections namely: small distance spaced section, large-span and triple arch section. The transition zone towards Zhangjiakou direction spans through a fault fracture zone which makes it vulnerable to seismic activity and needs to be investigated. Figure 1 shows the plan of the station.
Based on the prevailing geological conditions, seismic effects and station structure details form the comprehensive geological survey report, it is necessary to analyze the overall seismic performance of the Badaling underground station. The transition tunnel is of a maximum net width and height about 30.83m and 17.57m, respectively, with a height - span ratio of 0.57. The Zhangjiakou direction transition section passes through a fault fracture zone and is the focus of this investigation. The plan of this transition section is shown in figure 2. The surrounding rock is graded 3-5 and the Norwegian method is adopted for the excavation. Initial support system against the rock includes shotcrete, prestressed cables and prestressed anchors.
Liu, Xuejian (Institute of Geology and Geophysics, Chinese Academy of Sciences) | Liu, Yike (Institute of Geology and Geophysics, Chinese Academy of Sciences) | Hu, Hao (Department of Earth and Atmospheric Sciences, University of Houston) | Li, Peng (R & D Center, BGP, CNPC)
Recently, the reverse time migration (RTM) scheme has been used for imaging surface-related multiples, and additional illumination for subsurface can be provided. However, many crosstalk artifacts are inevitably generated by unwanted crosscorrelations. In order to reduce artifacts, we propose RTM of isolated first-order multiples, in which only primaries are forward propagated and crosscorrelated with backward propagated first-order multiples. With primaries and multiples separated during regular seismic data processing as input data, first-order multiples can be isolated by a proposed two-step procedure of prediction and adaptive subtraction. In numerical experiments with one synthetic and a South China Sea datasets, the proposed RTM of first-order multiples can provide much more interpretable image by avoiding many artifacts when compared with RTM of all-order multiples.
This paper has been withdrawn from the Technical Program and will not be presented at the 87th SEG Annual Meeting.