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.
Cao, Mengjing (China University of Petroleum -Beijing) | Wu, Xiaodong (China University of Petroleum -Beijing) | An, Yongsheng (China University of Petroleum -Beijing) | Zuo, Yi (China University of Petroleum -Beijing) | Wang, Ruihe (China University of Petroleum -Beijing) | Li, Peng (Shengli Oilfield, Sinopec)
Unconventional oil, such as tight oil and shale oil, has become one of the most significant contributors of oil reservoirs and production growth. Due to low porosity and ultra-low permeability, unconventional oil reservoirs require multistage hydraulic fracturing technique to maximize production. However, the primary recovery remains very low to narrow the profit margin heavily. Although CO2 huff-n-puff process holds great potential to increase oil recovery and has a chance to sequester CO2 to reduce environmental footprint, our current knowledge of the performance of this process is very limited.
With numerical simulation, we performed a series of sensitivity work to present the impacts of reservoir properties, fracture properties and operation parameters such as CO2 injection rate, injection time, soaking time, number of cycle of CO2 on enhanced oil recovery in the tight oil formation. What’s more, the method of analysis of variance (ANOVA) was used to evaluate the performance of CO2 huff-n-puff process and beneficial result from CO2 EOR technology. Simulation results showed that bottom hold pressure and injection cycles impose more significant impose on oil recovery increment than injection time, injection rate and production time per cycle. Based on the typical reservoir and fracture properties from tight oil reservoir, the numerical models were established to evaluate the performance of four EOR methods: CO2 huff-n-puff, water huff-n-puff, nanofluids huff-n-puff and water alternating gas (WAG). With the comparison of oil recovery and its increment of four EOR methods and depletion method, it is found that CO2 huff-n-puff method would lead to much more incremental oil recovery than other three methods, which reveals its huge potentials of enhancing oil recovery and improving development profit in unconventional reservoirs. The conclusion of this work has the potential to advance our understanding of the role of CO2 in developing unconventional oil reservoirs, which will benefit both energy economy and environment with CO2 geological sequestration.
Li, Peng (Chinese Academy of Sciences) | Zhang, Xuhui (Chinese Academy of Sciences) | Lu, Xiaobing (Chinese Academy of Sciences) | Liu, Lele (China Geological Survey) | Liu, Changling (China Geological Survey)
High efficiency, economic, and safe exploitation of natural gas hydrate is an important researching topic. Mechanical-Thermal exploitation is new presented potential efficient method for shallow marine hydrate exploitation, and contains the following procedures: In-situ mining o: hydrate-bearing sediments, cutting the sediments into small bodies mixing the sediments with surface injected seawater, transporting the multiphase fluid with hydrate dissociation in the exploitation well, and backfilling the sediments, etc. The physical processes of small bodies of hydrate-bearing sediments and water flow accompanying hydratt dissociation are described in the main controlling parameters. Ther some trial observational tests are conducted to obtain information or the dissociation process of gas hydrate in small bodies under water. heating condition.
Gas hydrate (GH) is a solid compound of hydrocarbon gas and water molecules. Gas hydrate-bearing sediments (GHBS) consist of hydrate water or/and gas, sand/clay etc. GH exists in cementing or filling status with soil skeleton, and widely distributes in the sea, permafrost and deep lakes (Kvenvolden and Lorenson, 2001; Koh, 2002; Song et al. 2014).
Countries such as Russia, Canada, America and Japan have carried ou trial productions of GH in the permafrost (Makagon et al., 2005, 2013 ConocoPhillips, 2012a, b; Collett et al., 2012;) and deep marine (Fuji et al., 2013; Chee et al., 2014; Terao et al., 2015). The methods of GI-exploitation include thermal injection, depressurization, and CO2 displacement. The trial production of GH gives the confidence tha increasing temperature or/and decreasing pressure could release methane from GHBS in a short period, but the efficiencies of these productions are hard to satisfy a commercial-viable application.
The physical processes in the production contain heat conduction, phase transformation, multiphase seepage and soil deformation (Moridis et al., 2009). The ratio of the characteristic times is 109:107:106:1. The heat conduction is the slowest physical effect, and controls the coupling processes. Lack lasting supply of heat into the GHBS leads to the low efficiencies of the in-situ trial production, and constrains the utilization of the methods such as depressurization and thermal injection (Hong et al., 2003; Zhang et al., 2014a).
The formation and geological characteristics of GHBS in South China Sea are more complex and inhomogeneous. The reserve is large but in a scattered spatial distribution. The sediment is soft and the permeability is low. Through a preliminary estimation of thermal injection, the expansion length of hydrate dissociation zone gets to merely about 30 m after 20 years, leading to a serious situation of high investment and low profit, especially at the period of low price of international oil and natural gas (Zhang et al., 2014a, b).
Su, Shengrui (Department of Geological Engineering, Changan University) | Li, Peng (Department of Geological Engineering, Changan University) | Wang, Qi (Department of Geological Engineering, Changan University) | Wang, Xiaojian (Department of Geological Engineering, Changan University)
Taking the Longmenshan complex geological environment as the study background, a geomechanical model with a reverse fault and subjected to horizontal tectonic stress is built and valley incision process is modeled. After excavation, the right slope has the contrary dip to faults but on the left slope the dip is similar to faults. Valley side slope presents tensile stress and the valley floor presents compressive stress. During valley incision the right slope display tensile stress state and its stress distribution show different characteristics of zonation from surface to inside of the slopes. As the valley incision depth increases, the position of tensile stress concentration area in right slope has changed from inside to surface, and lastly to the top of overlying fault. Stress state of left slope is complex and mainly performs tensile stress, but it also shows different characteristics in upper and lower slope.
The crustal stress refers to all stress distributed in the earth, which is a stable field in macroscopic and perform variety at one point with the time changing, namely, it is a function of the time and space (Su et al., 2002). When the concept of crustal stress was defined by A. Heim in 1912, it has become a focus to geologists all over the world and gotten a large number of acheivements (Cai et al., 1995; Lee et al., 1996).
The stress state of a slope adjusts continously with geological environment changing and determines it’s deformation and failure mode, therefore, systematically and accurately grasping stress distribution characteristics have a great significance to slope stability evaluation and protection (Tang, 2011).
Valley stress is a special stress field which is influced by regional tectonic stress and formed by stress adjusting in valley floor and valley side slopes along with river incised process (Tian et al., 2002). There are plentiful hydropower resources in China, especially in the alpine valleys of southwest China. Since valley incision has brought a series engineering geological problems, the distribution of valley stress field gets more and more attention in recent years. Zheng Xiaoyan (2012) and TianYuzhong (2002) discussed the characteristic of valley stress by numerical simulation. In recent years, a large number of measured data have been accumulated in water conservancy projects in southwest China (Zheng et al., 2012; Bai et al., 1982; Huang et al., 1996) and provided reference basis for valley stress field study.
Studying valley stress field, especially the stress distribution of valley slope which is influenced by tectonic stress has great significance. Current research techniques are mostly limited to the numerical simulation. Although there are a large number of measured data, its research scope is limited and both of them cannot reflect the real stress state in the slopes. Therefore, the geomechanical simulation experiment of the valley excavation to reseaching the valley stress distribution is necessary.
Yang, Jian (Oudeh Petroleum Company) | Gou, Xuemin (Oudeh Petroleum Company) | Hilmi, Nabil (Oudeh Petroleum Company) | Xia, Rick (Oudeh Petroleum Company) | Sun, Xiangyang (LandOcean Energy Services Co., Ltd.) | Li, Peng (LandOcean Energy Services Co., Ltd.) | Wu, Qiang (LandOcean Energy Services Co., Ltd.) | Liu, Hua (LandOcean Energy Services Co., Ltd.)