Liu, Guoqiang (PetroChina Exploration and Production Company) | Hou, Yuting (PetroChina Changqing Oilfield Company) | He, Junling (PetroChina Jilin Oilfield Company) | Zhang, Hao (PetroChina Xinjiang Oilfield Company) | Wu, Jinlong (Schlumberger) | Zhao, Xianran (Schlumberger) | Li, Huayang (Schlumberger) | Wu, Fangfang (Schlumberger) | Li, Shenzhuan (Schlumberger) | Wang, Yuxi (Schlumberger)
Most shale oil resources in China are lacustrine deposit. The reservoirs are usually characterized by complex lithology and high heterogeneity with various mineral compositions (quartz, carbonates, feldspars, pyrites and volcanic ash), total organic carbon and pore structure. How to delineate the shale oil reservoir, how to identify the ‘sweet spots’ and its distribution are the two major challenges and objectives for this study.
To answer the question, a systematic workflow was proposed by integrating the advanced logging technologies (such as nuclear magnetic resonance, micro-resistivity imager, spectroscopy data, array dielectric tool) with special core measurement data. Firstly, the shale oil reservoir was classified into different types according to the logging responses. Secondly, core samples were chosen from each type and sent out to lab for a series of core special experiments to test the microscopic properties. Finally, the advanced core analysis results and logging technologies were integrated to depict the characters of the different types of shale oil reservoirs from microscopic to macroscopic scale. And by comparing with testing data, the features of best shale oil reservoir type can be identified, and the distribution and potential of shale oil reservoir can be unraveled.
The new approach helped to get a thorough understanding of the shale oil reservoirs characteristics, such as lithology, mineral composition, pore types, pore size distribution, oil content, kerogen type and maturity of organic matter, organic carbon content and distribution. Six different kinds of shale oil reservoir facies were classfied from loging responses, inculding super high gamma ray siliceous shale, high gamma ray siliceous shale, high gamma ray argillaceous shale, high gamma ray tuffaceous shale, medium gamma ray siliceous shale and medium gamma ray argillaceous shale. High gamma ray siliceous shale and medium gamma ray siliceous shale are proved to be the best shale oil reserovir, which contains 2~8% of TOC, 2~12% of effective porosity, more than 50% of quartz content and high propotion of macropores.
The method proposed in this project has been implemented in many unconventional reservoirs in china to evaluate the resource potential and get a comprehensive understanding of the shale oil reservoir.
The wells tested based on the recommendation has got promising production after fracturing, which brought client big confidence for future exploration.
Hu, Zhenhua (PetroChina Liaohe Oilfield Company) | Zhang, Shenqin (PetroChina Qinghai Oilfield Company) | Wu, Fangfang (Schlumberger) | Liu, Xunqi (Schlumberger) | Wu, Jinlong (Schlumberger) | Li, Shenzhuan (Schlumberger) | Wang, Yuxi (Schlumberger) | Zhao, Xianran (Schlumberger) | Zhao, Haipeng (Schlumberger)
The igneous reservoir of Shahejie formation in eastern sag of Liaohe depression is characterized by complex geological environment, variable lithology and high heterogeneity. Reservoir evaluation is difficult only based on conventional logs due to complex lithology and pore structures. Effective igneous reservoirs were identified and reservoir controlling factors were analyzed based on effective porosity calculation, pore structure analysis, lithology identification, lithofacies analysis, fracture evaluation and heterogeneity analysis by combing nuclear magnetic resonance data, micro-resistivity image data, conventional logs as well as mud logging data.
Based on our study, the igneous reservoirs in the study area are more related with effective porosity and pore connectivity, and less related with fractures. Good reservoirs are mainly distributed on the top part of explosive facies and effusive facies, where lithologies are mainly Trachyte, volcanic breccia and breccia-bearing tuff. The weathering leaching process is quite important for igneous reservoirs, but the reservoir qulity would not be good if the weathering process is too strong as it will lead to low effective porosity.
The accuracy of igneous reservoir evaluation gets improved a lot by this integrated approach and the conclusion from this study will help to optimize igneous reservoire exploration plan.
Wang, Yuxi (State Key Laboratory of High-Efficient Mining and Safety of Metal Mines Ministry of Education, School of Civil and Environmental Engineering, University of Science and Technology Beijing) | Wang, Jin-an (State Key Laboratory of High-Efficient Mining and Safety of Metal Mines Ministry of Education, School of Civil and Environmental Engineering, University of Science and Technology Beijing) | Cao, Qiuju (China Electronics Engineering Design Institute)
The fractured rock surfaces were observed under different loading stages in creep shear by making use of computerized tomography (CT). Through the creep shear tests, the failure modes of the fractured rocks have been recognized based on the CT images. The study shows that the long-term shear strength of fractured rocks is mainly composed by two mechanisms: one is the anti-shear due to the interlocking of microasperities, the other is the anti-friction owing to the relative shear of macro waves on the fractured rock surfaces. The study concludes that the relationship between the peak shear strength and the normal force as follows: for the compressive shear of rocks, the shear strength of the rock would increase and approach to the critical value when the normal force becomes larger; for the tensile fractured rocks, on the other hand, the shear strength would become larger persistently when the normal force increases.
The mechanical behavior of fractured rocks has directly impact on the stability of slope, tunnel and dam. etc. The research on creep shear strength of fractured rocks can provide theoretic basis for predicting of long-term mechanical behavior of rock mass. The research of rock creep mechanism activate worldwide, since it has a great significance about long-term stability of rock mass (Sun 2007). At present, researches about the rock creep are approximately divided into three parts. Firstly, the creep mechanism of intact rocks is studied (Chen & Sun 1996). For instance, upon the experiment of tensile creep fracture in red sandstone, the creep fracture criterion is established, and combined with the rheology mechanical, further instructions about fracture parameters are concluded: presented by three threshold values of the rock, respectively, called lower limit of rheology, lower limit of destroy, upper limit of destroy. Using initial intensity factor, the rheology of the rocks can be judged among these threshold values. The natural rocks contain weak intercalation, slope instability mostly occurs, due to the existence of weak structure. The second part is focused on the creep shear character under the weak structural. Chen (Chen et al. 2009) analyzed the shear creep property of typical weak intercalation in redbed soft rock, which provided the shear strength parameters of rock creep for prospecting and design. Similar research could be found in literature (Shen & Zhang 2010), the shear creep test is carried out for the samples with greenschist discontinuities, and found the characteristic of shear creep failure is closely related to the development of the structure surface. Shen (Shen et al. 2012) carried out shear creep test on Barton’s standard profiles, and the long-term strength of the discontinuities were determined by using of three methods: the transition creep law, isochronous curve and the first inflection point method. The third part investigates the crack propagation in the creep shear. In order to obtain the further details of crack development, growth and creep failure in the rocks, some researchers studied the creep of rocks with the help of industrial CT. In the 1990s, industrial CT got into the new stage of research about the rock failure characters (Yang et al. 1996). At the present stage, industrial CT is widely used to study the rock crack and defect evolution (Lei & Zhang 2003), the micromechanics of rocks under different loads (Erik 2004) and technology of CT three-dimensional re-construction of rock or mixed soil (Zhao et al. 2011). Based on the industrial CT, the researches as mentioned above focus on description of cracks in the intact rock in creep process, and find out the defect development in mechanics and geometry. As well-known, engineering rocks consist many kinds of fracture surfaces and they are under different stress. These fracture surfaces become the major factor in controlling of the long term mechanical behavior. The research on long-term mechanical behavior of fractured rocks of micro-contact and fracture model can provide theoretic basis for predicting instability of rock masses.
Lu, Wendong (Schlumberger) | Murray, Doug (Schlumberger) | Wang, Yuxi (Schlumberger) | Li, Wei (Schlumberger) | Yang, Lei (Schlumberger) | Desport, Olivier (Schlumberger) | Xiao, Chengwen (Chinese National Petroleum Company) | Wei, Guo (SinoChem Corporation)