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.
Xi, Shengli (PetroChina Changqing Oilfield Company) | Hou, Yuting (PetroChina Changqing Oilfield Company) | Li, Xianwen (PetroChina Changqing Oilfield Company) | Hu, Xifeng (PetroChina Changqing Oilfield Company) | Liu, Peng (Schlumberger) | Zhao, Xianran (Schlumberger)
The Triassic Yanchang formation is rich in tight oil resource at Ordos Basin. The oil sandstone and oil shale of Chang 7 member are widely spread in the basin and have huge potential in oil production. Due to low porosity and low permeability, producing oil from tight oil reservoir depends on hydraulic fracturing. A successful hydraulic fracture requires accurate estimations of horizontal stresses and rock elastic properties in design and operation.
Chang 7-2 is shale and sandstone interbed reservoir and Chang 7-3 is shale oil reservoir with lamination sedimentary structure. The rocks with lamination structure are very anisotropic, and it needs to be considered in computation of horizontal stresses and rock elastic properties.
In this paper, we present a case study to illustrate the advantages of anisotropic geomechanics model. Anisotropic horizontal stresses and rock elastic properties were calculated and used in hydraulic fracturing design. The perforation intervals were selected at depths with low stress magnitude based on stress profile. The perforations efficiency was analyzed, and perforation interval with low efficiency was removed. Major stimulation operation parameters, total volume, proppant volume and slurry rate, were optimized with anisotropic geomechanics model. Fracturing operation results showed that the total volume was decreased by 16.5%, proppant pumped increased by 11.4% and daily oil production increased by 73.7%. This case study demonstrated that anisotropic geomechanics model help to improve operation efficiency and increase oil production.
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.
Zhang, Lixia (Research Institute of Shaanxi Yanchang Petroleum Group Co. Ltd.) | Ma, Fujian (Schlumberger) | Jiang, Chengfu (Research Institute of Shaanxi Yanchang Petroleum Group Co. Ltd.) | Xian, Chenggang (Schlumberger) | Liu, Chao (Research Institute of Shaanxi Yanchang Petroleum Group Co. Ltd.) | Zhao, Xianran (Schlumberger) | Gao, Yagang (Exploration and Development Research Center of Yanchang Oilfield Co. Ltd.) | Wang, Qing (Schlumberger) | Guo, Chao (Research Institute of Shaanxi Yanchang Petroleum Group Co. Ltd.) | Pan, Yuanwei (Schlumberger)
Marine shale gas plays have been well developed worldwide; however, continental shale plays have been untapped until recently. Globally, there are no or few successes for continental shale gas development, although marine shale gas has been commercially exploited worldwide for decades. Ordos Basin, China is a rich continental shale gas play in Mesozoic and Paleozoic target zones. The proven resource is about 1600×108m3 (5.6 Tcf). The first geoengineering project for continental shale gas globally was conducted in this play in China.
The paper presents a case study that illustrates the challenges of a lacustrine shale gas well from integrated study to fracturing and well testing. Although an integrated geoscience-engineering workflow is used in the study, only results from drilling and logging are presented in the paper. Discussions and recommendations for future exploitation are presented.
The deep or semi-deep lacustrine deposits in the Triassic Yanchang formation, Ordos basin is the interval of interest in the study. The study area is in the southeastern part of Ordos basin, China, and the area is characterized by a single westerly dipping monocline with undeveloped faults (
Hou, Yu Ting (Petrochina ChangQing Oilfield Company) | Xi, Sheng Li (Petrochina ChangQing Oilfield Company) | Wu, Yong (Petrochina ChangQing Oilfield Company) | Li, Huayang (Schlumberger) | Zhao, Xianran (Schlumberger) | Wu, Jinlong (Schlumberger) | Zhao, Haipeng (Schlumberger)
Unconventional reservoirs oil and gas resources have great potential for development, especially in North America, which has been successfully achieved commercial production. Shale oil is one of the unconventional resources. Most of the shale oil reservoirs have complex lithology, poor petrophysical characteristics, complex pore structure, and so on, especially for lacustrine shale oil formation. This paper describes an approach and workflow to characterize the Chang7-3 member shale oil reservoir in the Ordos basin, China by integrating the high tech digital rock physics core analysis data with other special core analysis data to calibrate the reservoir petrophysical properties. The special unconventional core analysis method taken for this project are Tight Reservoir Analysis technology (TRA), Thin Section scanning (TS scanning), Mercury Injection Capillary Pressure test (MICP), N2 and CO2 Gas sorption test, XRD and Nuclear Magnetic Resonance analysis (NMR), and the new logging technology employed are gamma ray spectroscopy logging (LithoScanner*), nuclear magnetic resonance logging (CMR*), dielectric logging (ADT*). The new core analysis and logging technology not only depict the characters of the shale oil reservoir from microscopic to macroscopic scale, but also guarantee to establish the accurate method for reservoir identification and evaluation. The data analysis from above led to the development of evaluation models for organic matter quality and reservoir quality. Analysis of the production data revealed that the hydrocarbon abundance of the Chang7-3 member lacustrine shale oil reservoir is controlled by both organic matter quality and reservoir quality. A production forecast chart of Chang7-3 Member lacustrine shale oil reservoir was constructed based on the organic matter quality and reservoir quality. The application of the developed methodology and workflow achieved very good results and is supported by the test data from multiple wells drilled in the study area.
Guantao oil reservoir of the Bohai Bay, is characterized by low formation water salinity, high pore structure heterogeneity and flooding, which complicates the logging response, especially the low contrast of resistivity response. Traditional methods by resistivity fail to estimate reservoir parameters accurately and cannot determine producible fluid type. In this study, the reservoir heterogeneity was investigated with advanced nuclear magnetic resonance data, and oil saturation was calculated using array dielectric data. Combining the two aspects, a special reservoir evaluation and fluid identification method was established.
Heterogeneity of properties along horizontal shale gas wells has a significant impact on the quality of completion as well as on production from each stage. This heterogeneity can exist in the quality of the reservoir, such as changes in kerogen content and maturity, free porosity, and water saturation, and it can also be seen in factors which directly affect the course of induced fracturing in the well. These factors can be faults, natural fractures, stress regime changes, etc.
Historically, it has been difficult to map these properties because some of the measurements required logging in openhole environments using wireline tools. Recently, logging-while-drilling and through-casing-logging measurement techniques have been developed to achieve similar results in a safer, more controlled environment.
A large number of horizontal wells have been drilled in gas shales in the USA and Canada. Some of these wells have been logged in an attempt to understand variability. The authors have studied these data sets in detail, and the concepts presented here are based on observations from these data sets. We use a data set acquired in a Canadian shale as an example to illustrate the concepts of property heterogeneity along the laterals. This well is a 1,000-m long lateral which was supposedly drilled in the same, homogeneous rock, yet it shows substantial property differences along its length, suggesting the importance of evaluating horizontal wells.
Once these properties have been mapped, many questions can be raised. Can we increase production from the same horizontal well, which has already been drilled (Potapenki et al SPE 119636; Ketter et al SPE 103232) ? Can we do something better in planning the completion to get more gas out of it? Would it be possible to save a well from geohazards if we knew how we might connect to them? Can we select the optimum perforation interval when we know the quality of cement behind pipe? The answer to each of these questions can result in substantial gains in efficiency and reduction in risk, while providing major production boosts. To determine definitive answers to these questions, production data over time would need to be analyzed. These data were not available at the time of writing this paper; hence, a detailed discussion on the specifics of the correlations between properties and production is left for another paper.