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Results
100% in the Sweet Section: An Effective Geosteering Approach for Silurian Longmaxi Shale Play in Sichuan Basin
Liang, Xing (Petrochina Zhejiang Oilfield Company) | Wang, Lizhi (Schlumberger) | Zhang, Jiehui (Petrochina Zhejiang Oilfield Company) | Xian, ChengGang (Schlumberger) | Wang, Gaocheng (Petrochina Zhejiang Oilfield Company) | Zhao, Chunduan (Schlumberger)
Abstract A new geosteering approach significantly improves effectiveness and efficiency of geosteering in shale gas fields such as the Silurian Longmaxi gas shale in the south Sichuan basin, China. This formation presents more challenges than in classical sand/shale formations even when logging while drilling (LWD) imaging is available because of the cyclic gamma ray (GR) response of the targeted shale formation, subseismic microfaults with unknown displacements, and sudden structure changes from subseismic microstructures. The new approach introduces more geosteering elements including correlation in the true stratigraphic thickness (TST) domain with considerations of the cyclic nature of shale gas zones; conducting multi-scenario modeling to verify the most likely scenario fitting the overall structural trend and the cyclic features; using an 3D geological model as the overall guidance of structural variations; and using a key bed detection strategy when the above methods can't precisely determine structural position. The sweet section of Longmaxi shale has five sub-zones with respectively regressive or transgressive sequences, and the bottom zone with extremely high GR readings. The cyclic nature often resulted in inconclusive structure correlation based on changes of GR readings only. Field experiences showed numbers of subseismic microfaults with unknown fault displacement, and sudden changes of structural dips due to sub-seismic microstructures can be encountered, which can make the standard geosteering method insufficient to judge the actual position of the horizontal lateral. The new approach especially the multi-scenario modeling method in TST domain and the downward detection geosteering strategy to track the bottom high GR marker shale zone can clarify in-situ geology and minimize potential out-of-zone risk. The new approach has ensured all drilled horizontal wells was implemented 100% in the sweet section during the pilot and factory drilling phases. This paper demonstrates several examples to highlight its capability to handle complex situations for effective geosteering in contrast to the standard approach. The field practices also show this new approach can help to reduce unnecessary changes of drilling directions to ensure a smoother wellbore for subsequent operations. Our experience suggests iteratively updating the 3D geological model with improving accuracy must be treated as part of the overall geosteering strategy. Also a real-time decision making scheme throughout all involved segmens must be ensured for seamless operation.
- North America > United States (0.70)
- Asia > China > Sichuan Province (0.62)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (1.00)
- Geology > Geological Subdiscipline > Stratigraphy (1.00)
- Geophysics > Seismic Surveying (0.93)
- Geophysics > Borehole Geophysics (0.70)
Characterization of Complex Multiscale Natural Fracture Systems of the Silurian LongMaXi Gas Shale in the Sichuan Basin, China
Liang, Xing (Zhejiang Oilfield Company, PetroChina) | Liu, Xiao (Schlumberger) | Shu, HongLin (Zhejiang Oilfield Company, PetroChina) | Xian, ChengGang (Schlumberger) | Zhang, Zhao (Zhejiang Oilfield Company, PetroChina) | Zhao, ChunDuan (Schlumberger) | Li, QingFei (Zhejiang Oilfield Company, PetroChina) | ZHANG, Lei (Zhejiang Oilfield Company, PetroChina)
Abstract The Silurian LongMaXi gas shale in the Sichuan basin is an emerging play in China. It experienced multiple major tectonic evolutions with uplifting and burying sequences in its geological time. As expected, this shale could develop tremendous small-scale discrete natural fractures (DNF) like many other notable North American gas shale plays. But only sparse DNFs were observed from several borehole images in a shale gas field. This paper presents a case study for characterizing complex multiscale natural fracture systems of the gas shale. In the study, natural fracture systems were classified as four types: large-scale faults, medium-scale fracture systems (including microfaults and crushed zones or fracture corridors), small-scale DNFs, and micro-scale fissures per their correspondingly scale-associated geological, geophysical, and petrophyscial features and responses. An optimized ant-tracking approach was implemented to track seismic abnormities and discontinuities as indicators of subseismic medium-scale fractures. Key components of this approach include optimized seismic gathers' angle-range, optimal scanning directions and angles, parameter adjustment criteria, and a comprehensive QC process. The QC process, which considers regional geological and tectonic evolution, fracture mechanical mechanism under strike-slip stress regime, and observations from all available resources, was implemented on each identified medium-scale fracture zone to ensure its reliability. This paper has more focuses on characterizing the medium-scale fracture system because of which can be a unique feature of LongMaXi gas shale compared to its North American counterparts. Characterizing of this medium-scale fracture system considers factors including fracture development mechanism and fracture pattern under strike-slip condition, structure control and curvature tendency, and intensity and amplitude of seismic discontinuity and abnormities. The study shows such medium-scale fractures are widely distributed across the study field. Complexities encountered while drilling and stimulation such as heavy mud loss or screen-out due to unexpected high leak-off rate had strong correlation with them. Two principle orientations of the medium-scale fractures were identified and further validated by outcrop observations and microseismic events observed from hydraulic fracturing monitoring. The study suggests that such medium-scale fractures may be mainly controlled by two major tectonic events during Himalayan movement because their principle orientations are almost exactly following the directions of two major tectonic movements. In combination with all types of natural fractures as defined, 3D multiscale natural fracture model and Geomechanical Earth model were established, which are two keystones for drilling quality and completion quality for further applications. These medium-scale fractured or crushed zones along with large-scale faults and small-scale DNFs across this shale gas field could significantly impact on efficiency and effectiveness of development. In particular, to understand how hydraulic fractures interact with such medium-scale fractures will be essential.
- Geology > Structural Geology > Tectonics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (1.00)
Technology Feasibility and Production Driver Study in the First Integrated Shale Gas Block in Sichuan Basin
Liang, Xing (PetroChina Zhejiang Oilfield Company) | Jiao, Yajun (PetroChina Zhejiang Oilfield Company) | Wang, Gaocheng (PetroChina Zhejiang Oilfield Company) | Zhang, Lei (PetroChina Zhejiang Oilfield Company) | Chen, Zhipeng (PetroChina Zhejiang Oilfield Company) | Zhou, Xin (Schlumberger) | Luo, Yin (Schlumberger) | Wang, Yue (Schlumberger) | Han, Shim Yen (Schlumberger) | Zhang, Rui (Schlumberger) | Wen, Cheng (Schlumberger)
Abstract As the pioneer of shale gas exploration in China, Longmaxi formation that located in the lower Silurian system in Sichuan basin has entered the developing phase. Under the geological background, seismic and multi-exploration wells’ data analysis, it has been proven that the shale gas play in Longmaxi is more complex than it's equivalents in North America. Though the deeper burying depth of Longmaxi has bring extra bonus by higher pore pressure (1.7 to 2.0), Longmaxi is lagging back in some key reservoir quality indicators such as kerogen content and porosity, same time, the compressional tectonic setting and relative active plate movement develop faults and fractures in an unpredictable way brings extra challenge. Driven by the complexity, more and more technologies have been deployed in the development phase to better define the play. Among them, well placement with real-time image, LWD or wireline logging for reservoir quality (RQ) and completion quality (CQ) evaluation and engineering optimized completion design have been recognized as critical steps in better understand shale gas production based on abroad experience. Although it's always appealing to run the integrated methodology with multi-source data for each horizontal well, the tight economic return is preventing field wide implementation. This paper studies multi-well data from an integrated project with PetroChina ZheJiang in Zhao Tong block; examines data acquired from 3 laterals drilled in the same direction in the same pad but utilized different combination of technologies including well placement with real-time image, LWD quad-combo logging with spectroscopy and engineering optimized fracture design. By investigating the micro seismic data and production rate from each lateral, correlation were made to identify the key production drivers and finally lead to the conclusion of the most economic and efficiency technology combination for the horizontal wells development pattern in Sichuan Basin. In conclusion, laterally the heterogeneity of reservoir quality for the same layer in the target platform is not the key production driver. However, reservoir quality and three principal stresses along vertical scope, combining with the nature fracture distribution make a big difference for the completion fracture extension and production rate. As a result, well placement with bedding identification ability being a prevention methodology is quite critical in the mountainous area in Sichuan basin. LWD logging and an engineering optimal completion design based on that provide comprehensive understanding for each lateral should be deployed based on several considerations including well trajectory, heterogeneity, etc. In the early stage of shale gas development of China, utilize the very first block with integrated service to grab the full value of seamless technology and move forward to solve the conflict between the exploration needs and economic return will shed some lights on the development direction in Longmaxi layer.
- North America > United States > Texas (1.00)
- Asia > China > Sichuan Province (1.00)
- Geology > Structural Geology (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geophysics > Seismic Surveying > Passive Seismic Surveying > Microseismic Surveying (1.00)
- Geophysics > Borehole Geophysics (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Government > Regional Government > Asia Government > China Government (0.34)
- North America > United States > Texas > Haynesville Shale Formation (0.99)
- North America > United States > Texas > Fort Worth Basin > Barnett Shale Formation (0.99)
- North America > United States > Louisiana > Haynesville Shale Formation (0.99)
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